Many types of lignocellulosic biomass show effective binding of toxic heavy metals from industrial and environmental effluents. Biosorption is an emerging option for conventional methods to remove heavy metals, some of them with even better efficiencies compared to conventional methods. Raw material for biosorption is typically low-cost and easily available, including agricultural waste or forest residues such as sawdust, bark, or needles. This review concentrates on the accumulation of heavy metals by lignocellulosic biosorbents. Thus far, biosorption has not been economically feasible on a large scale and needs further development for profitability. Industrial-scale wood-based biosorbent applications are especially still lacking. Moreover, due to legislative demands, there is an increasing need for accurate and reliable analytical methods for metal analysis of environmental and industrial effluents. In the future, biosorption processes are likely to become common, and the requirement for environmental monitoring will increase due to ever restricting regulations. This emphasizes not only the need for the development of feasible process solutions, but also a requirement for accurate analytical methods.
Biosorption of Heavy Metals by Lignocellulosic Biomass and Chemical Analysis
Petra C. Lindholm-Lehto *
Many types of lignocellulosic biomass show effective binding of toxic heavy metals from industrial and environmental effluents. Biosorption is an emerging option for conventional methods to remove heavy metals, some of them with even better efficiencies compared to conventional methods. Raw material for biosorption is typically low-cost and easily available, including agricultural waste or forest residues such as sawdust, bark, or needles. This review concentrates on the accumulation of heavy metals by lignocellulosic biosorbents. Thus far, biosorption has not been economically feasible on a large scale and needs further development for profitability. Industrial-scale wood-based biosorbent applications are especially still lacking. Moreover, due to legislative demands, there is an increasing need for accurate and reliable analytical methods for metal analysis of environmental and industrial effluents. In the future, biosorption processes are likely to become common, and the requirement for environmental monitoring will increase due to ever restricting regulations. This emphasizes not only the need for the development of feasible process solutions, but also a requirement for accurate analytical methods.
Keywords: Biosorption; Heavy metals; Inductively coupled plasma mass spectrometry; Inductively coupled plasma optical emission spectrometry; Lignocellulosic biomass; Wood-based biomass
Contact information: Natural Resources Institute Finland, Survontie 9A, FI-40500 Finland;
* Corresponding author: email@example.com
In industrialized countries, biomass contributes to approximately 10 to 15% of energy demand, while nuclear and fossil fuels cover the remaining percentage (Khan et al. 2009). In developing countries, biomass consumption can account for up to one third of total energy supplies (Faaij 2004). In the European Union (EU), the utilization of biomass has increased in recent decades and is expected to increase further in the future (Nakicenovic and Swart 2000). In the EU, the target has been set by the Renewable Energy Directive to reach a target of 20% final energy consumption from renewable sources by the year 2020. The member states have committed to reaching their own national renewables targets, ranging from 10% in Malta to 49% in Sweden (EC 2009).
Lignocellulosic biomass refers to plant material composed of cellulose, hemicellulose, lignin, and extractives. Extractives can be defined as a group of hydrophilic and hydrophobic, organic and inorganic components in wood other than cellulose, hemicellulose, and lignin. Lignocellulosic biomass can be classified into virgin and waste biomass, including wood-based biomass. Wood biomass is harvested for industrial purposes and often is available in large quantities at an economical price. In this context, wood biomass is defined as biomass derived from lignified plants, such as trees, bushes, and forest residues.
Metals and chemicals used in industrial processes have led to the generation of large volumes of effluents with toxic heavy metals, for example, in mining, mineral processing, and metallurgical operations. Metals are categorized as biologically essential and non‑essential, the latter including aluminum (Al), cadmium (Cd), mercury (Hg), tin (Sn), and lead (Pb), which have no known biological function but increasing toxicity at elevated concentrations (Sfakianakis et al. 2011). Essential metals, such as copper (Cu), chromium (Cr), cobalt (Co), iron (Fe), molybdenum (Mo), nickel (Ni), and zinc (Zn) play a biological role, showing either metabolic deficiencies or toxic effects at increased concentrations. Heavy metals are recalcitrant elements and can pollute water resources or accumulate and concentrate in living tissue (Mata et al. 2009). Heavy metals can enter the human diet and accumulate gradually in the human body. Depending on the element and the length of exposure, a variety of adverse health effects can occur, such as learning difficulties (Pb), neurological and psychological symptoms (Hg), nephrotoxicity, osteotoxicity, kidney damage (Cd), lung damage (Hg), negative gastrointestinal and central nervous symptoms (arsenic, As), and the increased risk of cancer (WHO 1992; Järup 2003; Li et al. 2006).
Heavy metal contamination is a serious concern in many countries (Mahar et al. 2016). For example, Cd pollution has become one of the most serious environmental problems worldwide (Folgar et al. 2009; Zacchini et al. 2009). Conventional treatment technologies are not economical and can generate large amounts of toxic sludge (Ahluwalia and Goyal 2007).
There is an urgent need to develop more cost-effective methods due to the high costs of traditional methods used to remove heavy metals from wastewaters. Sorption of metals by wood-based biomass has large potential in removing metals from aqueous solutions and their recovery for further use. Treetops and branches make up 20 to 30% of the aboveground biomass of trees, which provides a large potential quantity of material suitable for such a purpose (Werkelin et al. 2010).
This review aims at presenting suitable methods for the removal of heavy metals from aqueous environmental and industrial effluents. Although there are a variety of living (bacteria, molds, and fungi) and non-living (industrial and agricultural waste, forest residues) materials suitable for biosorption, the authors concentrated on the biosorption of wood-based biomass.
Expectedly, the use of biomass for a variety of forestry and wood-based industrial purposes on a commercial and municipal scale will become more common, as well as achieving policy goals on renewable energy. However, biosorption has not yet been cost-effective on a large scale, which limits its use in commercial applications (Crini 2006). This leads to the requirement of a variety of statutory follow-ups of chemicals and heavy metals. In the EU, the treatment of wastewater and sludge are controlled by the European Commission Urban Waste Water Directive 91/271/EEC (EC 1991). This regulation contains limits for metal content in reused sewage sludge. Additionally, the United States Environmental Protection Agency (EPA) has listed the maximum allowable limits for several heavy metals. For this purpose, standardized analytical methods are required to detect and quantify heavy metal concentrations. Therefore, a variety of analytical methods to detect and quantify heavy metals was reviewed.
INORGANICS IN BIOMASS
Metals in Biomass
The elemental composition of dry wood is typically approximately 50% carbon, 6% hydrogen, 44% oxygen, and trace amounts of inorganic compounds, varying based on wood species and the place of growth. Typically, coniferous species (softwood) have a higher cellulose and lignin content and a lower pentosane content compared to deciduous (hardwood) species. Additionally, ash content, the quantity of inorganics in wood, is often higher in hardwoods (Pettersen 1984; Rowell et al. 2013). In total, the proportion of inorganics ranges from 0.5 to 1%, and rarely exceeds 1% of dry wood in temperate zones (Sjöström and Alén 1998). However, wood in a tropical or subtropical region can contain inorganics of up to 5%.
Among the inorganics in wood, calcium (Ca), magnesium (Mg), and potassium (K) are the most common, comprising up to 80% of the inorganic material, wood ash being mainly Ca carbonate due to the high Ca content of wood material (Lambert 1981; Khan et al. 2009). There are also trace amounts of heavy metals, such as Al, barium (Ba), boron (B), Co, Cr, Cu, Fe, gallium (Ga), lithium (Li), manganese (Mn), Mo, Ni, Pb, rubidium (Rb), silicon (Si), silver (Ag), sodium (Na), strontium (Sr), titanium (Ti), Sn, vanadium (V), and Zn (Ellis 1965), some of them being essential for wood growth. In wood, they exist mostly as carbonates, sulfates, and oxalates or are bound to carboxyl groups of pectic materials (Hon and Shiraishi 1991). In biomass, sulfur (S) occurs in salts or as reduced in organic compounds, while chlorine (Cl) is mostly in soluble salts (Bryers 1996). In contrast, phosphorous (P) is in inorganic salts or organic compounds as esters and pyrophosphates, while silicon is mostly present as silica. Metal ions occur organically associated with biomass fibers or can remain in minerals precipitated as salts or occur in solution as free ions or complexes (Werkelin et al. 2010).
Environmental conditions, atmospheric pollutants, soil chemistry, and abiotic factors influence the tree growth, chemical composition, and location of inorganics within the tree (Jyske et al. 2014). For example, trees with compression wood show different elemental concentrations compared to unstressed wood (Prohaska et al. 1998). Chemical elements in annually formed tree rings are controlled by the cation‑binding capacity of wood, radial growth rates, transformation of sapwood into heartwood, and radial translocation of elements in the tree stem. Most trees show declining cation concentration with increasing tree age due to binding‑exchange properties in wood tissue as opposed to sap-soil chemistry. Due to translocation, the presence of an element in a specific year ring does not necessarily mean the presence of the element in the environment that year. This especially applies to young trees with no distinct heartwood formation (DeWalle et al. 1995).
There is an uneven distribution of inorganics in pine trees throughout wood tissues, needles, and bark. Cambium, the metabolically active boundary between sapwood and bark, can contain an order of magnitude of higher concentrations of Mg, Ca, K, and P compared to sapwood, while the lowest levels were found in heartwood (Yoshida et al. 2011). Werkelin et al. (2010) found higher levels of Cl in the shoots and needles of spruce compared to wood, twigs, and bark. Świetlik et al. (2012) studied the chemical distribution of Cd, Cu, Mn, Pb, and Zn in wood fly ash from pine sawdust and hardwood logs (acacia, alder, beech, birch, and oak). They found a higher proportion of heavy metals in hardwood than in softwood. Cd and Zn, which are regarded as bioavailable, pose the highest potential hazard for the environment and human health (Świetlik et al. 2012).
Inorganic compounds are transferred into the wood via the roots. There is a high variability between species and especially between the barks of different species (Lambert 1981). Typically, the content of inorganics is higher in the needles, leaves, and bark compared to the stem wood (Harder and Einspehr 1980). The lowest contents of inorganics have been detected in the heartwood, with the lowest variability in the heartwood of different species. In earlywood, higher contents have been found compared to latewood (Rowell et al. 2013). Based on Pettersen (1984), the highest levels of inorganic compounds in different wood species were found in the basswood Tilia americana (K, 2.8 parts per thousand (ppt)), in quaking aspen Populus tremuloides (Ca 1.1 ppt, K 1.2 ppt), and in white ash Fraxinus americana (K 2.6 ppt, Mg 1.8 ppt).
Generally, the term heavy metal refers to metals or metalloids having an atomic density of more than 4 g dm-3 or 5 times that of water (Hawkes 1997) that are toxic or poisonous even at low concentrations (Nagajyoti et al. 2010). Heavy metals include, Ag, As, Cd, Co, Cr, Fe, Ni, Pb, Zn, and the platinum group elements. Heavy metals are also called trace elements due to their presence in trace (10 mg kg-1) or ultratrace (1 µg kg-1) quantities. From the ecotoxicological perspective, the most dangerous metals are Pb, Cd, Cr(VI), and Hg (Ahluwalia and Goyal 2007). Heavy metals found in aquatic environments have been a concern for decades (Bengtsson et al. 1979). Heavy metals are considered bioavailable in both organic and dissolved ionic forms.
Pollution due to heavy metals originates both from natural and anthropogenic sources. Naturally, heavy metals occur in ore minerals in the earth’s crust and are released due to weathering, leading to a range of normal background concentrations in soil, sediments, water, and organisms (O’Connell et al. 2008). Among sedimentary rocks, shale has the highest concentrations of heavy metals, followed by limestone and sand‑stone. Volcanoes, wind dust from desert regions, forest fires, and marine aerosols all contribute to the transporting of heavy metals (Nagajyoti et al. 2010). Industrial processes and other human activities have led to the contamination of soils with heavy metals (Laureysens et al. 2004). Heavy metals are introduced into the aquatic environment via industrial activities, such as from ore refining, tanneries, paper industry waste, and as pesticides (Celik and Demirbaş 2005). For example, mining, smelting, and agriculture have contaminated large areas with heavy metals, mostly with Cd, Cu, and Zn (Herawati et al. 2000).
Exposure to heavy metals has been linked to various cancers, kidney damage, autoimmunity, developmental retardation, and even death (Hokkanen et al. 2013). Additionally, Cr, Fe, selenium (Se), V, Cu, Ni, Cd, Hg, As, Zn, and Pb have known toxic effects and are hazardous to human health. For example, an accumulation of Cd in a human affects the kidneys and bones, and causes cancer, while Cr compounds are nephrotoxic and carcinogenic (Chen and Hao 1998). In addition to human health, toxic metals are harmful for other life forms. Metal ions bioaccumulate in the environment and are magnified along the food chain, leading to more pronounced toxic effects in animals at higher trophic levels. The element Cd accumulates in aquatic organisms via dietary or aqueous exposure (Liao et al. 2011), with a half-life of 10 to 30 years (Moore and Ramamoorthy 1984). The main mechanism of toxicity is the antagonistic interaction between the uptake of the Ca2+ and Cd2+ ions, leading to acute hypocalcemia and growth reduction (McGeer et al. 2011).
The toxicity of heavy metals for plants varies by plant species, specific metal, concentration, chemical form, and pH. Some heavy metals (e.g., Cu and Zn) have catalytic properties or act as cofactors or activators in enzyme reactions, while others (e.g., As, Cd, and Hg) have toxic effects on enzymes. Many enzymes contain Zn, which is required to maintain the integrity of ribosomes (Nagajyoti et al. 2010). Some heavy metals are essential for animals and plants, such as Fe, Cu, and Zn as micronutrients (Wintz et al. 2002), but excess uptake can lead to toxic effects (Monni et al. 2000). For example, Cu is an essential micronutrient for living organisms, but it can be toxic at increased levels (Hernández et al. 2006). It is essential to plants for photosynthesis, a constituent of the primary electron donor, and a cofactor of several enzymes (Mahmood and Islam 2006). In contrast, the element Fe is a component of hemoglobin, myoglobin, and cytochrome.
Lead (Pb) is a persistent heavy metal characterized as a hazardous priority substance by EU directive 1907/2006 (EC 2006). Concentrations of Pb have increased in the environment due to anthropogenic activities (Mager 2011; Sfakianakis et al. 2015). The bioavailability of Pb depends on its adsorption into the sediment, the content of organic matter in water, pH, alkalinity, and hardness (Sepe et al. 2003; Mager 2011), with the Pb2+ ion being the most toxic form. At high levels, Pb causes encephalopathy, cognitive impairment, anemia, kidney damage, and behavioral disturbances (Pagliuca and Mufti 1990).
Biosorption can be defined as an ability of certain biomass to bind and concentrate heavy metals from even dilute aqueous solutions. In particular, the cell wall structure exhibits this property (Ahluwalia and Goyal 2007). Biosorption involves a solid sorbent, liquid phase, and the dissolved species to be sorbed. Biomass behaves as an ion-exchanger, taking only from minutes to a few hours to achieve an efficient metal uptake (Ahluwalia and Goyal 2007).
Many methods have been developed to remove heavy metals from effluents, but especially in the mining industry, mixtures of heavy metals in aqueous solutions pose challenges for traditional water treatment methods. Conventionally, heavy metals have been removed by precipitation, filtration, ion exchange, reverse osmosis, and electrodialysis ultrafiltration from aqueous solutions, or they have been adsorbed by activated carbon (Patterson 1985; Das et al. 2008). For example, by increasing the effluent pH, soluble metals can be converted into insoluble hydroxides. Unfortunately, chemical precipitation is ineffective, especially at low concentrations (< 50 mg L-1), while ion exchange, membrane, and adsorption processes have high operating costs (Das et al. 2008). Additionally, many traditional methods produce large amounts of sludge that requires further treatment (Sud et al. 2008). Activated carbon is a widely used adsorbent for the removal of heavy metals, but its use suffers from high operating costs and complex thermal regeneration (Hokkanen et al. 2013).
Biosorption can be a cost-effective alternative and is appropriate for removing metals from effluents (Sud et al. 2008). Biosorbents are readily available and can remove heavy metals at concentrations as low as 1 mg per ton (Montes-Atenas and Schroeder 2015), often unattainable by conventional methods. The main advantages of biosorption over conventional methods are the low cost of renewable organic material, the minimal use of chemicals, the possibility of metal recovery, and the regeneration of the biosorbent (Bailey et al. 1999; Vieira and Volesky 2000). In recent decades, a high number of studies have been conducted to find inexpensive and sustainable sorbent materials for the removal of heavy metal species from aqueous solutions (Al-Asheh et al. 2003; Cao et al. 2004; Jang et al. 2005). However, little effort has been made to design economically viable industrial applications (Sud et al. 2008). Seaweeds, molds, yeasts, other microbial biomass, and agricultural waste have been widely explored (Zhou and Kiff 1991; Bailey et al. 1999; Sudha and Abraham 2003), but recently the focus has been on studying waste and the by‑products of large‑scale industrial operations. Materials containing cellulose especially show potential in metal binding. Wood-based biomass has a suitable chemical composition, is renewable, abundant, and an economical option for adsorbing heavy metals.
Different biomass materials have been investigated as potential biosorbents for heavy metals. Such applications have been reviewed by Hubbe et al. (2011). Potential biosorbants include sawdust (Bryant et al. 1992; Volesky and Holan 1995), pine bark and needles (Vàzque et al. 1994), canola meal (Al-Asheh and Duvnjuk 1998; Al-Asheh et al. 1998), rice straw, soybean hulls, sugarcane bagasse, and peanut shells (Johns et al. 1998). Saeed et al. (2005) used papaya wood, generated as waste in papaya plantations with no other commercial use, to bind metals; the wood showed a high efficiency in removing heavy metals from aqueous solutions (Saeed et al. 2005). Additionally, biosorption of metals has been reported in a variety of biomaterials, including microalgae, seaweed, bacteria, fungi, and crop residues (Saeed et al. 2002). Some logging waste has been studied as a biosorbent, such as plant bark (Acacia arabica, eucalyptus) and pine needles, showing 90 to 100% for Cr removal efficiencies (Mohan et al. 2006; Sarin and Pant 2006; Venkateswarlu et al. 2007).
Lignocellulosic biosorbents produced as waste material and by-products of various industries have been used to adsorb metals ions from aqueous solutions. For example, mechanically treated peach stone particles have been used to bind copper ions from aqueous solutions (Lopičić et al. 2017). Peach stone particles showed interactions between copper ions and carboxyl and hydroxyl groups. Similarly, apricot (Prunus armeniaca) shells produced as waste product in fruit processing were able to adsorb copper, zinc, and lead ions (Cu2+, Zn2+, and Pb2+) after an alkali treatment (Šoštarićc et al. 2018). Vilardi et al. (2018) reported use of olive stones, the main solid waste from the olive oil industry, coated by iron and magnetite nanoparticles in binding Cr(VI) from aqueous solutions. Additionally, crushed chili seeds (Capsicum annuum) have been used to adsorb cadmium and lead ions (Cd2+, Pb2+) from aqueous solutions (Medellin-Castillo et al. 2017). They found that elevated pH and temperature increased electrostatic interactions between the negatively charged surfaces and the metal cations. Khan and Rao (2017) reported that copper and nickel ions can be adsorbed from wastewater by alkali treated butternut (Cucurbita moschata) biomass. The treatment increased the acidic functional groups on the surface of the biomass and led to increased adsorption efficiencies of copper and nickel.
Even less common agricultural waste has been tested (Cimino et al. 2000; Annadurai et al. 2002; Reddad et al. 2002b; Hashem et al. 2006a, 2006b), such as banana and orange peels, hazelnut shells, cellulose pulp, cotton stalks, particles of palm trees, and sugar beet pulp. Demirbaş (2008) showed that a biosorbent made of agricultural by-products can be used to remove heavy metals from industrial and municipal wastewater. The use of other plant parts as adsorbents, such as pea peels, fig leaves, broad beans, medlar peels, and jackfruits has shown high removal efficiencies at acidic pH levels (Benaissa 2006). Additionally, marine algal, coffee residues with clay, and cocoa shells have been effective as natural sorbents in binding metal ions from aqueous solutions (Boonamnuayvitaya et al. 2004; Meunier et al. 2004; Sheng et al. 2004).
Cellulose is a renewable, abundantly available biopolymer. However, there are few functional groups in the cellulose fiber that can bind heavy metals. Therefore, a derivatization is required to build binding sites (Navarro et al. 2001), for example, by catalytic and selective oxidation of primary hydroxyl groups (Isogai and Kato 1998), or succinylation (Gellerstedt et al. 2000). Modified cellulose has scarcely been studied as an adsorbent for heavy metals. However, Hokkanen et al. (2013) studied modified micro- and nanocellulose as an adsorbent for binding Zn, Ni, Cu, Co, and Cd in aqueous solutions. They found that the succinic anhydride modification of nanocellulose was effective in binding metals with a regeneration ability of 96 to 100%, showing potential for water treatment applications.
Typically, heavy metals are associated with finer-sized particle classes, the highest metal concentrations are in the less than 1 mm cluster (Sharma et al. 1997; Bardos 2004). Therefore, mechanical screening and the removal of the finest fraction have been suggested to produce a final product with an agricultural value (Zennaro et al. 2005). Furthermore, Pb is the most strongly bound element in typical organic material (Zheng et al. 2004; Reimann 2007), and Ni is the weakest. Lead is taken up by the roots and stored as pyrophosphate in cell walls (Dunn 2007). For example, Dunn et al. (1992) reported concentrations of 311 mg kg-1 Pb in spruce bark. The spruce bark was collected from Canada, a place distant from any contamination of anthropogenic origin.
Wood bark is mostly used as a combustible material with little added value, but it is also suitable as a sorbent. However, bark naturally contains tannins and other complexation agents that can be released in the solution (Montes-Atenas and Schroeder 2015). Therefore, a pretreatment of bark is required to inactivate the complexation agents. Acid activation increases the adsorption capacity, but the activation in acidic media varies depending on the activating agent, concentration, and temperature (Palma et al. 2003). Montes-Atenas and Schroeder (2015) showed that adsorption of Pb on pine bark (Pinus radiata) can achieve almost 100% removal of Pb(II) from a 100 mg L-1 solution. They concluded that the sorption mainly takes place at the lignocellulosic C‑O groups, while adsorption occurs at the phenolic sites. Su (2012) studied the sorption properties of metal ions in tree-related materials. Bark material showed the highest sorption capacity for metal ions, while the lowest was in wood sawdust. Su concluded that the sorption capacity of metals on wood material decreases in the following order: Fe3+>> Pb2+ >> Cu2+ >> Fe2+ > Cd2+ > Zn2+ > Ni2+ > Ba2+ ≥ Ca2+ ≥ Mn2+ ≥ Sr2+ > Mg2+ > Rb+ ~ K+ ~ Na+ ~ Li+ and Fe3+ >> Pb2+ > Cu2+ >> Cd2+ > Zn2+ > Ni2+ > Ba2+ > Ca2+ > Sr2+> Mn2+ > Mg2+ > K+ ~Na+ ~ Li+ for bark material.
Scots pine Pinus sylvestris (Taty-Costodes et al. 2003) and rubber wood sawdust (Raji et al. 1997) have shown 85 to 90% removal efficiencies of heavy metals, at an optimal pH of 5 to 6. Ucun et al. (2002) used the cone biomass of P. sylvestris as a biosorbent for Cr removal from artificial wastewater. They reported a high adsorption capacity of 84%, with the highest level detected at an acidic pH level of 1.0. Similarly, Nuhoglu and Oguz (2003) used cone biomass of oriental thuja (Thuja orientalis) as a biosorbent for the removal of Cu from aqueous effluents. However, they detected increased sorption at a neutral pH level of 7.7 and 98% adsorption of Cu(II).
Biosorption is a complex process, comprising of chemisorption, complexation, adsorption on surface and pores, ion exchange, chelation and adsorption due to physical forces on chemically active sites or functional groups (Volesky 2003), and entrapment by inter- and intrafibrillary capillaries as a result of concentration gradient and diffusion (Sarkanen and Ludwig 1971; Qaiser et al. 2007). Metal ions can be sequestered in biomass by, e.g., acetamide, amino, phosphate, amide, amine, sulfhydryl, and carboxyl groups (Ahluwalia and Goyal 2007). The binding capacity of a biomass is often in the same range with synthetic cation‑exchange resins (Wase and Foster 1997). However, the early saturation of biomass may be a problem or have the ability to biologically alter the metal valence state.
Typically, the metal uptake by biosorption proceeds in the passive mode (Madrid and Cámara 1997). Passive, not metabolically mediated biosorption is a dynamic reversible adsorption-desorption process, able to bind metal ions by (dead) biomass from solution. Metal ions are adsorbed onto the surface of biomass due to interactions between the metals and the functional groups of biomass (Das et al. 2008). In this context, biosorption includes several passive, i.e. non-metabolic mechanisms, such as coordination, complexation, ion‑exchange, and microprecipitation. It can be distinguished from bioaccumulation, an active, metabolically mediated transport of chemical species.
The type of biomass (living or non-living), the properties of the metal solution, and the ambient conditions affect the mechanism of biosorption. Initial metal concentration, temperature, pH, and biomass concentration are the main factors affecting biosorption. However, at a range of 20 to 35 °C, the temperature seems to be in minor role, with pH being the most important factor (Aksu et al. 1992; Pagnanelli et al. 2003). An increase in pH leads to decreased competition between protons and metal cations for the same functional groups. Pagnanelli et al. (2003) showed that at a pH level of 2, biosorption was minimal, while a sharp increase occurred at pH levels of 3 to 4 (95.5% Cu, 87.7% Cd, and 62.7% Zn). Adsorption can be performed as long as heavy metals remain in the solution, but the maximum adsorption capacity depends on the properties of the ion solution and the adsorbing substrate (Montes et al. 2006). Additionally, a decreased positive surface charge leads to a lower repulsion between the surface and metal ions (Reddad et al. 2002a).
The usefulness of a biosorbent material depends on its sorption capacity, but also on its regeneration ability and potential to be reused (Bishnoi and Garima 2005), which is important for industrial applications. If sorption occurs on the surface of a biosorbent, desorption occurs more easily via simple methods, while an intracellularly bound sorbate requires destructive methods such as incineration or dissolution into strong acids or bases (Gadd and White 1993). Destructive methods are only economical for a cheap biosorbent and recently the aim has been to use non-destructive methods (Vijayaraghavan and Yun 2008).
Modification of biomass
There are several physical and chemical modification methods to enhance the performance of biosorbent materials, including conversion into activated carbon or biochar (Ioannidou and Zabaniotou 2007; Suhas et al. 2007). Typically, physical modification is simpler and more inexpensive, but often less effective compared to chemical modification. An improved sorption ability can be obtained through modifying functional groups (Vijayaraghavan and Yun 2008; Wan Ngah and Hanafiah 2008). For example, acid washing can enhance the capacity of a biosorbent for cationic metals. Additionally, an increase of functional groups or a formation of new ones can enhance the biosorption capacity (Wan Ngah and Hanafiah 2008). Binding sites can be increased by adding long polymer chains onto the surface of a raw biomass, as was extensively reviewed by O’Connell et al. (2008). For living microbial biomass, optimum culture conditions can increase the biosorption capacity (Vijayaraghavan and Yun 2008).
Chemical modification may be required if the unmodified cellulosic biomass has an insufficient content of functional groups to perform well as a biosorbant. Modification is typically based on esterification, etherification, halogenation, or oxidation (O’Connell et al. 2008). For example, Low et al. (2004) used citric acid anhydride to react with cellulose hydroxyl groups, leading to esterification. The increased carboxylic content of the fiber surface was able to increase the sorption potential for divalent metal ions. Halogenation can be performed by reacting cellulose and bromine, yielding 6-bromo-6-deoxycellulose and finally 6-deoxy-6-mercaptocellulose, with its S-substituted derivatives (Aoki et al. 1999). The adsorption properties of cellulose can be improved via oxidation, for example, periodate oxidation yielding cellulose-hydroxamic derivatives (Maekawa and Koshijima 1990). Finally, etherification is achieved by reacting alkali cellulose with organic halides, such as epichlorohydrin, and yielding epoxy groups for further reactions with a chelating agent (Navarro et al. 1996).
Biosorption can work in batches or be continuous. The choice depends on the physical characteristics of the biosorbent, hydraulic flow, the type of target pollutant, plant space, and invested capital. Many alternatives have been investigated, such as stirred tank reactors, up‑flow or down‑flow packed bed reactors, fluidized bed reactors, rotating contactors, trickle filters, and airlift reactors (Atkinson et al. 1998; Malik 2004). Theoretically, the down-flow packed bed reactor is the most effective among the continuous process options. This is due to gravitational forces transferring water through the bed (Atkinson et al. 1998). Additionally, the column biosorption reactor is suitable for pollutant removal in a continuous mode (Volesky 2007). More recently, biosorption via biofunctional magnetic beads has been suggested (Li et al. 2008). Beads made of Rhizopus cohnii and Fe3O4 particles coated with alginate and polyvinyl alcohol were able to host Cr biosorption in the form of Cr(VI). Groups of NH3+, NH2+, and NH were the main binding sites of the Cr ions.
For industrial applications, the main factors affecting biosorption are solution pH, temperature, ionic strength, initial pollutant concentration, biosorbent dosage, biosorbent size, agitation speed, and the coexistence of other pollutants (Park et al. 2010), of which pH is the most important. It affects the solution chemistry, activity of the functional groups in the biosorbent, and the competition with coexisting ions (Vijayaraghavan and Yun 2008). Generally, an increase in pH leads to the enhanced removal of cationic metals and reduced removal in the case of anionic metals. Biosorption is typically enhanced as the temperature increases through increased kinetic energy and surface activity (Vijayaraghavan and Yun 2008), but an excessively high temperature can damage the biosorbent material’s surface.
Alkali metals, especially K and Na, are present naturally in biomass (Turn et al. 1997). For plant growth, alkali and alkaline earth metals are important nutrients, and typically present at low (ppt to ppm) levels. Alkali and alkaline earth metals often remain in the harvested plant material and react easily with other inorganics, such as silica, S, and Cl, forming deposits and exhibiting corrosion in facilities utilizing biomass (Wang et al. 2015a). Deposits are known to be composed of K, Ca silicate, chlorides, sulfates, carbonates, and hydrates. In combustion systems, alkali compounds foul heat transfer surfaces, leading to slag formation in grate-fired units and the formation of agglomerates in fluidized beds. Additionally, the formation of alkali vapor on turbine surfaces may lead to hot corrosion. The Cl‑based corrosion is affected by temperature as well as the concentrations of alkali metal, Cl, S, and oxygen, as reviewed by Nielsen et al. (2000). For example, Cl can influence the corrosion by forming Cl2, HCl, NaCl, and KCl, causing direct corrosion via the oxidation of metal alloys. Alkali compounds are largely water soluble and can be removed by mechanical and leaching methods (Kinoshita et al. 1991).
The first patents for specific types of biosorbents were applied for in the early 1980s. In the 1990s, commercial biomaterials were developed, such as BIO–FIX, AlgaSORBTM (C. vulgaris), and AMT-BIOCLAIMTM (Bacillus biomass) (Volesky 1990; Garnham 1997), for the removal of heavy metal ions from industrial or mining wastewater. The BIO–FIX sorbent can bind heavy metal ions from industrial wastewater and incorporate a biomass of cyanobacteria (Spirulina), yeasts, algae, or plants (Lemna sp., Sphagnum sp.), immobilized in polymeric (polysulphone, polyethylene, and polypropylene) porous beads (Tsezos et al. 2012). In contrast, Advanced Mineral Technologies Inc. used AMT-BIOCLAIMTM from an industrial fermentation process (Bacillus subtilis) and achieved a more than 99% removal efficiency of heavy metals from wastewater (Brierley 1990; Eccles 1995). Finally, MetaGeneR and RAHCO Bio-Beads have also used biosorbents for the removal of heavy metals in commercial‑scale plants (Chojnacka 2010).
Companies in North America have developed these biosorption processes. In Colorado, Advance Minera Technologies Inc. developed a biosorbent based on Bacillus sp. for metal removal, but production was suppressed in 1988. In Canada, a company named B. V. Sorbex Inc. produced different types of biomaterials based on algae (S. natans, A. nodosum, Halimeda opuntia,Palmyra pamata, Chondrus crispus, and C. vulgaris).
The first pilot plant installations, and some commercial-scale units, of biosorption technology have been constructed in the USA and Canada (Tsezos 1999, 2001). Among pilot-scale experiments, Zouboulis et al. (2002) used biosorptive flotation in 10-L columns to remove heavy metals from an aqueous solution with grape stalks from the wine industry. Artola et al. (2001) achieved a removal of Cu through using anaerobically digested sludge in a small pilot plant. For example, the biosorption of uranium and other pollutants has been tested and its applicability for the sequestering of metals and recovery has been confirmed (Volesky and Tsezos 1982).
In full-scale applications, the biosorption of metals is often based on peat-based biosorbents (Wase et al. 1997). Wastewater treatment using a peat biosorbent has been utilized in Maine, Alaska, Canada, and Ireland. For example, Harrison Western Environmental Services Inc. in Lakewood, Colorado used an application of peat moss capsules to bind As, Cd, Pb, Ni, and Se from wastewater. However, there were difficulties in regeneration, reusing biomass, and obtaining a constant supply of inexpensive raw material, while other attempts to commercialize biomass biosorption for wastewater treatment and the recovery of metals have not been successful (Tsezos and Noh 1987; Brierley et al. 1990, 1991).
Biosorption has been widely tested on a laboratory and pilot scale. However, the transfer of knowledge from laboratory‑scale to large‑scale industrial applications is a relatively slow process. Many biosorption processes are still being developed and patented for commercial use, but a very limited number of industrial processes or products in the biosorption area have been implemented. Thus far, there are no industrial full-size plants using commercialized biosorbents or wood-based biomass (Park et al. 2010). Some biosorbents have been commercialized as adsorbents for metals from aqueous solutions, mostly of algal or microbial origin, but according to the authors’ knowledge, there are no industrial processes utilizing wood-based biomass.
Biochar is typically defined as a non-liquefied carbonaceous solid material produced in the thermal decomposition of biomass in an oxygen-limited environment. Several studies have shown the ability of biochar to immobilize organic and inorganic pollutants (Lattao et al. 2014; Mohan et al. 2014; Inyang et al. 2015). Previously, biochar has been used for soil amendment (Chan et al. 2008; Abdel-Fattah et al. 2015) and as a long-term carbon sequestration agent (Wilson et al. 2009), but it also has adsorption potential for heavy metals in aqueous solutions (Chen et al. 2011; Mahmoud et al. 2012; Regmi et al. 2012).
Biochar can be produced from a variety of feedstock materials, such as industrial by-products, and agricultural and forest residues, but even from unconventional materials, such as municipal solid waste (Hwang et al. 2008), food waste (Rhee and Park 2010), newspapers (Li and Zhang 2004), and bones (Dimović et al. 2011). Additionally, biochar can be produced from animal waste, such as poultry litter and dairy manure (Duku et al. 2011). The main advantage of these materials is their low cost and abundance. Most forest residues are generated as by-products and waste from harvesting for bioenergy production, which are often scarcely utilized for other purposes. Recently, biochar made of industrial waste has raised interest due to its wide availability and low cost (Yao et al. 2011a, 2011b). During the production of biofuels, biochar is produced as a by-product and numerous studies have been conducted regarding the development of lignocellulosic non-food biomass into biofuels (Balan et al. 2013).
Biochar has a porous aromatic surface with oxygen-containing functional groups that play a crucial role in trapping metals (Abdel-Fattah et al. 2015). Typically, biochar has a large surface area with a network of micropores (< 2 nm), mesopores (2 to 50 nm), and macropores (> 50 nm) (Mukherjee et al. 2011). Biochar can adsorb metals, such as Pb, Cu, Ni, Cd, Hg, and As from aqueous solutions (Budinova et al. 2006; Amuda et al. 2007; Cao et al. 2009; Uchimiya et al. 2010, 2011). Heavy metals can be absorbed by raw biomass, for example, peat or sawdust (Hu et al. 2008; Sevilla and Fuertes 2009), but it carries the risk of leaching and metal remobilization (Liu and Zhang 2009). In contrast, biochar does not lead to such risks. Adsorption on biochar is strongly affected by the solution pH level, due its effects on the surface hydroxyl groups (Stumm 1992).
Uschmiya et al. (2011) studied the retention of Cu, Ni, Cd, and Pb by biochar made of broiler litter manure. Paradelo and Barral (2012) used biochar produced from municipal solid waste to study their retention of Cu, Zn, and Pb. Mohan et al. (2007) tested the adsorption of toxic materials with fast pyrolysis biochar from oak and pine bark as well as from wood. The authors concluded that the maximum adsorption occurred at pH levels of 3 to 4 for As and at levels of 4 to 5 for Pb and Ca; they also found that the adsorption of biochar occurred viaion‑exchange. Adsorption into the biochar strongly depends on the structure and chemical properties, which are a function of pyrolysis and activation processes (Han et al. 2013). Inyang et al. (2011) showed that biochar from anaerobically digested sugarcane bagasse is a more effective sorbent for Pb than undigested or activated carbon. Inyang et al. (2012) studied the sorption of heavy metals by biochar made of anaerobically digested dairy waste and sugar beet. They concluded that biochar is a suitable sorbent to remove Ni, Cu, Cd, and Pb from wastewater.
There are several ways to produce biochar from biomass, including slow pyrolysis, flash pyrolysis, and hydrothermal conversion. During slow pyrolysis, biomass is heated for an extended period of time (5 to 30 min) at 400 to 500 °C without oxygen, while moderate pyrolysis proceeds at approximately 500 °C for 10 to 20 s and fast pyrolysis occurs for 1 s (Kumar et al. 2011). Generally, temperatures over 650 °C favor the formation of gaseous products, while slower heating rates with moderate maximum temperatures lead to maximized char yield (Kumar et al. 2011). Biochar produced at a higher temperature has a high pH and surface area (Lehmann 2007), while lower temperatures lead to a higher oxygen content and more active sites for binding (Kumar et al. 2011). For example, Abdel-Fattah et al. (2015) studied biochar produced from pinewood waste via slow pyrolysis. The authors found that the biochar was effective in removing metal contaminants (Mg, Ca, Cr, and Pb ions) from drinking water and leather tannery effluent at up to 91.6% removal efficiencies.
Various methods of biochar production, including the pretreatment of feedstock or the modification of char surface, have led to efficient biochar types with good adsorption capacity that, in some cases, are even better than those of commercial activated carbons (Inyang et al. 2011, 2012). It has been reported that the removal efficiency of Pb and Cd with oak bark is similar to that of a commercial activated carbon (Calgon F-400) (Mohan et al. 2007). Furthermore, the sorption capacity of biochar can be enhanced by esterification (Tan et al. 1993). For example, physical treatment via the pulverization of feedstock prior to pyrolysis can enhance the sorption ability in aqueous solutions (Tong et al. 2011). Applications of biochar in binding contaminants in soils have been extensively reviewed by Kookana (2010) and Beesley et al. (2011), while the production of biochar has been reviewed by Mohan et al. (2014) and Ahmad et al. (2014).
Chemistry of Sorption
Native wood and other wood-based biomass are mostly composed of lignin and cellulose, hemicellulose, extractives, lipids, proteins, sugars, starches, water, hydrocarbons, and inorganics. In general, the functional groups of a biosorbent attract and sequester heavy metals. Functional groups, such as amide, amine, carbonyl, carboxyl, esters, hydroxyl, imine, imidazole, sulfonate, sulfhydryl, thioether, phenolic, phosphate, and phosphodiester groups enable biosorption (Gupta et al. 2000; Vieira and Volesky 2000; Sud et al. 2008). Additionally, steric, conformational, and other barrier properties can have an effect on the sorption process (Volesky 1994). Biosorption occurs via chemical and physical mechanisms, such as ion exchange, complexation, adsorption, precipitation, and entrapment in inner capillaries (Sud et al. 2008).
The carboxyl groups are mainly uronic in acid type, chemically bound to xylan hemicellulose, or are found in pectin. Carboxyl groups can also be found in native lignin and extractives (Bhardwaj et al. 2004). Phenolic hydroxyl groups mostly originate from lignin. Uronic acid groups often originate from 4-O-methyl glucuronic acid units in xylan and D‑galacturonic acid units in pectins, but also in D-glucuronic acid in arabinogalactan (Laine et al. 1996; Koljonen et al. 2004). In different wood species, these groups are mostly methyl-esterified and lactonized (Konn et al. 2007). The molar ratio of glucuronic acid to xylan is approximately 1:5 in softwood and 10:1 in hardwood (Fengel and Wegener 1989; Lindström 1992). On average, there is 1.5 times more hemicellulose in hardwood than in softwood.
The binding occurs in phenol and carboxyl groups, in which phenolic groups originate from residual lignin. The affinity of metal ions to lignin is much higher than to that of carbohydrates (Perat et al. 2001; Carrot and Carrot 2007). Most carboxylic groups in pulp are hexenuronic acids that are formed during kraft cooking (Buchert et al. 1995; Devenyns and Chaveheid 1997). Granholm et al. (2010) studied the chelation of hardwood and softwood kraft pulp. Many elements in kraft pulp were detected and the highest concentrations of elements (Na, Ca, Mg, Mn, and K) in hardwood pulp ranged between 48 and 750 ppm, while only trace amounts of As, Rb, zirconium (Zr), and Sn (0.04 to 0.11 ppm) were found.
Many studies have shown the importance of carboxylic groups in the sorption of metal ions to biomass material (Bakir et al. 2009; Hubbe et al. 2011). Wood and bark can have ion-exchange properties due to certain anionic functional groups. These functional groups include mostly phenolic hydroxyl groups and carboxyl groups, acting as binding sites of metal ions to wood and bark. Some remain during pulping and bleaching, while some new groups are formed in these processes (Fardim and Holmbom 2003). Additionally, the number and type of functional groups is higher in mechanical pulp compared to chemical pulp, due to lignin carrying the phenolic hydroxyl groups. However, in chemical pulp the binding sites are more evenly distributed.
Sorption mechanisms of biochar
The sorption ability of biochar is due to the surface properties that originate from feedstock material. Oxygen-containing groups, such as hydroxyl, carboxyl, and ether groups, for example, in oak bark biochar, originate from polyphenolic tannins, flavonoids, and suberin in bark. They give negatively charged surface sites for the biochar that can attract positively charged metal ions (Mohan et al. 2007). The pyrolysis of agricultural residues, such as sugar beet tailings, can lead to electron donor functional groups, due to the heteropolysaccharides of the feedstock (Aksu and Isoglu 2005). For example, hydroxyl, carboxyl, and ether functional groups allow the sorption of Cr (Dong et al. 2011).
Precipitation, complexation, ion exchange, physical sorption, and chemisorption are among the mechanisms that lead to the removal of heavy metals from aqueous solutions by biochar. Precipitation is the formation of solid compounds in a solution or on a surface during the sorption process. It is one of the main mechanisms binding heavy metals by biochar materials. In complexation, multi-atom structures are formed with specific metal-ligand interactions that are important for metals with partly filled d-orbitals with an affinity for ligands, such as transition metals (Crabtree 2009).
Heavy metals can be bound by electrostatic interactions with a biochar surface. High temperatures in carbonization promote graphene structures in biochar that favor electrostatic attractions (Keiluweit and Kleber 2009). In contrast, ion exchange on biochar begins via the selective replacement of positively charged ions, such as Na, Li, K, Ca, and Be, on biochar. High levels of cationic nutrients in wood material can yield a high cation‑exchange capacity of the biochar and enhance the sorption of metal ions, for example, Pb in acidic conditions (Mohan et al. 2007). Finally, sorption can occur due to the physical sorption of metal ions into the sorbent pores without the formation of chemical bonds. Inyang et al. (2016) have reviewed adsorption kinetics and thermodynamics describing the sorption characteristics of biochar.
ANALYSIS OF METALS
In previous decades, the distribution of free metals and their binding sites in wood has been determined via chemical stains and the autoradiography of radioisotopes. However, these methods are unable to quantify the total metal content. Currently, a large number of analytical tools are available for the detection of active sites for the binding of metals. Some of these tools include infrared absorption spectroscopy (IR) or Fourier transform infrared spectroscopy (FTIR) (Memon et al. 2008), scanning electron microscopy (SEM) (Memon et al. 2008), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) analysis, electron spin resonance spectroscopy (ESR), nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), X‑ray absorption spectroscopy (XAS), and chemical fractionation analysis (CFA) (Werkelin et al. 2010).
Metal species can be detected using X-ray spectroscopic techniques or a SEM with energy dispersive X-ray analysis (SEM-EDX), but X-ray spectroscopic techniques are not sensitive enough for trace metal imaging and often suffer from quantification problems. Sensitivity and quantification are limited by background scatter and abundant matrix elements (Becker et al. 2010; Blaske et al. 2014), unlike a sensitive graphite furnace atomic absorption spectrometry (GFAAS), which can directly detect heavy metal ions (Mirzaei et al. 2011).
Mass spectrometry is one of the most important techniques for the determination of element concentrations at trace and ultratrace levels, for isotope analysis, and for structural characterization. This is mostly due to its high sensitivity and low detection limits (Becker 2007). For example, in bioanalytics, the determination of essential trace metals, metalloids, and non-metals, such as S, P, and Cl is highly important. Many proteins with heteroelements or metals have been detected and quantified by inductively coupled plasma mass spectrometry (ICP‑MS) equipment (Tatar et al. 2007). Essential and toxic metals are often inhomogenously distributed in biological material, creating the need for analytical techniques with good spatial resolution and a high signal‑to‑noise ratio.
Before ICP‑MS techniques were established, imaging techniques, such as X‑ray spectroscopy (Majumdar et al. 2012) and secondary ion mass spectrometry (SIMS) (Guerquin-Kern et al. 2005), were used for solid samples. Secondary ion mass spectrometry provides resolution down to 50 nm with a penetration depth of only 0.2 to 10 nm, but it does not enable elemental quantification. Among ICP‑MS methods, laser ablation (LA)‑ICP‑MS is suitable for the quantification of metals from solid samples down to sub-ppm levels (Tokareva et al. 2010); but it provides mostly semi-quantitative results. Examples of different methods are listed in Table 1.
Table 1. Examples of Analysis Methods Applied to Study Metals in Aqueous Matrices and Wood-Based Biomass
Iminodiacetate chelating resin (Chelex-100), Chemical fractionation analysis (CFA), dispersive liquid–liquid microextraction (DLLME), electrothermal atomic absorption spectrometry (ETAAS), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), graphite furnace atomic absorption spectrometry (GFAAS), high performance liquid chromatography (HPLC), inductively coupled plasma (ICP), laser ablation (LA), limit of detection (LOD), mass spectrometry (MS), optical emission spectrometry (OES), quantitation (LOQ), scanning electron microscopy (SEM), secondary ion mass spectrometry (SIMS), solid phase extraction (SPE), X-Ray diffractometry (XRD) ; nd ‑ not determined
Technology for ICP-based methods was first developed in the 1960s, and the first application of induction plasma was described by Bâdârâu et al. (1956). The first commercial spectrometers were sold in the mid-1970s. Plasma is an electrically neutral gas composed of ions, electrons, and neutrals, often produced by argon and energized by a high electromagnetic field or a direct current. In ICP analysis, the sample is acidified and sprayed into the plasma for ionization. A high plasma temperature atomizes and ionizes all forms of compounds and gives a reproducible response. Currently, ICP is the most widely used plasma source and is routinely used in diverse fields of research, including geochemistry, the environment, industry, forensic science, and archaeology (Ammann 2007). Typically, ICP analysis is connected with mass spectrometry (MS) (Tokareva et al. 2010), optical emission spectrometry (OES) (Álvarez et al. 2007), or atomic emission spectrometry (AES) detectors (Nölte 2000).
Inductively coupled plasma optical emission spectrometry is an atomic spectroscopic technique used for the determination of elements in liquid samples (Su 2012). It can detect more than 70 elements simultaneously over a wide concentration range. The main components of an ICP-OES system include a nebulizer, an ICP torch, and a spectrometer (Boss and Fredeen 1997). Typically, a sample in the liquid phase is transported to the nebulizer through a thin tube. Argon gas is pumped through the nebulizer, which breaks down the droplets into an aerosol. The droplets are transported to a spray chamber between the nebulizer and the torch. Large droplets are removed, while smaller ones of uniform size are injected into the plasma. Atoms and ions are excited by the high temperature of argon plasma (8000 to 10000 K), emitting characteristic radiations at specific wavelengths. Intensities are measured in the detector and converted into concentrations based on the calibration curves of known standards.
The ICP-OES equipment has been widely used in various applications of metal analysis. For example, Özdemir et al. (2012) used ICP‑OES to detect and quantify Cd and Co ions in vegetables. The authors used fungi Pleurotus eryngii as a solid-phase biosorbent on Aberlite XAD-16 to concentrate trace levels of Cd and Co. They found the best performance at a pH level of 5 for Co and a pH level of 6 for Cd. The levels in vegetables (onion, aubergine, and okra) ranged up to 125.6 ng g-1 for Cd and up to 98.8 ng g-1 for Co. Wang and Dibdiakova (2014) studied levels of Al, Ca, K, Na, Si, and Zn among other elements in stem wood, bark, branches, and twigs of Norway spruce
Previously, application conditions, including the sample input method, radiofrequency, torch configuration, and gas flow (Vanini et al. 2015) were optimized, leading to a high number of experiments and a high requirement of reagents and time. Multivariable optimization methods are mathematical-statistical tools that can be used to optimize conditions for an analytical method (Bas and Boyaci 2007; Kumar et al. 2014) with a minimum number of experiments (Ferreira et al. 2007; Novaes et al. 2016). The main advantages of an ICP-OES are the capability of multi-elemental analysis, a large dynamic linear range, low detection limits, and high productivity (Suleiman et al. 2008).
After the introduction of the first commercial instrument in 1983, the ICP‑MS technique has been constantly improving and achieving very low detection limits with high spectral resolution (10000) for multielement isotope detection (Nelms 2005). Additionally, ICP‑MS is one of the most efficient and element-specific techniques, due to its wide linear range and isotope capability (Pu et al. 2005; Zhang et al. 2008). Inductively coupled plasma and other types of ion sources of MS, such as ESI, have been reviewed by Lobiński et al. (2006). Furthermore, ICP-MS is an ideal tool for the trace analysis of metals, allowing a broad dynamic range up to mg L-1 levels, a fast multi-elemental and isotopic analysis with high sensitivity, and detection limits of below 100 ng L-1.
Inductively coupled plasma mass spectrometry has become the method of choice in elemental speciation, including covalently bound elements, coordinated metals, metalloids, and organometallic metabolites (Hirner and Emons 2004). For example, elemental characterization in wines has been conducted by ICP‑MS (Marisa et al. 1999; Kment et al. 2005; Tatar et al. 2007), suitable for the fast determination of trace and ultratrace elements (Gonzálvez et al. 2008). An ICP is a versatile atomizer and ionizer in temperatures up to 5500 °C (Houk and Praphairaksit 2001). In plasma, chemical bonds are broken and the data regarding the total content of an element is acquired. The response is accurate and species-unspecific, allowing quantitation based on commercially available multielement standards (Zeisler et al. 2006). High ion density of argon provides the highest collision rate, generating much higher analyte ion densities compared to other ion sources (Ray et al. 2004).
Helium or mixtures of helium and argon are typically used as a carrier gas (Wang et al. 2013). A small amount of helium in plasma can reduce the formation of the polyatomic ions of argon. Higher sensitivities can be obtained in wet plasma with nebulized solutions of water and methanol in the carrier gas stream (Fliegel et al. 2011). Another strategy to increase spatial resolution is coupling a laser microdissection apparatus (LMD) to an ICP-MS. Such a system was originally designed to isolate specific tissue‑material cells. In LMD-ICP-MS, LMD works as an ablation system and is typically equipped with a Nd:YAG laser (at 355 nm wavelength), which provides a highly focused beam with a spot size of 1 µm. Overall, commercial systems give a resolution down to 2 to 5 µm.
There are at least four configurations for the vacuum system for an ICP-MS instrument: a cell entirely within the ion optics, within the mass analyzer chamber, within an additional vacuum chamber, and a cell communicating between the ion optics and the mass analyzer chambers. For a typical ICP-MS instrument, the source gas flow into the ion optics chamber is approximately 1019 atoms per second (Tanner 2002). The number of collisions for an ion is the length of the ion traveling in the chamber divided by the mean free path.
The two-dimensional collision cell was first introduced into triple quadrupole mass spectrometry by Yost and Enke (1978). The collision cell is placed between two mass analyzing quadrupoles (Ammann 2007). Ions of interest, parent ions, are mass-selected in the first quadrupole (Q1). The ions are led at a selected energy into the collision cell (Q2), which is pressurized with collision gas. Ions impact with the collision gas, leading to fragmentation and the formation of daughter ions. They are further transmitted to the second mass analyzer (Q3), where the daughter ions are detected. The fragmentation may include one or several collisions. Other modes are also possible, including neutral loss scan and parent ion scan. The triple quadrupole is often referred to as a tandem MS (MS/MS), differentiating the devices with higher order multipoles, such as hexapole and octapole (Ammann 2007). In contrast, an ion trap mass spectrometer confines and isolates the parent ion, excites the ion, and induces collision‑activated dissociation (CID), trapping the daughter ions with mass analysis (March and Todd 1995). The first application of tandem MS with ICP ion source was reported by Douglas (1989) and aimed to perform CID on polyatomic ions Ar2+, ClO+, ArCl+, and CeO+. The collision energy needs to be sufficient to promote fragmentation and exceed the bond strength.
A variety of separation and pretreatment techniques can be used before a sample is introduced into ICP equipment, including coprecipitation (Akagi and Haraguchi 1990), solvent extraction (Kokšal et al. 2002), solid phase extraction (SPE) (Costa et al. 2002), and on-line SPE applications (Zougagh et al. 2004). For aqueous samples, the pretreatment of metal content for ICP analysis can include microwave-assisted acid digestion (Kment et al. 2005; Álvarez et al. 2007), thermal digestion in an open reactor (Sperkova and Suchanek 2005; Iglesias et al. 2007), sample dilution (Marisa et al. 2003; Catarino et al. 2006), or dry ashing (Moreno et al. 2007). For example, wet digestion is suitable for the partial or total decomposition of organic matter, can be performed in open or closed vessels, and is heated by convective thermal energy or microwave radiation (Gonzálves et al. 2008).
Reimann et al. (2008) studied the metal contents of wood ash from Norwegian birch (Betula pubescens) and spruce (Picea abies). The authors leached the samples with nitric acid for 1 h, digested in hot water, and added a modified aqua regia to prepare the samples in HCl before analysis via ICP‑MS. The authors studied 39 elements of which Zn and Ba were among the highest concentrations and Fe and Hg among the lowest. The heavy metals Cd, Cr, Cu, and Pb were found at levels of 37 to 965 mg kg-1, with large variations between wood species, although they were collected from the same site.
A large variety of sample introduction systems have been developed for ICP-MS. The most economical is an often‑used liquid solution nebulization for sample introduction. Typically, solid samples need to be digested and dissolved to obtain a homogeneous sample. Alternatively, the direct access of solid analytes in laser ablation is a method of choice, with a spatial resolution on the micrometer scale of approximately 1 µm (Günther and Mermet 2000). This is a preferred technique in many fields, such as geology (Heinrich 2006), and material and forensic sciences (Berends-Montero et al. 2006). Electrothermal vaporization (ETV) allows for sample preparation in situ and sample preconcentration (Grégoire 2000). Compared to liquid samples, LA and ETV have enhanced reproducibility, but only with decreased detection limits (Grinberg et al. 2006).
Compared to other techniques, ICP‑MS is a relatively inexpensive analytical tool, excluding the higher running costs due to argon consumption. To cover the whole mass range of elements, a quadrupole mass analyzer is required to detect all the isotopes of an element. It gives element‑specific results, because an element has one or several isotopes that differ from the others. Detection limits are typically in the ng per liter range without preconcentration and, with a high resolution ICP‑MS instrument, even below (Moldovan et al. 2004). Approximately 80% of elements are composed of several isotopes, and naturally occurring isotopes are routinely measured. Kinetically fractioned isotope ratios require high-precision ICP‑MS with a multicollector detection unit (Wieser and Schwieters 2005). High concentrations can be measured by their low-abundance isotopes to protect the detector.
In ICP‑MS, multi-element capacity and feasibility of isotopic ratio determinations are important features, which make it an ideal tool for isotope analysis. Isotope dilution mass spectrometry (IDMS) is one of the most accurate methods in trace element and elemental species analysis (Heumann 1992). In IDMS, a known quantity of spike, one of the element isotopes, is added to the sample. The resulting isotope ratio is determined with the mass spectrometer, and only isotope ratios instead of absolute intensities are used to calculate concentrations.
With high accuracy and precision, ICP‑IDMS has been applied for different elements (Viczián et al. 1990; Buckley and Ihnat 1993). Better result accuracy was achieved with an isotope dilution technique compared to conventional calibration methods. Viczián et al. (1990) reported on-line isotope dilution with simultaneous injection of the spike and sample into ICP‑MS. Furthermore, IDMS can be performed either with species-specific or species-unspecific spike. For species-specific spike, the structure and composition of the species are known, and analytes are labeled with enriched isotopes. In contrast, for species-unspecific spike, spike is added after the sample and may be in another chemical form, is required of the structure, and composition of different analytes are not exactly known. Other calibration methods, such as standard addition, cannot be applied due to different behavior compared to the sample.
There are numerous reports on As analysis in water by ICP-MS (Chatterjee et al. 2000; Roig-Navarro et al. 2001; Nakazato et al. 2002). However, high levels of chloride can interfere with the analysis, due to the formation of argon chloride (40Ar35Cl) in the plasma with the same mass as 75As (Wei et al. 2001). To avoid this, sample introduction should be carried out viaETV, to increase sensitivity and decrease absolute detection limits (Hung et al. 2004).
The technique of ICP‑MS is sensitive to matrix interferences induced by high salt (> 1 g L-1) content, which can cause spectral interference (Marin et al. 1997; Sutton et al. 1997) and matrix effects due to analytical signal variations. Typically, these include suppression caused by reduced ionization efficiency and the clogging of tubes and cones (Jakubowski and Stuever 1997), but signal enhancement has also been reported (Heitmar et al. 1990). Trace elements are difficult to analyze from seawater due to their low concentrations and the influence of matrix elements, such as Na, Mg, Ca, K, and Cl. Specifically, ICP‑MS allows for the direct detection of trace elements at the µg L-1 level, but interferences caused by seawater limit their detection. Spectral interferences are caused by polyatomic species that cause disturbances in the analyte masses, such as 35Cl6O+ with 51V+ or 40Ar23Na+ with 63Cu+. Additionally, easily ionized matrix elements on the plasma (Na, K) cause signal suppression and signal drift, due to the accumulation of salts on the cones and lenses of ICP‑MS. Therefore, a pretreatment is required to concentrate the analyte to improve the detection limit, reduce matrix content, and enhance the analytical conditions (Nicolaï 1999).
Sample pretreatment by coprecipitation, solvent extraction (Ferreira et al. 1997; Wu and Boyle 1997), calibration by internal standard, isotope dilution (Alimonti et al. 1997), and alternative sample introduction (electrothermal vaporization, flow injection, or ultrasonic nebulization) are common ways to handle what ICP-MS lacks (Jakubowski and Stuever 1997). Additionally, the subtraction of interfering signal and the limitation of polyatomic species formation are ways to correct spectral interferences (Wu and Boyle 1997). Dilution with pure water can reduce matrix effects, but this often leads to inadequate instrument sensitivity. Therefore, trace elements in seawater samples are often preconcentrated on a chelating resin by rinsing the matrix elements from the resin, eluting the trace elements, and detecting with ICP‑MS (Beck et al. 2002; Veguería et al. 2013). Preconcentration can be performed off-line (Veguería et al. 2013; Minami et al. 2015) or on-line as part of the ICP‑MS work‑flow (Sumida et al. 2006; Veguería et al. 2013). On-line is preferred over the off-line step because it reduces the contamination risks of the latter.
Metal preconcentration and separation from seawater has been investigated with chelation by iminodiacetate chelating resin Chelex-100 (Sarzanini and Mentasti 1997). In 1968, Riley and Taylor (1968) reported the use of Chelex-100, which has been the most‑studied resin thus far (Miyazaki and Reimer 1993; Fernández et al. 1997). Another resin, CC-1, is a highly cross-linked macroporous copolymer that can withstand pressures above 100 bar and is suitable for high performance liquid chromatography (HPLC) applications (Bettinelli and Spezia 1995; Lu et al. 1998). Chelex-100 has a high affinity for most trace elements, and microcolumns filled with Chelex-100 have been applied for the on-line preconcentration of seawater (Rahmi et al. 2007). The adsorption is dependent upon pH level, with the optimum at around 6.5 (Pesavento and Biesuz 1997). This is often achieved with a buffer, such as ammonia acetate, before introducing through the column filled with Chelex-100 (Ferrarello et al. 2001).
Søndergaard et al. (2015) studied trace elements in seawater via ICP-MS with on-line preconcentration and a Babington nebulizer, which is suitable for samples with high amounts of salt. They found V, Mn, Co, Ni, Cu, Zn, Cd, and Pb with detection limits of 5 to 345 ng L-1, depending on the element. Excess seawater was pumped through the nebulizer of the ICP-MS during the preconcentration step, and the gas flow was adjusted to pump out the seawater without entering the instrument (Søndergaard et al. 2015). Therefore, no changes were required for the sample introduction and only a resin-filled (Chelex-100) microcolumn was added to the sample tube.
For metal separation, SPE (Birlik et al. 2007; Tuzen and Soylak 2007), HPLC (Grotti et al. 2014), and ion chromatography (IC) (Jackson and Bertsch 2001) are the most‑used methods. The method of SPE is suitable for a variety of environmental samples with high enrichment factors, including automation of the extraction procedure (Poole 2003). Adsorption materials have a crucial role in SPE. For example, silica gel immobilized with various organic compounds has a metal chelating ability with fast and quantitative sorption and elution (Chang et al. 2007), but unfortunately it does not enable specific metal ion selectivity (Jiang et al. 2006).
A method called molecular imprinting is used for preparing polymers with high molecular recognition by the polymerization of functional monomers in the presence of the template, the target compound used to prepare the polymer, and excess of the crosslinker. Molecular imprinted polymers (MIB) can rebind and react selectively with specific target analytes (Haupt 2001). Ion-imprinted polymers (IIPs) and MIBs have many similarities, but IIPs have the affinity for metal ions (Rao et al. 2004) and have been developed for SPE applications (Daniel et al. 2005). A type of molecular imprinting is a technique called surface molecular imprinting, which yields imprinted polymeric material with multiple accessible sites, high selectivity, and fast mass transfer and binding kinetics (Na et al. 2006). Additionally, IIPs prepared by surface printing are suitable for binding, for example, Pd, Ni, Fe, Cd, Zn, and Cu (Zhang et al. 2007). Zhang et al. (2008) studied a Cr(III)-imprinted modified silica gel sorbent, with 3-(2-aminoethylamino) propyl trimethoxysilane (AAPTS). The surface imprinted material was used as a selective SPE sorbent material to bind Cr(III) in environmental water samples analyzed with ICP-MS. The sorbent was suitable in selectively binding Cr(III) from water with good tolerance to other ions. Additionally, it had fast adsorption and desorption kinetics, and good stability under acidic conditions.
Accurate analytical results are a requirement for the study of the toxicity, bioavailability, and environmental behavior of different species. Various chromatographic methods combined with ICP-MS have become powerful techniques for elemental speciation. The method of HPLC coupled with ICP-MS is a sensitive system for the separation and detection of elemental species. Analysis can be performed without sample enrichment, which may influence the composition of the species in the sample.
For example, Rottmann and Heumann (1994) used HPLC with ICP-MS to study Cu and Mo in natural water. They used the on-line isotope dilution method for elemental characterization and detected pg mL-1 levels without a sample preparation step. Species (As III, As IV) have been detected in fish and crustaceans by HPLC coupled with ICP-MS equipment (Rattanachongkiat et al. 2004). They detected levels up to 17 µg g-1 from a Sn mining area. The HPLC separation was performed as an anion exchange HPLC with a phosphate-based eluent at a pH level of 6 to 7.5. Carignan et al. (2001) used HPLC prior to ICP-MS to remove isobaric interference and to eliminate signal suppression in the plasma. The authors analyzed rock samples, including basalt, serpentine, and granite, to detect the rare earth elements uranium (U) and thorium (Th). The authors used LC-ICP-MS and found on average 50.6 ng g-1(Th) and 15.3 ng g-1 (U).
Zheng et al. (2003) applied anion exchange HPLC coupled with ICP-MS to detect As in the surface water of the Moira River, Canada, and found levels up to 75 ng L-1. The river has been contaminated by heavy metals from a mine since the 1860s. Dos Santos et al. (2009) detected organic and inorganic Hg in water and sediment samples. The authors used SPE-HPLC for extraction and separation, coupled with ICP-MS, and found on average 30.7 (Hg2+) and 10.8 (MeHg+) ng L-1. Recently, analysis techniques for elements by small-bore HPLC coupled with ICP-MS were extensively reviewed by Grotti et al. (2014).
Therefore, ICP-MS coupled with high-performance separation is expanding in the identification of metal species. Moreover, HPLC offers many variations, such as ion‑exchange chromatography, ion-pairing chromatography, and size-exclusion chromatography (SEC), that can be coupled with ICP-MS. Thus far, HPLC can be considered one of the most effective instrumental techniques for speciation analysis (Michalke 2002a,b).
Biosorbents show great potential for binding heavy metals. The availability of forest residue material and its low price increase its value as a biosorbent. Pilot-scaled and full-size plants have been established that use biosorbents for binding heavy metals, but large-scale plants have not been economically viable. Thus far, wood-based material is not in commercial use, but sorbents based on living biomass, such as algae and bacteria, have been studied and patented. Overall, the main challenge in the near future will be to develop the sorption process at a commercial scale to meet economic demands and solve the process-related issues, including metal recovery and the uninterrupted availability of the sorbent material.
There is an ever‑increasing demand for utilizing waste as a raw material in different applications. This often includes the removal of heavy metals and collecting them for other purposes. Costly conventional methods for heavy metal removal from industrial effluents and ever‑increasing legislative demands require new methods to be found for their removal. Furthermore, the demand for the monitoring of heavy metal levels set by the EU has increased the demand for effective and reliable analytical methods. This requires both methods and equipment to handle even the most difficult sample matrices. The ICP‑MS-based methods have shown an ability to achieve low detection limits and reliability. Such methods can be coupled with other pretreatment methods or separate components, using chromatographic methods to meet the increasing demand for the detection of even the lowest concentrations in the future.
Abdel-Fattah, T. M., Mahmoud, M. E., Ahmed, S. B., Huff, M. D., Lee, J. W., and Kumar, S. (2015). “Biochar from woody biomass for removing metal contaminants and carbon sequestration,” J. Ind. Eng. Chem. 22, 103‑109. DOI: 10.1016/j.jiec.2014.06.030
Ahluwalia, S. S., and Goyal, D. (2007). “Microbial and plant derived biomass for removal of heavy metals from wastewater,” Bioresource Technol. 98(12), 2243‑2257. DOI: 10.1016/j.biortech.2005.12.006
Ahmad, M., Rajapaksha, A. U., Lim, J., Zhang, M., Bolan, N., Mohan, D., Vithanage, M., Lee, S., and Ok, Y. (2014). “Biochar as a sorbent for contaminant management in soil and water: A review,” Chemosphere 99, 19‑33. DOI: 10.1016/j.chemosphere.2013.10.071
Akagi, T., and Haraguchi, H. (1990). “Simultaneous multielement determination of trace metals using 10 mL of seawater by inductively coupled plasma atomic emission spectrometry with gallium coprecipitation and microsampling technique,” Anal. Chem. 62(1), 81‑85. DOI: 10.1021/ac00200a015
Aksu, Z., and Isoglu, I. A. (2005). “Removal of copper(II) ions from aqueous solution by biosorption onto agricultural waste sugar beet pulp,” Process. Biochem. 40(9), 3031‑3044. DOI: 10.1016/j.procbio.2005.02.004
Aksu, Z., Sag, Y., and Kutsa, T. (1992). “The biosorpnon of copperod by C. vulgaris and Z. ramigera,” Environ. Technol. 13(6), 579‑586. DOI: 10.1080/09593339209385186
Al-Asheh, S., Banat, F., and Al-Rousan, D. (2003). “Beneficial reuse of chicken feathers in removal of heavy metals from wastewater,” J. Clean. Prod. 11(3), 321‑326. DOI: 10.1016/S0959-6526(02)00045-8
Al-Asheh, S., and Duvnjuk, Z. (1998). “Binary metal sorption by pine bark: Study of equilibria and mechanisms,” Sep. Sci. Technol. 33(9), 1303‑1329. DOI: 10.1080/01496399808544985
Al-Asheh, S., Lamarche, G., and Duvnjuk, Z. (1998). “Investigation of copper sorption using plant materials,” Water Qual. Res. J. Can. 33(1), 167‑183. DOI: 10.2166/wqrj.1998.010
Alimonti, A., Petrucci, F., Fioravanti, S., Laurenti, F., and Caroli, S. (1997). “Assessment of the content of selected trace elements in serum of term and pre-term newborns by inductively coupled plasma mass spectrometry,” Anal. Chim. Acta 342(1), 75‑81. DOI: 10.1016/S0003-2670(96)00545-4
Álvarez, M., Moreno, I. M., Pichardo, S., Camean, A. M., and Gonzalez, A. G. (2007). “Metallic profiles of Sherry wines using inductively coupled plasma atomic emission spectrometry methods (ICP-AES),” Sci. Aliment. 27(1), 83‑92. DOI: 10.3166/sda.27.83-92
Ammann, A. A. (2007). “Inductively coupled plasma mass spectrometry (ICP MS): A versatile tool,” J. Mass Spectrom. 42(4), 419‑427. DOI: 10.1002/jms.1206
Amuda, O. S., Giwa, A. A., and Bello, I. A. (2007). “Removal of heavy metal from industrial wastewater using modified activated coconut shell carbon,” Biochem. Eng. J. 36(2), 174‑181. DOI: 10.1016/j.bej.2007.02.013
Annadurai, G., Juang, R. S., and Lee, D. L. (2002). “Adsorption of heavy metals from water using banana and orange peels,” Water Sci. Technol. 47(1), 185‑190. DOI: 10.2166/wst.2003.0049
Aoki, N., Fukushima, K., Kurakata, H., Sakamoto, M., and Furuhata, K. (1999). “6‑Deoxy-6-mercaptocellulose and its S-substituted derivatives as sorbents for metal ions,” React. Funct. Polym. 42(3), 223‑233. DOI: 10.1016/S1381-5148(98)00076-5
Artola, A., Martin, M. J., Balaguer, M., and Rigola, M. (2001). “Pilot plant biosorption in an integrated contact–settling system: Application to Cu(II) removal by anaerobically digested sludge,” J. Chem. Technol. Biot. 76(11), 1141‑1146. DOI: 10.1002/jctb.496
Atkinson, B. W., Bux, F., and Kasan, H. C. (1998). “Considerations for application of biosorption technology to remediate metal-contaminated industrial effluents,” Water SA 24(2), 129‑135.
Bâdârâu, E., Giurgea, M., Giurgea, G. H., and Truţa, A. T. H. (1956). “Hochfrequente Fackelentladung als Spektralquelle [High-frequency torch discharge as a spectral source],” Spectrochim. Acta 11, 441‑447. DOI: 10.1016/S0371-1951(56)80074-X
Bailey, S. E., Olin, T. J., Bricka, R. M., and Adrian, D. D. (1999). “A review of potentially low-cost sorbents for heavy metals,” Water Res. 33(11), 2469‑2479. DOI: 10.1016/S0043-1354(98)00475-8
Bakir, A., McLoughlin, P., Tofail, S. A. M., and Fitzgerald, E. (2009). “Competitive sorption of antimony with zinc, nickel, and aluminum in a seaweed based fixed-bed sorption column,” CLEAN – Soil Air Water 37(9), 712‑719. DOI: 10.1002/clen.200900164
Balan, V., Chiaramonti, D., and Kumar, S. (2013). “Review of US and EU initiatives toward development, demonstration, and commercialization of lignocellulosic biofuels,” Biofuel. Bioprod. Bior. 7(6), 732‑759. DOI: 10.1002/bbb.1436
Bardos, P. (2004). Composting of Mechanically Segregated Fractions of Municipal Solid Waste – A Review, Sita Environmental Trust, Falfield, Bristol, UK.
Bas, D., and Boyaci, I. H. (2007). “Modeling and optimization I: Usability of response surface methodology,” J. Food Eng. 78(3), 836‑845. DOI: 10.1016/j.jfoodeng.2005.11.024
Becker, J. S. (2007). Inorganic Mass Spectrometry: Principles and Applications, John Wiley & Sons, Chichester, England.
Becker, J. S., Breuer, U., Hsieh, H. F., Osterholt, T., Kumtabtim, U., Wu, B., Matusch, A., Caruso, J. A., and Qin, Z. Y. (2010). “Bioimaging of metals and biomolecules in mouse heart by laser ablation inductively coupled plasma mass spectrometry and secondary ion mass spectrometry,” Anal. Chem. 82(22), 9528‑9533. DOI: 10.1021/ac102256q
Beesley, L., Moreno-Jimenez, E., Gomez-Eyles, J. L., Harris, E., Robinson, B., and Sizmur, T. (2011). “A review of biochars’ potential role in the remediation, revegetation and restoration of contaminated soils,” Environ. Pollut. 159(12), 3269‑3282. DOI: 10.1016/j.envpol.2011.07.023
Benaissa, H. (2006). “Screening of new sorbent materials for cadmium removal from aqueous solutions,” J. Hazard. Mater. 132(2‑3), 189‑195. DOI: 10.1016/j.jhazmat.2005.07.085
Bengtsson, B. E., Coombs, T. L., and Waldichuk, M. (1979). “Biological variables, especially skeletal deformities in fish, for monitoring marine pollution,” Philos. T. Roy. Soc. B286(1015), 457‑464. DOI: 10.1098/rstb.1979.0040
Berends-Montero, S., Wiarda, W., De Joode, P., and Van der Peijl, G. (2006). “Forensic analysis of float glass using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS): Validation of a method,” J. Anal. Atom. Spectrom. 21(11), 1185‑1193. DOI: 10.1039/B606109E
Bettinelli, M., and Spezia, S. (1995). “Determination of trace elements in sea water by ion chromatography-inductively coupled plasma mass spectrometry,” J. Chromatogr. A 709(2), 275‑281. DOI: 10.1016/0021-9673(95)00454-U
Bhardwaj, N. K., Duong, T. D., Hoang, V., and Nguyen, K. L. (2004). “Determination of fiber charge components of Lo-solids unbleached kraft pulps,” J. Colloid Interf. Sci. 274(2), 543‑549. DOI: 10.1016/j.jcis.2003.12.062
Birlik, E., Ersöz, A., Aҫikkalp, E., Denizli, A., and Say, R. (2007). “Cr(III)-imprinted polymeric beads: Sorption and preconcentration studies,” J. Hazard. Mater. 140(1‑2), 110‑116. DOI: 10.1016/j.jhazmat.2006.06.141
Bishnoi, N. R., and Garima, A. (2005) “Fungus ‑ An alternative for bioremediation of heavy metal containing wastewater: A review,” J. Sci. Ind. Res. 64(2), 93‑100.
Blaske, F., Reifschneider, O., Gosheger, G., Wehe, C. A., Sperling, M., Karst, U., Hauschild, G., and Höll, G. (2014). “Elemental bioimaging of nanosilver-coated prostheses using X-ray fluorescence spectroscopy and laser ablation-inductively coupled plasma-mass spectrometry,” Anal. Chem. 86(1), 615‑620. DOI: 10.1021/ac4028577
Boonamnuayvitaya, V., Chaiya, C., Tanthapanichakoon, W., and Jarudilokkul, S. (2004). “Removal of heavy metals by adsorbent prepared from pyrolyzed coffee residues and clay,” Sep. Purif. Technol. 35(1), 11‑22. DOI: 10.1016/S1383-5866(03)00110-2
Boss, C. B., and Fredeen, K. J. (1997). Concepts, Instrumentation and Techniques in Inductively Coupled Plasma Optical Emission Spectrometry, Perkin-Elmer, San Jose, CA, USA.
Brierley, J. A. (1990). “Production and application of a Bacillus-based product for use in metals biosorption,” in: Biosorption of Heavy Metals, B. Volesky (ed.), CRC Press, Boca Raton, FL, pp. 305‑312.
Brierley, J. A., Brierley, C. L., Decker, R. F., and Goyak, G. M. (1990). “Metal recovery,” U.S. Patent No. 4898827.
Brierley, J. A., Brierley, C. L., Decker, R. F., and Goyak, G. M. (1991). “Metal recovery,” U.S. Patent No. 4992179.
Bryant, P. S., Petersen, J. N., Lee, J. M., and Brouns, T. M. (1992). “Sorption of heavy metals by untreated red fir sawdust,” Appl. Biochem. Biotech. 34(1), 777‑788. DOI: 10.1007/BF02920596
Bryers, R. W. (1996). “Fireside slagging, fouling, and high-temperature corrosion of heat transfer surface due to impurities in steam-raising fuels,” Prog. Energ. Combust. 22(1), 29‑120. DOI: 10.1016/0360-1285(95)00012-7
Buchert, J., Teleman, A., Harjunpää, V., Tenkanen, M., Viikari, L., and Vuorinen, T. (1995). “Effect of cooking and bleaching on the structure of xylan in conventional pine kraft pulp,” Tappi J. 78(11), 125‑130.
Buckley, W. T., and Ihnat, M. (1993). “Determination of copper, molybdenum and selenium in biological reference materials by inductively coupled plasma mass spectrometry,” Fresen. J. Anal. Chem. 345(2‑4), 217‑220. DOI: 10.1007/BF00322593
Budinova, T., Ekinci, E., Yardim, F., Grimm, A., Bjornbom, E., Minkova, V., and Goranova, M. (2006). “Characterization and application of activated carbon produced by H3PO4 and water vapor activation,” Fuel Process Technol. 87(10), 899‑905. DOI: 10.1016/j.fuproc.2006.06.005
Cao, X. D., Ma, L. Q., Gao, B., and Harris, W. (2009). “Dairy-manure derived biochar effectively sorbs lead and atrazine,” Environ. Sci. Technol. 43(9), 3285‑3291. DOI: 10.1021/es803092k
Cao, X. D., Ma, L. Q., Rhue, D. R., and Appel, C. S. (2004). “Mechanisms of lead, copper, and zinc retention by phosphate rock,” Environ. Pollut. 131(3), 435‑444. DOI: 10.1016/j.envpol.2004.03.003
Carignan, J., Hild, P., Mevelle, G., Morel, J., and Yeghicheyan, D. (2001), “Routine analyses of trace elements in geological samples using flow injection and low pressure on-line liquid chromatography coupled to ICP-MS: A study of geochemical reference materials BR, DR-N, UB-N, AN-G and GH,” Geostand. Geoanal. Res. 25(2‑3), 187‑198. DOI: 10.1111/j.1751-908X.2001.tb00595.x
Carrot, P. J. M., and Carrot, M. M. L. (2007). “Lignin-from natural adsorbent to activated carbon: A review,” Bioresource Technol. 98(15), 2301‑2312. DOI: 10.1016/j.biortech.2006.08.008
Catarino, S., Curvelo-Garcia, A. S., and Bruno de Sousa, R. (2006). “Measurements of contaminant elements of wines by inductively coupled plasma-mass spectrometry: A comparison of two calibration approach,” Talanta 70(5), 1073‑1080. DOI: 10.1016/j.talanta.2006.02.022
Celik, A., and Demirbaş, A. (2005). “Removal of heavy metal ions from aqueous solutions via adsorption onto modified lignin from pulping wastes,” Energ. Source. 27(12), 1167‑1177. DOI: 10.1080/00908310490479583
Chan, K. Y., Van Zwieten, L., Meszaros, I., Downie, A., and Joseph, S. (2008). “Using poultry litter biochars as soil amendments,” Aust. J. Soil Res. 46(5), 437‑444. DOI: 10.1071/SR08036
Chang, X. J., Jiang, N., Zheng, H., He, Q., Hu, Z., Zhai, Y. H., and Cui, Y. M. (2007). “Solid-phase extraction of iron(III) with an ion-imprinted functionalized silica gel sorbent prepared by a surface imprinting technique,” Talanta 71(1), 38‑43. DOI: 10.1016/j.talanta.2006.03.012
Chen, J. M., and Hao, O. J. (1998). “Microbial chromium(VI) reduction,” Crit. Rev. Env. Sci. Tec. 28(3), 219‑251. DOI: 10.1080/10643389891254214
Chen, X. C., Chen, G. C., Chen, L. G., Chen, Y. X., Lehmann, J., McBride, M. B., and Hay, A. G. (2011). “Adsorption of copper and zinc by biochars produced from pyrolysis of hardwood and corn straw in aqueous solution,” Bioresource Technol. 102(19), 8877‑8884. DOI: 10.1016/j.biortech.2011.06.078
Chatterjee, A., Shibata, Y., Yoshinaga, J., and Morita, M. (2000). “Determination of arsenic compounds by high-performance liquid chromatography-ultrasonic nebulizer-high power nitrogen-microwave-induced plasma mass spectrometry: An accepted coupling,” Anal. Chem. 72(18), 4402‑4412. DOI: 10.1021/ac0017077
Chojnacka, K. (2010). “Biosorption and bioaccumulation–The prospects for practical applications,” Environ. Int. 36(3), 299‑307. DOI: 10.1016/j.envint.2009.12.001
Cimino, G., Passerini, A., and Toscano, G. (2000). “Removal of toxic cations and Cr (VI) from aqueous solution by hazelnut shell,” Water Res. 34(11), 2955‑2962. DOI: 10.1016/S0043-1354(00)00048-8
Costa, A. C. S., Lopes, L., Korn, M. G. A., and Portela, J. G. (2002). “Separation and pre-concentration of cadmium, copper, lead, nickel and zinc by solid-liquid extraction of their cocrystallized naphthalene dithizone chelate in saline matrices,” J. Brazil Chem. Soc. 13(5), 674‑678. DOI: 10.1590/S0103-50532002000500022
Crabtree, R. H. (2009). The Organometallic Chemistry of the Transition Metals, Wiley, New York, USA.
Crini, G. (2006). “Non-conventional low-cost adsorbents for dye removal: A review,” Bioresource Technol. 97(9), 1061‑1085. DOI: 10.1016/j.biortech.2005.05.001
Daniel, S., Babu, P. E. J., and Rao, T. P. (2005). “Preconcentrative separation of palladium(II) using palladium(II) ion-imprinted polymer particles formed with different quinoline derivatives and evaluation of binding parameters based on adsorption isotherm models,” Talanta 65(2), 441‑452. DOI: 10.1016/j.talanta.2004.06.024
Das, N., Vimala, R., and Karthika, P. (2008). “Biosorption of heavy metals ‑ An overview,” Indian J. Biotechnol. 7(2), 159‑169.
Demirbaş, A. (2008). “Heavy metal adsorption onto agro-based waste materials: A review,” J. Hazard. Mater. 157(2‑3), 220‑229. DOI: 10.1016/j.jhazmat.2008.01.024
Devenyns, J., and Chauveheid, E. (1997). “Uronic acids and metals control,” in: Proceedings of 9th International Symposium on Wood and Pulping Chemistry, Montreal, Canada, pp. M5-1-M5-4.
DeWalle, D., Sharpeand, W., and Swistock, B. (1995). Tree Rings as Indicators of Ecosystem Health, CRC Press, Boca Raton, FL.
Dimović, S. D., Smičiklas, I. D., Šljivić-Ivanović, M. Z., Plećaš, I. B., and Slavković‑Beškoski, L. (2011). “The effect of process parameters on kinetics and mechanisms of Co2+ removal by bone char,” J. Environ. Sci. Heal. A 46(13), 1558‑1569. DOI: 10.1080/10934529.2011.609454
Dong, X. L., Ma, L. N. Q., and Li, Y. C. (2011). “Characteristics and mechanisms of hexavalent chromium removal by biochar from sugar beet tailing,” J. Hazard. Mater. 190(1‑3), 909‑915. DOI: 10.1016/j.jhazmat.2011.04.008
Dos Santos, J. S., De la Guárdia, M., Pastor, A., and Dos Santos, M. L. P. (2009). “Determination of organic and inorganic mercury species in water and sediment samples by HPLC on-line coupled with ICP-MS,” Talanta 80(1), 207‑211. DOI: 10.1016/j.talanta.2009.06.053
Douglas, D. J. (1989). “Some current perspectives on ICP-MS,” Can. J. Spectrosc. 34(2), 38‑49. DOI: 10.1007/s00216-009-2658-3
Duku, M. H., Gu, S., and Hagan, E. B. (2011). “Biochar production potential in Ghana ‑ A review,” Renew. Sust. Energ. Rev. 15(8), 3539‑3551. DOI: 10.1016/j.rser.2011.05.010
Dunn, C. E. (2007). Biogeochemistry in Mineral Exploration, Volume 9, Elsevier, Amsterdam, Netherlands.
Dunn, C. E., Adcock, S. W., and Spirito, W. A. (1992). Reconnaissance Biogeochemical Survey Southeastern Cape Breton Island Nova Scotia, Part 1—Black Spruce Bark (File 2558), Geological Survey Canada, Nova Scotia, Canada.
European Commission (EC) Directive 91/271/EEC (1991). “Council directive 91/271/EEC of 21 May 1991 concerning urban waste water treatment,” European Commission, Brussels, Belgium.
EC Directive 2009/28/EC (2009). “Council directive 2009/28/EC of 23 April 2009, on the promotion of the use of energy from renewable sources and amending and subsequently repealing Directives 2001/77/EC and 2003/30/EC,” European Commission, Brussels, Belgium.
EC Regulation 1907/2006 (2006). “Commission regulation of the European Parliament and of the Council of 18 December 2006 concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH),” European Commission, Brussels, Belgium.
Eccles, H. (1995). “Removal of heavy metals from effluent streams ‑ Why select a biological process?,” Int. Biodeter. Biodegr. 35(1‑3), 5‑16. DOI: 10.1016/0964-8305(95)00044-6
Ellis, E. L. (1965). Cellular Ultrastructure of Woody Plants, Syracuse University Press, Syracuse, New York, USA.
Faaij, A. P. C. (2004). “Biomass combustion,” in: Encyclopedia of Energy, C. J. Cleveland (ed.), Elsevier, New York, USA, pp. 175-191.
Fardim, P., and Holmbom, B. (2003). “Fast determination of anionic groups in different pulp fiber by methylene blue sorption,” Tappi J. 2(10), 28‑32.
Fengel, D., and Wegener, G. (1989). Wood ‑ Chemistry, Ultrastructure, Reactions, De Gruyter, New York, USA.
Fernández, F. M., Stripeikis, J. D., Tudino, M. B., and Troccoli, O. E. (1997). “Fully automatic on-line separation preconcentration system for electrothermal atomic absorption spectrometry: Determination of cadmium and lead in sea-water,” Analyst 122(7), 679‑684. DOI: 10.1039/A607598C
Ferrarello, C. N., Bayon, M. M., Alonso, J. I. C., and Sanz-Medel, A. (2001). “Comparison of metal pre-concentration on immobilized Kelex-100 and quadruple inductively coupled plasma mass spectrometric detection with direct double focusing inductively coupled plasma mass spectrometric measurements for ultratrace multi-element determinations in sea-water,” Anal. Chim. Acta 429(2), 227‑235. DOI: 10.1016/S0003-2670(00)01297-6
Ferreira, S. L. C., Korn, M. G. A., Ferreira, H. S., Da Silva, E. G. P., Araujo, R. G. O., Souza, A. S., Macedo, S. M., Lima, D. D. C., De Jesus, R. M., Amorim, F. A. C., et al. (2007). “Application of multivariate techniques in optimization of spectroanalytical methods,” Appl. Spectrosc. Rev. 42(5), 475‑491. DOI: 10.1080/05704920701551506
Ferreira, S. L. C., Queiroz, A. S., Quorn, M. D. A., and Costa, A. C. S. (1997). “Determination of nickel in alkaline salts by inductively coupled plasma atomic emission spectroscopy using 1-(2-thiazolylazo)-p-cresol for preconcentration and separation,” Anal. Lett. 30(12), 2251‑2260. DOI: 10.1080/00032719708001736
Fliegel, D., Frei, C., Fontaine, G., Hu, Z. C., Gao, S., and Günther, D. (2011). “Sensitivity improvement in laser ablation inductively coupled plasma mass spectrometry achieved using a methane/argon and methanol/water/argon mixed gas plasma,” Analyst 136(23), 4925‑4934. DOI: 10.1039/c0an00953a
Folgar, S., Torres, E., Pérez-Rama, M., Cid, A., Herrero, C., and Abalde, J. (2009). “Dunaliella salina as marine microalga highly tolerant to but a poor remover of cadmium,” J. Hazard. Mater. 165, 486‑493. DOI: 10.1016/j.jhazmat.2008.10.010
Gadd, G. M., and White, C. (1993). “Microbial treatment of metal pollution – A working biotechnology?,” Trends Biotechnol. 11(8), 353‑359. DOI: 10.1016/0167-7799(93)90158-6
Garnham, G. W. (1997). The Use of Algae as Metal Biosorbents, CRC Press, London, UK.
Gellerstedt, F., Wagberg, L., and Gatenholm, P. (2000). “Swelling behavior of succinylated fibers,” Cellulose 7(1), 67‑86.
Gonzálvez, A., Armenta, S., Pastor, A., and De la Guardia, M. (2008). “Searching the most appropriate sample pretreatment for the elemental analysis of wines by inductively coupled plasma-based techniques,” J. Agr. Food Chem. 56(13), 4943‑4954. DOI: 10.1021/jf800286y
Granholm, K., Harju, L., and Ivaska, A. (2010). “Desorption of metal ions from kraft pulps. Part 1. Chelation of hardwood and softwood kraft pulp with EDTA,” BioResources 5(1), 206‑226. DOI: 10.15376/biores.5.1.206-226
Grégoire, D. C. (2000). “Electrothermal vaporisation sample introduction for ICP MS,” in: Discrete Sample Introduction Techniques for Inductively Coupled Plasma Mass Spectrometry, D. Beauchemin, C. D. Grégoire, D. Günther, V. Karanassios, J.-M. Mermet, and T. J. Wood (eds.), Elsevier, Amsterdam, Netherlands, pp. 347.
Grinberg, P., Yang, L., Mester, Z., Willie, S., and Sturgeon, R. E. (2006). “Comparison of laser ablation, electrothermal vaporization and solution nebulization for the determination of radionuclides in liquid samples by inductively coupled plasma mass spectrometry,” J. Anal. Atom. Spectrom. 21(11), 1202‑1208. DOI: 10.1039/B607911C
Grotti, M., Terol, A., and Todolí, J. L. (2014). “Speciation analysis by small-bore HPLC coupled to ICP-MS,” TrAC-Trend. Anal. Chem. 61, 92‑106. DOI: 10.1016/j.trac.2014.06.009
Günther, D., and Mermet, J.-M. (2000). Discrete Sample Introduction Techniques for Inductively Coupled Plasma Mass Spectrometry, Elsevier, Amsterdam, Netherlands.
Guerquin-Kern, J.-L., Wu, T.-D., Quintana, C., and Croisy, A. (2005). “Progress in analytical imaging of the cell by dynamic secondary ion mass spectrometry (SIMS microscopy),” Biochim. Biophys. Acta 1724(3), 228‑238. DOI:10.1016/j.bbagen.2005.05.013
Gupta, R., Ahuja, P., Khan, S., Saxena, R. K., and Mohapatra, H. (2000). “Microbial biosorbents: Meeting challenges of heavy metal pollution in aqueous solutions,” Curr. Sci. India 78(8), 967‑973.
Han, Y., Boateng, A. A., Qi, P. X., Lima, I. M., and Chang, J. (2013). “Heavy metal and phenol adsorptive properties of biochars from pyrolyzed switchgrass and woody biomass in correlation with surface properties,” J. Environ. Manage. 118, 196‑204. DOI: 10.1016/j.jenvman.2013.01.001
Harder, M. L., and Einspehr, D. W. (1980). “Levels of some essential metals in bark,” Tappi 63(2), 110.
Hashem, A., Abou-Okeil, A., El-Shafie, A., and El-Sakhawy, M. (2006a). “Grafting of high-cellulose pulp extracted from sunflower stalks for removal of Hg (II) from aqueous solution,” Polym.-Plast. Technol. 45(1), 135‑141. DOI: 10.1080/03602550500373790
Hashem, A., Aly, A. A., Aly, A. S., and Hebeish, A. (2006b). “Quaternization of cotton stalks and palm tree particles for removal of acid dye from aqueous solutions,” Polym.-Plast. Technol. 45(3), 389‑394. DOI: 10.1080/03602550600553689
Haupt, K. (2001). “Molecularly imprinted polymers in analytical chemistry,” Analyst 126(6), 747‑756. DOI: 10.1039/B102799A
Hawkes, J. S. (1997). “What is a “heavy metal”?,” J. Chem. Educ. 74(11), 1369‑1374. DOI: 10.1021/ed074p1374
Heinrich, C. A. (2006). “From fluid inclusion microanalysis to large-scale hydrothermal mass transfer in the Earth’s interior,” J. Miner. Petrol. Sci. 101(3), 110‑117. DOI: 10.2465/jmps.101.110
Heitmar, E. M., Hinners, T. A., Rowan, J. T., and Riviello, J. M. (1990). “Minimization of interferences in inductively coupled plasma mass spectrometry using on-line preconcentration,” Anal. Chem. 62(8), 857‑864. DOI: 10.1021/ac00207a018
Herawati, N., Suzuki, S., Hayashi, K., Rivai, I. F., and Koyoma, H. (2000). “Cadmium, copper and zinc levels in rice and soil of Japan, Indonesia and China by soil type,” B. Environ. Contam. Tox. 64(1), 33‑39. DOI: 10.1007/s001289910006
Hernández, P. P., Moreno, V., Olivari, F. A., and Allende, M. L. (2006). “Sub-lethal concentrations of waterborne copper are toxic to lateral line neuromasts in zebrafish (Danio rerio),” Hearing Res. 213(1‑2), 1‑10. DOI: 10.1016/j.heares.2005.10.015
Heumann, K. G. (1992). “Isotope dilution mass spectrometry (IDMS) of the elements,” Mass Spectrom. Rev. 11(1), 41‑67. DOI: 10.1016/0165-9936(82)88024-2
Hirner, A. V., and Emons, H. (2004). Organic Metal and Metalloid Species in the Environment, A. V. Hirner and H. Emons (eds.), Springer, Berlin, Germany.
Hokkanen, S., Repo, E., and Sillanpää, M. (2013). “Removal of heavy metals from aqueous solutions by succinic anhydride modified mercerized nanocellulose,” Chem. Eng. J. 223, 40‑47. DOI: 10.1016/j.cej.2013.02.054
Hon, D. N.-S., and Shirashi, N. (1991). Wood and Cellulosic Chemistry, Marcel Dekker, Inc., New York, USA.
Houk, R. S., and Praphairaksit, N. (2001). “Dissociation of polyatomic ions in the inductively coupled plasma,” Spectrochim. Acta. B 56(7), 1069‑1096. DOI: 10.1016/S0584-8547(01)00236-1
Hu, B., Yu, S.-H., Wang, K., Liu, L., and Xu, X.-W. (2008). “Functional carbonaceous materials from hydrothermal carbonization of biomass: An effective chemical process,” Dalton T. 40, 5414‑5423. DOI: 10.1039/b804644c
Hubbe, M. A., Hasan, S. H., and Ducoste, J. J. (2011). “Cellulosic substrates for removal of pollutants from aqueous systems: A review. 1. Metals,” BioResources 6(2), 2161‑2287. DOI: 10.15376/biores.6.2.Hubbe
Hung, D. Q., Nekrassova, O., and Compton, R. G. (2004). “Analytical methods for inorganic arsenic in water: A review,” Talanta 64(2), 269‑277. DOI: 10.1016/j.talanta.2004.01.027
Hwang, I. H., Nakajima, D., Matsuto, T., and Sugimoto, T. (2008). “Improving the quality of waste-derived char by removing ash,” Waste Manage. 28(2), 424‑434. DOI: 10.1016/j.wasman.2006.11.015
Iglesias, M., Besalu, E., and Antico, E. (2007). “Internal standardization atomic spectrometry and geographical pattern recognition techniques for the multielement analysis and classification of catalonian red wines,” J. Agr. Food Chem. 55, 219‑225. DOI: 10.1021/jf0629585
Inyang, M. D., Gao, B., Ding, W., Pullammanappallil, P., Zimmerman, A. R., and Cao, X. (2011). “Enhanced lead sorption by biochar derived from anaerobically digested sugarcane bagasse,” Sep. Sci. Technol. 46(12), 1950‑1956. DOI: 10.1080/01496395.2011.584604
Inyang, M. D., Gao, B., Yao, Y., Xue, Y., Zimmerman, A. R., Pullammanappallil, P., and Cao, X. (2012). “Removal of heavy metals from aqueous solution by biochars derived from anaerobically digested biomass,” Bioresource Technol. 110, 50‑56. DOI: 10.1016/j.biortech.2012.01.072
Inyang, M. D., Gao, B., Zimmerman, A., Zhou, Y., and Cao, X. (2015). “Sorption and cosorption of lead and sulfapyridine on carbon nanotube-modified biochars,” Environ. Sci. Pollut. R. 22(3), 1868‑1876. DOI: 10.1007/s11356-014-2740-z
Inyang, M. I., Gao, B., Yao, Y., Xue, Y., Zimmerman, A., Mosa, A., Pullammanappallil, P., Ok, Y. S., and Cao, X. (2016). “A review of biochar as a low-cost adsorbent for aqueous heavy metal removal,” Crit. Rev. Environ. Sci. Tec. 46(4), 406‑433. doi.org/10.1080/10643389.2015.1096880
Ioannidou, O., and Zabaniotou, A. (2007). “Agricultural residues as precursors for activated carbon production – A review,” Renew. Sust. Energ. Rev. 11(9), 1966‑2005. DOI: 10.1016/j.rser.2006.03.013
Isogai, A., and Kato, Y. (1998). “Preparation of polyuronic acid from cellulose by TEMPO-mediated oxidation,” Cellulose 5(3), 153‑164. DOI: 10.1023/A:1009208603673
Jackson, B. P., and Bertsch, P. M. (2001). “Determination of arsenic speciation in poultry wastes by IC-ICP-MS,” Environ. Sci. Technol. 35(24), 4868‑4873. DOI: 10.1021/es0107172
Jakubowski, N., and Stuever, D. (1997). New Instrumental Developments and Analytical Applications in ICP-MS in Plasma Source Mass Spectrometry: Developments and Applications, The Royal Society of Chemistry, Cambridge, England.
Jang, A., Seo, Y., and Bishop, P. L. (2005). “The removal of heavy metals in urban runoff by sorption on mulch,” Environ. Pollut. 133(1), 117‑127. DOI: 10.1016/j.envpol.2004.05.020
Järup, L. (2003). “Hazards of heavy metal contamination,” Brit. Med. Bull. 68(1), 167‑182. DOI: 10.1093/bmb/ldg032
Jiang, N., Chang, X. J., Zheng, H., He, Q., and Hu, Z. (2006). “Selective solid-phase extraction of nickel(II) using a surface-imprinted silica gel sorbent,” Anal. Chim. Acta 577(2), 225‑231. DOI: 10.1016/j.aca.2006.06.049
Johns, M. M., Marshall, W. E., and Toles, C. A. (1998). “Agricultural by-products as granular activated carbons for adsorbing dissolved metals and organics,” J. Chem. Technol. Biot. 71(2), 131‑140. DOI: 10.1002/(SICI)1097-4660(199802)71:2<131::AID-JCTB821>3.0.CO;2-K
Jyske, T., Mäkinen, H., Kalliokoski, T., and Nöjd, P. (2014). “Intra-annual tracheid production of Norway spruce and Scots pine across a latitudinal gradient in Finland,” Agr. Forest Meteorol. 194, 241‑254. DOI: 10.1016/j.agrformet.2014.04.015
Keiluweit, M., and Kleber, M. (2009). “Molecular-level interactions in soils and sediments: The role of aromatic Π-systems,” Environ. Sci. Technol. 43(10), 3421‑3429. DOI: 10.1021/es8033044
Khan, A., Jong, W., Jansens, P., and Spliethoff, H. (2009). “Biomass combustion in fluidized bed boilers: Potential problems and remedies,” Fuel Process Technol. 90(1), 21‑50. DOI: 10.1016/j.fuproc.2008.07.012
Khan, U., and Rao, R. A. K. (2017). “A high activity adsorbent of chemically modified Cucurbita moschata (a novel adsorbent) for the removal of Cu(II) and Ni(II) from aqueous solution: Synthesis, characterization and metal removal efficiency,” Proc. Safe. Environ. Protect. 107, 238‑258. DOI: 10.1016/j.psep.2017.02.008
Kinoshita, C. M. (1991). “Cogeneration in the Hawaiian sugar industry,” Bioresource Technol. 35(3), 231‑237. DOI: 10.1016/0960-8524(91)90119-5
Kment, P., Mihaljevĭ, M., Ettler, V., Sěbek, O., Strnad, L., and Rohlová, L. (2005). “Differentiation of Czech wines using multielement composition – A comparison with vineyard soil,” Food Chem. 91(1), 157‑165. DOI: 10.1016/j.foodchem.2004.06.010
Kokšal, J., Synek, V., and Janos, P. (2002). “Extraction-spectrometric determination of lead in high-purity aluminium salts,” Talanta 58(2), 325‑330. DOI: 10.1016/S0039-9140(02)00247-3
Koljonen, K., Mustranta, A., and Stenius, P. (2004). “Surface characterisation of mechanical pulps by polyelectrolyte adsorption,” Nord. Pulp. Pap. Res. J. 19(4), 495‑505.
Konn, J., Pranovich, A., Fardim, P., and Holmbom, B. (2007). “Characterisation and effects of new anionic groups formed during chemithermomechanical pulping of spruce,” Colloid. Surface. A. 296(1‑3), 1‑7. DOI: 10.1016/j.colsurfa.2006.09.047
Kookana, R. S. (2010). “The role of biochar in modifying the environmental fate, bioavailability, and efficacy of pesticides in soils: A review,” Aust. J. Soil Res. 48(6‑7), 627‑637. DOI: 10.1071/SR10007
Kumar, N., Bansal, A., Sarma, G. S., and Rawal, R. K. (2014). “Chemometrics tools used in analytical chemistry: An overview,” Talanta 123, 186‑199. DOI: 10.1016/j.talanta.2014.02.003
Kumar, S., Loganathan, V. A., Gupta, R. B., and Barnett, M. O. (2011). “An assessment of U(VI) removal from groundwater using biochar produced from hydrothermal carbonization,” J. Environ. Manage. 92(10), 2504‑2512. DOI: 10.1016/j.jenvman.2011.05.013
Laine, J., Buchert, J., Viikari, L., and Stenius, P. (1996). “Characterization of unbleached kraft pulps by enzymic treatment, potentiometric titration and polyelectrolyte adsorption,” Holzforschung 50(3), 208‑214. DOI: 10.1515/hfsg.19188.8.131.52
Lambert, M. J. (1981). “Research note no. 45: Inorganic constituents in wood and bark of new south Wales forest tree species,” Forestry Commission N. S. W., Sydney, Australia.
Lattao, C., Cao, X., Mao, J., Schmidt-Rohr, K., and Pignatello, J. J. (2014). “Influence of molecular structure and adsorbent properties on sorption of organic compounds to a temperature series of wood chars,” Environ. Sci. Technol. 48(9), 4790‑4798. DOI: 10.1021/es405096q
Laureysens, I., Blust, R., De Temmerman, L., Lemmens, C., and Ceulemans, R. (2004). “Clonal variation in heavy metal accumulation and biomass production in a poplar coppice culture: I. Seasonal variation in leaf, wood and bark concentrations,” Environ. Pollut. 131(3), 485‑494. DOI: 10.1016/j.envpol.2004.02.009
Lehmann, J. (2007). “Bio-energy in the black,” Front. Ecol. Environ. 5(7), 381‑387. DOI: 10.1890/1540-9295(2007)5[381:BITB]2.0.CO;2
Li, H., Li, Z., Liu, T., Xiao, X., Peng, Z., and Deng, L. (2008). “A novel technology for biosorption and recovery hexavalent chromium in wastewater by bio-functional magnetic beads,” Bioresource Technol. 99(14), 6271‑6279. DOI: 10.1016/j.biortech.2007.12.002
Li, J. T., Qiu, J. W., Wang, X. W., Zhong, Y., Lan, C. Y., and Shu, W. S. (2006). “Cadmium contamination in orchard soils and fruit trees and its potential health risk in Guangzhou, China,” Environ. Pollut. 143(1), 159‑165. DOI: 10.1016/j.envpol.2005.10.016
Li, L., and Zhang, H. X. (2004). “Preparing levoglucosan derived from waste material by pyrolysis,” Energ. Source. 26(11), 1053‑1059. DOI: 10.1080/00908310490494559
Liao, C.-M., Ju, Y.-R., Chen, W.-Y., and Chen, B.-C. (2011). “Assessing the impact of waterborne and diet borne cadmium toxicity on susceptibility risk for rainbow trout,” Sci. Total Environ. 409(3), 503‑513. DOI: 10.1016/j.scitotenv.2010.10.044
Lindström, T. (1992). “Chemical factors affecting the behaviour of fibres during papermaking,” Nord. Pulp. Pap. Res. J. 7(4), 181‑192. DOI: 10.3183/NPPRJ-1992-07-04-p181-192
Liu, Z., and Zhang, F.-S. (2009). “Removal of lead from water using biochars prepared from hydrothermal liquefaction of biomass,” J. Hazard. Mater. 167(1‑3), 933‑939. DOI: 10.1016/j.jhazmat.2009.01.085
Lobiński, R., Schaumlöffel, D., and Szpunar, J. (2006). “Mass spectrometry in bioinorganic analytical chemistry,” Mass Spectrom. Rev. 25(2), 255‑289. DOI: 10.1002/mas.20069
Lopičić, Z. R., Stojanović, M. D., Kaluđerović Radoičić, T. S., Milojković, J. V., Petrović, M. S., Mihajlović, M. L., and Kijevčanin, M. L. J. (2017). “Optimization of the process of Cu(II) sorption by mechanically treated Prunus persica L. – Contribution to sustainability in food processing industry,” J. Clean. Prod. 156, 95‑105. DOI: 10.1016/j.jclepro.2017.04.041
Low, K. S., Lee, C. K., and Mak, S. M. (2004). “Sorption of copper and lead by citric acid modified wood,” Wood Sci. Technol. 38(8), 629‑640. DOI: 10.1007/s00226-003-0201-9
Lu, H., Mou, S., Yan, Y., Tong, S., and Riviello, J. M. (1998). “On-line pretreatment and determination of Pb, Cu and Cd at the μg l−1 level in drinking water by chelation ion chromatography,” J. Chromatogr. A 800(2), 247‑255. DOI: 10.1016/S0021-9673(97)01127-8
Madrid, Y., and Cámara, C. (1997). “Biological substrates for metal preconcentration and speciation,” TrAC-Trend. Anal. Chem. 16(1), 36‑44. DOI: 10.1016/S0165-9936(96)00075-1
Mager, E. M. (2011). Lead of the Fish Physiology, Academic Press, Elsevier, Inc., NewYork, USA.
Mahar, A., Wang, P., Ali, A., Awasthi, M. K., Lahori, A. H., Wang, Q., Li, R., and Zhang, Z. (2016). “Challenges and opportunities in the phytoremediation of heavy metals contaminated soils: A review,” Ecotox. Environ. Safe. 126, 111‑121. DOI: 10.1016/j.ecoenv.2015.12.023
Mahmood, T., and Islam, K. R. (2006). “Response of rice seedlings to copper toxicity and acidity,” J. Plant Nutr. 29(5), 943‑957. DOI: 10.1080/01904160600651704
Mahmoud, M. E., Osman, M. M., Ahmed, S. B., and Abdel-Fattah, T. M. (2012). “Enhanced removal of lead by chemically and biologically treated carbonaceous materials,” Sci. World J. Article ID 604198, 1-11. DOI: 10.1100/2012/604198
Maekawa, E., and Koshijima, T. (1990). “Preparation and characterisation of hydroxamic acid derivatives and its metal complexes derived from cellulose,” J. Appl. Polym. Sci. 40(9‑10), 1601‑1613. DOI: 10.1002/app.1990.070400916
Majumdar, S., Peralta-Videa, J. R., Castillo-Michel, H., Hong, J., Rico, C. M., and Gardea-Torresdey, J. L. (2012). “Applications of synchrotron mu-XRF to study the distribution of biologically important elements in different environmental matrices: A review,” Anal. Chim. Acta 755, 1‑16. DOI: 10.1016/j.aca.2012.09.050
Malik, A. (2004). “Metal bioremediation through growing cells,” Environ. Int. 30(2), 261‑278. DOI: 10.1016/j.envint.2003.08.001
March, R. E., and Todd, J. F. J. (1995). “Practical aspects of ion trap mass spectrometry,” in: Modern Mass Spectrometry Series, CRC press, Boca Raton, FL, pp. 448.
Marin, B., Valladon, M., Polve, M., and Monaco, A. (1997). “Reproducibility testing of a sequential extraction scheme for the determination of trace metal speciation in a marine reference sediment by inductively coupled plasma-mass spectrometry,” Anal. Chim. Acta 342(2‑3), 91‑112. DOI: 10.1016/S0003-2670(96)00580-6
Marisa, C., Almeida, R., Tiresa, M., and Vasconcelos, S. D. (1999). “Determination of lead isotope ratios in port wine by inductively coupled plasma mass spectrometry after pre-treatment by UV-irradiation,” Anal. Chim. Acta 396(1), 45‑53. DOI: 10.1016/S0003-2670(99)00356-6
Marisa, C., Almeida, R., and Vasconcelos, M. T. S. D. (2003). “Multielement composition of wines and their precursors including provenance soil and their potentialities as fingerprints of wine origin,” J. Agr. Food. Chem. 51(16), 4788‑4798. DOI: 10.1021/jf034145b
Mata, Y. N., Blázquez, M. L., Ballester, A., González, F., and Muñoz, J. A. (2009). “Sugar-beet pulp pectin gels as biosorbent for heavy metals: Preparation and determination of biosorption and desorption characteristics,” Chem. Eng. J. 150(2‑3), 289‑301. DOI: 10.1016/j.cej.2009.01.001
McGeer, J. C., Niyogi, S., and Smith, S. D., (2011). Cadmium of the Fish Physiology, Academic Press, Elsevier, Inc., New York, USA.
Memon, J. R., Memon, S. Q., Bhanger, M. I., Memon, G. Z., El-Turki, A., and Allen, G. C. (2008). “Characterization of banana peel by scanning electron microscopy and FT-IR spectroscopy and its use for cadmium removal,” Colloid. Surface. B 66(2), 260‑265. DOI: 10.1016/j.colsurfb.2008.07.001
Medellin-Castillo, N. A., Padilla-Ortega, E., Regules-Martínez, M. C., Leyva-Ramos, R., Ocampo-Pérez, R., and Carranza-Alvarez, C. (2017). “Single and competitive adsorption of Cd(II) and Pb(II) ions from aqueous solutions onto industrial chili seeds (Capsicum annuum) waste,” Sustain. Environ. Res. 27(2), 61‑69. DOI: 10.1016/j.serj.2017.01.004
Meunier, N., Blais, J. F., and Tyagi, R. D. (2004). “Removal of heavy metals from acid soil leachate using cocoa shells in a batch counter-current sorption process,” Hydrometallurgy73(3‑4), 225‑235. DOI: 10.1016/j.hydromet.2003.10.011
Michalke, B. (2002a). “The coupling of LC to ICP-MS in element speciation: I. General aspects,” TrAC-Trend. Anal. Chem. 21(3), 142‑153. DOI: 10.1016/S0165-9936(01)00146-7
Michalke, B. (2002b). “The coupling of LC to ICP-MS in element speciation – Part II: Recent trends in application,” TrAC-Trend. Anal. Chem. 21(3), 154‑165. DOI: 10.1016/S0165-9936(02)00303-5
Minami, T., Konagaya, W., Zheng, L., Takano, S., Sasaki, M., Murata, R., Nakaguchi, Y., and Sohrin, Y. (2015). “An off-line automated preconcentration system with ethylenediaminetriacetate chelating resin for the determination of trace metals in seawater by high-resolution inductively coupled plasma mass spectrometry,” Anal. Chim. Acta 854, 183‑190. DOI: 10.1016/j.aca.2014.11.016
Mirzaei, M., Behzadi, M., Abadi, N. M., and Beizaei, A. (2011). “Simultaneous separation/preconcentration of ultra trace heavy metals in industrial wastewaters by dispersive liquid–liquid microextraction based on solidification of floating organic drop prior to determination by graphite furnace atomic absorption spectrometry,” J. Hazard. Mater. 186(2‑3), 1739‑1743. DOI: 10.1016/j.jhazmat.2010.12.080
Miyazaki, A., and Reimer, R. A. (1993). “Determination of lead isotope ratios and concentrations in sea-water by inductively coupled plasma mass spectrometry after preconcentration using Chelex-100,” J. Anal. Atom. Spectrom. 8(3), 449‑452. DOI: 10.1039/JA9930800449
Mohan, D., Pittman, C. U., Bricka, M., Smith, F., Yancey, B., Mohammad, J., Steele, P. H., Alexandre-Franco, M. F., Gómez-Serrano, V., and Gong, H. (2007). “Sorption of arsenic, cadmium, and lead by chars produced from fast pyrolysis of wood and bark during bio-oil production,” J. Colloid Interf. Sci. 310(1), 57‑73. DOI: 10.1016/j.jcis.2007.01.020
Mohan, D., Sarswat, A., Ok, Y., and Pittman, Jr., C. U. (2014). “Organic and inorganic contaminants removal from water with biochar, a renewable, low cost and sustainable adsorbent: A critical review,” Bioresource Technol. 160, 191‑202. DOI: 10.1016/j.biortech.2014.01.120
Mohan, D., Singh, K. P., and Singh, V. K. (2006). “Chromium (III) removal from wastewater using low cost activated carbon derived from agriculture waste material and activated carbon fabric cloth,” J. Hazard. Mater. 135(1‑3), 280‑295. DOI: 10.1016/j.jhazmat.2005.11.075
Moldovan, M., Krupp, E. M., Holliday, A. E., and Donard, O. F. X. (2004). “High resolution sector field ICP-MS and multicollector ICP-MS as tools for trace metal speciation in environmental studies: A review,” J. Anal. Atom. Spectrom. 19(7), 815‑940. DOI: 10.1039/b403128h
Monni, S., Salemaa, M., and Millar, N. (2000). “The tolerance of Empetrum nigrum to copper and nickel,” Environ. Pollut. 109(2), 221‑229. DOI: 10.1016/S0269-7491(99)00264-X
Montes-Atenas, G., and Schroeder, S. L. M. (2015). “Sustainable natural adsorbents for heavy metal removal from wastewater: Lead sorption on pine bark (Pinus radiata D.Don),” Surf. Interface Anal. 47(10), 996‑1000. DOI: 10.1002/sia.5807
Moore, J. W., and Ramamoorthy, S. (1984). Heavy Metals in Natural Waters, Springer-Verlag, New York, USA.
Moreno, I. M., González-Weller, D., Gutierrez, V., Marino, M., Cameán, A. M., Gustavo González, A., and Hardisson, A. (2007). “Differentiation of two canary DO red wines according to their metal content from inductively coupled plasma optical emission spectrometry and graphite furnace atomic absorption spectrometry by using Probabilistic Neutral Networks,” Talanta72(1), 263‑268. DOI: 10.1016/j.talanta.2006.10.029
Mukherjee, A., Zimmerman, A. R., and Harris, W. (2011). “Surface chemistry variations among a series of laboratory-produced biochars,” Geoderma 163(3‑4), 247‑255. DOI: 10.1016/j.geoderma.2011.04.021
Na, J., Chang, X. J., Hong, Z., Qun, H., and Zheng, H. (2006). “Selective solid-phase extraction of nickel(II) using a surface-imprinted silica gel sorbent,” Anal. Chim. Acta 577(2), 225‑231. DOI: 10.1016/j.aca.2006.06.049
Nagajyoti, P. C., Lee, K. D., and Sreekanth, T. V. M. (2010). “Heavy metals, occurrence and toxicity for plants: A review,” Environ. Chem. Lett. 8(3), 199‑216. DOI: 10.1007/s10311-010-0297-8
Nakazato, T., Tao, H., Taniguchi, T., and Isshiki, K. (2002). “Determination of arsenite, arsenate, and monomethylarsonic acid in seawater by ion-exclusion chromatography combined with inductively coupled plasma mass spectrometry using reaction cell and hydride generation techniques,” Talanta 58(1), 121‑132. DOI: 10.1016/S0039-9140(02)00261-8
Nakicenovic, N., and Swart, R. (2000). “Special report on emission scenarios,” in: InterGovernmental Panel on Climate Change, Cambridge University Press, Cambridge, England, pp. 599.
Navarro, R. R., Sumi, K., Fujii, N., and Matsumura, M. (1996). “Mercury removal from wastewater using porous cellulose carrier modified with polyethyleneimine,” Water Res. 30(10), 2488‑2494. DOI: 10.1016/0043-1354(96)00143-1
Navarro, R. R., Tatsumi, K., Sumi, K., and Matsumura, M. (2001). “Role of anions on heavy metal sorption of a cellulose modified with poly(glycidylmethacrylate) and polyethyleneimine,” Water Res. 35(11), 2724‑2730. DOI: 10.1016/S0043-1354(00)00546-7
Nelms, S. (2005). Inductively Coupled Plasma Mass Spectrometry Handbook, Blackwell, Carlton, Australia.
Nicolaï, M., Rosin, C., Tousset, N., and Nicolai, Y. (1999). “Trace metals analysis in estuarine and seawater by ICP-MS using on line preconcentration and matrix elimination with chelating resin,” Talanta 50(2), 433‑444. DOI: 10.1016/S0039-9140(99)00130-7
Nielsen, H. P., Frandsen, F. J., Dam-Johansen, K., and Baxter, L. L. (2000). “The implications of chlorine-associated corrosion on the operation of biomass-fired boilers,” Prog. Energ. Combust. 26(3), 283‑298. DOI: 10.1016/S0360-1285(00)00003-4
Nölte, J. (2000). “Trinkwasser analyse per ICP-OES/ Ultraschallzerstaubung [Analysis of drinking water with ICP-OES/ultrasound atomization],” Labor Praxis 24(7‑8), 30‑32.
Novaes, C. G., Bezerra, M. A., Paranhos da Silva, E. G., Pinto dos Santos, A. M., Da Silva Romão, I. L., and Neto, J. H. H. (2016). “A review of multivariate designs applied to the optimization of methods based on inductively coupled plasma optical emission spectrometry (ICP OES),” Microchem. J. 128, 331‑346. DOI: 10.1016/j.microc.2016.05.015
Nuhoglu, Y., and Oguz, E. (2003). “Removal of copper (II) from aqueous solutions by biosorption on the cone biomass of Thuja orientalis,” Process Biochem. 38(11), 1627‑1631. DOI: 10.1016/S0032-9592(03)00055-4
O’Connell, D. W., Birkinshaw, C., and O’Dwyer, T. F. (2008). “Heavy metal adsorbents prepared from the modification of cellulose: A review,” Bioresource Technol. 99(15), 6709‑6724. DOI: 10.1016/j.biortech.2008.01.036
Özdemir, S., Okumus, V., Kılınc, E., Bilgetekin, H., Dündar, A., and Ziyadanogˇullari, B. (2012). “Pleurotus eryngii immobilized Amberlite XAD-16 as a solid-phase biosorbent for preconcentrations of Cd2+ and Co2+ and their determination by ICP-OES,” Talanta 99, 502‑506. DOI: 10.1016/j.talanta.2012.06.017
Pagliuca, A., and Mufti, G. J. (1990). “Lead poisoning: An age-old problem,” BMJ-Brit. Med. J. 300(6728), 830. DOI: 10.1136/bmj.300.6728.830
Pagnanelli, F., Esposito, A., Toro, L., and Veglio, F. (2003). “Metal speciation and pH effect on Pb, Cu, Zn and Cd biosorption onto Sphaerotilus natans: Langmuir-type empirical model,” Water Res. 37(3), 627‑633. DOI: 10.1016/S0043-1354(02)00358-5
Palma, G., Freer, J., and Baeza, J. (2003). “Removal of metal ions by modified Pinus radiata bark and tannins from water solutions,” Water Res. 37(20), 4974‑4980. DOI: 10.1016/j.watres.2003.08.008
Paradelo, R., and Barral, M. T. (2012). “Evaluation of the potential capacity as biosorbents of two MSW composts with different Cu, Pb and Zn concentrations,” Bioresource Technol. 104, 810‑813. DOI: 10.1016/j.biortech.2011.11.012
Park, D., Yun, Y.-S., and Park, J. M. (2010). “The past, present, and future trends of bio-sorption,” Biotechnol. Bioproc. E. 15(1), 86‑102. DOI: 10.1007/s12257-009-0199-4
Patterson, J. W. (1985). Industrial Wastewater Treatment Technology, Butterworth Publisher, Stoneham, USA.
Perat, C., and Ni, Y. (2001). “UV-Vis spectra of lignin model compounds in the presence of meal ions and chelants,” J. Wood Chem. Technol. 21(2), 113‑125. DOI: 10.1081/WCT-100104222
Pesavento, M., and Biesuz, R. (1997). “Sorption of divalent metal ions on a iminodiacetic resin from artificial seawater,” Anal. Chim. Acta 346(3), 381‑391. DOI: 10.1016/S0003-2670(97)90083-0
Pettersen, R. C. (1984). “The chemical composition of wood,” in: The Chemistry of Solid Wood, Advances in Chemistry, Volume 207, R. M. Rowell (ed.), American Chemical Society, Washington D.C., USA, pp. 57‑126.
Poole, C. F. (2003). “New trends in solid-phase extraction,” TrAC-Trend. Anal. Chem. 22(6), 362‑373. DOI: 10.1016/S0165-9936(03)00605-8
Prohaska, T., Stadlbauer, C., Wimmer, R., Stingeder, G., Latkoczy, C., Hoffmann, E., and Stephanowitz, H. (1998). “Investigation of element variability in tree rings of young Norway spruce by laser-ablation-ICPMS,” Sci. Total Environ. 219(1), 29‑39. DOI: 10.1016/S0048-9697(98)00224-1
Pu, X. L., Hu, B., Jiang, Z. C., and Huang, C. Z. (2005). “Speciation of dissolved iron (II) and iron (III) in environmental water samples by gallic acid-modified nanometer-sized alumina micro‑column separation and ICP-MS determination,” Analyst 130(8), 1175‑1181. DOI: 10.1039/b502548f
Qaiser, S., Saleemi, A. R., and Ahmad, M. M. (2007). “Heavy metal uptake by agro based waste materials,” Electron. J. Biotechn. 10(3), 409‑416. DOI: 10.2225/vol10-issue3-fulltext-12
Rahmi, D., Zhu, Y., Fujimori, E., Umemura, T., and Haraguchi, H. (2007). “Multielement determination of trace metals in seawater by ICP-MS with aid of down-sized chelating resin-packed minicolumn for preconcentration,” Talanta 72(2), 600‑606. DOI: 10.1016/j.talanta.2006.11.023
Raji, C., Shubha, K. P., and Anirudhan, T. S. (1997). “Use of chemically modified sawdust in the removal of Pb (II) ions from aqueous media,” Indian Journal of Environmental Health 39, 230‑238.
Rao, T. P., Daniel, S., and Gladis, J. M. (2004). “Tailored materials for preconcentration or separation of metals by ion-imprinted polymers for solid-phase extraction (IIP-SPE),” TrAC-Trend. Anal. Chem. 23(1), 28‑35. DOI: 10.1016/S0165-9936(04)00106-2
Rattanachongkiat, S., Millwarda, G. E., and Foulkes, M. E. (2004). “Determination of arsenic species in fish, crustacean and sediment samples from Thailand using high performance liquid chromatography (HPLC) coupled with inductively coupled plasma mass spectrometry (ICP-MS),” J. Environ. Monitor. 6(4), 254‑261. DOI: 10.1039/b312956j
Ray, S. J., Andrade, F., Gamez, G., McClenathan, D., Rogers, D., Schilling, G., Wetzel, W., and Hieftje, G. M. (2004). “Plasma-source mass spectrometry for speciation analysis: State-of-the-art,” J. Chromatogr. A 1050(1), 3‑34. DOI: 10.1016/S0021-9673(04)01309-3
Reddad, Z., Gerente, C., Andres, Y., and LeCloirec, P. (2002a). “Adsorption of several metal ions onto a low-cost biosorbent: Kinetic and equilibrium studies,” Environ. Sci. Technol. 36(9), 2067‑2073. DOI: 10.1021/es0102989
Reddad, Z., Gerente, C., Andres, Y., Ralet, M.-C., Thibault, J.-F., and Cloirec, P. L. (2002b). “Ni (II) and Cu (II) binding properties of native and modified sugar beet pulp,” Carbohyd. Polym. 49(1), 23‑31. DOI: 10.1016/S0144-8617(01)00301-0
Regmi, P., Garcia Moscoso, J. L., Kumar, S., Cao, X., Mao, J., and Schafran, G. (2012). “Removal of copper and cadmium from aqueous solution using switchgrass biochar produced viahydrothermal carbonization process,” J. Environ. Manage. 109, 61‑69. DOI: 10.1016/j.jenvman.2012.04.047
Reimann, C., Arnoldussen, A., Englmaier, P., Filzmoser, P., Finne, T. E., Garrett, R. G., Koller, F., and Nordgulen, Ø. (2007). “Element concentrations and variations along a 120 km long transect in south Norway ‑ anthropogenic vs. geogenic vs. biogenic element sources and cycles,” Appl. Geochem. 22(4), 851‑871. DOI: 10.1016/j.apgeochem.2006.12.019
Reimann, C., Ottesen, R. T., Andersson, M., Arnoldussen, A., Koller, F., and Englmaier, P. (2008). “Element levels in birch and spruce wood ashes ‑ green energy?,” Sci. Total Environ. 393(2‑3), 191‑197. DOI: 10.1016/j.scitotenv.2008.01.015
Rhee, S.-W., and Park, H.-S. (2010). “Effect of mixing ratio of woody waste and food waste on the characteristics of carbonization residue,” J. Mater. Cycles. Waste Manage. 12(3), 220‑226. DOI: 10.1007/s10163-010-0291-z
Riley, J. P., and Taylor, D. (1968). “Chelating resins for the concentration of trace elements from sea water and their analytical use in conjunction with atomic absorption spectrophotometry,” Anal. Chim. Acta 40, 479‑485. DOI: 10.1016/S0003-2670(00)86764-1
Roig-Navarro, A. F., Martinez-Bravo, Y., López, F. J., and Hernández, F. (2001). “Simultaneous determination of arsenic species and chromium(VI) by high-performance liquid chromatography–inductively coupled plasma-mass spectrometry,” J. Chromatogr. A 912(2), 319‑327. DOI: 10.1016/S0021-9673(01)00572-6
Rottmann, L., and Heumann, K. G. (1994). “Development of an on-line isotope dilution technique with HPLC/ICP-MS for the accurate determination of elemental species,” Fresen. J. Anal. Chem. 350(4‑5), 221‑227. DOI: 10.1007/BF00322473
Rowell, R. M., Pettersen, R., and Tshabalala, M. A. (2013). Handbook of Wood Chemistry and Wood Composites, CRC Press, Boca Raton, FL.
Saeed, A., Akhter, M. W., and Iqbal, M. (2005). “Removal and recovery of heavy metals from aqueous solution using papaya wood as a new biosorbent,” Sep. Purif. Technol. 45(1), 25‑31. DOI: 10.1016/j.seppur.2005.02.004
Saeed, A., Iqbal, M., and Akhtar, M. W. (2002). “Application of biowaste materials for the sorption of heavy metals in contaminated aqueous medium,” Pak. J. Sci. Ind. Res. 45(3), 206‑211.
Saidur, A., Abdelaziz, E., Demirbaş, A., Hossain, M., and Mekhilef, S. (2010). “A review on biomass as a fuel for boilers,” Renew. Sust. Energ. Rev. 15(5), 2262‑2289. DOI: 10.1016/j.rser.2011.02.015
Sarin, V., and Pant, K. K. (2006). “Removal of chromium from industrial waste by using eucalyptus bark,” Bioresource Technol. 97(1), 15‑20. DOI: 10.1016/j.biortech.2005.02.010
Sarkanen, K. V., and Ludwig, C. H. (1971). Lignins ‑ Occurance, Formation, Structure and Reactions, Wiley-Interscience, New York, USA.
Sarma, H. (2011). “Metal hyperaccumulation in plants: A review focusing on phytoremediation technology,” J. Environ. Sci. Technol. 4(2), 118‑138. DOI: 10.3923/jest.2011.118.138
Sarzanini, C., and Mentasti, E. (1997). “Determination and speciation of metals by liquid chromatography,” J. Chromatogr. A 789(1‑2), 301‑321. DOI: 10.1016/S0021-9673(97)00988-6
Sepe, A., Ciaralli, L., Ciprotti, M., Giordano, R., Funari, E., and Costantini, S. (2003). “Determination of cadmium, chromium, lead and vanadium in six fish species from the Adriatic Sea,” Food Addit. Contam. 20(6), 543‑552. DOI: 10.1080/0265203031000069797
Sevilla, M., and Fuertes, A. B. (2009). “The production of carbon materials by hydrothermal carbonization of cellulose,” Carbon 47(9), 2281‑2289. DOI: 10.1016/j.carbon.2009.04.026
Sfakianakis, D. G., Leris, I., and Kentouri, M. (2011). “Effect of developmental temperature on swimming performance of zebrafish (Danio rerio) juveniles,” Environ. Biol. Fish. 90(4), 421‑427. DOI: 10.1007/s10641-010-9751-5
Sfakianakis, D. G., Renieri, E., Kentouri, M., and Tsatsakis, A. M. (2015). “Effect of heavy metals on fish larvae deformities: A review,” Environ. Res. 137, 246‑255. DOI: 10.1016/j.envres.2014.12.014
Sharma, V. K., Canditelli, M., Fortuna, F., and Cornacchia, G. (1997). “Processing of urban and agro-industrial residues by aerobic composting: Review,” Energ. Convers. Manage. 38(5), 453‑478. DOI: 10.1016/S0196-8904(96)00068-4
Sheng, P. X., Ting, Y. P., Chen, J. P., and Hong, L. (2004). “Sorption of lead, copper, cadmium, zinc and nickel by marine algal biomass: Characterization of biosorptive capacity and investigation of mechanisms,” J. Colloid Interf. Sci. 275(1), 131‑141. DOI: 10.1016/j.jcis.2004.01.036
Shi, G., and Cai, Q. (2009). “Cadmium tolerance and accumulation in eight potential energy crops,” Biotechnol. Adv. 27(5), 555‑561. DOI: 10.1016/j.biotechadv.2009.04.006
Šoštarić, T. D., Petrović, M. S., Pastor, F. T., Lončarević, D. R., Petrović, J. T., Milojković, J. V., and Stojanović, M. D. (2018). “Study of heavy metals biosorption on native and alkali-treated apricot shells and its application in wastewater treatment,” J. Mol. Liq. 259, 340‑349. DOI: 10.1016/j.molliq.2018.03.055
Sjöström, E., and Alén, R. (1998). Analytical Methods in Wood Chemistry, Pulping, and Papermaking, Springer-Verlag, Berlin, Germany.
Søndergaard, J., Asmund, G., and Larsen, M. M. (2015). “Trace elements determination in seawater by ICP-MS with on-line pre-concentration on a Chelex-100 column using a ‘standard’ instrument setup,” MethodsX 2, 323‑330. DOI: 10.1016/j.mex.2015.06.003
Sperkova, J., and Suchanek, M. (2005). “Multivariate classification of wines from different Bohemian regions (Czech Republic),” Food Chem. 93(4), 659‑663. DOI: 10.1016/j.foodchem.2004.10.044
Stumm, W. (1992). Chemistry of the Solid-Water Interface: Process at the Mineral-Water and Particle-Water Interface in Natural Systems, Wiley, New York, USA.
Su, P. (2012). Sorption of Metal Ions to Wood, Pulp and Bark Materials, Ph.D. Thesis, Åbo Akademi University, Turku, Finland.
Sud, D., Mahajan, G., and Kaur, M. P. (2008). “Agricultural waste material as potential adsorbent for sequestering heavy metal ions from aqueous solutions – A review,” Bioresource Technol. 99(14), 6017‑6027. DOI: 10.1016/j.biortech.2007.11.064
Sudha, B. R., and Abraham, E. (2003). “Studies on chromium (VI) adsorption using immobilized fungal biomass,” Bioresource Technol. 87(1), 17‑26. DOI: 10.1016/S0960-8524(02)00222-5
Suhas, P., Carrott, J. M., and Ribeiro Carrott, M. M. (2007). “Lignin – from natural adsorbent to activated carbon: A review,” Bioresource Technol. 98(12), 2301‑2312. DOI: 10.1016/j.biortech.2006.08.008
Suleiman, J. S., Hu, B., Huang, C., and Zhang, N. (2008). “Determination of Cd, Co, Ni and Pb in biological samples by microcolumn packed with black stone (Pierre noire) online coupled with ICP-OES,” J. Hazard. Mater. 157(2‑3), 410‑417. DOI: 10.1016/j.jhazmat.2008.01.014
Sumida, T., Nakazato, T., Tao, H., Oshima, M., and Motomizu, S. (2006). “On-line preconcentration system using mini-column packed with a chelating resin for the characterization of seasonal variations of trace elements in seawater by ICP-MS and ICP‑AES,” Anal. Sci. 22(9), 1163‑1168. DOI: 10.2116/analsci.22.1163
Sutton, K., Sutton, R. M. C., and Caruso, J. A. (1997). “Inductively coupled plasma mass spectrometric detection for chromatography and capillary electrophoresis,” J. Chromatogr. A789(1‑2), 85‑126. DOI: 10.1016/S0021-9673(97)00970-9
Świetlik, R., Trojanowska, M., and Rabek, P. (2012). “Distribution patterns of Cd, Cu, Mn, Pb and Zn in wood fly ash emitted from domestic boilers,” Chem. Spec. Bioavailab. 25(1), 63‑70. DOI: 10.3184/095422912X13497968675047
Takuwa, D. T., Sawula, G., Wibetoe, G., and Lund, W. (1997). “Determination of cobalt, nickel and copper in flowers, leaves, stem and roots of plants using ultrasonic slurry sampling electrothermal atomic absorption spectrometry,” J. Anal. Atom. Spectrom. 12(8), 849‑854. DOI: 10.1039/A701266G
Tan, W. T., Ooi, S. T., and Lee, C. K. (1993). “Removal of chromium(VI) from solution by coconut husk and palm pressed fibres,” Environ. Technol. 14(3), 277‑282. DOI: 10.1080/09593339309385290
Tanner, S. D., Baranov, V. I., and Bandura, D. R. (2002). “Reaction cells and collision cells for ICP-MS: A tutorial review,” Spectrochim. Acta B 57(9), 1361‑1452. DOI: 10.1016/S0584-8547(02)00069-1
Tatar, E., Mihucz, V. G., Virag, I., Rácz, L., and Záray, G. (2007). “Effect of four bentonite samples on the rare earth element concentrations of selected Hungarian wine samples,” Microchem. J. 85(1), 132‑135. DOI: 10.1016/j.microc.2006.05.009
Taty-Costodes, V. C., Favdvet, H., Porte, C., and Delacroix, A. (2003). “Removal of cadmium and lead ions from aqueous solutions, by adsorption onto saw dust of Pinus sylvestris,” J. Hazard. Mater. B 105(1‑3), 121‑142. DOI: 10.1016/j.jhazmat.2003.07.009
Tokareva, E. N., Pranovich, A. V., Ek, P., and Holmbom, B. (2010). “Determination of anionic groups in wood by time-of-flight secondary ion mass spectrometry and laser ablation-inductively coupled plasma-mass spectrometry,” Holzforschung 64(1), 35‑43. DOI: 10.1515/hf.2010.002
Tong, X. J., Li, J. Y., Yuan, J. H., and Xu, R. K. (2011). “Adsorption of Cu(II) by biochars generated from three crop straws,” Chem. Eng. J. 172(2‑3), 828‑834. DOI: 10.1016/j.cej.2011.06.069
Tsezos, M. (1999). “Biosorption of metals. The experience accumulated and the outlook for technology development,” Process Met. 9, 171‑173. DOI: 10.1016/S1572-4409(99)80105-9
Tsezos, M. (2001). “Biosorption of metals: The experience accumulated and the outlook for technology development,” Hydrometallurgy 59(2‑3), 241‑243.
Tsezos, M., Hatzikioseyian, A., and Remoudaki, E. (2012). “Biofilm reactors in mining and metallurgical effluent treatment: Biosorption, bioprecipitation, bioreduction processes,” ResearchGate, (https://www.researchgate.net/publication/242547154_BIOFILM_REACTORS_IN_MINING_AND_METALLURGICAL_EFFLUENT_TREATMENT_BIOSORPTION_BIOPRECIPITATION_BIOREDUCTION_PROCESSES), Accessed 19 Dec 2018.
Tsezos, M., and Noh, S. H. (1987). “Particle encapsulation technique,” U.S. Patent No. 4828882.
Turn, S. Q., Kinoshita, C. M., and Ishimura, D. M. (1997). “Removal of inorganic constituents of biomass feedstocks by mechanical dewatering and leaching,” Biomass Bioenerg. 12(4), 241‑252. DOI: 10.1016/S0961-9534(97)00005-6
Tuzen, M., and Soylak, M. (2007). “Multiwalled carbon nanotubes for speciation of chromium in environmental samples,” J. Hazard. Mater. 147(1‑2), 219‑225. DOI: 10.1016/j.jhazmat.2006.12.069
Uchimiya, M., Chang, S., and Klasson, K. T. (2011). “Screening biochars for heavy metal retention in soil: Role of oxygen functional groups,” J. Hazard. Mater. 190(1‑3), 432‑441. DOI: 10.1016/j.jhazmat.2011.03.063
Uchimiya, M., Lima, I. M., Klasson, K. T., Chang, S. C., Wartelle, L. H., and Rodgers, J. E. (2010). “Immobilization of heavy metal ions (Cu-II, Cd-II, Ni-II, and Pb-II) by broiler litter-derived biochars in water and soil,” J. Agr. Food Chem. 58(9), 5538‑5544. DOI: 10.1021/jf9044217
Ucun, H., Bayhan, Y. K., Kaya, Y., Cakici, A., and Algur, O. F. (2002). “Biosorption of chromium(VI) from aqueous solution by cone biomass of Pinus sylvestris,” Bioresource Technol. 85(2), 155‑158. DOI: 10.1016/S0960-8524(02)00086-X
Vanini, G., Souza, M. O., Carneiro, M. T. W. D., Filgueiras, P. R., Bruns, R. E., and Romao, W. (2015). “Multivariate optimisation of ICP OES instrumental parameters for Pb/Ba/Sb measurement in gunshot residues,” Microchem. J. 120, 58‑63. DOI: 10.1016/j.microc.2015.01.003
Vàzque, G., Antorrena, G., Gonzàlez, J., and Doval, M. D. (1994). “Adsorption of heavy metal ions by chemically modified Pinus pinaster bark,” Bioresource Technol. 48(3), 251‑255. DOI: 10.1016/0960-8524(94)90154-6
Veguería, S. F. J., Godoy, J. M., De Campos, R. C., and Gonçalves, R. A. (2013). “Trace element determination in seawater by ICP-MS using online, offline and bath procedures of preconcentration and matrix elimination,” Microchem. J. 106, 121‑128. DOI: 10.1016/j.microc.2012.05.032
Venkateswarlu, P., Ratnam, M. V., Rao, D. S., and Rao, M. V. (2007). “Removal of chromium from aqueous solution using Azadirachta indica (neem) leaf powder as an adsorbent,” Int. J. Phys. Sci. 2(8), 188‑195. DOI: 10.5897/IJPS
Viczián, M., Lásztity, A., Wang, X., and Barnes, R. M. (1990). “On-line isotope dilution and sample dilution by flow injection and inductively coupled plasma mass spectrometry,” J. Anal. Atom. Spectrom. 5, 125‑133. DOI: 10.1039/JA9900500125
Vieira, R. H. S. F., and Volesky, B. (2000). “Biosorption: A solution to pollution?,” Int. Microbiol. 3(1), 17‑24.
Vijayaraghavan, K., and Yun, Y.-S. (2008). “Bacterial biosorbents and biosorption,” Biotechnol. Adv. 26(3), 266‑291. DOI: 10.1016/j.biotechadv.2008.02.002
Vilardi, G., Ochando-Pulido, J. M., Verdone, N., Stoller, M., and Di Palma, L. (2018). “On the removal of hexavalent chromium by olive stones coated by iron-based nanoparticles: Equilibrium study and chromium recovery,” J. Clean. Prod. 190, 200‑210. DOI: 10.1016/j.jclepro.2018.04.151
Volesky, B. (1990). Biosorption of Heavy Metals, CRC press, Boca Raton, FL, USA.
Volesky, B. (1994). “Advances in biosorption of metals: Selection of biomass types,” FEMS Microbiol. Rev. 14(4), 291‑302. DOI: 10.1111/j.1574-6976.1994.tb00102.x
Volesky, B. (2003). Sorption and Biosorption, BV-Sorbex, Inc., Quebec, Canada.
Volesky, B. (2007). “Biosorption and me,” Water Res. 41(18), 4017‑4029. DOI: 10.1016/j.watres.2007.05.062
Volesky, B., and Holan, Z. R. (1995). “Biosorption of heavy metals,” Biotechnol. Progr. 11(3), 235‑250. DOI: 10.1021/bp00033a001
Volesky, B., and Tsezos, M. (1982). “Separation of uranium by biosorption,” U.S. Patent No. 04320093.
Wan Ngah, W. S., and Hanafiah, M. A. K. M. (2008). “Removal of heavy metal ions from wastewater by chemically modified plant wastes as adsorbents: A review,” Bioresource Technol. 99(10), 3935‑3948. DOI: 10.1016/j.biortech.2007.06.011
Wang, H. A., Grolimund, D., Giesen, C., Borca, C. N., Shaw-Stewart, J. R., Bodenmiller, B., and Günther, D. (2013). “Fast chemical imaging at high spatial resolution by laser ablation inductively coupled plasma mass spectrometry,” Anal. Chem. 85(21), 10107‑10116. DOI: 10.1021/ac400996x
Wang, L., and Dibdiakova, J. (2014). “Characterization of ashes from different wood parts of Norway spruce tree,” Chem. Eng. Transact. 37, 37‑42. DOI: 10.3303/CET1437007
Wang, K., Zhang, J., Shanks, B. H., and Brown, R. C. (2015a). “The deleterious effect of inorganic salts on hydrocarbon yields from catalytic pyrolysis of lignocellulosic biomass and its mitigation,” Appl. Energ. 148, 115‑120. DOI: 10.1016/j.apenergy.2015.03.034
Wang, L., Li, T., Güell, B. M., Løvås, T., and Sandquist, J. (2015b). “An SEM-EDX study of forest residue chars produced at high temperatures and high heating rate,” Energy Proced. 75, 226‑231. DOI: 10.1016/j.egypro.2015.07.312
Wase, D. A. J., Forster, C. F., and Ho, Y. S. (1997). “Low-cost biosorbents: Batch processes,” in: Biosorbents for Metal Ions, J. Wase and C. Forster (eds.), CRC Press, London, England.
Wase, J., and Foster, C. (1997). Biosorbent for Metal Ions, Taylor and Francis, Ltd., London, England.
Wei, X., Brockhoff-Schwegel, C. A., and Creed, J. T. (2001). “A comparison of urinary arsenic speciation via direct nebulization and on-line photo-oxidation–hydride generation with IC separation and ICP-MS detection,” J. Anal. Atom. Spectrom. 16(1), 12‑19. DOI: 10.1039/B004257I
Werkelin, J., Skrifvars, B.-J., Zevenhoven, M., Holmbom, B., and Hupa, M. (2010). “Chemical forms of ash-forming elements in woody biomass fuels,” Fuel 89(2), 481‑493. DOI: 10.1115/FBC2005-78128
Wieser, M. E., and Schwieters, J. B. (2005). “The development of multiple collector mass spectrometry for isotope ratio measurements,” Int. J. Mass Spectrom. 242(2‑3), 97‑115. DOI: 10.1016/j.ijms.2004.11.029
Wilson, G. W. T., Rice, C. W., Rillig, M. C., Springer, A., and Hartnett, D. C. (2009). “Soil aggregation and carbon sequestration are tightly correlated with the abundance of arbuscular mycorrhizal fungi: Results from long-term field experiments,” Ecol. Lett. 12(5), 452‑461. DOI: 10.1111/j.1461-0248.2009.01303.x
Wintz, H., Fox, T., and Vulpe, C. (2002). “Responses of plants to iron, zinc and copper deficiencies,” Biochem. Soc. T. 30(4), 766‑768. DOI: 10.1042/BST0300766
World Health Organization (WHO) (1992). “Cadmium,” in: Environmental Health Criteria, WHO, Geneva, Switzerland.
Wu, F., Yang, W., Zhang, J., and Zhou, L. (2010). “Cadmium accumulation and growth responses of a poplar (Populus deltoids×Populus nigra) in cadmium contaminated purple soil and alluvial soil,” J. Hazard. Mater. 177(1‑3), 268‑273. DOI: 10.1016/j.jhazmat.2009.12.028
Wu, J., and Boyle, E. A. (1997). “Low blank preconcentration technique for the determination of lead, copper, and cadmium in small-volume seawater samples by isotope dilution ICPMS,” Anal. Chem. 69(13), 2464‑2470. DOI: 10.1021/ac961204u
Xian, X., and Shokohifard, G. I. (1989). “Effect of pH on chemical forms and plant availability of cadmium, zinc and lead on polluted soils,” Water Air Soil Poll. 45(3‑4), 265‑273.
Yao, Y., Gao, B., Inyang, M., Zimmerman, A. R., Cao, X., Pullammanappallil, P., and Yang, L. (2011a). “Biochar derived from anaerobically digested sugar beet tailings: Characterization and phosphate removal potential,” Bioresource Technol. 102(10), 6273‑6278. DOI: 10.1016/j.biortech.2011.03.006
Yao, Y., Gao, B., Inyang, M., Zimmerman, A. R., Cao, X., Pullammanappallil, P., and Yang, L. (2011b). “Removal of phosphate from aqueous solution by biochar derived from anaerobically digested sugar beet tailings,” J. Hazard. Mater. 190(1‑3), 501‑507. DOI: 10.1016/j.jhazmat.2011.03.083
Yoshida, S., Watanabe, M., and Suzuki, A. (2011). “Distribution of radiocesium and stable elements within a pine tree,” Radiat. Prot. Dosim. 146(1‑3), 326‑329. DOI: 10.1093/rpd/ncr181
Yost, R. A., and Enke, C. G. (1978). “Selected ion fragmentation with a tandem quadrupole mass spectrometer,” J. Am. Chem. Soc. 100(7), 2274‑2275. DOI: 10.1021/ja00475a072
Zacchini, M., Pietrini, F., Mugnozza, G. S., Iori, V., Pietrosanti, L., and Massacci, A. (2009). “Metal tolerance, accumulation and translocation in poplar and willow clones treated with cadmium in hydroponics,” Water Air Soil Poll. 197(1‑4), 23‑34. DOI: 10.1007/s11270-008-9788-7
Zeisler, R., Murphy, K. E., Becker, D. A., Davis, W. C., Kelly, W. R., Long, S. E., and Sieber, J. R. (2006). “Standard reference materials (SRMs) for measurement of inorganic environmental contaminants,” Anal. Bioanal. Chem. 386(4), 1137‑1151. DOI: 10.1007/s00216-006-0785-7
Zennaro, M., Cristofori, F., Formigoni, D., Frignani, F., and Pavoni, B. (2005). “Heavy metal contamination in compost. A possible solution,” Ann. Chim-Rome 95(3‑4), 247‑256. DOI: 10.1002/adic.200590027
Zhang, N., Hu, B., and Huang, C. Z. (2007). “A new ion-imprinted silica gel sorbent for on-line selective solid-phase extraction of dysprosium(III) with detection by inductively coupled plasma-atomic emission spectrometry,” Anal. Chim. Acta 597(1), 12‑18. DOI: 10.1016/j.aca.2007.06.045
Zhang, N., Suleiman, J. S., He, M., and Hu, B. (2008). “Chromium (III)-imprinted silica gel for speciation analysis of chromium in environmental water samples with ICP-MS detection,” Talanta 75(2), 536‑543. DOI: 10.1016/j.talanta.2007.11.059
Zheng, G. D., Chen, T. B., Gao, D., and Luo, W. (2004). “Dynamic of lead speciation in sewage sludge composting,” Water Sci. Technol. 50(9), 75‑82. DOI: 10.2166/wst.2004.0539
Zheng, J., Hintelmann, H., Dimock, B., and Dzurko, M. S. (2003). “Speciation of arsenic in water, sediment, and plants of the Moira watershed, Canada, using HPLC coupled to high resolution ICP–MS,” Anal. Bioanal. Chem. 377(1), 14‑24. DOI: 10.1007/s00216-003-1920-3
Zhou, J. L., and Kiff, R. J. (1991). “The uptake of copper from aqueous solution by immobilized fungal biomass,” J. Chem. Technol. 52(3), 317‑330. DOI: 10.1002/jctb.280520305
Zhu, Y. G., Zhao, Z. Q., Li, H. Y., Smith, S. E., and Smith, F. A. (2003). “Effect of zinc–cadmium interactions on the uptake of zinc and cadmium by winter wheat (Triticum aestivum) grown in pot culture,” B. Environ. Contam. Tox. 71(6), 1289‑1296. DOI: 10.1007/s00128-003-0230-y
Zouboulis, A. I., Lazaridis, N. K., and Matis, K. A. (2002). “Removal of toxic metal ions from aqueous systems by biosorptive flotation,” J. Chem. Technol. Biot. 77(8), 958‑964. DOI: 10.1002/jctb.663
Zougagh, A., Torres, A. G., Alonso, E. V., and Pavon, J. M. C. (2004). “Automatic on line preconcentration and determination of lead in water by ICP-AES using a TS-microcolumn,” Talanta 62(3), 503‑510. DOI: 10.1016/j.talanta.2003.08.033
Article submitted: November 21, 2018; Peer review completed: February 17, 2019; Revised version received: February 22, 2019; Accepted: February 23, 2019; Published: March 1, 2019.