Abstract
Wood has been used in many areas including the marine environment due to its important properties. However, marine borers cause damage that shortens the service life of wooden materials. Marine borers have a wide distribution and employ different attack mechanisms depending on the geographical region. In this study, wood samples prepared from the Pinus sylvestris L. species were subjected to marine exposure for seven months in the Eastern, Central, and Western Black Sea Regions. Results showed that Teredo navalis marine borer was observed in all three regions. The N, Mg, S, Cl, Ca, Fe, Zn, and Pb content of the samples noticeable increased after the marine trial. According to Fourier transform infrared analysis, carbohydrate content of the samples decreased noticeable, while lignin content increased.
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Evaluation of Marine Wood Boring Organism’s Attack on Wood Materials in the Black Sea Coastal Region
Ahmet Can,* and Hüseyin Sivrikaya
Wood has been used in many areas including the marine environment due to its important properties. However, marine borers cause damage that shortens the service life of wooden materials. Marine borers have a wide distribution and employ different attack mechanisms depending on the geographical region. In this study, wood samples prepared from the Pinus sylvestris L. species were subjected to marine exposure for seven months in the Eastern, Central, and Western Black Sea Regions. Results showed that Teredo navalis marine borer was observed in all three regions. The N, Mg, S, Cl, Ca, Fe, Zn, and Pb content of the samples noticeable increased after the marine trial. According to Fourier transform infrared analysis, carbohydrate content of the samples decreased noticeable, while lignin content increased.
Keywords: Cellulose content; Chemical composition of wood; Marine environment; Teredo navalis
Contact information: Department of Forest Industrial Engineering, Faculty of Forestry, Bartin University, Bartin, Turkey; *Corresponding author: acan@bartin.edu.tr
INTRODUCTION
The destruction of wood materials by marine borers and the economic loss due to this damage have led to an increase in the use of concrete and steel. However, the use of wood is preferred because of its performance and low specific gravity compared to other constructional materials (concrete, steel, etc.) in addition to its low greenhouse gas effect (Borges et al. 2003; Bergman et al. 2014). Wood has been used in maritime construction due to its mechanical strength and elasticity, low energy production costs, and renewability (Cragg 1996). Moreover, wood is known to be more resistant to seawater than steel and concrete (Williams et al. 2005). However, marine wood borers, molluscs, and crustaceans attack wood materials in a marine environment.
There are many species of organisms that attach themselves to the surface of wood materials submerged in seawater and cause the wood to deteriorate. These organisms erode wood and shorten its service life. Marine borers that damage wood in the sea are classified as molluscs and crustaceans. The presence of any wood boring organism in a particular area is largely restricted by the temperature, salinity, contamination, and the availability of suitable host material of the seawater. In addition, the depth, oxygen content, turbidity, amount of the sea water, and the suspended organic matter also affect the spread of the borers (Cragg et al. 1999; Perçin 2007; Eriksen et al. 2014). Borges et al. (2014) reported that Teredo navalis and Nototeredo norvagica showed the widest distribution in European waters, and that T. navalis was one of the few species considered to present the greatest hazard to wooden maritime structures in the European coastal areas. In the past, some studies were conducted on the wood-destroying marine borers in Turkish coastal waters (Sivrikaya et al. 2008, 2009, 2012; Sen et al. 2010; Borges 2014). According to an earlier study, Teredo navalis, Limnoria tripunctata, and Chelura terebrans were identified in the Western Black Sea Region (Amasra) at different periods from 1968 to 1969 (Pınar 1997). Bobat (1994) found only one species, T. navalis, in an Eastern Black Sea site (Trabzon), whereas Sen et al. (2010), in addition to T. navalis, also reported the species of Lyrodus pedicellatus and Nototeredo norvagica in Trabzon and L. pedicellatus of the Western Black Sea Region (Ereğli).
The aim of this research was to determine the changes in the properties of Scots pine wood caused by marine borers through submergence of wood samples in the Eastern, Central, and Western Black Sea Regions for a period of seven months, the results were compared with the properties of twin control samples that had not been submerged in seawater. A number of aspects were investigated, including changes in physical appearance, X-ray imaging, the pH of the wood, and the mineral content determined via inductively coupled plasma atomic emission spectroscopy (ICP-AES). In addition, the cellulose, hemicellulose, and lignin content were determined via attenuated total reflection-Fourier-transform infrared (ATR-FTIR) analysis.
EXPERIMENTAL
Materials
In this study, Scots pine panels (Kartal Ahşap, Bartin, Turkey) were prepared from sapwood blocks at air-dried weight. Five replicates were used for each variation. The samples were free of knots and insect and fungal attack. The test samples were prepared by cutting tangentially in dimensions of 25 × 75 × 200 mm3 according to TS EN 275 (2000).
Fig. 1. Test sites chosen for the study
The test panels were attached to a polypropylene rope with a stone weight to hold them underwater. They were suspended vertically 6 m from sea surface when in low tide, with the larger dimension of the panels oriented horizontally. Literature studies have stated that the impregnated control samples are destroyed in a short time and one summer period is sufficient for testing (Sivrikaya et al. 2008, 2009). Therefore, for this study, the samples were left in seawater for seven months. According to the TS EN 275 (2000) standard (CEN), if the attack destroyed more than 50% of the tunnels ratio created by marine borers in the wood panel, it is rated as a ‘number 4’. Earlier studies in the Turkish waters showed that the exposition of wood panels in the marine environment for one summer season is sufficient for the destroyed attack experiment (Sivrikaya et al. 2008, 2009, 2012). The test sites (Fig. 1) were selected to involve the Black Sea. The test panels were deployed in the coastal sites of Trabzon (41°00’27.5″N, 39°44’15.7″E) in the Eastern, Samsun (41°18’29.9″N, 36°20’27.9″E) in the Central, and Zonguldak (41°27’19.5″N, 31°47’12.9″E) in the Western Black Sea Regions in Turkey. The average seawater temperature in the Black Sea was 15.2 °C and pH values were measured as 9.06 for Trabzon, 8.97 for Samsun, and 10.02 for Zonguldak during test (from Sep. 2016 to April 2017). Salinity of the seawater in the Black Sea has been recorded as 18‰ (Muhiddin et al. 2002).
Methods
At the end of the 7-month test period, the test samples were removed from the sea to evaluate the marine boring activity and identify the wood-boring species. Four of five test panels were analyzed via destructive methods and the fifth one was retained for non-destructive X-ray testing. The panels were split open to reveal the extent of interior damage and to extract the wood boring organisms. The severity of attack was visually apparent in cases where whole shipworms were removed from the panels, while in others, only pallets and shells were found (Fig. 2). The teredinid were preserved in 70% ethanol and identified using the pellet (Turner 1971) and descriptions (Turner 1966) of Turner.
Fig. 2. Teredo navalis: (A) pallets and (B) shell valves
Wood samples used for pH measurement were prepared according to TAPPI standard TAPPI Tm-45 (1992). The air-dried samples representing each test group were screened in 40- and 60-mesh sieves after grinding in a Wiley mill, and the material remaining in the 60-mesh sieve was used for pH measurement. Approximately 5 g of wood sample from each test group were placed in an Erlenmeyer flask containing 150 mL of distilled water and shaken mechanically for 24 h. At the end of the period, the pH was measured by water filtration.
The quantity of the typical elements of seawater (N, P, K, Ca, Mg, Na, Cl, S, Fe, Mn, Zn, Cu, B, Cd, Pb, and Al) found in the pine wood samples prior to and after submersion in the test sites was determined by ICP-AES (ICP OES; Spectro Genesis, Kleve, Germany). This analysis investigated how the seawater changed the mineral content of the wood, i.e., to reveal the mineral content of the wood samples exposed to seawater in the different regions, because it is known that mineral substances in seawater have an effect on the life of marine organisms. Sample preparation was completed according to AWPA standard AWPA A7 (1993). Wood samples were ground in a Wiley mill (IKA, Staufen, Germany) to a sieve size of 0.2 mm and oven dried at 103 ± 2 °C. A total of 1 g of the ground wood was weighed to the nearest 0.01 g and placed in a 100-mL flask. Nitric acid (65%) was then added to the flask, which was placed on a hot plate. After the formation of brown vapor, hydrogen peroxide (30%) was added dropwise to form a clear solution. After cooling, the contents in the flask were filtered through Whatman #4 filter paper (Merck, Taufkirchen, Germany) and diluted with distilled water for measurement.
The X-ray imaging was performed using a Siemens AXIOM Iconos R200 system (Siemens Medical Solutions, Malvern, PA, USA) under 85 to 90 kV and 10.4 to 11.9 mA, for which a focal distance of 150 cm was used. The photographs were taken from the same side before and after the experiment without being dried to enable comparison. The tunnel area was estimated from the X-ray images, and the rating system, based on TS EN 275 (2000), was employed to score the severity of the attack: “0”, no attacks present; “1”, tunnel area is less than 15% of the wooden object seen on the image; “2”, tunnel area is 15 to 25%; “3”, tunnel area is 25 to 50%; and “4”, tunnel area is more than 50%. Therefore, the results were qualitative estimations from a visual inspection of the images as per TS EN 275 (2000).
The ATR-FTIR analysis was conducted using a Shimadzu IRA Affinity-1 spectrometer (Shimadzu Corp., Beijing, China) equipped with a single reflection ATR pike MIRacle sampling accessory (MIRacle Single Reflection ATR accessory, Beijing, China). Samples for the ATR-FTIR analysis were prepared by grinding in a Wiley mill to a mesh size of 0.2 mm. Four accumulated spectra were collected in the wavenumber region of 700 to 4000 cm-1, with a spectral resolution of 4 cm-1.
RESULTS AND DISCUSSIONS
Visual Results
After the 7-month trial, the marine wood borer species Teredo navalis was identified in all three test sites of Trabzon, Samsun, and Zonguldak, located along the Black Sea coast. This fınding demonstrated that the species of wood boring organisms did not differ in the Eastern, Central, or Western Black Sea Region locations (Fig. 3). Some researchers also conducted similar experiments in different test sites along the Black Sea in the past (Sivrikaya et al. 2008; Sivrikaya et al. 2009). In 1968, Pınar (1997) reported higher T. navalis activity in Amasra after 12-month exposure. At the same test site, heavy attack on Scots pine samples was mentioned by Sivrikaya et al. (2012, 2016). In the present study, heavy teredinid attack was shown in the Scots pine samples and at the end of seven months, the samples from the Trabzon and Samsun test sites were brittle, while the samples from Zonguldak were slightly firmer (Fig. 3). All samples were rated as “4” because more than 50% of each panel had been bored by marine organisms.