International Research Group (IRG) on Wood Protection
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ItemTesting a diffusion and reaction model for the leaching of CCA components from unfixed CCA-treated wood(2002)A previously described physical model applicable to the leaching of any substance undergoing a first-order fixation reaction with wood is applied to the leaching of CCA components from unfixed wood. Using this model and laboratory leaching experiments with small wood samples immersed in water, the diffusion coefficients and reaction rate constant of Cr6+, total Cr, Cu and As in unfixed CCA-treated red pine (Pinus resinosa Ait) are measured. Modelled reaction rate constants are in general agreement with pure fixation experiments except when determined from experiments involving small samples severely depleted by longitudinal leaching, but this effect is seen to decrease for larger sample sizes. The operation of the model for predicting intermittent Cr6+ leaching is explained through a visual demonstration. The model is shown to have good predictive ability when compared to a leaching experiment involving intermittent immersion and changing temperatures.
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ItemRemoval of CCA from Spent CCA-Treated Wood(2002)A novel method for the removal of CCA components from spent CCA-treated wood has been developed. The CCA-treated wood was first converted into liquid in the presence of polyethylene glycol and glycerin at mild temperatures (120 – 150 0C) by using sulfuric acid as catalyst. The resulting viscous liquefied wood was then resolved in acetone/water solvent. The hazardous components (i.e., Cr, As, and Cu) in the solution were then removed through precipitation by addition of complexing agents. It was found that more than 85% of CCA could be removed from spent CCA-treated wood. The detoxified wood can be used as chemicals for the preparation of polyurethane materials and the recovered CCA can be reused in the CCA wood treatment industries.
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ItemLeaching of CCA from Bombax ceiba catamarans in operation for 15 years(2002)Core samples of wood at random were collected from all the timber pieces of each of the three catamarans made of CCA treated logs of Bombax ceiba put to continuous service for the last 15 years at the Lawson's Bay fishing village, Visakhapatnam. The samples were dried to constant weight, powdered, digested and analyzed for the residual salts of the preservative. The residual content of CCA was found to be 6.90, 6.24 and 7.43 kg/m3 in CAT I, II and III, respectively. The values for individual components of arsenic, copper and chrome were 0.24 to 0.34 kg/m3, 3.34 to 4.37 kg/m3 and 2.66 to 3.03 kg/m3, respectively. Making use of the initial absorptions of the preservative determined at the time of treatment and the residual contents estimated now, the leaching rates of CCA and it's components were calculated. While the annual leaching rate of CCA was observed to be 1.22 kg/m3 (CAT I), 0.81 kg/m3 (CAT II) and 0.83 kg/m3 (CAT III), at elemental level, it was found to be 0.05, 0.04 and 0.05 kg/m3 in the case of arsenic, 0.15, 0.10 and 0.09 kg/m3 in the case of copper and 0.20, 0.12 and 0.14 kg/m3 in the case of chromium for CAT I, II and III, respectively. The results thus indicate that while about 2/3rd the initial amount of CCA had been leached out of the catamarans during the last 15 years, still 1/3rd the amount is present in the logs. Thus, the preservative left out in the catamarans appears to be sufficient to offer protection to the craft for a good number of years to come.
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ItemBalance of arsenic and recycling(2002)Instead of importing considerable quantities of arsenic to Europe, it would be sensible to utilize the arsenic recovered in the recycling process in the manufacture of CCA-wood, in the metallurgical industry as well as in other ways. When copper is also processed into a form easy to utilize, it may be possible to utilize chrome as well. When these developments are implemented, it can be said that CCA-treated wood is an ecologically sound product. When the recycling process is introduced in Europe on a large scale, an amount of energy equivalent to a nuclear power unit can be conserved.
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ItemEffectiveness of CCA fixation to avoid hexavalent chromium leaching(2002)It is generally assumed that hexavalent chromium in chromated copper arsenate wood preservative is substantially reduced to trivalent chromium during fixation and that the potential to leach the more toxic CrVI is minimal. However, there are occasional claims some hexavalent chromium remains in wood after fixation and that small amounts of CrVI are available for leaching. One problem is that other metals such as iron can develop the same colour reactions as CrVI with the standard indicator, diphenyl-carbazide which may result in false measurements of CrVI. Ion chromatography can measure CrVI to 0.5 parts per billion and distinguish the reaction from that with other metals. In this study a number of CCA treated wood samples of different wood species and ages and wood cement and wood plastic composites containing CCA treated wood were collected and exposed to laboratory leaching. The leach water was analysed for CrVI and total Cr, Cu and As. For CCA treated wood and wood plastic composites, CrVI in the leachate was near or below the detection limit of the ion chromatograph (<1ppb) compared to total chromium levels of 200 – 2700 ppb. The amount of hexavalent chromium relative to total chromium leached was generally less than 0.1 %. Leachate from wood cement composites showed significant levels of CrVI (up to 50% of the total chromium leached). However, both hexavalent and total chromium levels in the leachate were low (0.2 – 0.4 ppm). These results show that once the CCA is properly fixed in wood, there is no health or environmental risk associated with toxic hexavalent chromium being released from treated wood.
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ItemSemi-Solid State Bioremediation of CCA-Treated Wood Using Malted Barley as a Nutrient Source(2002)Bioremediation processes for recovery and reuse of CCA-treated wood invariably increase the cost of any secondary products manufactured from the remediated fiber. Microbial remediation using either bacteria or fungi has been shown to remove heavy metals from CCA-treated southern yellow pine (SYP). In a two-step remediation process utilizing oxalic acid extraction and the metal-tolerant bacterium Bacillus licheniformis, 70-100% of the copper, chromium and arsenic can be removed from CCA-treated SYP, but the liquid culture medium used to support the bacterial growth renders this process costly. Processing costs could be partially offset if the culture medium were replaced with an industrial by-product. In this study, an abundant by-product of the brewing industry, malted barley, was evaluated as a replacement for commercial nutrient broth in the bioremediation process for CCA-treated SYP. Malted barley’s high moisture and nutrient content should support bacterial growth. When malted barley was substituted as a growth substrate for nutrient broth, it was discovered that either the culture inoculum or wood itself provided sufficient nutrients for the growth of B. licheniformis. Seventeen percent of the copper and 15% of the arsenic was removed from an aqueous slurry of CCA-treated SYP following bacterial remediation with B. licheniformis. When oxalic acid extraction preceded the aqueous bacterial culture of CCA-treated SYP, 21% Cu, 54% Cr and 63% As were removed. Incidentally, malted barley acted as a biosorbent, removing heavy metals from the liquid culture upon their release from CCA-treated SYP.
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ItemImpact of leachates from CCA- and copper azole-treated pine decking on soil-dwelling invertebrates(2002)This study assessed the short-term effects on non-target soil invertebrates of leachates from a naturally durable hardwood and timber treated with two copper-based wood preservatives. Natural rainwater leachates from kwila decking, and radiata pine-decking treated with CCA or copper-azole, were collected and applied on mown lawn soil in Brisbane, Queensland. The soil study consisted of 5 treatments: an independent control (replicates untreated), wet control (replicates treated with rainwater only), CCA, copper azole and kwila-extractive leachates. Two applications of each treatment were made. Soil samples were collected before application and then twice after the first application (3 and12 days) and 3 times after the second (3, 8 and 12 days). Soil arthropods were extracted from soil cores using Tullgren funnels. Frequency analysis and multivariate techniques were used to analyse the data for treatment effects. Soil invertebrates were dominated by mites (84%), which were identified to family level. We did not detect any difference in the density of mites except in the kwila-extractive leachate, where mite density increased significantly. However, there were detectable differences in mite community structure between all treatments, indicating differential effects of the treatments on the soil arthropod community.
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ItemFouling assemblage development on copper-chromium-arsenic-treated timber submerged in European waters(2002)The effect of the anti-marine-borer timber preservative CCA on community development of non-target marine fouling animals was investigated. Panels of Scots pine treated to target retentions of 12, 24 and 48 kg CCA per m3 of wood, plus untreated controls were submerged at seven coastal sites (Portsmouth, UK; La Tremblade (2 sites), France; Ria Formosa, Portugal; Sagres, Portugal; Kristineberg, Sweden; Athens, Greece). Inspections were made after 6, 12 and 18 months exposure and the fouling community on the surface of the panels was assessed both qualitatively and quantitatively. Multivariate statistical methods were used to compare community structure between panel treatments. Results showed that panels treated to the three CCA loadings supported very similar fouling assemblages which, in most cases, had higher numbers of taxa and individuals compared to assemblages on untreated panels. There were no detectable detrimental effects on epibiota community development caused by the presence of CCA preservatives within the matrix of the wood at any of the treatment levels. Similar trends were found at all seven exposure sites. This indicates that the range of environmental conditions at the sites had no bearing on preservative impact on fouling biota. Differences in community structure between CCA-treated and untreated panels may be due to enhanced larval settlement on CCA-treated timber by some species as a result of modifications to the surface properties of the timber by the CCA preservative. Possible reasons for the higher numbers of certain species on the surface of CCA-treated panels are discussed.
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ItemPreservative absorption response of planks of Anogeissus acuminata for plank-built catamarans(2002)Due to shortage of timber coupled with other compelling factors, traditional fishermen along the east coast of India, especially of Andhra Pradesh, of late, are departing from conventional log type wooden catamarans. Instead, they are fabricating catamarans out of timber planks of hard woods and utilizing thermocol for buoyancy. Mostly, locally available timber of a Combretaceae species, Anogeissus acuminata (Yon) is used to fabricate these plank-built catamarans. Since these catamarans are also built with untreated timber, there is every need to extend wood preservation technology to these craft also so as to achieve enhanced service life and conserve the resources. Therefore, the Institute of Wood Science and Technology took up treatment of timber meant for five such craft with copper-chrome-arsenic (CCA). Thirteen different logs were procured and converted into planks and batons of suitable sizes, debarked, cleaned and air dried under shade. While the length of the planks ranged from 0.81 to 6.53 m, the width varied from 16 to 44 cm. After sufficient seasoning, the material was pressure treated with 6% CCA by full cell method as per IS: 401 (1982). Chemical retentions were computed from the weight gained by the individual planks and sets of 20 batons immediately after treatment. The preservative absorption in the planks ranged from 13.05 to 69.80 kg/m3 averaging at 25.90 kg/m3 and that in the batons averaged at 32 kg/m3. The quantity of CCA absorbed by the planks was analyzed with reference to their length, width, thickness and volume. Planks when categorized to different length and volume groups exhibited clear difference in the intake of chemical by them but when categorized into different width and thickness classes showed not much variation. All the treated planks and batons after air drying in shade for 15 days were fabricated into five catamarans. Thus, though the planks of A. acuminata are either very long or very wide, they showed a positive response to CCA treatment by absorbing reasonably good quantities of preservative. Similarly, on fabrication of the catamarans, an average retention of 21.79 to 25.43 kg/m3 of CCA per craft could be achieved. These values fall into the recommended preservative absorption range of 16 to 32 kg/m3 (IS: 401, 1982) for marine structures.