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An approach to modeling leaching and leaching impacts of preservative components from treated wood is presented based on three simple laboratory determinations: the amount of preservative component available for leaching (Le), equilibrium dissociation of preservative into free water in wood (Di) and diffusion coefficients for component leaching in different wood directions (D). In this study, the following inorganic wood preservative systems were investigated: chromated copper arsenate (CCA), the copper component of copper azole (CA) and alkaline copper quaternary (ACQ), and boron in disodium octaborate tetrahydrate (DOT). Aggressive leaching of finely ground wood showed that amounts of preservative compounds available for leaching were highest for borates, followed by copper in copper amine systems and arsenic in CCA, copper in CCA and chromium in CCA. The equilibrium dissociation or solubility of components in free water in the wood was much higher for borates and copper amine, followed by copper and arsenic in CCA and chromium in CCA. Use of the applicable diffusion coefficient (D) and Di or Le values in a diffusion model allows the prediction of total amount leached and emission or flux rate at different times of exposure for products with different dimensions and geometries. The approach was tested and generally validated through application of the model to results of laboratory water spray leaching of full-size lumber samples. The approach explains the rapid leaching of boron compounds (large diffusion coefficient and high initial dissociated concentration) compared to other preservative components and predicts that ACQ will have higher initial leaching rates compared to CCA and CA, but the latter preservatives will continue to leach copper at a measurable rate for a much longer time. The practical implications and limitations of the approach are discussed.

Until recently, most research on the leaching of preservatives from treated wood was conducted in the laboratory. Although these studies have contributed to the understanding of leaching, the data generated under controlled conditions often do not apply to leaching during natural exposure and weathering. In addition, little is known about the effects of climatic variables and long-term emission rates. This paper examines leaching of chromated copper arsenate (CCA) from lumber exposed above ground to 685 mm of precipitationduring 351 days of natural weathering. Stepwise multiple regression analysis revealed relationships between leaching and a number of treatment and climatic variables, including: species of wood, initial preservative loading, amount of precipitation, average air temperature, average light intensity, pH and duration of rain event. Regression models explained approximately 30% of the variation in chromium and arsenic leaching and 44% of the variation in copper leaching.

Spent chromated copper arsenate (CCA)-treated wood was liquefied in polyethylene glycol 400/glycerin (2:1w/w). Sulfuric acid (95–98%) and ferrous salts (FeSO4·7H2O or FeCl2·4H2O) were used as catalysts and additives, respectively. The resulting liquefied CCA-treated wood was diluted with aqueous solvents and was then mixed with complexion/precipitation agents, followed by precipitation or filtration to remove the toxic metal-bearing sediment. As a result, more than 90% of Cu, Cr or As was removed.

A 558-h laboratory leaching test (AWPA E-11) was carried out on both commercially and laboratory chromated copper arsenate (CCA) type C-treated southern pine. Arsenic, chromium, and copper concentrations in the leachate collected were examined. Leaching of chromium and copper from CCA-treated wood cubes were nearly undetectable using flame atomic absorption spectroscopy after 174 and 366 h, respectively. Less than 10% of the total chromium in the leachate was present as hexavalent chromium [Cr(VI)] after leaching for 30 h. Selective ion-exchange chromatography was used to speciate arsenic in the leachate. In the first 270 h, approximately 70–90% of the total arsenic in the leachate was inorganic pentavalent arsenic [As(V)] and 10–30% was inorganic trivalent arsenic [As(III)].

Summary Two field test sites with different soil types were selected. Analysis showed that the two soils had considerable between-site variation in texture, base saturation, acidity, levels of metals, and cation exchange capacity. The sites also had moderate differences in average seasonal temperatures and rainfall. Stakes, made from defect-free southern yellow pine (SYP) sapwood and measuring 19×19×559mm, were treated to about 0.40 pcf (6.4 kg/m3) with chromated copper arsenate (CCA-type C). The stakes were installed at the two sites and sets of ten or more samples pulled after 55 and 66 months of exposure. The depletion of the individual components (chromium, copper and arsenic, oxide basis) from below-ground sections of each stake was then determined. No significant site effect on depletion was observed despite the large contrasts in chemical and physical properties between the two soils. Of the individual components, copper generally had the least depletion on a pcf weight loss basis while the greatest loss was observed with arsenic in three of the four time/site sets. The exposure times examined had no influence on depletion.

Summary Chromated copper arsenate (CCA) working solution is partially destabilized over time as a result of hexavalent chromium (CrVI) reduction by wood extractives and reactive additives such as water repellents and polyethylene glycol (PEG) wood softening agents. Hot water extracts of several softwood and hardwood species were used to prepare 2% CCA type C solutions. The softwoods included sapwood and heartwood of red pine (Pinus resinosa Ait.), jack pine (Pinus banksiana Lamb.), black spruce (Picea mariana Mill.), balsam fir (Abies balsamea (L.) Mill.) and sapwood of southern yellow pine (Pinus spp.). Hard wood samples were mixed sapwood and heartwood of red maple (Acer rubrum L.), basswood (Tilia americana L.), yellow poplar (Liriodendron tulipifera L.) and red oak (Quercus rubra L.). In a similar way, 2% CCA solutions were prepared containing 4% PEG and 1% paraffin wax formulated water repellent. The pH and hexavalent chromium content of the CCA solutions were monitored over time until sludge formation was observed. The obtained sludges were separated and analyzed by Fourier Transform Infrared Spectroscopy (FT-IR) in the mid-infrared range and by atomic absorption spectroscopy (AAS) for chromium, copper and arsenic contents. The results of FT-IR and AAS analyses of the sludges indicate that the products of sludging are of comparable chemical nature regardless of the agent responsible for the destabilization of CCA solutions. Arsenic and chromium are the major and copper the minor constituent of the sludges produced by destabilization of CCA solutions examined here.

Seven North American hardwood species were vacuum or vacuum/pressure treated with 2% CCA-C solution and fixed at temperatures of 21°C and 50°C under conditions of high relative humidity (95%). The rates of fixation results are presented in Part 1 of this study. Red maple (Aver rubrum L.), red oak (Quercus rubra L.), American beech (Fagus grandifolia Ehrh), white birch (Betula papyrifera Marsh.), trembling aspen (Populus tremuloides Michx.), basswood (Tilia americana L.) and yellow poplar (Liriodendron tulipifera L.) were evaluated. The softwood red pine (Pinus resinosa Ait.) was included for comparison. Adequately fixed wood blocks (99.9% chromium reduction) were exposed to leaching by the AWPA El I procedure. All CCA components were leached in high quantities from oak wood, while from red maple and beech, high arsenic leaching occurred. Leaching losses from aspen, basswood and yellow poplar were low and comparable for both fixation temperatures. In most species, the amount of leaching was affected by the treating method, with lower leaching from pressure treated wood blocks than from vacuum treated blocks. Removal of extractives from maple and oak blocks before treatment affected the CCA leaching performance in these species. Extracted red oak had lower chromium and copper leaching, but higher arsenic leaching. In contrast, extracted red maple had reduced leaching of all CCA components compared to unextracted wood. The examined hardwoods can be classified into three groups according to their CCA fixing and leaching characteristics: fast fixing/high leaching group (beech, red oak and red maple), intermediate fixation rate and leaching group (white birch and red pine) and slow fixing and low leaching group (aspen, yellow poplar and basswood).

SummaryStanding bamboo culms have an attractive greenish skin. Once harvested, however, they turn yellow and the color starts to decay. These adverse properties limit their applications and degrade their performance. Chromated copper arsenate (CCA) based preservatives have been reported to be good protectors for preserving the green color of bamboo culms. An alkali pretreatment was required before applying CCA. However, the mechanism of alkali pretreatment on color conservation is not fully understood. In this study, morphology, wettability, chemical and pigment changes of moso bamboo (Phyllostachys pubescensMazel) were studied after treating with four alkali reagents. The results showed that 2% KOH effectively removed the waxes and capes of silica cells on moso bamboo surface and also increased the surface wettability much better than treatments with 4% K2CO3, 10% K2CO3, 4% Na2CO3, or 4% NaHCO3. The KOH pretreatment also results in a better penetration and reaction with the green color protector (5% Boliden K-33, type-B CCA), and subsequently preserved the green color appearance of moso bamboo.

Summary X-ray diffraction (XRD) technique was used to analyze qualitatively and semi-quantitatively solid crystal deposits in wood treated with some preservatives. Chromated copper arsenate type-C (CCA), copper ethanolamine (Cu-EA), copper naphthenate (Cu-N), copper dimethyldithiocarbamate (CDDC) and boric acid treated southern pine was investigated. The solid deposit in post-treatment steamed Cu-N and Cu-EA treated wood samples was identified as cuprous oxide (Cu2O) by using XRD. The presence of CDDC crystals was observed in CDDC treated wood samples. The XRD pattern of boric acid treated wood shows that crystalline boric acid is present in the treated wood. After washing boric acid treated wood with distilled water, the crystalline signal of boric acid disappeared. An XRD technique was also developed to semi-quantify the amount of solid crystals in post-treatment steamed Cu-N treated and CDDC treated samples. It was estimated that about 50% of cupric copper was converted to cuprous oxide (Cu2O) in Cu-N treated wood after post treatment steaming whereas no cuprous oxide was found in non post-treatment steamed Cu-N treated samples. The CDDC content determined by XRD was consistently 10–20% lower than the value calculated from the copper content using atomic absorption spectroscopy (AAS) analysis.

This study compared environmental emissions from a wood-treating plant using ammoniacal copper/quaternary ammonium compound, Type B formulation (ACQ-B) as an alternative wood preservative to chromated copper arsenate (CCA). The most obvious change in environmental emissions was the elimination of arsenic (As) and chromium (Cr), which eliminated the generation of Resource Conservation and Recovery Act (RCRA) wastes and the risk of contaminating the environment with these RCRA-regulated metals. ACQ-B, however, produced a greater amount of air emissions, mainly as ammonia (NH 3 ). Wood products treated with either preservative demonstrated leachable characteristics. The amounts of active ingredients leached were estimated based on exposure of treated rough-cut timber to about 114 mm of artificial rainfall 4 days after treatment.

Scanning electron microscopy coupled with energy dispersive X-ray analysis is used to study the preservative distribution and the anatomical structure at the micro-level in CCA treated wood and its pyrolysis residue. The type of wood used in these analyses is Pinus sylvestris peeling and sapwood, treated with chromated copper arsenate. The sapwood was treated only once instead of twice as was done with the peeling. Examination of the peeling reveals a uniform distribution of the metals throughout the total volume of the peeling due to the porous structure, which enables the CCA solution to penetrate deep into the wood, and which explains the high retention level of CCA solution. The relative amounts of Cr, Cu and As which occur at different locations vary and differ from the ratio in the CCA treating solution. The same conclusions can be drawn for the pyrolysis residue resulting from pyrolysis of the CCA treated peeling, in which vestures and warty layers are observed. Examination of the CCA treated sapwood reveals lower metal concentrations due to the lower retention level of CCA solution during treatment. The three metals are also found at each location examined. The anatomical structure of sapwood differs from peeling in the sense that it is less porous and clusters containing predominantly copper can be observed. The pyrolysis residue of CCA treated sapwood has a more porous structure and the metals are more concentrated in the ray cells, indicating a migration of metal compounds during the pyrolysis process. Tears are also observed, probably as a result of the thermal degradation process.

Les premiers essais realises montrent que l'extrait methanolique de Robinia pseudoacacia possede un potentiel important pour la preservation du bois de tremble et de pin contre l'attaque par Gloeophyllum trabeum et Pleurotus ostreatus