EFFECTS OF DECK WASHES AND BRIGHTENERS ON THE LEACHING OF CCA COMPONENTS.
There has been concern that bleaching and other agents in commercial deck washes and brighteners could aggressively leach chromated copper arsenate (CCA) components from treated wood. Natural rain water drippage was collected over several rain events from small-scale CCA type C treated southern pine decks and from an approximately 12-year-old CCA-C treated spruce/pine/fir deck installed in New Brunswick, Canada. The decks were then treated with a number of commercial deck washes/brighteners, and the CCA components in the wash solution were compared to those from water wash only and from the natural rain events. Treatments containing phosphoric acid, citric acid, and oxalic acid resulted in relatively high copper losses during the washing treatment and slightly increased losses of the other components. Strong oxidizing agents such as sodium hypochlorite and sodium percarbonate resulted in oxidation of chromium to the hexavalent state and subsequent loss of soluble hexavalent chromium. Alkaline sodium hydroxid e and sodium borate treatments also mobilized some hexavalent chromium. Losses were much higher from new decking than from a deck that had been in service for approximately 12 years.
Wood treated with chromated copper arsenate (CCA) is widely accepted for residential construction because of its effectiveness against decay fungi and insects, its low maintenance requirements, and its ability to protect wood surfaces against ultraviolet light degradation. However, it is common practice to refurbish treated decks and other residential structures that have been in service for some time by application of brush-on or spray-on deck washes, cleaners, or brighteners to bring the wood color back to its original new wood appearance .
Studies on the feasibility of extracting CCA treatment from spent treated wood and other CCA-contaminated wastes have shown that many organic and mineral acids can dissolve CCA components. Examples include extraction with organic acids such as citric acid, acetic acid, formic acid, oxalic acid, fumaric acid, tartaric acid, gluconic acid, and malic acid [3,4,7,9,12], and mineral acids such as sulphuric, hydrochloric, nitric, and phosphoric acids [6,9,12]. Also, biodegradation using microorganisms such as bacteria, yeast, and fungi can extract CCA from spent wood by the action of organic acid metabolites .
Many of these compounds that are most effective for the chemical remediation of CCA-treated wood are components of deck brighteners and cleaners . There have been suggestions in the popular press [8,10] that the use of these materials on CCA-treated decks could result in excessive extraction of CCA components and lead to increased levels of contaminants in the soil under treated products. Such an effect could help explain anomalous high soil contamination results observed by Stillwell and Gorny .
In this, study, the effects of a number of deck wash/brightener products on leaching of CCA-C components were evaluated.
SMALL, NEW SOUTHERN PINE DECKS
Fourteen 1.32 [m.sup.2] (14.2 [ft..sup.2] deck units were made with 44-inch (1.12-m) lengths of nominal 2- by 6-inch (38- by 140-mm) pressure-treated southern pine (Pinus spp.) lumber, treated to approximately 6.4 kg/[m.sup.3] (0.4 pcf) retention with CCA-C. The boards were spaced approximately 6 mm (1/4 in.) apart on two 2- by 6-inch (38- by 140-mm) treated southern pine stringers. The treated samples were fixed at high temperature and humidity (90[degrees]C, 99% relative humidity) until all of the chromium was reduced before assembly of the decks. The decks were equipped with a polyethylene collection drape under the decks. All rain or wash water was collected in polyethylene containers placed under a hole cut in the center of the draped plastic under the decks. The decks were placed out-of-doors in Fredericton, New Brunswick, Canada, in May 1998 and the natural rain drippage was collected over a 6-week period (five rain events). The collected water was filtered through a nylon millipore filter with a pore size of 0.45 [micro]M, then analyzed for total copper (Cu), chromium (Cr), and arsenic (As) content using a Varian-SpectrAA-400 atomic absorption spectrometer. A graphite furnace attachment was used for arsenic analysis. The detection limits were: Cu, 0.02 ppm; Cr, 0.02 ppm; and As, 0.05 ppm. Hexavalent chromium (CrVI) content was determined by the diphenyl-carbazide method (2) using a Shumadzu, UV-l 6 spectrophotometer at a wavelength of 540 nm (detection limit 0.05 ppm).
The rate of rainfall was estimated by collecting rain in cylindrical buckets and determining the rainfall per [m.sup.2] of surface. Before application of the deck treatments, all decks were scrubbed with 8 L of water (6 L/[m.sup.2]) and the water was collected and analyzed. The decks were then treated (two decks per treatment) with seven commercial deck wash or brightener treatments (Table 1) according to the manufacturers' recommendations, and the decks were rinsed with 6 L of water per [m.sup.2] of deck. The emissions of all CCA components were converted to standard units of [micro]g/[cm.sup.2] surface area per event (natural rain or wash treatment). This was calculated by: concentration in leachate [micro]g/mL) multiplied by the volume of leachate (mL) divided by the deck surface area ([cm.sup.2]).
The decks remained exposed to the weather for 12 months, and in the summer of 1999, natural rain samples were collected again (three rain events), the five highest leaching deck wash formulations were applied, and the rinsings from the treatment were collected, filtered, and analyzed as described previously.
AGED IN-SERVICE SPRUCE-PINE-FIR DECK
An approximately 12-year-old Canadian spruce-pine-fir (SPE) (Picea mariana (Mill.) BSP, Pinus banksiana Lamb., Abies balsamea (L.) Mill.) deck, also located in Fredericton, New Brunswick, with an average retention of 2.5 kg/[m.sup.3] (0.16 pcf) was selected. The SPF species are difficult to penetrate with preservatives and the treatment was confined to the surface 5 mm of the boards. The deck was partitioned into five 0.45-[m.sup.2] (4.8-[ft..sup.2]) areas and polyethylene sheets were stapled under them to collect all rain drip water. The drip water was collected from each area for three rain events and the trapped water was measured for volume, filtered, and analyzed for CCA components as described previously. The areas were then treated according to manufacturers' instructions with one of five deck wash treatments selected from those evaluated in the previous study (only one replicate sample per deck treatment). Each treated area was rinsed with 6L/[m.sup.2]) and the rinsings were collected for analysis as previously described.
The amounts of CCA-C components leached from the decking were expressed as micrograms per square centimeter ([micro]g/[cm.sup.2]) of deck surface for comparison with leaching during the rain events.
RESULTS AND DISCUSSION
SMALL, NEW SOUTHERN PINE DECKS
Several of the deck treatments evaluated increased the amounts of CCA components leached, and especially the amounts of copper and chromium extracted (Table 2). Deck cleaners based on phosphoric acid, oxalic acid, or citric acid caused high copper leaching. The oxalic acid and citric acid treatments also increased arsenic leaching compared to a water-only treatment. The amount of chromium leached was also increased to some extent by the oxalic acid treatment. Treatments based on strong oxidizing agents such as sodium hypochlorite and sodium percarbonate resulted in higher-than-normal chromium losses by oxidizing the trivalent chromium in the wood to the soluble hexavalent state (CrVI). These treatments also resulted in higher copper and arsenic losses compared to water treatment. The alkaline sodium hydroxide treatments also resulted in release of some hexavalent chromium. The sodium borate based treatment had no effect on leaching of copper and arsenic, but increased leaching of chromium due to some oxidati on of the trivalent chromium.
In most cases, even though the leach-ate concentrations were elevated in the deck wash rinsings, the absolute amounts of CCA components removed were not excessively high compared to losses by natural rain extraction, where the volumes of leachate were much higher. For the five rain events monitored before application of the deck wash, an average of about 14 L of drip water was collected per square meter of deck, with the following average concentrations: Cu, 3.8 ppm; Cr, 0.9 ppm; and As, 2.8 ppm. When the amounts of elements extracted under these conditions are compared to the amounts released when the decks were washed with the deck treatments and rinsed with 6 L/[m.sup.2] of water, the total amounts extracted are generally in the same order of magnitude or lower (Table 2). Exceptions are the high copper levels from the citric acid treatment and high hexavalent chromium levels when oxidizing chemicals were used. Citric acid is a strong chelating agent and is known to aggressively extract copper and other CCA components from treated wood . Since hexavalent chromium is more toxic and mobile in the environment compared to trivalent chromium , oxidizing tr eatments should be avoided on CCA-treated wood.
After 1 year in service, the amounts of CCA components removed by the natural rainfall and by the deck wash treatments were decreased by about 50 percent (Table 2). The phosphoric acid, oxalic acid, and citric acid still removed more copper than the other treatments, but the amounts were relatively low compared to natural rain leaching, again, because of the large volumes of rain water. The sodium hypochlorite and sodium percarbonate treatments removed higher-than-normal amounts of chromium, as hexavalent chromium, but at much lower levels than for the first treatment. The amount of water drippage collected from the decks was always less than expected from the amount of rainfall due to absorption of water by the decks (Table 3). A higher percentage of water reached the ground when the rainfall was intense. This usually resulted in lower CCA component concentrations in the leachate.
OLD SPRUCE-PINE-FIR DECK IN SERVICE
The amounts of CCA components leached from the older deck during natural rain events and after application of deck treatments were much lower than from the newer decks (Table 4). The same trends were seen, however: higher copper losses from the phosphoric, oxalic, and citric acid treatments and higher chromium losses from the oxidizing treatments.
SUMMARY AND CONCLUSIONS
Commercial deck wash and brightening treatments were applied to new CCA-treated decks, to the same decks after 1 year of natural exposure, and to an older deck in service about 12 years, and the emissions of copper, chromium, and arsenic were compared to those from natural rain leaching. Depending on the active ingredients, most of the deck washes resulted in increased leaching of CCA components, compared to washing with the same volume of water. The greatest effects were higher copper extraction by phosphoric acid, oxalic acid, and citric acid treatments and conversion of trivalent chromium to leachable hexavalent chromium by strong oxidizing treatments such as sodium hypochlorite and sodium percarbonate and alkaline sodium hydroxide and sodium borate. These latter treatments should not be used on CCA-treated wood because of the health and environmental concerns associated with hexavalent chromium.
Apart from the chromium losses from the oxidizing treatments and copper losses from citric acid treatment, most losses were comparable to losses experienced during normal rain events, due to the larger volumes of leaching water during rains.
The amounts of contaminants in the leachate were lower in older decks for both natural rain leaching and subsequent deck treatments.
The authors are, respectively, Graduate Student, Dept. of Forest Prod., Oregon State Univ., 230 Richardson Hall, Corvallis, OR, 97331; and Associate Professor and Research Associate, Faculty of Forestry, Univ. of Toronto, 33 Willcocks St., Toronto, Ontario, M5S 3B3, Canada. The authors gratefully acknowledge the financial support of the Natural Sciences and Engineering Research Council of Canada, and the industrial supporters under the NSERC Industry Collaborative Research Program: LPB Poles Inc., Guelph Utility Pole Co., Timber Specialties Ltd., Hicksons Building Products Ltd., Stella Jones Inc., and Pastway Planing Ltd. This paper was received for publication in January 2000. Reprint No. 9099.
(*.) Forest Products Society Member.
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Description of deck treatments evaluated. Formulation Description Active ingredients Application procedures 1 Cleaner and Phosphoric acid Mix 1:1 with water brightener Apply with sprayer Agitate with a brush Let stand 5 minutes Rinse with water 2 Cleaner and Oxalic acid Mix 1:4 with water brightener Wet wood surface with water Apply cleaner and scrub with a brush Wait 15 minutes, re-scrub, and rinse with water 3 Brightener Citric acid Dissolve powder in water (4.2% solution) Apply with sprayer Wait 5 to 15 minutes Rinse with water 4 Wood restorer Sodium hydroxide Apply as provided with brush Agitate lightly Wait 5 minutes Rinse with water 5 Deck cleaner Sodium hypochlorite Apply as provided with and sodium hydroxide sprayer Wait 5 to 10 minutes Rinse with water 6 Deck brightener Sodium percarbonate Dissolve powder in water and cleaner (5% solution) Apply with sprayer Scrub, wait 5 minutes, and rinse with water 7 Glaze remover Sodium borate Dissolve powder in water and cleaner (2.8% solution) Apply with sprayer Agitate with brush Rinse with water Leaching of CCA components from new decks after installation and after 1 year (means (SD) in [micro]g/[cm.sup.2] of deck surface per event). After installation Treatment Total Cr CrVI Cu Natural rain 1.36 (0.36) [greater than].05 4.39 (0.87) Water wash 0.33 (0.25) [greater than].05 0.47 (0.27) Phosphoric acid 0.18 (0.04) [greater than].05 4.39 (0.09) Oxalic acid 1.59 (0.38) 0.06 (0.04) 5.54 (0.66) Citric acid 0.43 (0.15) [greater than].05 13.1 (2.31) Sodium borate 0.32 (0.09) 0.25 (0.02) 0.49 (0.33) Sodium hydroxide 3.80 (0.43) 0.45 (0.10) 2.44 (0.32) Sodium hypochlorite 8.27 (0.04) 6.14 (2.47) 2.30 (0.17) Sodium percarbonate 5.41 (0.22) 4.75 (0.68) 1.84 (0.20) After 1 year Treatment As Total Cr CrVI Cu Natural rain 3.32 (0.66) 0.91 (0.24) [greater than].05 1.31 (0.80) Water wash 0.39 (0.05) 0.13 (0.03) [greater than].05 0.30 (0.12) Phosphoric acid 0.31 (0.07) 0.27 (0.04) 0.08 (0.02) 1.88 (0.77) Oxalic acid 3.22 (0.65) 0.32 (0.08) [greater than].05 1.11 (0.43) Citric acid 1.34 (0.30) 0.23 (0.14) [greater than].05 2.54 (0.25) Sodium borate 0.48 (0.28) -- -- -- Sodium hydroxide 3.06 (0.41) -- -- -- Sodium hypochlorite 3.22 (0.23) 1.00 (0.15) 0.26 (0.02) 0.88 (0.24) Sodium percarbonate 1.94 (0.01) 0.62 (0.013) 0.09 (0.004) 0.33 (0.06) Treatment As Natural rain 2.51 (0.70) Water wash 0.11 (0.04) Phosphoric acid 0.31 (0.14) Oxalic acid 0.42 (0.68) Citric acid 0.30 (0.18) Sodium borate -- Sodium hydroxide -- Sodium hypochlorite 0.37 (0.08) Sodium percarbonate 0.21 (0.01) Relationship between rainfall intensity, leachate concentration, and amount of water passing through the decks. Rain Water % pass Concentration in leachate Rain event intensity collected through Cr Cu As (mL/[m.sup.2]) (ppm) New decks Year 1 - 1 20,800 -- [a] -- 1.11 4.31 2.56 - 2 13,250 -- -- 0.61 3.61 2.34 - 3 7,580 -- -- 0.34 1.52 1.23 - 4 16,300 -- -- 1.06 4.23 3.33 - 5 19,300 -- -- 0.54 2.41 2.11 Year 2 - 1 1,490 830 56 1.08 2.46 3.16 - 2 29,860 26,060 87 0.61 0.92 1.74 - 3 18,390 15,860 86 0.96 1.26 2.54 Old deck Year 2 - 1 -- 3,300 -- 0.39 0.30 0.18 - 2 -- 30,000 -- 0.41 0.32 0.37 - 3 -- 30,000 -- 0.30 0.29 0.33 Leaching of CCA components from 12-year-old spruce-pine-fir deck (one replicate only for deck treatments) in [micro]g/[cm.sup.2] of deck surface per event. After installation Treatment Total Cr CrVI Cu Natural rain 0.48 (0.08) [a] [less than] .05 0.40 (0.02) [a] Phosphoric acid 0.23 [less than] .05 1.51 Oxalic acid 0.33 [less than] .05 2.20 Citric acid 0.21 [less than] .05 1.00 Sodium hypochlorite 0.80 0.30 0.27 Sodium percarbonate 0.70 0.44 0.28 Treatment As Natural rain 0.44 (0.17) [a] Phosphoric acid 0.13 Oxalic acid 0.61 Citric acid 0.07 Sodium hypochlorite 0.33 Sodium percarbonate 0.11 (a.)Standard deviations are in parentheses.
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|Author:||TAYLOR, ADAM; COOPER, P. A.; UNG, Y. T.|
|Publication:||Forest Products Journal|
|Article Type:||Statistical Data Included|
|Date:||Feb 1, 2001|
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