Rate of CCA leaching from commercially treated decking.

Conflicting reports on levels of arsenic in soil beneath decks treated with chromated copper arsenate (CCA) have raised concerns about arsenic exposure from this type of treated wood. This paper reports on an evaluation of the rate of release of copper, chromium, and arsenic from commercially treated lumber as a function of treatment additive (with or without water repellent) and rate of rainfall. Treated lumber was purchased from several retailers at three times over the course of a year, and exposed under laboratory conditions to simulated rainfall at rates of 2.5, 8.0, or 25.4mm/hr., up to a total of 762 mm of rainfall. Water running off the specimens was periodically collected and analyzed for the concentration of leached arsenic, chromium, and copper. The amount of arsenic released from each specimen ranged from 0.16 percent when rainfall was delivered at 25.4 mm/hr. to 0.72 percent when rainfall was delivered at 2.5 mm/hr. The rate of arsenic release was highest initially and then stabilized at an average of 0.0143, 0.0079, and 0.0062 g/cm2/mm rainfall for the 2.5, 8.0, and 25.4 mm/hr. rainfall rates, respectively. The inclusion of water repellent in the CCA treatment did not have a consistent effect on leaching. In most cases, leaching of arsenic was greater in specimens containing the water-repellent additive, but the water repellent did appear to reduce leaching of copper. Using similar methodology, a secondary study was conducted to evaluate the ability of several finishes to reduce leaching. The results indicate that finishing decking with a semi-transparent water-repellent stain, latex paint, or oil-based paint will greatly reduce the leaching of arsenic, chromium, and copper. 2004
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Rate of CCA leaching from commercially treated decking.   (2004)

Conflicting reports on levels of arsenic in soil beneath decks treated with chromated copper arsenate (CCA) have raised concerns about arsenic exposure from this type of treated wood. This paper reports on an evaluation of the rate of release of copper, chromium, and arsenic from commercially treated lumber as a function of treatment additive (with or without water repellent) and rate of rainfall. Treated lumber was purchased from several retailers at three times over the course of a year, and exposed under laboratory conditions to simulated rainfall at rates of 2.5, 8.0, or 25.4mm/hr., up to a total of 762 mm of rainfall. Water running off the specimens was periodically collected and analyzed for the concentration of leached arsenic, chromium, and copper. The amount of arsenic released from each specimen ranged from 0.16 percent when rainfall was delivered at 25.4 mm/hr. to 0.72 percent when rainfall was delivered at 2.5 mm/hr. The rate of arsenic release was highest initially and then stabilized at an average of 0.0143, 0.0079, and 0.0062 g/cm2/mm rainfall for the 2.5, 8.0, and 25.4 mm/hr. rainfall rates, respectively. The inclusion of water repellent in the CCA treatment did not have a consistent effect on leaching. In most cases, leaching of arsenic was greater in specimens containing the water-repellent additive, but the water repellent did appear to reduce leaching of copper. Using similar methodology, a secondary study was conducted to evaluate the ability of several finishes to reduce leaching. The results indicate that finishing decking with a semi-transparent water-repellent stain, latex paint, or oil-based paint will greatly reduce the leaching of arsenic, chromium, and copper.

Author: Lebow, Stan; Foster, Daniel; Lebow, Patricia.


Source: Forest Products Journal. Vol. 54, no. 2 (Feb. 2004). Pages 81-88.

Citation: Lebow, Stan; Foster, Daniel; Lebow, Patricia.   2004.  Rate of CCA leaching from commercially treated decking.  Forest Products Journal. Vol. 54, no. 2 (Feb. 2004). Pages 81-88..