Effectiveness of CCA fixation to avoid hexavalent chromium leaching
2004
Cooper, P.A. | Jeremic, D. | Ung, Y.T.
It is generally assumed that hexavalent chromium in wood treated with chromated copper arsenate (CCA) preservative is substantially reduced to trivalent chromium during fixation and that the potential to leach the more toxic Cr(VI) is minimal. However, there are occasional claims that some hexavalent chromium remains in wood after fixation and that small amounts of Cr(VI) are available for leaching. A number of CCA-treated wood samples of different wood species and ages, as well as wood-cement and wood-plastic composites containing CCA-treated wood were collected and exposed to laboratory leaching. The leach water and expressate from water-saturated wood samples were analyzed for Cr(VI), total Cr, Cu, and As. For CCA-treated wood and wood-plastic composites, Cr(VI) in the leachate was near or below the detection limit for analysis by ion chromatograph (< 1 ppb) compared to total chromium levels of 200 to 2700 ppb. The amount of hexavalent chromium relative to total chromium leached was generally less than 0.1 percent. Leachate from wood-cement composites showed significant levels of Cr(VI) (up to 50% of the total chromium leached). However, both hexavalent and total chromium levels in the leachate were low (200 to 400 ppb). These results show that once the CCA is properly fixed in wood, there is little health or environmental risk associated with toxic hexavalent chromium being released from treated wood by water leaching.
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