Statistical Analysis of Influence of Soil Source on Leaching of Arsenic and Copper from CCA-C Treated Wood

Leaching of wood preservatives affects the long-term efficacy and environmental impact of treated wood. Soil properties and wood characteristics can affect leaching of wood preservatives, but these effects are not well understood. This paper reports a statistical analysis of the effects of soil and wood properties on leaching of arsenic (As) and copper (Cu) from southern yellow pine sapwood treated with chromated copper arsenate (CCA-C). Specimens were leached by an accelerated laboratory method for 12 weeks in soil obtained from different locations or in water. Loss of Cu and As was measured using X-ray fluorescence and correlated with various physical and chemical soil properties. Leaching was greater from specimens with higher initial As and Cu retentions. Average Cu loss was approximately equal to or greater than As loss for specimens exposed to soil; for specimens leached in water, As loss was about twice that of Cu loss. Generally, more Cu leaching occurred from specimens in soil contact compared to specimens in water, suggesting that ground-contact leaching studies of the new copper-rich systems should employ soil-based methods for realistic depletion measurements. The amount of As and Cu leached was influenced by soil properties. Depletion of Cu and As from CCA-treated wood appears to be differentially related to various soil properties as well as to initial As and Cu retention in the wood. This research will help develop a standard laboratory method for soil-contact leaching of metals from CCA and other copper-based preservative systems