For many years, Chromated Copper Arsenate (CCA) was widely applied as a wood preservative, and though its use for most residential uses has been phased out, concerns about CCA leaching into soil from existing structures remain. In this study, we determined the effects of coating CCA wood on reducing such leaching. Ten boxes were constructed, 6 of which were coated with opaque film forming (FF) or penetrating finishes (PF), filled with soil, and weathered for 2 years. The soil was periodically sampled up to 2 years, and then romaine lettuce, arugula, basil and chives were grown under greenhouse conditions in these boxes. After 2 years, average amounts of arsenic (As) in the soil 2 cm from the CCA wood was 29 mg/kg, dry weight, 27 from wood coated with PF finishes and 6 in those coated with FF finishes. Soil As in all samples 6 cm from the wood were near the background value of 3.4. The average amount of As in arugula grown 2 cm from the edge of the CCA wood was 60 mg/kg, dry weight, 61 in wood coated with PF finishes and 24 in those coated with FF finishes. Similarly, in chives the amounts were 75 in CCA, 75 in PF, 12 in FF, in lettuce they were 5 in CCA, 5 in PF, in 1.4 FF and in basil they were 6 CCA, 10 PF, 3 FF. The amounts of As in plants grown in the control boxes were all <1. Compared to uncoated CCA wood, there was no reduction in As in plants grown along the edge of CCA wood coated with penetrating finishes, while the reduction in plant As ranged from 50-84% in plants grown next to the opaque finished wood. The reduction in arsenic in samples grown 6 cm from the wood compared to 2 cm from the wood ranged from 55-84%. The amounts of arsenic in the arugula and chives exceed the British limit for plant As of 1 mg/kg (fresh weight). As a result, gardeners should avoid growing certain vegetables in soils near CCA wood.
Stilwell, David E.; Musante, Craig L.; and Sawhney, Brij L.
"Copper, Chromium And Arsenic In Soil And Plants Near Coated And Uncoated CCA Wood,"
Proceedings of the Annual International Conference on Soils, Sediments, Water and Energy: Vol. 11
, Article 10.
Available at: http://scholarworks.umass.edu/soilsproceedings/vol11/iss1/10