Soils naturally contain copper, chromium, and arsenic because these elements and their oxides are natural constituents of rock from which soil originates. These elements are actually essential micronutrients, meaning plant and animal cells require very small amounts for normal functioning. Even food naturally contains measurable levels of chromium, copper, and arsenic. The U.S. EPA and the wood products industry recognize that treated wood has some hazard. Thus, CCA-treated wood is sold strictly for outdoor use.
Gardeners can avoid treated wood by using rot resistant alternatives such as plastic lumber.
If they decide to use treated wood for raised beds, they can further reduce any hazard by lining the inside of the bed with plastic before filling with soil. For furthern information contact your local WSU Cooperative Extension Office. From The Gardener Vo. 5, No. 4, Winter 1994-1995.