Treated lumber is often used for outdoor projects – from raised garden beds, to decks and children”s play structures. But treated lumber is slow to decay because it is treated with chemicals some people fear could contaminate soil and jeopardize our health.
Chemicals used to preserve lumber include organic compounds such as pentachlorophenol, cresote and coal tars. Other preservatives contain metallic compounds such as chromated copper arsenate (CCA), ammonical copper arsenate (ACA), and acid copper chromate (ACC).
These are not ingredients you”d like to find in your salad.
However, Sherry Combs, a soil scientist and outreach specialist with University of Wisconsin-Extension, reviewed research on treated lumber and says the research indicates that risks from using lumber treated with these chemicals are quite small.
“The risk of plant damage or metal uptake from treated wood is slight,” Combs said. “Growing vegetables in raised beds constructed from treated wood should not be discouraged.
Combs said research to evaluate whether plants take up metals when planted near treated wood showed no significant uptake. For example, the copper content of grapes was unaffected by the presence of CCA-treated southern pine posts, while the levels of chromium and arsenic were below the ability of laboratory instrumentation to detect.
Researchers found no visual differences between tomato plants or fruit grown in containers containing treated wood and those grown away from treated wood.
However, Combs said, if children have play areas underneath treated lumber decks that are unstained and unpainted, parents should take care that they don”t ingest soil that might be found underneath.
Researchers found that more metal leached from treated lumber if the wood was not painted or stained and was exposed to very acidic conditions. The research was done in the Northeastern United States, where rain water is much more acidic than in the Midwest, but caution is still wise.
“As a precaution, even though the Midwest does not experience acid rain, insist that children wash their hands thoroughly after playing in soil under decks, or consider relocating under-deck play areas to another place,” Combs said.
As an alternative, parents might consider staining or painting the treated deck to create a barrier and prevent the possiblity of metal leaching from the lumber.