Concern has been raised about the safety of using treated lumber in food gardens. Pressure-treated lumber using CCA (chromated copper arsenate) as a preservative prompted this concern. CCA-treated wood was banned for residential use by the Environmental Protection Agency (EPA), and its production was phased out. Any remaining stock probably should not be used in raised beds for growing food crops.
ACQ (akaline copper quaternary) is an alternative preservative choice for pressure-treated lumber. Unlike CCA, it does not contain arsenic or chromium. It does, however, contain copper, which can leach into the soil from treated lumber. Although copper is an essential element for both plants and animals, excessive amounts can be harmful. A 2007 study of the safety of ACQ published in Human and Ecological Risk Assessment concluded that exposure to copper from contact with ACQ-treated wood is not expected to have adverse effects on the health of adults or children.