Use of treated wood for raised beds in a vegetable garden
The relatively new chemical treatment- ACQ (alkaline copper quaternary) for treated wood does not contain arsenic or chromium, the two elements of concern used in the discontinued CCA treated lumber. According to the U.S. EPA: All ACQ types contain 2 active ingredients which may vary within the following limits: copper oxide (62%-71%), which is the primary fungicide and insecticide, and a quaternary ammonium compound (29%-38%), which provides additional fungicide and insect resistance properties.
Some of the copper may leach over time from the lumber, but the risk to human health is considered to be low. From the research that we have seen, a toxic level of copper would kill the plants before the edible fruit, roots, or plants would be harvested. If you have doubts, select a different material such as concrete blocks, brick, stone, and untreated or plastic lumber. You could forego any enclosure by mounding the soil 4-6 inches above grade, leveling the top and sloping the sides.
Some people handle the issue by simply not planting root crops near the wood.