Safety of Pressure-Treated Wood in Gardens: Arsenic Leaching Concerns

Pre-2004 pressure-treated wood (CCA) contains arsenic, chromium, and copper. Most stays in the wood, but some leaches, especially in acidic soil. Don't build compost bins with CCA wood.

University of Minnesota study: background soil arsenic ~4.4 ppm. Within 2 inches of treated wood: ~20 ppm. At 6+ inches, levels drop to background. Vegetables absorb arsenic but well below US (2.6 ppm) and Canadian (1 ppm) standards. For absolute safety, plant edibles >10 inches from treated wood or replace adjacent soil.