Acid copper chromate (ACC) has been in use as a wood preservative in industrial/commercial settings in Europe and in the USA since 1920. USEPA has now taken steps to ensure it continues to be excluded from sale for domestic purposes. Their concern is that chromate (Hexavalent Chromium) is both carcinogenic, an irritant and an allergen and that there will be some uncontrolled exposure. Treated wood should be disposed of as if hazardous waste (not just burnt).
Evidence from:
US EPA 8th Jan 2007
“Acid Copper Chromate (ACC) Residential Uses Won’t be Registered”
Metal based wood preservatives have been in use for decades and pressure treated woods contain several kg of metal per cubic metre.
Further detail: