Some wood ground into dyed mulch can include dangerous chemicals, including creosote and CCA (chromium, copper and arsenic), according to the UMass Amherst Center for Agriculture, Food and the Environment. CCA has been banned as a chemical used in pressure-treated wood since 2003 but treated wood still exists in old outdoor structures and is often scrapped out and made into mulch. (Courier & Press [Evansville, Ind.], 4/25/19)