Evacuated residence due to dioxin contamination, Times Beach, Missouri. Dioxins, or polychlorinated dibenzodioxins (PCDDs) are a group of compounds that occur as by-products in the manufacture of organochlorides, in the incineration of chlorine-containing substances such as PVC (polyvinyl chloride), in the bleaching of paper, and from natural sources such as volcanoes and forest fires. They have adverse effects on the environment and human health.