ABSTRACT
Neither of these groups of polychlorinated lipophilic compounds occurs naturally, and neither of them is synthesized intentionally. Both occur as by-products of chemical synthesis, industrial processes, and occasionally of interaction between other organic contaminants in the environment. Because of human exposure to them during the Vietnam War, industrial accidents, and the high mammalian toxicity of some of them, they have received much attention as hazards to human health. There has also been concern about some polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) from an ecotoxicological point of view because they combine marked biological persistence with high toxicity. The following account will deal mainly with PCDDs, which have been studied in some detail and have been important in developing the concept of Ah receptor-mediated toxicity. Less is known about PCDFs, which will be described only briey.
