The commonly accepted, though chemically imprecise, name for the compound 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), which is only one of more than 70 members of the family of chlorinated dioxins. It was found to be a contaminant of the herbicide 2,4,5-T (trichlorophenoxyacetic acid) some ten years after the latter was approved for use; it was then banned by FDA for most purposes. Synthesized in 1957, dioxin is a white, crystalline solid in pure form. It was present as a contaminant in defoliants used in Vietnam (Agent Orange), and its toxicity was widely publicized. Though it is undoubtedly harmful to humans, no deaths have occurred. It is a carcinogen, teratogen, and mutagen. Its toxicity to laboratory animals varies widely with the species; it is lethally toxic to guinea pigs, but hamsters appear relatively unaffected. Where soil contamination occurs, the concentration is no greater than several parts per million at most. Wastes contaminated with dioxin must be disposed of in officially approved landfills. Human toxicology is under continuing investigation.
