Tetrachlorodibenzo-p-dioxin, commonly known as dioxin or TCDD, is one of a group of more than 70 chlorinated phenolics occurring as contaminants produced during the manufacture of herbicides and defoliants such as trichlophenol and trichlorophenoxyacetic acid. Dioxins reach the environment as the result of disposal of industrial wastes, particularly by way of incinerators and landfill techniques. Although occurring in very low concentrations, they have produced porphyrinuria, porphyria cutanea tarda and chloracne in workers exposed during trichlorophenol manufacture, and have been held responsible for anorexia, weight loss, liver dysfunction, gastric ulcers and cancers in others remotely exposed.
A report in Science for June 16 on the risks to human health posed by dioxins in the environment gives new information issued by the United States Environmental Protection Agency, claiming that many Americans may have enough dioxin in tissues to induce delayed development and hormonal changes. The EPA maintains that the risk of cancer from dioxins is 10 times as high as was previously believed. The report is the outcome of six years' study of the situation since the last draft statement was given a hostile reception.
Much of the dioxin contamination is attributed to the bleaching and later incineration of paper to meet current requirements. Once loosed into the environment, the dioxins accumulate in food chains and reach the body fat of people who consume contaminated animal products. No safe level of exposure to them is now recognised. Even at low background levels they may induce subtle immune and neurobehavioural effects. They were ranked as "probable carcinogens" in the past, and are now classified as "known carcinogens". The most dangerous exposure, in persons who consume large quantities of animal fats, may involve a cancer risk between one in 1000 and one in 100, according to the EPA. These figures are derived from studies of exposed industrial workers in the US, Germany and the Netherlands, where information regarding levels of exposure was available.
Although the report has again received severe criticism, the EPA considers that there is an urgent need for new precautionary measures to restrict the progress of dioxins through the food chain, for example, the discontinuation of the feeding of lard and fish meal to cattle and pigs to promote their growth.