Dioxins collectively refers to hundreds of chemical compounds that share certain structures and biological characteristics. See Dioxin.
Dioxins fall into three closely related groups: the chlorinated dibenzo-p-dioxins (CDD's) chlorinated dibenzofurans (CDF's), and certain polychlorinated biphenyls (PCBs). The most studied is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). CDD's and CDF's have been listed as carcinogenic under California's Prop. 65 since 1992 and TCDD has been listed as a carcinogen since 1988 and as a developmental toxicant since 1991. An overview of the human health effects from TCDD can be found by searching at Toxnet Toxicology Data Network. TCDD is considered to be a Group 1 carcinogen. Search at Toxnet Toxicology Data Network. PCBs are no longer produced in the U.S.
The primary exposure pathway (at least insofar as TCDD is concerned) is food. Search at Toxnet Toxicology Data Network and see Dioxins and Furans. It would appear that they enter the food chain, and then as is common with all contaminants, are concentrated as they "move up" the chain. See, for example, http://www.ajcn.org/content/61/3/682S and http://www.guardian.co.uk/science/2004/jan/09/sciencenews.society. Some view high-fat animal food as a primary source. [A 1996 study by EPA of dioxins in beef fat can be found at http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=54869.]
EPA has undertaken a study of dioxins in the food supply, and is expected to recommend an intake limit of 0.7 picograms of dioxin per kilogram body weight per day. [A picogram is one trillionth of a gram.] WHO and the EU have higher limits, from one to four picograms per kilogram per day. According to news reports, the chemical and food industries are lobbying against release of the report, asserting that the recommended intake limit is too low.
As they say, stay tuned.
For more information about LexisNexis products and solutions connect with us through our corporate site.