Health effects of dioxins

Dioxins are a family of polyhalogenated aromatic hydrocarbons that induce a similar toxicity profile. There is consensus in the scientific community that high-level exposure to dioxins poses human health risks. Several human cohorts demonstrate an association between TCDD exposure and increased cancer risk and numerous studies in experimental animals demonstrate that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a complete carcinogen. These data are so compelling that NIH and IARC panels have designated TCDD, the most potent dioxin, as a known human carcinogen. What is much less certain are the quantitative estimates of the potential human health risks associated with background exposure to TCDD and other dioxins in the general population. Dioxins induce a variety of toxic effects in experimental animals, ranging from biochemical alterations to adverse affects such developmental, reproductive, dermal and hepatic toxicities. A number of recent epidemiological studies suggest an association between dioxin exposures and increased risk for non-cancer effects, such as diabetes, cardiovascular disease and developmental delays and alterations. Estimating potential human health risks from background dioxin exposures requires an understanding of the dose-response relationships for the various biological effects of TCDD and related chemicals. However, a simpler approach examines the difference between present background human body burdens of dioxins and the body burdens in animals and human studies where effects have occurred. These analyses indicate that the margin of exposure is less than a factor of 20 for some adverse effects observed in humans and animals. Releases of dioxins to the environment from characterized sources have decreased significantly over the last decade and are expected to continue to decrease. Human body burdens have also declined and are anticipated to be further reduced as additional, recently implemented, dioxin emission controls impact environmental and food levels and, ultimately, human exposure. (This abstract does not represent USEPA policy).