CDDs and CDFs are byproducts of combustion and some industrial processes. The principal contributors to the WHO reassessments of dioxin risks that are discussed in this report have been (1) the International Agency for Research on Cancer, which coordinates and conducts both epidemiological and laboratory research into the causes of cancer; (2) the WHO European Centre for Environment and Health, which coordinates comprehensive efforts, in collaboration with the International Programme on Chemical Safety, to evaluate the possible health risks of dioxins as well as methods of prevention and control of environmental exposure of the general population to these chemicals; and (3) the Joint Expert Committee on Food Additives of the United Nations’ Food and Agriculture Organization and WHO, which provides scientific evaluations as a basis for the development of food standards by the Codex Alimentarius (food code) Commission. EPA Used Data on the Presence of Dioxins, Toxicity, and Food Consumption to Estimate Human Dietary Exposure

To estimate dietary exposure to dioxins, EPA obtained and reviewed information on (1) the dioxins present in 10 types of foods with high fat content, (2) the toxicity of individual dioxins contained in these food types, and (3) the quantities of these foods that people in the United States typically eat. EPA has incorporated new studies into its analysis of dietary exposure to dioxins to try to develop more reliable national estimates of such exposure. may have different effects on dioxin levels. 106, No. EPA and WHO Used Similar Analytical Methods

Despite differences in some of the specific objectives and processes of their respective reassessment efforts, EPA and WHO used similar analytical methods to identify and assess the potential health risks of dioxins. Cancer Threshold

EPA and WHO disagreed about whether there is a threshold below which exposure to dioxins would not cause cancer. But WHO noted that its estimates for this benchmark dose ranged quite widely and strongly depended on the assumptions made during the modeling. EPA’s Draft Dioxin Reassessment Report Generally Reflects the Views of Recent Peer Reviews

Two independent peer review panels, including an EPA Science Advisory Board panel, reviewed major sections of EPA’s draft dioxin reassessment report in 2000. In such cases, the panels refrained from making recommendations or suggestions to the agency. by dioxins. mixtures of dioxins. is pending. is pending. assessments. 12.
What GAO Found

Dioxins--chemical compounds that share structural and biological characteristics--have been linked to human illnesses, including cancer. Often the byproducts of combustion and industrial processes, complex mixtures of dioxins enter the food chain and human diet through emissions into the air. The Environmental Protection Agency (EPA) and the World Health Organization (WHO) noted the potential human health risks of dioxins in the 1970s when animal studies showed them to be among the most potent cancer-causing chemicals. EPA derived its estimates of human dietary exposure to dioxins in the United States from (1) chemically analyzed samples of 10 food types, (2) toxicity estimates of levels of individual dioxins in these foods, and (3) estimates of the quantities of these foods consumed by Americans. To develop more reliable national estimates of dietary exposure, EPA incorporated into its analysis some food studies that were nationally representative. Although both EPA and the WHO have assessed the human health risks of dioxins during the last decade, some of their objectives and processes have differed. Nonetheless, the analytical methods used and the conclusions reached have much in common. A major difference in the assessments is whether there are threshold levels below which exposure to dioxins would pose a negligible risk of cancer. EPA assumed there is no safe threshold level for cancer effects, but the WHO assumed there is. EPA's draft reassessment report reflects the recommendations and suggestions provided to the agency by the two most recent independent peer review panels. The panels, one consisting of 12 independent reviewers and the other convened by EPA's Science Advisory Board, concurred with many key assumptions and approaches that EPA used.