A review of the significance of animal food products as potential pathways of human exposures to dioxins.

The polychlorinated dibenzo-p-dioxins and dibenzofurans (dioxins) are groups of compounds with similar chemical and toxicological properties. Carcinogenicity was considered the most serious toxic end point when setting previous regulatory policies, but recent concerns have focused on the possible endocrine-disrupting activities of the dioxins. Toxicity is related to the 2,3,7,8 pattern of chlorine substitution, a pattern that also leads to chemical and metabolic stability. Dioxins are practically insoluble in water and concentrate in lipids of biological systems, leading to low background concentrations in fat of the general human population. Major environmental sources of dioxins are emissions from industrial chlorination processes and combustion of materials containing chlorine. Inhalation and water have been ruled out as significant exposure pathways, which suggests that food is the primary source. Pathways of entry into food chains are atmospheric transport of emissions and their subsequent deposition on plants, soils, and water. The major food sources seem to be fat-containing animal products and some seafoods. This conclusion is based on evaluations of potential environmental pathways involving dioxins and related compounds. Generally, dioxins and other lipophilic compounds are not taken up and translocated by plants, so residues in foods and feeds derived from seeds should be negligible. Animals on high-roughage diets, or those that ingest contaminated soil, are the most likely to accumulate dioxin residues from the environment. The conclusion that animal products are a major source of human exposure requires verification by appropriate food sampling programs and animal metabolism studies. If it is desirable to reduce human exposure to dioxins via the food supply, reduction of sources would be a more effective strategy than changing agricultural practices and food consumption patterns.