Abstract

Information about the possible human health effects of dioxin is available from studies of chemical plant workers, sprayers of dioxin-contaminated herbicides, and other exposed people. No human illness, other than the skin disease chloracne, which has occurred only in highly exposed people, has been convincingly associated with dioxin. Some epidemiologic studies have suggested associations between dioxin and stomach cancer, soft tissue sarcomas, and lymphomas, but other studies, powerful enough to detect excesses of those diseases, if they exist, have not done so. With the exception of one study of chemical plant workers that reported an excess of stomach cancer, all the suggested associations of increased cancer risks and dioxin exposures are from studies of herbicide applicators. Both direct measurements of the concentrations of dioxin in the body fat of chemical plant workers and the occurrence of chloracne in those men support the conclusion that they were exposed to far greater amounts of dioxin than herbicide applicators. Therefore, if the cancers found in herbicide users were associated with dioxin, even more of those cancers would be expected among the chemical plant workers; the expected increases are not found. In short, epidemiologic studies in which dioxin exposures are known to have been high, either because of the appearance of chloracne or from measurements of dioxin in exposed people, have failed to reveal any consistent excess of cancer. In those studies that have reported associations between exposure and disease, no chloracne was reported, and there are no measurements of higher-than-background levels of dioxin in the people who are classified as exposed.