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Opinion: Even without a "smoking gun," data supports the danger of dioxins Dioxins are in the news again-and the news is bad and controversial. The U.S. Environmental Protection Agency announced a draft revision of the 1994 nine-volume report on the health effects of the pollutant dioxin. Although the revised draft is not available yet, it is reported to say that dioxin is 10 times more likely to cause cancer than originally reported. Chapter nine of the 1994 draft report reaches a consensus that dioxin probably causes cancer in wildlife and humans, and harms the immune system and the reproductive systems in fish, birds, and mammals, including humans, at minuscule doses. The final report has been in limbo until recently, an indicator of the controversy of the conclusions. The EPA Scientific Review Board questioned the conclusions of the original report that dioxins were probable carcinogens and asked that the work be repeated. Needless to say, when the conclusions of the new draft were stronger, the responses of scientists formerly on the board have fueled the controversy. Just what is dioxin and what is its risk to human health? Dioxins are a family of polychlorinated dibenzo-p-dioxins that are found everywhere in the environment, generally at low levels. These large, complex molecules do not biodegrade easily and are extremely persistent. The most toxic and readily found is 2,3,7,8-tetrachlorodibenzo-p-dioxin, commonly known as TCCD. There are a total of 219 dioxin and dioxin-like chlorinated substances. Dioxins do not occur naturally in the environment, but are the unintended results of human activity. They can be formed in the manufacture of chlorophenols and phenoxy herbicides, in the chlorine bleaching of paper, and in the incineration of organic waste containing chlorine products. The largest sources of dioxin discharge are factories that make polyvinyl chloride products, and incinerators burning chlorine waste. The major route of human exposure is ingestion of dioxin-contaminated food. According to the EPA, 38% of total exposure to dioxin in the U.S. comes from eating beef; 24.1% from dairy products other than milk; 17.6% from milk; and, a total of 37% divided among chicken, pork, fish and eggs. Dioxins pass to the fetus through the placenta during pregnancy and to the newborn through breast milk. Dioxins have also been found in human sperm. However, exposure to pure dioxin is unlikely. Dioxin's toxicity results cumulatively from repeated small exposures and in combination with other associated chemicals that produce additive and possibly synergistic effects. Since dioxins are fat-soluble, they bioaccumulate, moving up the food chain from smaller to larger organisms. Levels in fish can be 100,000 times that of the surrounding water. Bioaccumulation continues in human fat cells, because dioxins have an elimination half-life-the time it takes a body to eliminate half of its accumulation-in mammals of about seven to 10 years. The EPA estimates that the average U.S. citizen without any direct exposure to dioxins other than routine diet has an average body burden of 13 nanograms of dioxin per kilogram of body weight or parts per trillion. The level increases with age. Dioxin has been found in the sperm of Vietnam veterans 20 years after exposure. Studies in humans have shown that the risk of cancer rises significantly when the body burden of dioxin reaches 109 ppt-about eight times the current U.S. average. Public health policy usually aims to keep the public's exposure to poisons at least 100 times below levels known to harm humans or animals. Various animal and human studies have suggested associations with specific types of cancer. Hodgkin's Disease and non-Hodgkin's Lymphoma are linked with exposure to chlorophenoxy herbicides that are contaminated with dioxins during manufacture. There is also evidence that links dioxins to respiratory and prostate cancer, multiple myeloma, and soft tissue sarcomas. Other studies report increased incidents of thyroid and breast cancer, and increased deaths from stomach and brain cancer. The controversy over dioxin manifests itself in the positions of the environmentalists and some members of the scientific community in evaluating the existing data. The scientific community claims that there aren't enough definitive studies to prove with scientific certainty that dioxin causes cancer, therefore more studies are required before a conclusion is valid. This "something is not toxic until proved so without a shadow of a doubt" point of view requires dead bodies and a smoking gun. Environmentalists claim that there is adequate proof of an association and steps should be taken to eliminate the risk until the substance is proved safe. The existing data on body burdens and toxic levels would appear to prove a clear and present danger. Kay M. Yeuell, a former FDEP and GOAA environmental specialist, now does research for the Association of Birth Defect Children Inc. in Orlando. |