Word: dioxins
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Dates: during 1990-1999
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According to sources familiar with drafts of the EPA report, it will say that dioxin remains a serious potential threat to human health and that possible links between the chemical and health problems, among them reproductive ills, should be further explored. "This study ranks with the Surgeon General's pronouncement that smoking causes lung cancer," says Sierra Club pollution expert George Colling, prematurely and hyperbolically, in the latest issue of the organization's monthly newspaper. And Peter deFur of the Environmental Defense Fund predicts that the document will lead to much tighter regulations, and in some cases even...
...question, many of which contain chlorine, are clearly toxic and carcinogenic. On the other hand, the case that humans are being affected by very low concentrations remains far from certain. The existing evidence is largely circumstantial, based on extrapolations from animal studies, laboratory work on the chemistry of dioxin and other molecules, and statistics on human disease that may or may not turn out to be accurate or relevant...
Finally, several hormone-related human disorders, including low sperm counts, testicular and breast cancers and endometriosis (a painful condition in which uterine cells migrate to other parts of the pelvic area), have arguably been on the rise in the decades since DDT, dioxin and the like first entered the food chain. Says Thomas Burke of the Johns Hopkins School of Public Health: "What we have now is identification of a potential hazard, and that's all we have. What the implications are we don't know yet, and we need to clarify that...
...evidence from laboratory studies suggests there are also effects at lower concentrations. Endocrinologist David Crews has discovered, for example, that small PCB doses can dramatically influence the ratio of male to female offspring in red-eared slider turtles. When University of Wisconsin toxicologist Richard Peterson investigated the impact of dioxin on male rats, he found that the dose needed to cause reproductive-system problems was relatively high. "But when we exposed pregnant rats to a dose 1/100th as large," he says, "we found the male offspring showed signs of reproductive dysfunction," including smaller sex organs, reduction in sperm counts...
What is especially disturbing about Peterson's work is that the levels of dioxin needed to do that kind of damage were as low as 64 nanograms per kg of body weight -- only a little greater than the 5 or 10 nanograms of dioxin and comparable chemicals found in a typical kilogram of human tissue. It is not surprising that these compounds are so biologically active, since they are metabolized in a fashion similar to natural chemicals. Says Linda Birnbaum of the EPA's Health Effects Research Laboratory, who was one of the driving forces behind the agency's decision...