You could get whiplash watching the scientific back-and-forth on dioxin. In 1982 the federal government evacuated Times Beach, Mo., after waste oil laced with the toxic chemical was spread on streets to control dust; in 1991, the official who ordered the residents out called the move "unnecessary." In the 1980s dioxin was branded the most potent man-made carcinogen known to science; in 1991 it became "no more risky than spending a week sunbathing," according to a New York Times article. One 1991 government study blamed high levels of dioxin for numerous cancers in chemical workers; another found no excess cancers among veterans who handled Agent Orange, the Vietnam defoliant contaminated with dioxin. Given this history, few would expect any pronouncement on dioxin to be the last word. But a much-delayed, 2,000-page report by the U.S. Environmental Protection Agency, to be released this week, comes as close as anything. In a shock to the industries that promoted the recent dioxin revisionism, its estimate of dioxin's cancer potency is as high as ever. Moreover, says the EPA's Dr. Lynn Goldman, who oversees the three-year study, "we [now] have stronger evidence that dioxin exposure can result in a number of noncancer health effects."
Dioxin is not a commercial product but a contaminant. It is created during high-temperature combustion in municipal and hospital incinerators, for instance, and produced inadvertently during the chlorine-bleaching of pulp for paper and the manufacture of some pesticides. Some comes from forest fires and volcanoes. From all these sources it gets onto plants and into the food chain. (Cows eat dioxin-laced clover, and animal fat accounts for 90 percent of Americans' "body burden" of dioxin.) So while there was no doubt that dioxin is around, there were lots of questions about whether that mattered: decades of lab data suggested dioxin was a potent carcinogen in rodents, but effects in humans were equivocal. In 1991 scientists thought they'd figured out why. In order to exert any biological effect, went the new hypothesis, dioxin must first bind to thousands of molecules on cells called receptors. The receptors carry the dioxin to the cells' DNA, where it disrupts genes for hormones, enzymes and growth factors. This cascade can unleash effects from birth defects to cancer. As science, this was pretty interesting. As a guide to policy, it was shocking: since it takes thousands of dioxin-filled receptors to unleash the genetic cascade, there might be a "safe" level of the chemical. The EPA launched its reassessment.
The result is not nearly what the chlorine and paper industries hoped for. "Industry," says toxicologist Peter deFur of the Environmental Defense Fund, "is about to be bitten by the snake it loosed." Although the data is not strong enough to call dioxin a "known" human carcinogen (like nicotine), the EPA says it is "likely to present a cancer hazard in humans." Dioxin does this by messing with genes that regulate cell growth and differentiation. Even more devastating are dioxin's noncancer effects: reproductive abnormalities, liver damage, diabetes-like symptoms and immune-system suppression, which increases susceptibility to infection and metastatic cancer. Some of the immune-system effects occur at or near levels to which Americans are already exposed. "If there is [a safe level of dioxin]," says the EPA's Goldman, "the general population is already above that." This is not a case of toxicity showing up at levels equivalent to 800 cans of diet soda; they appear at real-world exposure levels.
Scientists, industry and everyone else now have 120 days to comment on this week's report before the EPA starts to act on it. Already, the cattle and chemical industries are sniping that the EPA overestimated how much dioxin people are exposed to. But if the basic conclusions stand, the EPA will probably come down hard on sources of dioxin. The pulp and paper industry, which has already slashed dioxin emissions by 92 percent since 1988, may have to do even more. States, which may set dioxin standards for industrial waste water based on "sound science," will have less leeway: Georgia set a standard, for instance, 550 times higher than the federal one. But beyond any practical effects, EPA's report restores, for better or worse, dioxin's status as the pre-eminent symbol of the age of toxics.