Dioxin is much worse for human health than previously believed, according to a new, eagerly awaited draft report from the U.S. Environmental Protection Agency (EPA). The report suggests that many Americans may have enough dioxin in their bodies to trigger a range of effects, from subtle developmental delays to cancer. But, as with earlier pronouncements on dioxin's risks, the judgment is controversial and may be appealed.
Dioxins are chlorinated chemicals produced mainly by incinerators and paper bleaching. They accumulate in the food chain, winding up in body fat when people eat animal products. In the 1980s, EPA concluded there was no safe level of dioxin--even the lowest exposure was hazardous. Then new molecular studies led dioxin experts to think EPA might have overestimated the risk, and the agency set out to reassess it again in 1991.
But agency scientists came back in 1994 with a draft report that supported EPA's earlier conclusion that any level of dioxin is harmful. EPA's Science Advisory Board then blasted parts of the reassessment and sent it back for revision, charging that agency scientists mixed science and policy. They also accused the scientists of failing to mention alternate hypotheses and data that contradicted their conclusions.
As requested, EPA has now rewritten parts of the report. The agency has also incorporated "quite a bit of new information," says William Farland, chief of risk assessment in EPA's Office of Research and Development--for instance, new studies of three groups of workers exposed to dioxin in the United States, Germany, and Holland. Those studies result in a dioxin cancer potency that is 30 times higher than the 1985 estimate. The agency factors in the threefold drop in dioxin exposure since the mid-1980s to conclude that the cancer risk today is 10 times higher.
That conclusion has flabbergasted many outside researchers. Several who spoke with ScienceNOW asserted that the worker studies of cancer effects are inconclusive. Even to those who have closely watched EPA's new analysis, the 10-fold increase "is a lot more than anybody expected," says Dennis Paustenbach, a risk assessment consultant with Exponent in Menlo Park, California. "It's going to require a lot of discussion before there's widespread acceptance."