Made notorious when it was fingered as the toxic component in Agent Orange -- used to clear forests in the Vietnam War -- dioxin caused the evacuation of the town of Times Beach, Missouri, in 1983. The town was later bulldozed because it was found to be contaminated with the chemical.
The report, described by EPA officials familiar with it, concludes that the cancer risk from dioxins among individuals who eat large amounts of fatty meats and dairy products may as high as 1 in 100, or 10 times as great as previously projected.
The National Toxicology Program of the National Institute of Environmental Health Sciences (NIEHS) also tried to declare dioxin a known human carcinogen in its report on cancer-causing substances released this week. But a lawsuit by New York restaurant owners, who claim the link to cancer will scare customers away from their food, has blocked the publication.
The health effects of dioxins, a group of toxic compounds produced through a number of chemical processes including combustion, have been the focus of research for more than 20 years. Despite the extensive literature, the health effects remain in some cases uncertain.
The EPA, which began reviewing the literature in 1991, is to make public its findings in a report to be released next month. The draft report has not yet been scientifically peer reviewed and EPA officials acknowledged in interviews it is likely to generate sharp debate.
Greenpeace says it has sent a letter to the EPA calling on the agency to immediately release the dioxin report and implement a plan to prevent and eliminate new dioxins.
According to agency officials, who discussed the report on condition of not being identified by name, said it concludes that at least one form of dioxin --the most potent form known as TCDD -- should be classified as a definite human carcinogen. Other dioxin-like compounds were considered by the EPA reviewers as "likely" carcinogens.
The report also links exposure to dioxin to a variety of other health problems, including diabetes, developmental problems and irregularities in the immune system, they said. It also concludes that children's intake of dioxin is greater than adult's, because the chemical is often found in dairy products and even breast milk.
EPA officials emphasized, however, that the draft report's conclusions should not discourage people from eating a well balanced diet, including dairy products, certain meats and vegetables, because their benefits outweigh any dangers posed from dioxin. And officials said the benefits of breast feeding also continue to outweigh the risks from dioxin.
Dioxin, a chlorine byproduct, can be dangerous even at very low levels because it is believed to be idespread in the food chain and can accumulate in the body over a lifetime. A product of combustion as well as the pulp- and paper-making processes, it is released into the air and into water and finds its way onto pastures and into fish and animals and in turn into humans.
In recent years, the EPA has imposed tougher regulations on many dioxin emitters including municipal, medical and hazardous waste incinerators and the pulp and paper companies. As a result, dioxin emissions have been reduced by about 80 percent since the 1980s, according to the agency.
The EPA's findings are expected to be used by the agency as evidence for additional actions to curtail dioxin. "The findings validate the policies that have been taken," said one agency official, speaking on condition of not being further identified.
According to the report, as described by these officials, the risks of getting cancer from dioxin may be zero or extremely slight for most of the population.
The report said its new projections were based on new evidence developed in recent years on cancer risk, officials said.
Although studied for more than 20 years with hundreds of articles in the scientific literature, the health effects of dioxin on humans remains somewhat uncertain. For example, dioxins have been found to cause birth defects in mice, but no such causation has been established in humans.
EPA officials acknowledged that its findings likely will prompt extensive debate. Industry groups as well as some scientists over the years have accused the EPA of exaggerating the dangers of dioxins.
The findings in the draft report were first reported in Wednesday's Washington Post, which said it had obtained a copy of the document.