Doubts arise about federal ranking of dioxin as most deadly chemical

WASHINGTON -- For years, the federal government has ranked the chemical compound dioxin as toxic enemy No. 1 and has required industrial companies to invest billions of dollars to prevent its release into the environment and to clean up what is already there.

In 1982 and early 1983, in the most dramatic move to protect citizens, the government permanently evacuated all 2,240 residents of Times Beach, Mo., where the dirt roads had become contaminated with dioxin.


Now, in a rare official reassessment, several top federal health authorities are backing away from the position that dioxin is so dangerous. Exposure to dioxin, once thought to be much more hazardous than chain smoking, is now considered by some experts to be no more risky than spending a week sunbathing.

The scientists think the government's stringent health standards for dioxin are not supported by the latest scientific evidence.


The Environmental Protection Agency has opened a yearlong review aimed at developing a new formal opinion of the risks of dioxin.

"I don't want to prejudge the issue, but we are seeing new information on dioxin that suggests a lower risk assessment for dioxin should be applied," said EPA Administrator William K. Reilly, who asked for the review.

"I know the stakes and that I'm unraveling something here," Mr. Reilly said. "There is not much precedence in the federal establishment for pulling back from a judgment of toxicity. But we need to be prepared to adjust, to raise or lower standards, as new science becomes available."

The human dimension of the change in approach emerged most starkly several months ago when the federal scientist who made the original decision to evacuate Times Beach said he thought he had made a mistake.

"We used the best scientific evidence at the time to make the decision we did," Dr. Vernon N. Houk said.

"Given what we now know about this chemical's toxicity and its effect on human health, it looks as though the evacuation was unnecessary," Dr. Houk, assistant surgeon general and director of the Center for Environmental Health and Injury Control at the Centers for Disease Control in Atlanta, said in a recent interview.

"If it's a carcinogen," he said of dioxin, "it's a very weak carcinogen, and federal policy needs to reflect that."

The revised view of the dangers of dioxin has raised serious concerns within the EPA, which used many of the same procedures to determine the hazards of dioxin as it did to set air and water pollution limits for most of the other chemicals the agency regulates.


If Dr. Houk is right and dioxin is much less dangerous than had been determined, the government's regulations for other compounds will need to be adjusted.

Under current federal guidelines, the EPA says that ingesting more than 0.006 trillionths of a gram of dioxin for each kilogram (2.2 pounds) of body weight daily over an average lifetime could cause one fatal cancer for each 1 million people.

The same statistical method used to calculate the safe exposure to dioxin was used by the Centers for Disease Control to set safe limits for dioxin in soil at 1 part per billion and in water at 13 parts per quintillion.

But the World Health Organization supports the revised view of dioxin's danger and suggests that U.S. exposure standards are wrong. The group officially set a new limit this year for the daily intake of dioxin at 10-trillionths of a gram of dioxin per kilogram of body weight, a concentration that is 1,600 times greater than the EPA level and closer to the concentration considered scientifically accurate by Dr. Houk and others.

Scientists for leading environmental groups say the government's original assessment of dioxin's dangers is supported by the new data.

They also contend that researchers are narrowly interpreting the new data in an effort to reduce the cleanup and disposal costs for industries whose manufacturing processes produce dioxin as a byproduct, particularly paper pulp mills, hazardous-waste incinerators and municipal incinerators.


"Nothing that has been learned about dioxin since 1985, when EPA first published its risk assessment finding on dioxin in the environment, supports a revision of science-based policy or action," said Dr. Ellen K. Silbergeld, professor of pathology at the University of Maryland at Baltimore.