The U.S. Environmental Protection Agency yesterday said it would not prevent malathion's use to control mosquitoes but will further study the "suggestive evidence" that it can cause cancer in lab animals. The announcement was a reversal of a previously undisclosed plan to declare the insecticide a "likely human carcinogen."

In releasing its long-awaited preliminary risk assessment for malathion, the EPA did little to quell the controversy over the chemical that was sprayed from helicopters last fall in New York City and parts of northwestern Suffolk County to kill mosquitoes carrying the virus that causes West Nile encephalitis.

New York City Mayor Rudolph Giuliani has already declared that the city will not use malathion again this year if the West Nile threat resurfaces, but Suffolk County Health Commissioner Clare Bradley said yesterday that Suffolk will keep malathion in its mosquito-fighting arsenal, although she added that she hopes not to have to use it.

EPA officials yesterday emphasized that the agency does not consider malathion spraying to be a significant risk to the public- even to people who were directly exposed to the chemical mist last fall.

"We don't believe there's any cancer risk problem associated with mosquito spraying, even if someone was inadvertently directly sprayed. That's really the most important message," said Stephen Johnson, the agency's deputy assistant administrator for prevention, pesticides and toxic substances.

Johnson acknowledged, however, that as recently as April 28 the EPA was preparing to classify malathion as a "likely human carcinogen" based on tests on laboratory animals.

Internal EPA documents that were posted on the EPA's Web site after yesterday's announcement show that the agency changed its view after objections from malathion's manufacturer, Cheminova A/S. The Denmark-based company argued that a key study on lab rats had been assessed incorrectly by a pathologist at Cheminova, which had conducted the study to satisfy EPA requirements. The company pathologist had concluded that malathion caused liver tumors and a small number of nasal tumors in lab rats.

After Cheminova objected, Johnson said, the EPA asked a panel of independent pathologists to review slides of rat tumors. That panel concluded that malathion caused far fewer cancerous tumors than had been thought, so the EPA decided to classify malathion as "suggestive evidence of carcinogenicity but not sufficient to assess human carcinogenic potential."

Anti-pesticide activists yesterday said the EPA since 1984 has had relatively strong evidence of malathion's carcinogenicity in animals and of other health problems in humans.

They also suggested that the agency backed down because it wanted to avoid the criticism it would receive by labeling as a "likely human carcinogen" a chemical that the agency eight months earlier had allowed to be sprayed over large areas of metropolitan New York.

"It may be that he EPA is backing off because of the concerns of the manufacturer, and because it doesn't want to be in a situation with public health officials who could say, 'you told us it was safe before, and now you're saying it's not safe'," said Jeff Fullmer of Massapequa-based Citizen's Campaign for the Environment.

But Johnson said that even if the agency had decided to classify malathion as a likely human carcinogen, the EPA's risk assessment showed that the risk posed by aerial spraying for mosquitoes would still be so low that the agency would not have banned malathion's use for mosquito control.

"We certainly did not cave in on this. We need to make sure that all of our regulatory decisions are based on sound science, and we need to do so in an open and transparent way," Johnson said. A spokesman at Cheminova's U.S. headquarters in Wayne, N.J., did not return a telephone message seeking comment.

Environmental activists who are opposed to any kind of aerial insecticide spraying in residential areas have focused their criticism on malathion because by most measures it is slightly more toxic than other chemical sprays, such as the synthetic pyrethroids used by Nassau County.

Suffolk and New York City also used pyrethroids, but in combination with malathion, which has a longer track record in controlling mosquitoes.

Yesterday, Giuliani reiterated that the city used malathion last fall because it had been "cleared by the federal government" but will not use it this year because "there is a question" about its health risks.

Bradley, however, said malathion will remain an option in Suffolk County, which has the state's most active mosquito-control program and has been using malathion for many years, mostly on the South Shore until last fall's spraying in northwest Suffolk.

"We pick the safest chemical to accomplish what we need to accomplish," Bradley said, adding that she hopes that no aerial spraying will be needed this year.

In Washington, meanwhile, Reps. Joseph Crowley (D-Queens) and Gary Ackerman (D-Queens/L.I.) said at a news conference that the EPA's announcement has not cleared up the uncertainty about malathion's risks.

"We still have questions about the application of malathion. But I am seriously disturbed. The people of New York were assured this was safe," Ackerman said.

In an effort to prevent another outbreak of West Nile, which last fall killed seven people in the metro area and seriously sickened more than 60, New York City and more than a dozen suburban counties this year have all begun intensive monitoring to track mosquito populations and determine if they are carrying the virus.

Municipalities are also increasing their use of lower-toxicity biological sprays in swamps and catch basins to kill mosquito larvae before they can fly and spread the disease. Health officials have said that they will repeat last fall's aerial spraying of insecticides over residential areas only as a last resort.

© Copyright 2000, Newsday Inc.

Dan Fagin. STAFF WRITER, EPA Won't Prevent Malathion Use / Changes 'likely carcinogen' ruling, 05-12-2000, pp A03.