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Dursban,  the Common Organophosphate Pesticide,
Deemed "Highly Risky" in New Review

By Cat Lazaroff

WASHINGTON, DC, October 28, 1999 (ENS) - A common, popular insecticide used on crops, lawns and Christmas trees poses higher risks to human health and the environment than previously believed, the U.S. Environmental Protection Agency revealed Wednesday.

An EPA official who asked not to be identified told ENS today that, in light of the new risk assessment, the EPA will likely seek to curb the use of the insecticide chlorpyrifos.

Chlorpyrifos, the active ingredient in Dursban* and Lorsban* insecticides, trademarked names of Dow AgroSciences LLC, is a broad-spectrum, organophosphate insecticide first registered in the United States in 1965. Registered uses include a wide variety of food crops, turf and ornamental plants, structural pest control and residential uses.

Dow AgroSciences markets chlorpyrifos as Dursban Pro and Dursban 50W for general pest control, and Dursban TC for termite control.

The reassessment of the widely used pesticide chlorpyrifos casts the agency’s planned reevaluation of thousands of chemicals in a new light, indicating that new data and improved techniques may reveal toxins in our own backyards.

Chlorpyrifos and other pesticides are being reviewed under the process developed by the Tolerance Reassessment Advisory Committee to determine whether their existing Environmental Protection Agency (EPA) registrations meet stringent, new safety standards required by the Food Quality Protection Act of 1996.

As part of the retesting, the EPA is using controversial animal tests, as well as a review of existing data, to determine safe exposure limits for adults, children, land animals and aquatic animals.

The EPA’s reassessment of chlorpyrifos finds significant risks to humans and wildlife from outdoor uses of the pesticide. The chemical is so widely used that "the majority of the U.S. population is exposed to chlorpyrifos," the EPA’s preliminary risk report states.

The report notes that previous studies have shown that 82 percent of American adults and 92 percent of children studied have traces of the chemical in their urine.

The EPA found that risks from chlorpyrifos use on crops, primarily sweet corn, are not as high as the agency had feared. But risks from household uses, including mosquito fogging, lawn maintenance, and spraying on golf courses and Christmas tree farms, pose risks that "exceed levels of concern" for humans, pets and wildlife.

The agency documents numerous cases of fish kills in surface waters near sprayed areas, including one incident in which 2,000 blue gill sunfish were killed in a small lake adjacent to a motel, where just two rooms were treated with chlorpyrifos for termites.

Bird deaths are also seen, though the EPA notes that chlorpyrifos is unlikely to produce large visible bird kills, as birds have time to fly elsewhere before showing symptoms.

"Birds have adequate time to feed in chlorpyrifos treated fields, leave the treated area and disperse to other habitats before they begin to experience to toxic symptoms, then they seek refuge and hide before dying," the report states.

The chemical is also highly toxic to honey bees, already in a crisis due to an epidemic of exotic diseases and parasites.

Another common use of chlorpyrifos is the aerial spraying of Christmas tree farms, and drenching freshly cut stumps to retard decay after consumers take the trees home. Previous risk assessments were based on exposure to a single drop of the 3,595 parts per million spray. But, "few species drink only one drop when they drink or are thirsty," the report says.

Wild animals are placed at high risk by normal drinking of the spray or bathing in the runoff. Birds are at risk when preening wet feathers.

The insecticide solution "may pose acute risks to aquatic organisms, if rainfall washed the spray solution off the tree stumps into adjacent aquatic areas," the report notes. And aerially spraying Christmas trees, "exceeds the levels of concern for most non-target aquatic and terrestrial animals."

Treated lawns and shrubs pose the same threat, as "it is evident that species .. are capable of drinking more than a single drop off leaves and other vegetation."

While the EPA cautions against drawing premature conclusions from these preliminary results, it seems likely that the agency will set lower thresholds for safe exposure to chlorpyrifos, reducing the possible uses for the chemical.

Dow AgroSciences has already responded to the study, saying that it includes a "tremendous number of errors and omissions." The company says chlorpyrifos is quite safe.

"Dow AgroSciences believes the extensive use of chlorpyrifos during the last three decades is a clear indication of the value of this compound and the benefits that chlorpyrifos provides to growers and the American public generally," the company told EPA in an October 19 report.

According to the company’s own risk database, the report says, "realistic risk concerns are minimal and are clearly outweighed by the significant benefits provided by chlorpyrifos."

Yet in eight of nine of EPA’s tests on chlorpyrifos, the agency calculated risk levels well above the EPA cutoff for further action to reduce the chemical’s health risks.

Without the additional testing required by the Food Quality Protection Act of 1996, the EPA’s safe exposure levels for organophosphate pesticides such as chlorpyrifos would remain at their current levels, regardless of actual risk.

The EPA official said today that testing programs, including the controversial high production volume chemical testing program, may also lead to a net reduction in the amount of toxins released to the environment. The HPV program, fast tracked last fall by Vice President Al Gore, calls for tests on 2,800 widely produced industrial chemicals.

Last week, People for the Ethical Treatment of Animals (PETA), the Doris Day Animal League and the Physicians Committee for Responsible Medicine reached an agreement with the EPA to amend the high production volume program. The agreement greatly reduces the number of animals that will be used in the high production volume program. The EPA and other agencies originally estimated that up to 1.3 million laboratory animals of all kinds would have be sacrificed to complete the testing. Under the amended plan, as many as 800,000 animals will be saved.

Under the agreement, the EPA sent a letter to some 900 top chemical companies with new high production volume testing guidelines. One major change is that the agency will no longer require companies to perform a checklist of individual tests for each of the chemicals. If existing data from animal or human testing provides enough information, chemical companies will not be required to perform new tests.

EPA officials were unclear today on whether databases such as the internal resource used by Dow AgroSciences to reach its conclusions about the safety of chlorpyrifos would be considered sufficient by the EPA.

Copies of the preliminary risk assessment are available on EPA's web site at:

The EPA will accept public comments on the report for 60 days.
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