U.S. Toxicologist Questions Malathion Safety : Medfly: Arguing against EPA position, he says differences over pesticide research at least warrant further study.

A U.S. government toxicologist who reviewed studies about the health effects of malathion--the pesticide being sprayed throughout the Los Angeles Basin to eradicate the Mediterranean fruit fly--argued repeatedly in an internal report that there was enough evidence to warrant further study of the chemical’s cancer-causing potential, it was learned Wednesday.

In his July, 1989, internal memorandum, U.S. Environmental Protection Agency toxicologist Brian Dementi dissented sharply from the EPA’s official position that it has no concern that malathion could cause cancer.

Dementi, a toxicologist in the EPA’s hazard evaluation section, was asked by his superiors to review a request by the chemical’s manufacturer to waive studies the agency wanted as part of a routine review of the pesticide. In a mostly technical memorandum, Dementi concluded that more studies were needed because of evidence in previous investigations that pointed to potential problems.

Among these was a study that found a threefold increase in tumors in rats fed malaoxon, a break-down product of malathion. The conclusion of that study was “equivocal,” meaning there was not enough evidence to conclude whether a cancer risk exists.

Dementi, however, apparently found the study disturbing.

“At the very least,” the toxicologist wrote, “these findings support a reexamination by EPA pathologists and statisticians. These findings also support requiring the (pesticide maker) to include the oncogenic (tumor causing) component in the required chronic rat study on malathion.”

Dementi’s superiors at the EPA agreed that more studies should be done and the results of the rat investigation should be “clarified.” But top agency officials said they wanted the additional studies not because of any particular concern, but to meet routine review requirements.

“EPA does not have concerns that malathion may be a carcinogen,” Rick Tinsworth, an EPA director in charge of pesticide reviews, said in December. “Existing data are negative. We are asking for additional studies to complete the data base for malathion. These studies are not being required because of any identified problem.”

Tinsworth, reached in Washington on Wednesday, said he believes Dementi’s internal memo “overstated” the potential risks of the pesticide.

“This was Brian’s opinion, not the agency’s,” said Tinsworth. “I’m not trying to be critical of Brian because there is room for differences of opinion in this area. He sees more in the cancer potential than the agency does. . . .

“We both agreed we need data. I wanted to fill out the data base. He is more concerned about what he sees there (in the current data) than we are.”

The discovery of the agency’s internal differences over the pesticide surprised some environmental activists, and it comes at a time when regular applications of malathion over Southern California are stirring increasing public opposition. The California chapter of the Sierra Club recently called for the spraying to be halted until more is learned about malathion.

“This shows there is even more controversy than we had thought,” said Mary Nichols, a senior staff attorney for the Natural Resources Defense Council who served as former Gov. Jerry Brown’s secretary of environmental affairs.

“When the EPA announced they were requiring further testing . . . they simply said that some of the studies were old and not very well done. The jury is out even more than we thought.”

The internal document is expected to be used by homeowner groups in their attempt to get the spraying stopped.

“This suggests that the EPA’s own staffers feel there really are questions and the questions merit further research,” said Dean Hansell, an attorney representing homeowner groups opposed to spraying.

But state officials largely dismissed the memorandum, saying it merely represents the EPA’s strongest case for asking for more studies and remained the viewpoint of only one toxicologist.

Dr. James Stratton of the California Department of Health Services stressed that experts who reviewed the study of thyroid tumors in rats were divided on whether malaoxon causes cancer. Moreover, he said, an occasional “equivocal” finding in hundreds of laboratory examinations is expected and should not be cause for any particular concern.

The rat study initially was done by the National Cancer Institute in the late 1970s and was reanalyzed in 1985 by the National Toxicology Program. In reexamining laboratory slides, the National Toxicology Program decided that although there was a statistically significant increase in tumors among rats fed malaoxon, the study had to be classified “equivocal.”

In describing its reasons for the finding, the program scientists indicated there could have been other unknown factors, besides the malaoxon, to explain the tumors. The scientists concluded that they did not believe the finding represented concern for public health nor did it require any action.

Dementi, in arguing for further research, concluded that the agency’s toxicology branch felt the study “may reveal, albeit weakly, an oncogenic (tumor-causing) response” in animals.

In any case, said Stratton, a medical epidemiologist in the state health department’s hazard evaluation section, the amount of malaoxon contained in the malathion now being sprayed over Southern California is too minute to cause health problems.

Nicholas B. Kalm, a spokesman for American Cyanamide Co., the New Jersey-based firm that manufactures malathion, said his company is involved in “ongoing negotiations” with the EPA and the California Department of Food and Agriculture over which studies need to be done.