Drops of Mistrust Cloud Malathion Spray

The Medfly, that scourge of California farmers, is back. The trapping of a few specimens of the pesky insect in the Elysian Park, Echo Park and Silver Lake areas since late July has led to an increasingly familiar chain of events: The declaration by the governor of a state of emergency, aerial spraying of the pesticide malathion over populated areas, and concern by residents of the affected communities about the possible health effects of the chemical.

As in the past, health and agricultural officials quickly attempted to reassure residents living in the sprayed zones that malathion poses no danger. Thousands of leaflets were distributed, declaring that the pesticide is “considered one of the safest insecticides in use today” and that “at this extreme low dose, pregnant women have no cause for concern.”

These days, it seems that there is a strong inverse correlation between the certitude with which the experts state that a potentially toxic chemical is safe and the degree to which the public feels reassured. One reason is that the experts sometimes turn out to be wrong. Over the years, a long list has accumulated of pesticides and other chemicals that we once thought were safe and now know are dangerous, such as DDT.

In the case of malathion, officials have consistently strained their credibility by continuing to overstate the case for the pesticide’s safety. In fact, serious investigation of malathion’s ability to cause genetic damage has been under way for only about 10 to 15 years, and the results so far do not at all exonerate the chemical. Back in 1976, a comprehensive survey of the scientific literature by the National Institute of Occupational Safety and Health concluded that “information on the mutagenic and carcinogenic potentials of malathion is very scanty” and urged that studies of these effects “be initiated as soon as possible.”

Since that time, study after study has shown that malathion is capable of causing a variety of types of genetic damage in both human and animal cells. For example, researchers at Roswell Park Memorial Institute in Buffalo found that malathion, which is generally considered one of the weaker of its class of insecticides, was one of the most potent in causing disruption of the cycle of dividing cells.

These findings have given rise to concern that pregnant women exposed to malathion might be at higher risk for miscarriages or for giving birth to malformed infants. Health and agricultural officials have long argued that the doses of malathion received from aerial spraying are too low to cause these problems. However, an epidemiological study completed two years ago of San Francisco Bay Area residents sprayed with malathion during the 1981-1982 “Medfly crisis,” has left open the possibility that malathion could cause birth defects.

The study was conducted jointly by the California Department of Health Services and the Department of Preventive Medicine at the USC and compared the outcomes of the pregnancies of women who had lived in the spray zones with those who had not. Epidemiological studies are notoriously insensitive to relatively small effects and are easily biased by other factors that can affect the analysis. Nevertheless, after carefully controlling for these errors, the researchers found a positive correlation between malathion exposure and stillbirths and a significant correlation between exposure and defects of the gastrointestinal tract in the newborn children.

The author of the study concluded, however, that although the results were “suggestive” of an association with malathion exposure, it was “unlikely” that malathion was the cause, in part because the fetal gastrointestinal system was already formed by the time the exposure occurred. He may well be right. On the other hand, far from giving malathion a clean bill of health, the study only raises more questions about the safety of the pesticide--questions that leave us far from the certitude expressed in the public reports of health and agricultural officials.

By making exaggerated claims for malathion’s safety and by misrepresenting the scientific evidence, our officials contribute heavily to the clouds of mistrust and anger that trail the helicopters each time they take to the air.