Melon Poisoning--Was Insecticide Misused?

The recent watermelon poisoning episode in the San Joaquin Valley probably resulted from deliberate misuse of the highly toxic insecticide aldicarb and not from residues that stayed in the soil from years past, according to several industry and university researchers who buttressed the position of Union Carbide Co. and state officials.

Several scientists said in interviews that studies of aldicarb in a variety of soils have shown that the insecticide normally degrades to insignificant amounts in a matter of months.

Most expressed skepticism about statements by some farmers that the melons could have been tainted by aldicarb applied to different crops in the same fields several years before. Aldicarb, marketed exclusively by Union Carbide under the trade name Temik, is registered for use on cotton and several food crops, including potatoes, peanuts, citrus fruits and sugar beets. But it can not legally be applied to melons, which are more likely to accumulate large amounts of the chemical’s residue.

“I think Union Carbide’s got a good case here,” said Wray Winterlin, an environmental chemist at the University of California, Davis, who has studied aldicarb movement in various soils. “I think that was a misapplication by someone.”

‘Decomposes Fairly Rapidly’

“Once it’s in the soil, (aldicarb does) decompose fairly rapidly,” said Dr. Chris Wilkinson, director of Cornell University’s Institute for Comparative and Environmental Toxicology and a member of the Environmental Protection Agency’s scientific advisory panel on pesticide issues.

Dr. Barbara Erickson, an entomologist at the University of Wisconsin, said that research by scientists “in many parts of the country” has shown that “aldicarb will generally persist” for about 100 days in the soil.

The views of these scientists, who were contacted by The Times, follow the main thrust of an investigation by the state Department of Food and Agriculture. That agency has said flatly that one or more farmers used aldicarb illegally, contaminating enough melons to make dozens of people sick and sparking an unprecedented recall of a California crop.

Investigators, who are interviewing farmers and studying pesticide sales records, have vowed to prosecute any violators.

Nonetheless, Erickson and others said that causes other than deliberate misuse are possible. For one thing, she said, chemical decomposition can vary widely in different areas, depending on climate, soil and the rate of microbial action.

“We have not studied every soil type and every specific microbe climate that’s out there,” she said. “There’s no way you can do that.”

In addition, some scientists said, aldicarb could have ended up in a melon field by some peculiar circumstance, such as a chemical spill that was plowed under rather than cleaned up or through the use of contaminated irrigation water.

A study published in 1982 at the U.S. Department of Agriculture research lab in Yakima, Wash., showed that aldicarb mixed into soil in one growing season can show up in trace amounts in crops grown the next.

Traces of Aldicarb Found

That study involved application of both regular and excessive quantities of aldicarb to separate test plots of potatoes. After the potatoes had matured, a second generation of crops--including radishes, mustard greens and potatoes--were planted in the same plots.

The new crops were harvested from 13 to 15 months after the aldicarb was applied, and measurable amounts of the chemical were found even in crops that had been only moderately treated.

Jay C. Maitlen, the research chemist who ran the study, said he did not know if melons grown in fields previously treated with aldicarb could absorb enough of the chemical to make anyone sick. But he said that his study did show “that aldicarb will carry over sufficiently to produce at least detectable residues . . . in other crops that are planted in the second year.”

Another researcher who said flatly that there had been “absolutely no evidence anywhere” that aldicarb “survives for longer than a year in any soil” expressed surprise at hearing about Maitlen’s findings. But Dr. John Harkin, a professor of soil science and water resources at the University of Wisconsin, said that he was “still extremely skeptical that a pesticide used years before in California would get into watermelons” in sufficient quantities to make people sick.

Called More Persistent

A University of Illinois entomologist, while saying that the melon episode could involve deliberate misuse, said that aldicarb is more persistent in soil than Union Carbide has acknowledged.

“I don’t think you can underestimate the toxicity and persistence of Temik,” Dr. Robert Metcalf said, adding that Union Carbide scientists had failed to anticipate the widespread aldicarb pollution of ground water that has been found in several states.

In one celebrated case, the best technical information about the breakdown of a toxic substance in soil turned out to be absolutely wrong.

The case involved the contamination of dozens of sites in Missouri by dioxin, an extremely toxic chemical that is suspected of causing cancer. It is unavoidably created during manufacture of certain pesticides.

10 Became Ill

In 1971, dioxin waste from a rural Missouri pesticide plant was hauled off by a waste-oil dealer, who mixed the material with oil and sprayed it on dirt roads and horse arenas to hold down dust. Dozens of horses died soon after, and at least 10 people became ill.

But there was no effort to clean up other dioxin sites, in part because of the prevailing scientific view that dioxin breaks down quickly in soil once it is exposed to sunlight. Only in 1982, when the EPA decided to test some of the sprayed locations, was it learned that unacceptably high levels of dioxin remained at some of the sites. The discoveries prompted evacuation of some residential areas, including the entire town of Times Beach, Mo.

In the aldicarb case, however, officials with the state and Union Carbide say that there is convincing evidence, besides soil decomposition studies, to support the misuse theory.

State officials said that when the watermelon case began to unfold, they took more than 100 soil samples from fields in Imperial and Riverside counties, where aldicarb had been used on cotton during the previous growing season. They said that they found no aldicarb in the soil, which suggested that the traces found in the melons had been applied quite recently.

Union Carbide Study

And Union Carbide officials said that tests they conducted between 1979 and 1981 convinced them that the high aldicarb residues found in some of the California melons resulted from a recent application.

According to Dr. Edwin Quattlebaum, manager of product development for Union Carbide’s agricultural chemicals unit in Research Triangle Park, N.C., the company’s studies showed that melons grown in fields sprayed with moderate amounts of aldicarb contained an average of 0.25 to 0.3 parts of aldicarb per million parts of the fruit. State officials said that some of the tainted melons contained up to three parts per million, which Quattlebaum said indicates that substantial amounts of of the insecticide had been applied to the melon fields during the recent growing season.

Jay Feldman, national coordinator of the National Coalition Against Misuse of Pesticides, said that even if farmers deliberately misapplied aldicarb, chemical companies and pesticide regulators are equally to blame.

In incidents like this, Feldman said, chemical companies and regulators adopt the “public relations posture” that only a few “bandits” or unscrupulous pesticide users are to blame.

‘Ferocious Marketing’

He said that the real problems are “ferocious marketing techniques and promotional tactics” by pesticide manufacturers and the limited training of farmers in the safe use of pesticides and non-chemical alternatives to pest control.

Lawrie Mott, a project scientist with the Natural Resources Defense Council and a member of the EPA administrator’s Pesticide Advisory Committee, said that the American public is also to blame. She said consumers demand “cosmetically perfect produce” without recognizing that heavy pesticide use is “the price they have to pay for their apples being large and red all year-round, and their watermelons being big and green and smooth.”