Pesticide Used on Citrus Is Found to Thin Dove Eggshells

A study by a UC Davis researcher says dicofol, a pesticide used to kill mites in cotton fields and citrus orchards, can cause thinning of bird eggshells the way the banned pesticide DDT does.

The study, affirmed by a U.S. Environmental Protection Agency review, doesn’t say whether dicofol threatens birds in their natural environment. That’s because the chemical is unstable and tends to decay in an alkaline environment, according to Steven Schwarzbach, a UC Davis researcher in charge of the study.

The chemical is sold under the brand name Kelthane and has been banned by one state. Farmers in California, Texas and Florida use the chemical.

In laboratory tests, ringed doves ate food containing a pure form of dicofol. The pesticide caused thinning of the doves’ eggshells, an effect similar to that of exposure to DDE, the main breakdown product of DDT, Schwarzbach said.

“If dicofol is in the diet of a bird, you’ll find it in the fat of the bird and it will accumulate in egg yolks,” Schwarzbach said in a telephone interview.

Ringed Doves Less Sensitive

The study’s purpose was to see whether the chemical threatened endangered species such as the peregrine falcon and other birds. The ringed doves used in the tests are less sensitive to the chemical than the falcons.

He said researchers now should find out whether dicofol might threaten other species such as sandhill cranes, storks, and wading birds throughout the San Joaquin Valley.

A separate study on dicofol’s impact on bird embryos is being conducted at McGill University in Montreal.

Patrick McNulty of the Philadelphia-based Rohm & Haas Co., which sells dicofol, said the UC Davis test “is a lab finding. The critical point is that you don’t find those concentrations (used in the tests) in the environment.”

Rohm & Haas Inc. sells about two-thirds of the 3 million pounds of dicofol products sold each year in the United States.

“The risks associated with dicofol have been fully appraised, and it is just another registered pesticide at this point. We’re generating other data to confirm its environmental safety,” said McNulty, the company’s director of registration and regulatory affairs.

Firm Funding Research

The company, in conjunction with dicofol’s other producer, Makhteshim-Agan Inc., is funding some of the bird research.

Dicofol was the target of a proposed EPA ban in 1984 because it contained as much as 10% DDT as an impurity. But the EPA allowed dicofol to stay on the market if the DDT impurities were reduced from 10% to 2.5% immediately and to 0.1% in 1989.

The EPA canceled Rohm & Haas’ license to produce and sell the pesticide in September, 1986. The company had failed to reduce dicofol impurities to the 2.5% limit. Rohm & Haas regained its license in August after it met the requirements.

Wisconsin banned dicofol in June, 1985, because of the DDT impurities, said Jay Feldman of the National Coalition Against the Misuse of Pesticides.

The laboratory tests showing that dicofol thins eggshells to the same degree as DDT and DDE “in and of itself is a significant finding,” said Larry Turner, the EPA’s project manager for the endangered species protection program.

Turner said that before the dicofol study scientists thought that only DDT and its derivative DDE thinned eggshells.

“If dicofol can do the same kind of thing, we need to be concerned about it,” Turner said in a telephone interview. He said the EPA and Rohm & Haas are negotiating over a new study to gauge how much dicofol actually is present in the environment during normal use. Such research could take several years, he said.

Although dicofol is very similar to DDT, Turner said there is a major chemical difference.

McNulty said, “The difference with dicofol is that it breaks down faster and does not bio-magnify,” or accumulate through the food chain, like the insidious DDT.

The company isn’t aware of any data that shows dicofol accumulating in the food chain, McNulty said.

Dicofol is used as part of an integrated pest management program to kill mites in cotton fields and citrus orchards. Growers used DDT at 20 pounds per acre, but dicofol is applied at one pound per acre per year, McNulty said.