5 Targeted Pesticides Still a Mystery

The five pesticides targeted by Cesar Chavez in his monthlong fast have been used for decades in California agriculture, but in spite of their longevity there is little agreement over the dangers they pose to farm workers and consumers.

Chavez, president of the United Farm Workers union, has vowed to force a ban on the five pesticides, which he has described as “the most lethal substances used in the growing of table grapes.” The UFW, which is engaged in a campaign to win labor contracts for grape workers, has asked consumers to boycott table grapes until the pesticide ban is accomplished.

For their part, agricultural industry leaders have responded angrily, saying that detectable residues of the chemicals on grapes have fallen well within tolerances established by the federal Environmental Protection Agency. The dangers to consumers and farm workers are negligible, they contend.

Behind the public wrangling lies a long history of scientific studies that have sought to establish the safety--or lack of it--for each of the targeted pesticides. Much has been learned about their potential impact on human health, but much also remains a mystery. In all, the group of agricultural poisons reveal a common truth about pesticide regulation: Government scientists are still in the process of discovering basic facts about major pesticides, some of which have been in use since the 1940s.

Two of the five pesticides already are under serious indictment. Dinoseb has been virtually withdrawn from the market because it is suspected of causing birth defects. It has not been used in California since 1986.

Another, captan, has been the subject of a special review by the EPA since 1980 after tests revealed it to be a suspected carcinogen. Captan remains in use pending the outcome of the review.

Others, such as phosdrin, are regarded by the EPA as relatively safe if used properly. Even here, however, the government is conducting new studies to gauge new concerns about the toxic effects of phosdrin on farm workers.

While the UFW’s call for a boycott is aimed exclusively at grapes, the targeted pesticides are used on a wide variety of food crops, ranging from lettuce, oranges and broccoli to carrots and peas. There is, in fact, little produce grown commercially in California that is not treated by one or another of the five pesticides.

What follows is a capsule profile of each of the pesticides, based on studies provided by the EPA, the state Department of Food and Agriculture and a variety of independent researchers:

-Methyl bromide. Introduced in 1932, methyl bromide is a gas used to fumigate soils on farms, killing nematodes and other earth-borne insects. It is also used in warehouses and homes as an anti-termite treatment. Methyl bromide does not pose a residue risk to consumers since only soils are treated and the pesticide is not absorbed by fruits and vegetables.

However, farm workers exposed to the gas by accident or improper handling can suffer serious injury or death. Methyl bromide is highly toxic and symptoms of poisoning range from nausea and vomiting to convulsions. In some cases, injured people have suffered chronic impairment of the central nervous system. While a substantial number of overall injuries have occurred with methyl bromide, most cases have involved the fumigation of buildings. Actual farm worker injuries have been low.

Methyl bromide has not been assigned a cancer rating by the EPA, but some studies have suggested that it may be a potent carcinogen. The pesticide belongs to same family of chemicals as EDB and DBCP, both of which were banned in 1979 because they produced sterility in male workers and some birth defects. There is also some evidence that the gas may deteriorate the atmosphere’s ozone layer, much like fluorocarbons used in plastic manufacturing and refrigeration.

-Dinoseb. First used in 1945, dinoseb is a herbicide used to control weeds on the margins of farm fields. The EPA, acting under emergency procedures, withdrew it from the market in 1986 when researchers discovered a pattern of birth defects in experiments on laboratory animals. The EPA also found risks of cancer and male sterility from exposure to very small amounts of dinoseb. Since the withdrawal, modifications of the order and court decisions have allowed limited use in the states of Washington, Oregon and Idaho. EPA officials say there have been no attempts to reintroduce the use of dinoseb in California.

Because of extreme limitations on the use of dinoseb, threats to the consumer are considered negligible. California farm workers, likewise, are no longer exposed. Farm workers in the states where continued use is allowed still incur risk of exposure and injury.

-Captan. Introduced in 1945, captan attacks fungi on a variety of crops. Since 1980, it has been undergoing a special review by the EPA because of suspected carcinogenic effects. In addition to producing cancers in laboratory animals, captan has also caused genetic mutations. The pesticide has been assigned a B-2 cancer rating by the EPA, meaning it is a “probable human carcinogen.” EPA officials say they expect the special review to be completed within the next nine months, at which time the agency will decide whether to restrict or withdraw captan. The review, under way for more than eight years, has taken so long, the officials say, because it required whole, new studies to be designed and completed.

In the meantime, captan continues to be used widely in California. The California Department of Food and Agriculture is conducting tests to determine typical exposure to field workers. As for consumer exposure, laboratory tests have shown the presence of captan residues on 32 out of 344 food samples, and all residues were below tolerances established by the EPA. However, such tolerances are designed as protection against short-term toxic effects and do not address cancer threats. Residues of captan on food products can be removed by washing.

-Phosdrin. Originally used in 1953, phosdrin (also called mevinphos) belongs to a family of pesticides known as organophosphates. Such pesticides kill their targets by paralyzing central nervous systems and are used on a wide variety of crops. Phosdrin rapidly breaks down after treatment, usually within 48 hours of treatment, allowing workers to re-enter fields.

Phosdrin, like all organophosphates, is highly toxic and overexposure can produce a variety of neurological symptoms, from ringing of the ears to loss of eyesight. Occasionally field workers have been injured by entering fields too quickly after treatment and from exposure to wind-blown sprays. The number of such injuries is subject to debate and the EPA is conducting field tests to determine the extent of the danger.

Because of the rapid breakdown, residues are not a serious threat to consumers. In tests on 344 food products conducted in 1986-87 by the state of California, no phosdrin residues were detected. Should residues remain on a food product, they cannot be removed by washing. Phosdrin is not suspected of being a serious cancer threat but thus far its carcinogen potential has not been investigated.

-Parathion. Introduced in 1947, parathion is also an organophosphate. Unlike phosdrin, however, parathion has a relatively long and unpredictable break-down period. This characteristic has led parathion to be more dangerous to farm workers re-entering fields after treatment.

Like phosdrin, parathion is now under study by the EPA to determine the exposure danger to field workers. It has not been assigned a cancer rating by the EPA but some government studies have shown parathion to cause malignant tumors in laboratory animals. In California tests, residues of parathion were found on one sample out of 344. It is unknown whether washing removes residues from fruits and vegetables.