Many of the tests under consideration use compounds called organophosphates, which are at the top of the EPA’s list of concerns because they are among the most toxic and widespread pesticides. In the United States, organophosphates are applied to 60 million acres of crops like corn and cotton every year. They are neurotoxins: They poison the nervous system of both insects and humans by disabling an enzyme called cholinesterase that helps regulate signals between nerve cells. First discovered in the 19th century, they were later developed as insecticides and nerve-gas agents in Germany in the 1920s. Nonlethal overdoses of organophosphates can cause headaches, sweating, blurred vision, twitching, abdominal cramps, and in severe cases, paralysis and difficulty breathing. Recent human studies monitor levels of cholinesterase in the blood rather than overt signs of illness. Even so, the ethics of such tests are dubious. Clinical trials of new pharmaceuticals are sanctioned by government and society alike because there may be some benefit to the individuals involved in such a study: protection from disease or relief of an illness—if not for themselves, then for a loved one.

“Where’s the benefit from pesticides?” says Christopher Portier, a biostatistician at the National Institute of Environmental Health Sciences in Research Triangle Park, North Carolina. “The individual benefit of having pesticides in society is really hard to pin down.”

Manufacturers contend that a more refined understanding of the chemicals’ hazards to humans can benefit both individuals and society. “Like it or not, pesticide use is an integral part of our food production and public-health programs,” said Monty Eberhart, director of product safety management at Bayer CropScience, in a presentation to a panel from the National Academy of Sciences this past January. “The fact is that pesticides are used and people are exposed. The people that are participating in these studies have much more of a direct benefit than anybody participating in a phase I clinical trial would have.”


But critics are also worried by the science behind human pesticide tests. Unlike drug trials, the procedures for testing pesticides on people are neither specified nor reviewed by scientists outside the company doing the testing. Many of the experiments involve so few subjects—as few as six in a test of the organophosphate chlorpyrifos—that the results can’t be trusted. There isn’t even agreement that blood levels of cholinesterase should be used as a proxy for damage to the central nervous system, Portier says. “If [the testing] is ethical, but you do it wrong, it’s still not ethical.”

Top Five Pesticides Found in Food*

• 23% DDT (organochlorine) First used as an insecticide in 1939. Once the most commonly used pesticide. Banned in 1972 in the United States because it persists in the environment. Still used abroad (.0001–.031 parts per million found in the samples).

• 20% Chlorpyrifos-methyl (organophosphate) Used on stored grain since 1985. Most applications have been voluntarily canceled. Moderately persistent in the soil (.0001–.537 ppm).

• 18% Endosulfan (organochlorine) Introduced in 1954. Recently limited to agricultural and commercial uses. Moderately persistent in the soil (.0001–.266ppm).

• 16% Malathion (organophosphate) One of the earliest organophosphates—introduced in 1950. Low persistence in the soil (.0007–.080 ppm).

• 15% Dieldrin (organochlorine) Second only to DDT in use between 1950 and 1970. Banned in the United States for crop use in 1974 (.0001–.020 ppm).

*Fourteen other pesticides were found in more than 2 percent, but less than 8 percent, of all foods sampled. See the Total Diet Study for details: www.cfsan.fda.gov/˜dms/pes01rep.html#tdsresults.