Study Connects Banned Pesticides To Brain Ailments

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Study connects banned pesticides to brain ailments
By TONY LEYS
May 15, 2005

Farmers who say they used the now-banned chemicals reported more health problems.


Evidence is mounting that farm chemicals designed to kill insects can damage people's brains.

A new study of 19,000 Iowa and North Carolina farmers suggests that those who routinely used certain types of insecticides on their crops can be left with lasting problems.

Compared with other farmers, the heavy users of insecticide were more than twice as likely to say they had suffered dizziness, numb feet, trembling hands or twitching arms and legs. They also were more than twice as likely to report blurred or double vision, poor night vision, depression, absent-mindedness or difficulty speaking.

The study's lead author, Dr. Freya Kamel, said she believes her research is the broadest look ever into the long-term effects of insecticides on farmers.

"We've always known they were harmful to the brain," she said. "The question is whether they're only harmful if you have a very high level of exposure. What this study does is expand the level of concern to more moderate levels of exposure."

It also feeds suspicion that insecticides can contribute to Parkinson's disease, which destroys brain cells and causes tremors and other serious problems.

The government banned several of the chemicals amid safety concerns raised in the 1970s. But many of the farmers with neurological problems told researchers that they had used those products before they were taken off the market.

Kamel works for the National Institute of Environmental Health Sciences, a federal agency based in North Carolina. Her new article focused on participants in the Agricultural Health Study, a 12-year-old project designed to uncover the risks of farm-chemical use. Iowans make up about two-thirds of the farmers Kamel's team looked at.

Nearly 3,000 participants said in questionnaires that they had used insecticides more than 500 days in their lifetime, the researchers said. Nearly 800 of them reported suffering more than 10 neurological symptoms.

The study, which is being published next month in Environmental Health Perspectives, found no strong association between neurological problems and use of weed killers or anti-fungus chemicals. It also didn't directly address the suspicion that insecticides can help cause Parkinson's disease. Kamel's team is following the participants who reported tremors to see if they develop Parkinson's. She also is involved in another study that is looking into whether other Parkinson's patients were exposed to insecticides.

A scientist who works for a national farm-chemical industry group said those studies will be crucial. Dr. Angelina Duggan, who represents CropLife America, cautioned against reading too much into the current article from Kamel's team.

"The Ag Health Study has made some associations that they intend to follow up on," she said. "What they propose is a theory. That theory is as yet unproven."

Duggan stressed that the new findings are based on voluntary questionnaires that asked about broadly defined symptoms. They are not based on physicians' diagnoses of actual diseases.

She also noted that some of the chemicals in question have been banned for decades. Their replacements are much safer, she said, and the products carry strict warnings on how farmers should safely use them.

Duggan said that, overall, the Agricultural Health Study has indicated that farmers live longer than non-farmers. She said chemical manufacturers support research into the long-term effects of pesticides on farmers.

"It's really an important issue for our industry," she said. "These are our customers, and we want them to use our products safely."

A Des Moines neurologist also said she looked forward to the results of Kamel's follow-up studies. Dr. Lynn Struck, who treats many Parkinson's patients, said she shares suspicions that pesticides can be a cause. But she said Kamel's current study doesn't prove a link.

Struck said she's sure the farmers in the study did their best to answer the questions honestly. She wonders, however, if the ones who routinely used chemicals are more likely to remember that they had suffered a bad headache or other passing symptom. Most farmers have heard about the possible dangers of farm chemicals, she said, and the ones who used the most tend to worry about their health. "A lot of these guys are extremely tuned into this," she said. "They're always asking, 'Could this have hurt me?' "

Struck also said it's difficult for farmers to remember exactly what poisons they used decades ago.

Kamel acknowledged the concerns about the accuracy of the participants' reports of their health and their chemical use. But she contended that the large number of participants should ease those problems. She also noted that the pattern of symptoms was strong only among farmers who used insecticides, not among those who mainly used herbicides. That seems to negate the theory that farmers are biased against chemicals in general, she said.

The studies and the debate will go on for years. But Struck said the main lesson is already clear: Pesticides are strong chemicals, and no one should take them lightly. "You have to use extreme care," she said.