Many people handle chemicals at work, but farmers frequently work with ones that are especially dangerous. Those are pesticides that kill insects, plants, fungi, and weeds. However, little is known about the long-term effects of working with many of these chemicals. Rose Hoban reports on new research into pesticides' risk to human health.

Researchers from the U.S. National Institute of Environmental Health Sciences have been studying 80,000 farmers and their families for more than a decade in the Agricultural Health Study. They want to see what kinds of risks farmers experience from working on their farms.

Epidemiologist Jane Hoppin says one thing they did was to collect data from armwomen about how often they handle pesticides. The women answered questionnaires about 50 pesticides used commonly both in the home and in agriculture. About half of them reported applying pesticides in their lifetime.

Hoppin and her colleagues focused on women who started handling the chemicals when they were adults and then developed health problems. Their study excluded women who said they had asthma when they were young.

The researchers looked at adult women to see if they had a problem known as allergic asthma. "People who have allergic asthma had both asthma and hay fever or eczema," Hoppin explains. "And their asthma may be triggered by an allergic response."

Hoppin reports that these women were 50 percent more likely to have developed allergic asthma in adulthood, and the condition was associated with a number of common pesticides. "Coumaphos, which is used on animals had a twofold risk increase," Hoppin says, "and Malathion, which is used to kill the Medfly, has an odds ratio of 1.6." That translates into a 60 percent increase in the chance of having asthma.

Hoppin's study also lists some other pesticides that showed increased risk:

- Paraquat, used widely on banana plantations had an elevated risk

- A class of pesticides called organophosphates had an almost 50% increase in risk. Organophosphates include malathion (above), also Parathion, Methyl parathion, Chlorpyrifos, Diazinon, Dichlorvos, and Phosmet, among others.

- Some farmwomen reported having used DDT before it was banned. Those women showed increased rates of asthma.

Hoppin says there's surprisingly little information on the health effects of many pesticides, despite the fact they're used around the world. As a result, she says she's had inquiries from many countries about her study results.

Her research came out this month in the Journal of Respiratory and Critical Care Medicine, a publication of the American Thoracic Society.