Pregnant women who live near farms where pesticides are used face a higher risk of miscarriage due to birth defects than unexposed women, according to a study in heavily farmed areas of California. The results, published in the March issue of Epidemiology, are the strongest to date suggesting that at least some pesticides raise the risk of birth defects in humans, experts say.
Unlike other chemicals used by industry, pesticides are designed to kill living animals, making researchers particularly concerned that they may harm humans. Earlier studies showed that some pesticides raised the risk of birth defects and fetal death in rats and mice. But studies in agricultural areas have failed to show clearly whether humans face a similar risk, says epidemiologist Irva Hertz-Picciotto of the University of North Carolina, Chapel Hill. Part of the problem is that it's hard to determine exactly who was exposed, to what chemical, and in what amount. Instead, researchers often rely on people's memory of pesticide use--which can be biased--or on average pesticide application data over an entire county, Hertz-Picciotto says.
For the current study, she and her colleagues zoomed in on 10 counties, most of them in California's Central Valley, using a statewide database of pesticide applications that listed the specific chemical applied, the date, and the location within 1 square mile, for 1984. They combined those data with state health records of 73 women in the same area who had a miscarriage or whose child died within 24 hours after birth, and 611 controls who gave birth to healthy babies.
Women who lived within 2 miles of a place where so-called halogenated hydrocarbons were used during the first 2 months of their pregnancy--when fetal organs are formed--were more than twice as likely to have a miscarriage caused by fetal defects. Other common classes of pesticides--organophosphates and carbamates--raised the risk by about 40%. Strengthening the case, the risk was higher if women lived within 1 mile of the farm where the chemicals were applied. While such an epidemiological study can't prove that pesticides cause birth defects, it raises a red flag, Hertz-Picciotto says.
"I think it's really a step forward," says epidemiologist Andrew Rowland of the National Institute of Environmental Health Sciences in Research Triangle Park, North Carolina. But because most of the women were exposed to several chemicals, it's still not clear which one might be responsible, he adds. The researchers next hope to "home in on which of the pesticides is toxic," Hertz-Picciotto says.