Women who drink water contaminated with low levels of the weed-killer atrazine may be more likely to have irregular menstrual cycles and low estrogen levels, scientists concluded in a new study.
The most widely used herbicide in the United States, atrazine is frequently detected in surface and ground water, particularly in agricultural areas of the Midwest. Approximately 75 percent of all U.S. cornfields are treated with atrazine each year.
The newest research, which compared women in Illinois to women in Vermont, adds to the growing scientific evidence linking atrazine to altered hormones.
The women from Illinois farm towns were nearly five times more likely to report irregular periods than the Vermont women, and more than six times as likely to go more than six weeks between periods. In addition, the Illinois women had significantly lower levels of estrogen during an important part of the menstrual cycle.
Tap water in the Illinois communities had double the concentration of atrazine in the Vermont communities’ water. Nevertheless, the water in both states was far below the federal drinking water standard currently enforced by the U.S. Environmental Protection Agency.
The amount of water consumed also seemed to make a difference: Women who said they drank more than two cups of Illinois tap water daily reported an even greater occurrence of irregular periods.
In recent years, some tests on lab animals have linked the herbicide to fertility issues, including altered hormone levels, delayed puberty and pregnancy loss.
Co-author Lori Cragin, an epidemiologist with Colorado State University at the time of the study, said the new findings fit with the results of the animal studies, as well as with some limited research that reported human effects.
In 2009, a study tied atrazine in drinking water to low birth weight in Indiana newborns. And in a study of more than 3,000 women enrolled in the Agricultural Health Study, those who described using atrazine and other pesticides had an increased risk of missed periods and bleeding between periods. The Agricultural Health Study is a nationwide project sponsored by the National Institutes of Health.
The manufacturer of atrazine says some unknown factor – not atrazine – might have caused the menstrual irregularities.
“Many things can cause changes to a woman’s menstrual cycle – stress, exercise, diet,” said Tim Pastoor, principle scientist for Syngenta, the Switzerland-based company that makes atrazine.
Pastoor noted that the company’s mice studies have not found reproductive effects, even at atrazine levels far greater than those found in the drinking water in the new study.
The researchers did not test the water for other contaminants.
“It is possible that the difference we found is due to pesticide exposure in general or another, unmeasured chemical in the drinking water,” said Cragin, who now is an epidemiologist at the Vermont Department of Public Health.
Cragin and her team, which included researchers from Colorado State University, Emory University and the Centers for Disease Control and Prevention, collected questionnaires from 102 premenopausal women in the Illinois farm towns of Mount Olive and Gillespie, and in the Vermont towns of Waterbury and Fair Haven, where atrazine is not used. The authors said they considered lifestyle factors, such as physical activity, weight and foods, and found no significant differences between the two groups of women.
The findings, which were published in the journal Environmental Research earlier this month, were based on municipal tap water tested between July and September of 2005.
Cragin was surprised to see a significant effect in the women whose water contained atrazine levels far below the EPA’s standard of 3 parts per billion.