Weed killer atrazine may be linked to birth defect

Living near farms that use the weed killer atrazine may up the risk of a rare birth defect, according to a study presented this past Friday at the annual meeting of the Society for Maternal-Fetal Medicine in Chicago.

About 1 in 5000 babies born in the U.S. each year suffers from gastroschisis, in which part of the intestines bulges through a separation in the belly, according to the March of Dimes. The rate of gastroschisis has risen 2- to 4-fold over the last three decades, according to Dr. Sarah Waller, of the University of Washington, Seattle, and colleagues.

Waller’s team studied the potential link between the weed killer and the birth defect because, as they note in their conference abstract, “during the last 10 years, the highest percentage per population of gastroschisis was in Yakima County, in the eastern part of the state, where agriculture is the primary industry.”

Overall, Washington state has about double the national average of gastroschisis cases - an average of 43 cases per year, Waller told Reuters Health.

The researchers looked at more than 4,400 birth certificates from 1987-2006 - including more than 800 cases of gastroschisis—and U.S. Geological Survey databases of agricultural spraying between 2001 and 2006.

Using Environmental Protection Agency (EPA) standards to define high chemical exposure levels in surface water, they found that the closer a mother lived to a site of high surface water contamination by atrazine, the more likely she was to deliver an infant with gastroschisis.

The birth defect occurred more often among infants who lived less than 25 km (about 15 miles) from one of these sites, and it occurred more often among babies conceived between March and May, when agricultural spraying is common.

A mother’s tobacco use, and being the first born, were also linked to a higher rate of the birth defect. Two other commonly used farm chemicals - nitrates and 2,4-dichlorophenoxyacetic acid (2,4-D) - were not linked to gastroschisis.

However, Steven Goldsmith, a spokesperson for atrazine manufacturer Syngenta, told Reuters Health that the study “is not credible for a number of reasons.”

According to a Syngenta press statement, studies designed like Waller’s “make broad generalizations about environmental conditions and often overlook” factors that might affect the rate of a given condition.

The study, said Syngenta, “provides no direct or credible link between atrazine and the kind of birth defect, gastroschisis, which it examined.”

“Through thousands of studies, atrazine has been found again and again to not cause any variety of health effects, including those in this Washington study,” Goldsmith said. “Use of atrazine in Washington state is the second lowest amount in the country, and in eastern Washington, so little is used that it barely appears in surface water.”

But Dr. Waller’s group is not the first to report a link between gastroschisis-like birth defects and surface water atrazine levels. In 2007, Indiana researchers reported in the Journal of Pediatric Surgery that in their state, where rates of such birth defects are also very high, atrazine levels were significantly linked with the rate of gastroschisis and other defects. That study was done using data from the Centers for Disease Control and from the Indiana State Department of Health.

Another study, published last year in Acta Paediatrica, found similar results for the general rate of birth defects in the U.S. population. Atrazine, that study found, upped the risk of nine birth defects in babies born to mothers whose last menstrual period was from April to July—that is, when surface water levels of the pesticide were highest.

The U.S. Department of Health and Human Services’ Agency for Toxic Substances and Disease Registry has also reported that high levels of the chemical have been shown to cause birth defects in animals.

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By Karla Gale

NEW YORK (Reuters Health)