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Science & the Public

EPA reviews hints of weed killer's fetal risks

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Last October, the Environmental Protection Agency announced it was reopening what the pesticide industry had hoped was a closed chapter on allegations of a popular herbicide’s toxicity. The agency will be convening meetings of its Scientific Advisory Panel on pesticides throughout 2010 to probe concerns about the safety of atrazine, a weed killer on which most American corn growers rely.

The first meeting of these outside experts started Tuesday. And although a large number of studies have indicated that atrazine can perturb hormones in animals and human cells — and might even pose a possible risk of cancer amongst heavily exposed people, these outcomes were not the focus of EPA’s review Tuesday. Risks to babies were.

During the SAP’s morning session, Aaron Niman, an EPA scientist, reviewed five recent studies linking atrazine to birth defects and other risks in newborns.

Two of the papers he cited were by Paul Winchester of the Indiana University School of Medicine and his colleagues. The most recent of these papers linked the presence of agricultural chemicals in surface waters around the nation — especially atrazine — at the time a woman conceived a baby to a heightened risk that her infant would develop a serious birth defect. This risk, although not huge, was statistically sound, he noted.

I’ve talked about this with Winchester, and he acknowledges that this link is no slam dunk in terms of indicting atrazine.

The U.S. Geological Survey data on contaminants in surface water around the nation, which Winchester’s team used, turned up plenty of agrochemicals. Take the White River in Indiana, Winchester says, “one of the study sites that is particularly relevant to me: In every sample, [USGS] found a mixture of pesticides. But far and away the most prevalent pesticide — and the one which exceeds the [federal] safety limits most often — is atrazine.”

Niman noted that this study, published almost a year ago in Acta Paediatrica, was unable to calculate probable atrazine exposures for each U.S. mom who gave birth over the study period: 1995 to 2002. He noted that this is a limitation of such “ecologic” studies, which analyze trends “at the group level” — such as the data, used here, on all births reported to the Centers for Disease Control and Prevention over that period. But “its strength,” Niman said, “is that it provides sort of an overall snapshot of trends in both birth defects and atrazine levels in the environment.” As such, he argued earlier this week, these ecologic studies are “useful in hypothesis generation,” even if they can’t establish causality.

Indeed, Winchester argues, even if atrazine isn't the operant risk factor, that won't necessarily let agrochemicals off the hook. A number of studies that he’s recently been reporting at scientific meetings have shown, he says, “that preterm birth rates at the population level are significantly increased by pesticide exposure” and that among Californians exposed to farm chemicals, “birth weights are lower in more heavily exposed pregnancies.”

These trends really disturb the neonatalogist because “the number one reason I’m in business is birth defects and preterm births. Those are the two things that kill babies. And we’re very disturbed that both have been increasing steadily over the last two decades.” So it's imperative to find out what is contributing to these trends, he says. And small babies: “Lowering birth weight percentiles will cause delays in physiological maturity in preterm babies,” he notes.

Niman spent a lot of time Tuesday also reviewing another study by researchers in the Hoosier State, this one by Hugo Ochoa-Acu±a and his colleagues at Purdue. It mined drinking-water-contaminant data to calculate when women in the state would have been most exposed to atrazine.

In a paper published last October in Environmental Health Perspectives, the scientists linked relatively high atrazine concentrations in the drinking water to which a woman had access late in pregnancy with an elevated chance that her baby would be born especially small for its gestational age.

Niman described this as “probably the strongest of the studies” that he reviewed on possible fetal risks for the SAP, because it included individual atrazine-exposure estimates, contained drinking-water-atrazine data over a period of years, and established birth weights — the outcome of concern — from state registries.

Such a study still can’t conclusively link atrazine to problems in babies, Niman acknowledged, but it points to where further research is warranted.

Tim Pastoor, principal scientist for Syngenta Crop Protection of Greensboro, N.C., disagrees. The studies that Niman reviewed “all have fundamental flaws," he said. For example, the increased incidence of birth defects that Winchester’s group found in spring, when atrazine is heavily used, could just as easily have been linked “with almost any other seasonal occurrence, including rainfall, lightning strikes, and tornadoes." Indeed, he noted in a prepared statement yesterday, “the same uptick in birth defects in spring months is seen throughout the United States, regardless of atrazine usage."

Counters Winchester, environmental contamination with atrazine can be found throughout most of the nation, as a recent USGS map illustrates. Even in areas that ostensibly use relatively little of this weed killer, he says — well outside the Corn Belt, for instance — atrazine is commonly found tainting water. Perhaps from its use on turf.

Or perhaps atrazine shows up far from where it was applied because its persistence allows it to move widely around the environment, posits Tyrone Hayes, a biologist at the University of California, Berkeley. This scientist, who has studied atrazine’s impacts on amphibians, said a USGS scientist, Perry Jones, told him that residues of the weed killer can travel long distances with the wind. Indeed, Hayes reports that Jones told him USGS “can measure atrazine in the rainwater in Minnesota that was applied in Kansas.”

Clearly, plenty of people value atrazine. EPA is now reevaluating the long-used weed killer to probe whether science confirms that babies and others aren’t suffering undue risks from this chemical’s continuing widespread use.


Environmental Protection Agency. 2010. Draft Framework and Case Studies on Atrazine, Human Incidents, and the Agricultural Health Study: Incorporation of Epidemiology and Human Incident Data into Human Health Risk Assessment. Docket ID: EPA-HQ-OPP-2009-0851(Feb. 2-5). [Go to]

Mattix, K.D., P.D. Winchester, L.R. Scherer. 2007. Incidence of Abdominal Wall Defects Is Related to Surface Water Atrazine and Nitrate Levels. Journal of Pediatric Surgery 42(June):947.

Ochoa-Acu±a, H., Carbajo, C. 2009. Risk of Limb Birth Defects and Mother’s Home Proximity to Cornfields. Science of the Total Environment 407(July 15):4447.

Ochoa-Acu±a, H., et. al. 2009. Drinking Water Herbicide Exposure in Indiana and Prevalence of Small-for-Gestational-Age and Preterm Delivery. Environmental Health Perspectives 117(October): 1619.

Villanueva, C., et. al. 2005. Atrazine in Municipal Drinking Water and Risk of Low Birth Weight, Preterm Delivery, and Small-for-Gestational-Age Status. Occupational and Environmental Medicine 62(June):400.

Winchester, P.D., Huskins, J., and Ting J. 2009. Agrichemicals in Surface Water and Birth Defects in the United States. Acta Paediatrica, 98(April): 664.

U.S. Geological Survey. 2009. USGS Releases Online Interactive Tool to Predict Atrazine in Streams Across U.S. (Aug. 20). [Go to]
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