NRDC releases new atrazine report today

For our new 2010 report on atrazine water contamination, I have reviewed the studies on the environmental impacts and health effects of atrazine and many other agriculture chemicals. The findings confirm our 2009 report that showed widespread water contamination, but also provide a summary of the new science showing harmful impacts from atrazine. I have included studies of wildlife, of lab science, and of human epidemiology. The evidence just keeps growing. Atrazine shouldn’t be in our rivers, streams, or tap water.

The regulation of hazardous materials in the U.S. is generally based on the scientific dogma that the dose makes the poison: the notion that larger doses are more toxic than smaller doses.  This belief leads to the presumption that the chemical is “safer” at lower doses. For chemicals like atrazine that interfere with the development of critical organs or systems, such as the immune system and reproductive system, there is now a substantial amount of scientific proof that when exposure occurs at the same time that these critical systems are developing, even transient low-dose exposures can cause irreparable harm. That is, the timing of exposure may actually be even more critical than the dose.  For example, pre-birth exposure to mercury, at levels so low that effects are not detectable in a pregnant woman, will prevent proper connections between the brain cells of the fetus, resulting in lifelong alterations in brain structure and function (Grandjean et al, 2008).  Exposures to endocrine- (or hormone-) disrupting chemicals such as atrazine during critical windows of development have been shown to have permanent effects in lab animal studies (Colborn et al, 2006).  Some of these effects, such as infertility or cancer, may not be obvious until adulthood even though the exposure occurred during fetal or neonatal life.  This phenomenon has been demonstrated for atrazine in laboratory animals such as amphibians, where short exposures during early developmental stages have had long lasting or even permanent irreversible effects on adult behavior and longevity, including increased susceptibility to infection, alterations in survival behavior,  and reduced long-term survival (Rohr and McCoy, 2010).

In early 2010, well-known frog expert Dr. Tyrone Hayes published a startling study.  He reported that 10 percent of male frogs that were born and raised in water contaminated with only 2.5 ppb atrazine (that is, less than the federal allowable standard for drinking water of 3 ppb) grew up with female sex characteristics, including reduced levels of male testosterone, reduced sperm levels, and eggs in their testes (Hayes et al, 2010).  Even more disturbing, these atrazine-feminized males showed female mating behavior, attracted normal males, mated with them, and produced viable larvae that grew into male frogs.

A 2010 article published by University of South Florida researchers Rohr and McCoy analyzed the findings of over 125 independently published research studies of atrazine effects on freshwater fish and amphibians (Rohr and McCoy, 2010). Their meta-analysis found that many of the studies reported the same health outcomes, even though the studies were in several wildlife species and used different research methods.  In particular, atrazine affected the hormone systems of freshwater fish and amphibian species in most studies, including effects such as altered time of metamorphosis (delayed in some studies and accelerated in other studies), impaired sperm production, and abnormal gonadal development.  The consistent finding of endocrine disruption effects of atrazine across diverse species and in different independent studies strengthens the conclusions of each experiment and increases the scientific confidence that the findings are generally true.

New evidence links atrazine to poor birth outcomes in people.  A 2009 study found a significant correlation between prenatal atrazine exposure and reduced body weight at birth (Ochoa-Acuña et al, 2009). The authors reviewed the birth records of over 24,000 babies born in Indiana and localized each birth to the particular community water system where the mother lived. Their analysis showed that the mothers having the highest atrazine in their tap water for the duration of the pregnancy (above 0.7 ppb) also had the highest risk of having a baby with low birth weight, compared with the lowest exposed group (below 0.3 ppb).

Another 2009 study analyzed over 30 million births across the U.S. and reported an increased risk of birth defects associated with mothers who became pregnant between April and July, when pesticides in waterways are at their highest levels (Winchester et al, 2009). The authors reported that among the pesticides monitored in the waterways, the risk was most closely associated with atrazine contamination. While this study did not measure drinking water levels specifically, the fact that the risk is highest when conception is timed with peak pesticide contamination in rivers and streams raises red flags.

According to EPA’s own assessment in 2006, residential uses of atrazine may lead to unsafe exposures for homeowners who apply the products to their lawns (EPA atrazine RED, 2006). EPA also expressed concern that children who play on atrazine-treated lawns are also at risk for potentially unsafe exposures.

People can drink filtered water to remove atrazine. What about wildlife? Let's cancel further use of this widespread water contaminant.

About the Authors

Jennifer Sass

Senior Scientist, Federal Toxics, Health and Food, Healthy People & Thriving Communities Program

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