In 2002, a young Berkeley professor, Tyrone Hayes, reported that deformed frogs were most prevalent in farm ponds in counties across the United States where the herbicide atrazine was sold in the largest quantities. Atrazine is a widely used herbicide, especially in corn, to control weeds at planting time. Atrazine affects the photosynthetic mechanism in plants, but its molecular structure is an endocrine disruptor, inasmuch as it resembles the growth hormones of other organisms, including frogs and potentially humans.

Hayes has spent the past 20 years investigating atrazine’s effects on amphibians, finding that at levels of less than a part per billion, atrazine produced growth abnormalities, including the “demasculinization” of male frogs. Needless to say the work was hotly contested, especially by Syngenta (now owned by ChemChina Inc.) who was the major producer. Citing the precautionary principle, the European Union banned the use of atrazine in 2004, but the U.S. Environmental Protection Agency has approved atrazine for continued use in the U.S. Various studies attempting to reproduce Hayes’work have reported somewhat inconsistent results, but deformed frogs are still observed in many areas without unequivocal explanation.

One of the problems with atrazine is that it is mobile in the environment. It is easily soluble in water, so it is found in runoff and groundwater from fields of application. It is sparingly volatile, but it is often found in rainfall downwind of use. A just-published study has found atrazine in 32% of 900 waterbodies that were sampled across the U.S., at levels of 0.17 parts per billion when detected—within the range that Hayes has found harmful to amphibians. While most atrazine is decomposed by soil microbes within days, a certain fraction can persist for years, accounting for its persistence in groundwater.

Atrazine is a classic example of the tradeoffs we face in environmental issues: a chemical that is useful to the farmers who grow our food, enormously profitable to the companies that produce it, yet potentially threatening to humans who are directly and inadvertently exposed. Is its continued use a risk to human health, or are the risks to food prices and corporate profits more important? The producers are few, focused, with deep pockets, and the greatest influence with regulators.

The frogs may be speaking to us, but who speaks for the frogs?

References

Beaulieu, M., H. Cabana, Z. Taranu, and Y. Huot. 2020. Predicting atrazine concentrations in waterbodies across the contiguous United States: the importance of land use, hydrology, and water physiochemistry. Limnology and Oceanography doi: 10.1002/lno.11568

Burt, G. 1974. Volatility of atrazine from plant, soil and glass surfaces. Journal of Environmental Quality 3: 114-117.

Dankwardt, A., S. Wust, W. Elling, E.M. Thurman, and Bertold Hock. 1994. Determination of atrazine in rainfall and surface water by enzyme immunoassay. Environmental Science and Pollution Research 1: 196-204.

Hayes, T., K. Haston, M. Tsu, A. Hoang, C. Haeffele, and A. Vonk. 2002. Herbicides: feminization of male frogs in the wild. Nature 419: 895-896

Hayes, TB; Khoury, V; Narayan, A; Nazir, M; Park, A; Brown, T; Adame, L; Chan, E; et al. 2010. Atrazine induces complete feminization and chemical castration in male African clawed frogs (Xenopus laevis). Proceedings of the National Academy of Sciences of the United States of America. 107 (10): 4612–7.

Johnson, P.T.J. et al. 2007. Aquatic eutrophication promotes pathogenic infection in amphibians. Proceedings of the National Academy of Sciences 104: 15781-15786