Figure 1.10 Comparative Experiments Look for Differences Among Groups

Figure 1.10 Comparative Experiments Look for Differences among Groups

In Figure 1.9, Hayes and colleagues took a laboratory approach to studying the effect of the herbicide atrazine on amphibian reproductive development. In the laboratory there was a clear effect of atrazine on the level of gonadal dysgenesis and testicular oocytes in male frogs. But what happens in the field? Is release of atrazine into the environment via herbicide application on crop fields actually detrimental to natural frog populations? To address this question Hayes and colleagues collected and euthanized 100 newly metamorphosed frogs from eight field locations from Utah to Iowa. Based on records of atrazine sales, the researchers were able to predict in advance the locations more likely to be contaminated with the herbicide. At each location, actual levels of atrazine were determined by water sampling and liquid chromatography/mass spectrometry analysis. All sites except site one had atrazine levels above the detection limit of 0.1 ppb. As with the laboratory experiments, Hayes and colleagues prepared and examined under the microscope gonadal tissue sections from 20 male frogs and a subset of female frogs per site. Male frogs from all sites except site one had testicular oocytes, and frogs from one site showed gonadal dysgenesis. In concordance with the laboratory experiments, reproductive abnormalities did not increase with higher levels of atrazine (above 0.2 ppb) at metamorphosis. Thus, both the laboratory and field studies taken together suggest a strong effect of atrazine at low levels. As a result of his research and work of other researchers suggesting a relationship between atrazine and human cancers of the breast and prostate, Hayes has become an outspoken advocate for restrictions on atrazine use. Although atrazine is now banned by the European Union, its use is still permitted in the United States, often with few controls. Despite roadblocks by powerful manufacturers, Hayes continues to reach out beyond the traditional realm of scientists to create awareness and push toward restrictions on the use of this herbicide.

Original Papers

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

Hayes, T., K. Haston, M. Tsui, A. Hoang, C. Haeffele, and A. Vonk. 2003. Atrazine-induced hermaphroditism at 0.1 ppb in American leopard frogs (Rana pipiens): laboratory and field evidence. Environmental Health Perspectives 111: 568–575.

Links

Site created by Dr. Tyrone Hayes with many useful links about atrazine and its effects

New York Times: Debating How Much Weed Killer Is Safe in Your Water Glass

Natural Resources Defense Council: August 2009 report on atrazine contamination

Home page of Dr. Hayes and laboratory
http://ib.berkeley.edu/research/interests/research_profile.php?person=85

African reed frogs, color change, and contamination

The Chronicle of Higher Education: Hayes research and atrazine manufacturer Syngenta

Journal of Young Investigators: For the Love of Frogs Featuring Dr. Tyrone Hayes