Frog Sex-Change Claims Flawed
October 30, 2002
Jumping to conclusions could hurt farmers and the environment
Contact: Alex Avery of the Center for Global Food Issues, 540-337-6354, or aavery@rica.net.
Churchville, VA, Oct 30, 2002 - A recent study by Tyrone Hayes and colleagues published in Environmental Health Perspectives and soon to be published in Nature, purports that low concentrations of the herbicide atrazine cause hermaphroditism in North American frogs. The study suffers from methodological shortcomings and data inadequacies that make data interpretation difficult and call into question the authors’ conclusions. Scientific research favorably reviewed by the Center for Global Food Issues released this week also finds this study to be flawed (see paper following).
Prematurely accepting the authors’ conclusions as fact could have profound effects on farms where atrazine is used to save topsoil, protect water quality and conserve precious natural resources. Indeed, the vast majority of published scientific research contradicts the findings of this one report.
American farmers have successfully used atrazine to increase crop yields while using less land and fewer resources, such as fossil fuel. Herbicides such as atrazine allow farmers to use no-tillage weed control methods, which reduce soil erosion by 65-95%. No-till methods, using selective herbicides such as atrazine for weed control rather than mechanical methods, have prevented the erosion of untold billions of tons of topsoil and significantly improved the water quality in our nations rivers and streams. These methods enhance the sustainability of our farms and have been endorsed by agricultural heroes like Norman Borlaug, environmentalists such as Greenpeace co-founder Dr. Patrick Moore, and Nobel Prize Winner Oscar Arias (see http://www.highyieldconservation.org/).
Hermaphroditism in frogs is a well-known phenomenon which has been observed for decades in all parts of the world. There are many reports of frog hermaphroditism occurring prior to the use of atrazine and in areas where atrazine has never been used.
According to Alex Avery, Director of Research and Education at the Center for Global Food Issues (CGFI), many other variables likely play a role in amphibious hermaphroditism, including temperature, parasites, viruses, and other natural factors. “Hayes’s latest study is reminiscent of recent peer-reviewed studies that tried to link pesticides to frog limb abnormalities, but were debunked after further studies found natural parasitic flatworms to be the cause,” Avery said. “Until this work has been corroborated by other labs, it must be considered preliminary and inconclusive.”
Above Referenced Paper Follows.
Comments on the paper entitled “ATRAZINE-INDUCED HERMAPHRODITISM AT 0.1 PPB IN AMERICAN LEOPARD FROGS (RANA PIPIENS): LABORATORY AND FIELD EVIDENCE” BY HAYES, T., HASTON, K., TSUI, M., HOANG, A., HAEFFELE, C., AND VONK, A. ENVIRONMENTAL HEALTH PERSPECTIVES (HTTP://DX.waOI.ORG, ONLINE 10/23/02).
The field of environmental toxicology is a maturing science with well-established principles for evaluating the response of organisms to toxicants in laboratory studies and then evaluating hypotheses at the field level. The recent paper by Hayes et al. does not aspire to the fundamental principles of laboratory ecotoxicological studies as applied to field interpretation. For instance, Hayes et al. attempt to associate the well-documented phenomenon of hermaphroditism in frogs with exposure to atrazine under laboratory conditions and in the field. There are many shortcomings in their study design that make interpretation of the data difficult and raise serious concerns about their conclusions:
- Interpreting the laboratory effects reported by Hayes et al. is difficult, as data on mortality and number of males analyzed are not presented. The authors do not report whether the observed abnormalities were equally represented across treatment tanks. In fact, the authors make no attempt to statistically analyze the data, and there is no indication of the level of variation between treatments.
- Although the authors claim that effects were observed at nominal concentrations of 0.1 ppb, the actual concentrations in the exposure tanks are not reported.
- Although the authors attempt to explain the laboratory results by invoking a u-shaped (or inverted) dose response, the authors only examined two concentrations of atrazine, making it impossible to draw conclusions regarding a concentration-response relationship. This is particularly true when exploring a u-shaped dose response curve.
- Like the laboratory work, the field studies suffer from major inadequacies:
- First, the authors attempt to relate atrazine concentrations measured in July when the frogs were sampled to developmental events that took place months earlier. Because field sites were not sampled for atrazine during the period of larval development, there is no way to link effects on gonadal differentiation, which occurs during larval life, to concentrations of the herbicide that are measured much later.
- Secondly, even if there is a relationship between concentration measured at sampling time and earlier exposures, there are major inconsistencies in the data that argue against atrazine as the cause of the gonadal abnormalities reported. In Fig. 11, atrazine concentrations are identical at sites 2 and 3, but there is approximately a 9-fold difference in the incidence of gonadal abnormalities between the two sites.
- Furthermore, the pattern of gonadal abnormalities observed in the field does not agree with what was observed in the laboratory studies. In the laboratory studies, gonadal dysgenesis was the most frequently occurring abnormality observed in atrazine-exposed tadpoles, but gonadal dysgenesis was observed at only one field site (site 5).
- Statements by Hayes et al. that atrazine may be linked to declining amphibian populations seem to contradict their own finding that juvenile frogs were abundant at all of their collection sites. The suggestion that these animals are resistant to atrazine is pure speculation and is not supported by any empirical data.
- The observation that the incidence of hermaphrodites was greatest in Carbon County WY is inconsistent with the reported use of atrazine. Neither Carbon County, nor any of the counties in the surrounding vicinity, including Jackson County (the North Platte origin), Rout, Grand and Larimer counties in CO, nor the 2 counties West and East (Sweetwater, Albany) reported atrazine use in the 1999-2001 period.
- Many species within the genus Rana have an atypical process of sex differentiation. The fact that Hayes et al. have never observed hermaphroditism in 7000 frogs from several sites within the U.S. is inconsistent with the many reports of hermaphroditism and sex reversal in North American, European, and Asian populations of Rana, with many reports of these phenomena occurring decades before the commercial introduction of atrazine.
The occurrence of hermaphrodites in the genus Rana has been previously observed, with the earliest reports appearing decades before the introduction of atrazine. Recent studies in other frog species have found no significant relationship between the occurrence of hermaphrodites and the historical and spatial usage patterns of this herbicide. These observations, combined with the inconsistencies in the data reported by Hayes et al., suggest that geographical differences or possibly other stressors are likely potential causes of the hermaphroditism observed in wild-caught Rana pipiens.
Signed,
Atrazine Endocrine Ecological Risk Assessment Panel, Ecorisk, Inc., Ferndale, Washington
Panel members:
James A. Carr, Ph.D.
Associate Professor, Department of Biological Sciences,
Texas Tech University, Lubbock 79409
806-742-2724
Louis Du Preez, Ph.D.
Associate Professor, Associate Professor in Zoology, School of Environmental Sciences and Development, Potchefstroom University for CHE, Private Bag X6001,
Potchefstroom 2520, South Africa
011-27-18-299-2372
John P. Giesy, Ph.D.
Professor, Department of Zoology, National Food Safety and Toxicology Center,
Institute for Environmental Toxicology,
Michigan State University, East Lansing 48824
517-353-2000
Tim S. Gross, Ph.D.
USGS-BRD, Florida Caribbean Science Center, Gainesville 32653
352-378-8181 x323
Ronald J. Kendall, Ph.D.
Professor and Chair, Department of Environmental Toxicology, and Director, The Institute of Environmental and Human Health, Texas Tech University, Lubbock 79416
806-885-4567
Ernest E. Smith, Ph.D.
Assistant Professor, of Environmental Toxicology, and Research Scientist,
The Institute of Environmental and Human Health, Texas Tech
University, Lubbock 79416
806-885-0233
Keith R. Solomon, Ph.D.
Professor, Centre for Toxicology and Department of Environmental Biology,
University of Guelph, Ontario Canada NIG 2W1
519-837-3320
Glen Van Der Kraak, Ph.D.
Professor and Chair, Department of Zoology,
University of Guelph, Ontario Canada NIG 2W1.
519-824-4120 x3598
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