| Survivorship Patterns of Larval Amphibians Exposed to Low Concentrations of Atrazine Sara I. Storrs and Joseph M. Kiesecker Department of Biology, Pennsylvania State University, University Park, Pennsylvania, USA Abstract
Amphibians can be exposed to contaminants in nature by many routes, but perhaps the most likely route is agricultural runoff in amphibian breeding sites. This runoff results in high-level pulses of pesticides. For example, atrazine, the most widely used pesticide in the United States, can be present at several parts per million in agricultural runoff. However, pesticide levels are likely to remain in the environment at low levels for longer periods. Nevertheless, most studies designed to examine the impacts of contaminants are limited to short-term (~ 4 days) tests conducted at relatively high concentrations. To investigate longer-term (~ 30 days) exposure of amphibians to low pesticide levels, we exposed tadpoles of four species of frogs--spring peepers (Pseudacris crucifer) , American toads (Bufo americanus) , green frogs (Rana clamitans) , and wood frogs (Rana sylvatica) --at early and late developmental stages to low concentrations of a commercial preparation of atrazine (3, 30, or 100 ppb ; the U.S. Environmental Protection Agency drinking water standard is 3 ppb) . We found counterintuitive patterns in rate of survivorship. Survival was significantly lower for all animals exposed to 3 ppb compared with either 30 or 100 ppb, except the late stages of B. americanus and R. sylvatica. These survival patterns highlight the importance of investigating the impacts of contaminants with realistic exposures and at various developmental stages. This may be particularly important for compounds that produce greater mortality at lower doses than higher doses, a pattern characteristic of many endocrine disruptors. Key words: amphibian, atrazine, endocrine disruption, NMDRC, nonmonotonic dose-response curve. Environ Health Perspect 112:1054-1057 (2004) . doi:10.1289/ehp.6821 available via http://dx.doi.org/ [Online 25 March 2004]
Address correspondence to S.I. Storrs, University of Missouri, Division of Biological Sciences, 105 Tucker Hall, Columbia, MO 65211 USA. Telephone: (573) 882-1421. Fax: (573) 882-0123. E-mail: sisk95@mizzou.edu We thank M. Rubbo, L. Belden, T. Raffel, R. Mirza, J. Falkenbach, A. Schroeck, R. Semlitsch, M. Boone, and two anonymous reviewers for assistance. Financial support was provided by the National Institutes of Health/National Science Foundation Ecology of Infectious Disease Program (grant 1R01ES11067-01 to J.M.K.) . S.I.S. received support through a Teaching Assistantship from the Pennsylvania State University Department of Biology. The authors declare they have no competing financial interests. Received 27 October 2003 ; accepted 25 March 2004.
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