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ToxSci Advance Access originally published online on November 13, 2008
Toxicological Sciences 2009 107(2):376-384; doi:10.1093/toxsci/kfn232
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© The Author 2008. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org.
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Does Atrazine Influence Larval Development and Sexual Differentiation in Xenopus laevis?

Werner Kloas*, Ilka Lutz*, Timothy Springer{dagger}, Henry Krueger{dagger}, Jeff Wolf{ddagger}, Larry Holden§ and Alan Hosmer,1

* Leibniz-Institute of Freshwater Ecology and Inland Fisheries, 12587 Berlin, Germany {dagger} Wildlife International Ltd., Easton, Maryland 21601 {ddagger} Experimental Pathology Laboratories, Reston, Virginia § Sielken and Associates, Bryan, Texas 77802 Syngenta, Crop Protection Inc., Greensboro, North Carolina 27409

1 To whom correspondence should be addressed at 410 Swing Road, Building L, Greeensboro, NC 27409. Fax: (336) 632-7581. E-mail: alan.hosmer{at}syngenta.com.

Received June 20, 2008; accepted October 30, 2008


  Abstract

Debate and controversy exists concerning the potential for the herbicide atrazine to cause gonadal malformations in developing Xenopus laevis. Following review of the existing literature the U.S. Environmental Protection Agency required a rigorous investigation conducted under standardized procedures. X. laevis tadpoles were exposed to atrazine at concentrations of 0.01, 0.1, 1, 25, or 100 µg/l from day 8 postfertilization (dpf) until completion of metamorphosis or dpf 83, whichever came first. Nearly identical experiments were performed in two independent laboratories: experiment 1 at Wildlife International, Ltd. and experiment 2 at the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB). Both experiments employed optimized animal husbandry procedures and environmental conditions in validated flow-through exposure systems. The two experiments demonstrated consistent survival, growth, and development of X. laevis tadpoles, and all measured parameters were within the expected ranges and were comparable in negative control and atrazine-treated groups. Atrazine, at concentrations up to 100 µg/l, had no effect in either experiment on the percentage of males or the incidence of mixed sex as determined by histological evaluation. In contrast, exposure of larval X. laevis to 0.2 µg 17β-estradiol/l as the positive control resulted in gonadal feminization. Instead of an even distribution of male and female phenotypes, percentages of males:females:mixed sex were 19:75:6 and 22:60:18 in experiments 1 and 2, respectively. These studies demonstrate that long-term exposure of larval X. laevis to atrazine at concentrations ranging from 0.01 to 100 µg/l does not affect growth, larval development, or sexual differentiation.

Key Words: atrazine; amphibians; endocrine; sexual differentiation; development; Xenopus laevis.


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