Frogs, atrazine effects

More controversially, endocrine disruption as a consequence of exposure to the herbicide atrazine (2-chloro-4-ethylamine-6-isopropylamine-s-triazine), one of the most widely used herbicides in the world, has also been hypothesized to explain various adverse biological effects in frog populations in the United States. Exposure to atrazine in the laboratory at high concentrations, far exceeding those found in the natural environment, has been reported to induce external deformities in the anuran species Rana pipiens, Rana sylvatica, and Bufo americanus (Allran and Karasov 2001). Studies by Hayes et al. have suggested that atrazine can induce hermaphroditism in amphibians at environmentally relevant concentrations (Hayes et al. 2002 Hayes et al. 2003). Laboratory studies with atrazine also indicated the herbicide... 

Coady, K.K., Murphy, M.B., and Villeneuve, D.L. et al. (2004). Effects of atrazine on metamorphosis, growth, and gonadal development in the green frog (Rana clamitans). Journal of Toxicology and Environmental Health, Part A Current Issues 67, 941-957. 

Sullivan, K.B., and Spence, K.M., Effects of sublethal concentrations of atrazine and nitrate on metamorphosis of the African clawed frog, Environ. Toxicol. Chem., 22, 627, 2003. 

Hecker, M., J.-W. Park, M.B. Murphy, P.D. Jonens, K.R. Solomon, G. Van Der Kraak, J.A. Carr, E.E. Smith, L. Du Preez, R.J. Kendall, and J.P. Giesy (2005a). Effects of atrazine on CYP19 gene expression and aromatase activity in testes and on plasma sex steroid concentrations of male African clawed frogs (Xenopus laevis). Toxicol. Sci., 86(2) 273-280. 

In light of all of the lines of evidence, atrazine does not cause endocrine-modulated or reproductive effects in amphibians at small concentrations such as are found in the environment (Solomon et al., 2005). The USEPA recently reviewed the literature and a comprehensive laboratory study and concluded that atrazine does not affect gonadal development in amphibians (USEPA, 2007). Given that atrazine does not cause these responses, it is unlikely that other structurally related chlorotriazines cause responses in frogs however, no studies on reproductive or endocrine effects of other triazines on amphibians have been reported in the literature. 

There is compelling evidence on the effects of exposure to EDCs on wildlife. These include imposex of molluscs by organotin compounds," developmental abnormalities, demasculization, and feminization of alligators in Elorida by organochlorines, feminization of fish by wastewater effluent from sewage treatment plants, paper mills, and hermaphrodism in frogs from pesticides such as atrazine. ... 

Allran, J. Karasov, W. (2000). Effects of atrazine and nitrate on northern leopard frog Rana pipience) larvae exposed in the laboratory from posthatch through metamorphosis. Environ. Toxicol. Chem. V. 19, N2.ll, pp. 2850-2855. 

Orton, F., Carr, J.A. Handy, R.D. (2006). Effects of nitrate and atrazine on larval development and sexual differentiation in the northern leopard frog Rana pipiens. Environ Toxicol Chem. V. 25(1) p>p. 65-71. 

Changes in plasma corticosterone and thyroxine concentrations were reported in salamander larvae Ambystoma tigrinum) exposed to atrazine at concentrations of 75 and 250 g/L (29). The authors did not suggest that this was an atrazine-specific mechanism but rather that it was a conq>ensatory response to stress from an environmental contaminant. In addition, since die development of the laryngeal dilator muscle is dependent on both androgen and thyroid hormone, the fact that effects were not observed in male X, laevis in all but one of the studies conducted with atrazine supports the conclusion that atrazine did not disrupt thyroid hormone status in these frogs (17,19,27), Overall, there is no evidence that atrazine affects thyroid-mediated processes in amphibians. 

If and when consistent and robust responses to atrazine are identified in frogs, the mechanisms by which these effects are mediated should be elucidated. This will better allow the application of biomarkers to assess the significance of responses in the field situations and increase the precision and accuracy of extrapolation of effects to other an hibians and assessment of their relevance at the level of the population. 

Hayes, T.B., Stuart, A.A., Mendoza, M., et al., 2006. Characterization of atrazine-induced gonadal malformations in African clawed frogs Xenopus laeuis) and comparisons with effects of an androgen antagonist (cypterone acetate) and exogenous estrogen (17-estradiol) support for the demasculinization/femi-nization hypothesis. Environ. Health Perspect. 114 (S-1), 134-141. 

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