Amphibians, 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... 

Howe, G.E., R. Gillis, and R.C. Mowbray. 1998. Effect of chemical synergy and larval stage on the toxicity of atrazine and alachlor to amphibian larvae. Environ. Toxicol. Chem. 17 519-525. 

Reviews by the Australian Pesticides and Veterinary Medicines Authority (APVMA) in 1997 and again in 2004 concluded that properly used and applied, atrazine and simazine are safe for humans and the environment [Australian Pesticides and Veterinary Medicines Authority (APVMA), 1997, 2004], The APVMA also reviewed additional data on potential effects of atrazine on amphibians and concluded that taken together, these data indicate that it is unlikely that atrazine is impacting adversely on populations of Australian amphibians at current levels of exposure (APVMA, 2004). 

USEPA (2007). White paper on the potential for atrazine to affect amphibian gonadal development, in support of an Interim Reregistration Eligibility Decision on Atrazine. Submitted to FIFRA Scientific Advisory Panel, October 9-12. Office of Prevention, Pesticides, and Toxic Substances, Office of Pesticide Programs, Environmental Fate and Effects Division. Washington, DC. September 21. 

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. 

Allran, J. Karasov, W. (2001) Effects of atrazine on embryos, larvae and adults of anuran amphibians. Environ. Toxicol. Chem. V. 20, Nq. 4, pp. 769-775. 

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. 

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