Date of Award

12-2008

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Wildlife and Fisheries Biology

Advisor

Bowerman, William

Committee Member

Rodgers , John

Committee Member

Yarrow , Greg

Abstract

Roundup¨ has been implicated as a possible cause for the declining amphibian populations in North America. Carefully designed laboratory toxicity tests are crucial for accurate risk assessment of the responses of anuran populations to incidental exposures of Roundup¨ herbicides. The overall objective of these studies was to determine the response of North American anuran species to exposures of Roundup¨ formulations and components to support or refute the claim that Roundup¨ is a factor in amphibian decline in North America. Aqueous 96 hour static non-renewal laboratory tests were utilized to (1) evaluate the effectiveness of copper sulfate as a reference toxicant in larval anuran toxicity testing for six species of anurans; (2) compare the toxicity of two formulations of Roundup¨ containing different salts of glyphosate and surfactant mixtures for three larval ranid species; (3) determine the relative contribution of the two components in the original formulation of Roundup¨ to the toxicity of the formulation for five species of anurans. Our results indicate that copper sulfate can serve as a suitable reference toxicant in larval amphibian toxicity testing because low concentrations of copper can be used to elicit significant responses in larval anurans which allow for detection of differences in sensitivities between species and accessions of organisms. The results of our study on the comparative toxicity of two formulations of Roundup¨ herbicides indicate that Roundup WeatherMax¨ is more toxic to larval anurans than the original formulation of Roundup¨. Many Roundup¨ formulations, including WeatherMax¨ have proprietary mixtures of surfactants making it difficult to evaluate the source of the toxicity of the formulation, but we can speculate that the difference in surfactant between the two formulations is the cause for the difference in toxicity. Larval amphibian toxicity testing procedures should be standardized to facilitate spatial and temporal comparisons between species, acquisitions, and laboratories. Our studies also suggest the importance of evaluating whole formulations in risk assessments rather than just the active ingredient to ensure safety for non-target species. The best way to mitigate risk to anuran species could be to control the surfactant portion of Roundup¨ formulations.

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