Date of Award

12-2008

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Wildlife and Fisheries Biology

Advisor

Bowerman, William W

Committee Member

Rodgers, Jr , John H

Committee Member

Yarrow , Gregory K

Abstract

The contribution of incidental exposures of Roundup¨ herbicide to amphibian declines can be evaluated with carefully designed laboratory tests. Sensitive, sentinel species of larval anurans were exposed to two formulations: the original formulation of Roundup¨ and Roundup WeatherMax¨ in 96-hour acute, aqueous and water-sediment tests. An experimental design was developed that considered and held constant relevant laboratory conditions which produced precise, replicable data. Experimental design factors decreased variability and increased precision by considering and incorporating the following: 1) range-finding tests; 2) reference toxicity tests; 3) the relative sensitivity of the species tested; 4) differences in formulation; 5) the number of concentrations; 6) the amount of replication; 7) test duration; 8) verification of exposures; and 9) other conditions necessary for acceptability of tests. Responses of larval anurans to the two formulations were discerned in unconfounded aqueous toxicity testing, and although these data are inherently conservative, tests provided information regarding potency of the two formulations which isolated the exposures of interest. Responses of Hyla chrysoscelis, Bufo fowleri, and Rana catesbeiana differed significantly between the two formulations (p¨ and the proprietary surfactant in Roundup WeatherMax¨. We were able to discern the importance of competing ligands such as sediments in laboratory toxicity testing by conducting controlled experiments contrasting responses of B. fowleri, H. chrysoscelis, R. pipiens, R. sphenocephala, R. catesbeiana, and R. clamitans in water-only versus sediment-and-water exposures. Sediment significantly altered the toxicity in all cases except for H. chrysoscelis exposures to Roundup WeatherMax¨. We suggest that bioavailability was altered in the presence of sediments due to the majority of significantly different potency slopes between aqueous and water-sediment exposures. From these data, sediments have a significant role in decreasing the toxicity by altering bioavailability in the majority of exposures. Margins of safety for anurans would increase further in actual field situations due to the presence of environmental ligands. Data from these laboratory tests provide a predictive model for future field and semi-field experiments.

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