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(19-19) Multiple stressor effects on Canadian amphibian species: pH/ herbicide interactions. Edginton, Andrea1, Boermans, Herman*,1, Stephenson, Gerald1, 1 University of Guelph, Guelph, Ontario, Canada ABSTRACT- Aerially applied herbicides Vision [glyphosate (amine salt) + a polyethoxylated tallow amine surfactant] and Release (triclopyr butoxyethyl ester) are used in Northern Ontario for forest management. In this study, multiple stressor effects caused by acid deposition and herbicide exposure were studied using native Canadian species of amphibians, northern leopard frog (Rana pipiens), green frog (Rana clamitans), American toad (Bufo americanus) and the laboratory surrogate African clawed frog (Xenopus laevis). Life stage sensitivity of Gosner stage 8-10 (blastula) and Gosner stage 25 (first larval) were subjected to varying concentrations and a pH range of 4.5 to 8.5 using a central rotatable composite design. Embryonic exposures followed the FETAX (Frog Embyro Teratogenesis Assay - Xenopus) assay. Larval exposures protocols were developed with experimental units consisting of two litre aquariums containing one litre of pH buffered solution and ten organisms. Both tests were 96hr static renewal with a four day water only recovery for the larval assay. Endpoints were mortality, growth and malformations with an additional larval endpoint of behaviour. The four species of amphibians were equally sensitive to treatments. Thus, Xenopus appears to be an appropriate surrogate for native toxicity testing. The larval stage was the most sensitive life stage by a magnitude of ten which shows that both stages should be considered during testing. Lethal concentrations for larvae were within expected environmental levels. The pH interaction was significant with increasing toxicity at higher pH with Vision and a decreasing toxicity at higher pH with Release. The surfactant component significantly increased the toxicity of Vision over the glyphosate salt. Toxicokinetic studies are investigating the cause of these interactions. These results were used in a larger collaborative project integrating lab and field studies on multiple stressor effects on amphibians. Key words: amphibians, pH, herbicides, multiple stressors |
