Photo-Enhanced Toxicity in Amphibians: Synergistic Interactions of Solar Ultraviolet Radiation and Aquatic Contaminants

Amphibians experience a broad range of multiple environmental stressors that occur in natural systems. However, the impact of combinations of these stressors on amphibians are rarely examined. The effect of two stressors on amphibians, solar ultraviolet radiation (SUV) and environmental contamination, was investigated. To examine the interactive effects of SUV and environmental contaminants, Hyla venicolor and Rana sphenocephala were exposed in the laboratory to a carbamate insecticide and the water soluble fraction of a weathered petroleum in combination with various intensities of simulated solar radiation (SSR). The contaminants were tested at environmentally relevant concentrations. Synergistic interactions between SSR and these substances were observed during the exposures. Mortality of H. versicolor exposed to 2.51 mg/I carbaryl increased from 5% under control SSR conditions to 100% under low SSR irradiance (4 μ W/cm2). Exposure to a 10% solution of a water soluble fraction of petroleum under control SSR conditions was not lethal to R. sphenocephala; however under high SSR irradiance (17 μ W/cm2) a 5% water soluble fraction of petroleum was lethal. Relatively limited SSR irradiance is necessary to initiate photoenhanced toxicity, thus a range of amphibian habitats may be impacted by SUV. These studies indicate the importance of evaluating the interactive influence of environmental stressors present in amphibian habitats