Effects of PCB 126 and Ammonia, Alone and in Combination, on Green Frog (Rana clamitans) and Leopard Frog (R. pipiens) Hatching Success, Development, and Metamorphosis

The Green Bay watershed in Wisconsin is polluted with polychlorinated biphenyls (PCBs), dioxin, heavy metals, ammonia, and over 100 organic contaminants. In this study we exposed embryos and larvae of two ranid species commonly occurring in the Green Bay ecosystem, the green frog (Rana clamitans) and the leopard frog (R. pipiens), to PCB 126 (3,3\u27, 4,4\u27, 5-Pentachlorobyphenil, nominal concentrations 0-50 μg/l, two control treatments: water plus 0.08% acetone as carrier for the PCB, water alone), unionized ammonia (0-2 mg/I), and mixtures of both contaminants. Exposure to PCB 126 did not cause significant mortality of embryos before hatching. However, exposure to unionized ammonia (NH3) concentrations in excess of 0.6 mg/I (green frogs) or 1.5 mg/I (leopard frogs) caused a decline in hatching success and an increase in prevalence of deformities. PCB 126 and NH3 in combination had a significant negative effect on hatching success. Survival of larvae was significantly reduced at the highest PCB concentration (50 mg/I) for both species. Few skeletal deformities were observed in tadpoles at this concentration, but the incidence of edema was significantly increased. A slowing of growth was also observed in anuran tadpoles exposed to PCB 126. NH3 exposure caused a decrease in the survival and growth of green frog tadpoles. When exposed to mixtures of both chemicals, green frog tadpoles showed a decrease in survival. However, growth was not affected. Fewer tadpoles metamorphosed with increasing PCB 126 and NH3 concentrations. In tadpoles exposed to PCB 126, tissue concentrations of PCB 126 at the end of the experiment increased with increasing nominal concentrations, ranging from 1.2-9600 ng/g wet weight. Our data indicate that anurans may not be particularly sensitive to NH3 as compared to many fish species, and that water quality criteria determined using data collected on fish species will be protective for many anuran amphibians. At high concentrations, PCB 126 and unionized NH3 affected both ranid species. However, no sublethal effects were apparent at water concentrations that occur in the Green Bay ecosystem