Effects of 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD) on development of anuran amphibians

Abstract

AbstractWe exposed anuran eggs and tadpoles to vehicle control (0.7% acetone) or waterborne [3H]2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD) for 24 h (American toad, 0.003‐30 μg/L; leopard frog, 3 μg/L; green frog, 0.3‐100 μg/L) and subsequently raised them in clean water. Neither American toads nor green frogs exhibited TCDD‐related mortality, but leopard frogs showed significantly increased (10%) mortality over controls. Eggs and tadpoles eliminated TCDD relatively quickly compared with published data for other vertebrates, with t1/2 of 1 to 5 d (American toad), 2 to 7 d (leopard frog), and 4 to 6 d (green frog). Elimination rates were slowest for tadpoles fed nothing, fastest for those fed a low‐fat diet, and intermediate for those fed a high‐fat diet. Although not significant, American toads exposed to ⩾0.03 μg TCDD/L appeared to metamorphose earlier, and those exposed to higher TCDD treatments appeared to metamorphose at a larger body mass than controls. Comparisons of these results with studies of fish early life stages suggest that anuran eggs and tadpoles eliminate TCDD more rapidly and are 100‐ to 1,000‐fold less sensitive to its deleterious effects during development. These differences may be related to differences in metabolic rate, patterns of lipid storage and utilization, and aryl hydrocarbon receptor binding and signal transduction.