Effect of Oral Exposure to Polychlorinated Biphenyls (PCBs) on the Development and Metamorphosis of Two Amphibian Species (Xenopus laevis and Rana temporaria)

Tadpoles of the South African clawed frog Xenopus laevis and the European common frog Rana temporaria were either dosed with the technical PCB mixture, Clophen A50, the PCB congener 126, or 2-mercapto-1-methyl-imidazole, a known goitrogen, and effects on larval development and metamorphosis were examined. Dosing was initiated prior to the thyroid hormone-dependent development stage and lasted until completed metamorphosis. Tadpoles of both species showed a dose-dependent increase in mortality as a result of long-term oral exposure to PCB-spiked diets, but X. laevis exhibited no mortality after 10 d of exposure of stage 49 tadpoles. In terms of developmental malformations, a dose-response effect was observed for tail and eye anomalies only in X. laevis. Froglets in the feeding experiment were lighter and the percentage of metamorphosed animals was lower compared with the control group. Concentrations of PCBs accumulated significantly in all exposed groups.