Effects of polychlorinated biphenyl exposure on development and sexual differentiation in ranid tadpoles

The effects of AroclorRTM1242 exposure on developing amphibians were examined by exposing southern leopard frogs, Rana sphenocephala, to a contaminated diet throughout the larval period. Treatment groups consisted of an untreated control, a solvent control, 17beta-estradiol, and three PCB doses (10, 100, and 1000 mug/g). PCB accumulation and biotransformation were examined. Effects of PCB exposure on metamorphosis and sexual differentiation were assessed. PCB accumulation was not statistically different between the egg masses. Levels of PCBs in the tissues differed in a dose related manner. Within treatments, body weight appeared to be the major factor correlated with PCB concentration. Congener patterns varied between AroclorRTM1242 and tadpole tissues. Hydroxybiphenyls were not detected in individual tadpoles, but were present in pooled samples. Mortality was similar among the treatment groups. The untreated food control had slightly higher mortality. The effects of AroclorRTM 1242 exposure differed between the egg masses. From the first egg mass, there were no treatment differences in the proportion of survivors metamorphosing. Treatment with 17beta-estradiol affected sexual differentiation relative to the controls. Exposure to AroclorRTM1242 had no effect. This may be due to the nature of gonadal maturation in this population, which was entirely female. In the second egg mass, PCB treatment was associated with an increased rate of metamorphosis in the highest dose. The high dose significantly (alpha = .05) altered sexual differentiation relative to the solvent control (88% female). This effect was similar to 17beta-estradiol treatment (94% female). Exposure to high and medium doses of PCBs produced five individuals with asynchronous gonads. The effect of body weight on PCB levels may be a result of greater ingestion of the contaminated diet by larger animals, relative to their smaller siblings. The apparent stimulation of metamorphosis in the second egg mass by PCB exposure may be due to an endocrine disrupting effect on the corticosterone stress axis. A thyroid-mediated mechanism of effect is also possible. While the effects on sexual differentiation may be due to estrogenic activity, a corticosterone-like effect cannot be ruled out. Higher level endocrine function, such as feedback regulation, could also be affected