Occurrence and Effects of Endocrine-disrupting Chemicals in Frogs and Soil Samples

We analyzed the occurrence and effects of endocrine-disrupting chemicals in 2 species of frog, Yama-aka-gaeru (Rang ornativentris) and Nihon-aka-gaeru (Rang japonica), and in water and soil samples. Our aim was to determine the cause of malformation in Yama-aka-gaeru frogs that had been found with extra forelimbs. Frogs, not including malformed ones, and soil samples were collected at 3 sites: the study site where the malformed frogs had been found, and 2 reference sites where only normal individuals of both frog species were observed. We also performed a histological examination of the gonads of the frogs. We found significant levels of DDTs and oxychlordane in both species and soils collected at the study site. These chemicals are persistent and bioaccumulative. We did not detect less-stable chemicals such as simazine and atrazine. High concentrations of benzo (a) pyrene were detected in the soil samples at the study site, but not in the frogs. In both species the chemicals we detected occurred at significantly higher concentrations in males than in females; this difference was probably caused by transference of chemicals to the eggs. The chemical concentrations that we detected in the frogs were lower than the lowest levels reported to cause adverse effects. However, there was a significant negative correlation between DDT concentrations and testis size, and aspermatogenesis was demonstrated in some of the Nihon-aka-gaeru frogs. We suspect that endocrine-disrupting chemicals present in the eggs affect early embryogenesis.