Endocrine Disrupting Effects Of Tributyltin (TBT) At Environmentally Relevant Concentrations On Xenopus

Tributyltin (TBT) is one of the most toxic substances which are introduced into the marine environment. TBT is also a known endocrine disrupting chemical. The populations of amphibians have declined greatly since 1980s',and chemical pollution is regarded as one of the main reasons leading to the decline of amphibian populations. In the present paper, endocrine disrupting effects of TBT was studied using Xenopus as the model species.Firstly, the Amphibian Metamorphosis Assay (AMA) was used to study the effects of TBT on the growth, development and thyroid histology of X. laevis tadpoles. The results showed that 12.5-200 ng-L-1 TBTCl retarded the development of tadpoles greatly, decreased the number of follicle and induced thyroid follicle cell hyperplasia. These results suggest that TBT was a thyroid hormone disrupting chemical.Secondly, the Xenopus Completed Metamorphosis Assay (XCMA) was conducted to study the effect of TBT on the growth, metamorphosis and gonad histology of X. laevis.The results showed that 10 and 100 ng-L-1 TBTC1 led to various malformations of gonad, including:intersex, segmental aplasia and multiple ovary cavities.The intersexed gonad showed an ovarian cavity with a male testis tissue like structure. The sex ratio (female/male) was 1.5:1 in control group,while they were 1.1:1 (10 ng-L-1) and 0.88:1 (100 ng-L-1) in treatment groups. These results showed that TBT was an anti-androgen.Thirdly, the junior X. laevis frogs were exposed to 50 and 100 ng-L-1 TBTCl. The experiment lasted for 3 months for the observations of the growth and accumulation of lipid. The results showed that 100 ng-L-1 TBTC1 increased the body weight and induced the accumulation of fat droplets in the liver in X. laevis.These results suggest that TBT showed obesogen effects on X.laevis.Finally, the Frog Embryo Teratogenesis Assay-Xenopus (FETAX) was applied to detect the developmental toxicity of TBT. TBT significantly decreased the survival rate, reduced the body length and retarded the development of embryos after 24,36 and 48 h of exposure. TBT also led to malformations in all embryos, which suggests that TBT is a strong teratogen. Thyroid hormone signaling might be one of the mechanisms involved in TBT-mediated teratogenicity inâ…©. tropicalis embryos.In brief, these assays indicate that TBT has thyroid hormone, sex hormone and obesogen disrupting effects. TBT affects the survival and adaptation of Xenopus greatly. TBT might be one of the reasons leading to the decline of amphibian embryos.