Toxic Effects Of Tributyltin On Xenopus Laevis And Carassius Auratus

Tributyltin(TBT)is widely used in antifouling paints and regarded as one of the most toxic substances which are introduced into the marine environment.TBT-based antifoutants should not be present in all the ships and yards after 2008,which will make the contamination of TBT in the marine environment under control.However, TBT is still used as bactericide and antiseptics.Therefore,it is very important to enhance ecotoxicological research of TBT in freshwater organism.Larval African clawed frogs(Xenopus laevis)were exposed to low dose of tributyltin(25 ng·L^-1TBTCl)for 2 months for thyroid histology observation.One month after exposure,TBT could induce the depletion of colloid and vacuolation. Two months after exposure,the incidence of follicle malformation also significantly increased,the relative transverse thyroid gland area and follicle area decreased sharply, and the number of follicle did not show any significant changes.Neither hypertrophy nor hyperplasia was observed between exposure groups and control.Therefore,the shrink of thyroid gland was arisen from the reduction of follicle area but not follicle number,and the depletion of colloid and follicle malformation was nothing with hypertrophy or hyperplasia.This study indicates that the low concentration of TBT can heavily damage thyroid histology of X.laevis,and TBT can be regarded as one of thyroid disrupting chemicals(TDCs).In the same experiment above,the histology of gonad was also observed.There were no obvious differences in the results between the treatment groups and control ones.This indicated that TBT showed no significant reproductive disrupting effects at low dose.In the same experiment above,the histological and ultramicro structure were also observed in the liver of Xenopus laevis.TBT could induce the change of ultramicro structure with the increase of fat droplets and aggrandizement of intercelular space. This indicated TBT could damage the liver.In addition,goldfish(Carassius auratus)were exposed to 1μg·L^-1and 0.1μg·L^-1 TBTCl for 28 days.The activities of acetylcholinesterase(AChE)and monoamine oxidase(MAO)were detected in the liver and brain.No significant differences were observed between the treatment groups and the control ones.Therefore,no obvious points could be stated on the neurotoxicity from the present study.In brief,these results indicated that TBT could affect the thyroid system of X. laevis and could be regarded as a thyroid disrupting chemical.TBT showed no obvious reproductive toxicology and showed slight damage to liver in X.laevis. Further study is needed in neurotoxicity of TBT in fish.TBT is one of the most typical endocrine disrupting chemicals and has received high attention in the freshwater environment.In addition,emerging endocrine disrupting effects related to thyrotoxicity and obesogens were revealed.Therefore,more studies should be enhanced on the ecotoxicity in freshwater and the mechanisms of endocrine disruption.