Toxic Effects And Thyroid Disruption Of Bisphenol AF On Zebrafish Embryos And Larvae

Bisphenol AF(BPAF),which is a compound of fluorinated BPA and acts as an alternative to BPA,has been found ubiquitously in the environment(especially aquatic environment).BPAF has been proved as an endocrine disrupting compound(EDC)due to its much stronger estrogenic activity than BPA.BPAF almost exists everywhere and does harm to ecosphere and human being through various exposure pathways.However,the details about the toxicity and endocrine disrupting effects of BPAF remain largely unknow.Therefore,the toxicity and endocrine disrupting effects of BPAF have been becoming increasingly attractive and deserve further studied.The research was conducted by exposing zebrafish embryos and/or larvae to BPAF.The main research contents are as follows.(1)Exposing the embryos and larvae to BPAF directly at a acute level to test the susceptibility of zebrafish to BPAF during the embryos and larvae developmental stages.(2)Zebrafish embryo acute toxicity tests(OECD 236)combined with both techniques microinjection and dechorionation were carried out to investigate the role of chorion around embryos.(3)Exposing the embryos and larvae to BPAF directly at a subacute level to test the disruptive effects of BPAF on thyroid hormones and expression of the representative genes along the hypothalamus-pituitary-thyroid axis in embryos-to-larvae zebrafish.The main research results are as follows.1.During acute toxicity tests,malformation of zabrafish embryos was observed,including the pericardial edema,abnormal yolk sac,reduced heart rate,and cardiac arrest.The malformation rates of embryos exposed to BPAF at 2.00,2.50,3.00 mg/L for 96 h reached to 100%.Based on the malformation rate,the 24 h EC50 value of BPAF was 2.00 mg/L for the embryos.The 96 h LC50 value was 1.84 mg/L.2.During acute toxicity tests,the swim bladders of the larvae closed with 72 h exposure at all BPAF concentrations,except for 10%at 1.00 mg/L BPAF.The swim bladders inflation rates of the larvae in control groups were 100%.With the deepening intoxication,the pericardial edema,yolk sac edema,curvature of the spine,and cardiac arrest were observed in sequence for the larvae.Based on the pericardial edema,the 48 and 72 h EC50 values of BPAF were 1.76 and 1.56 mg/L for the larvae,respectively,and the 96 h LC50 was 1.77 mg/L.3.Accoding to the different responses of zebrafish embryos and larvae in acute toxicity tests,zebrafish larvae were more susceptible to BPAF exposure than zebrafish embryos.The pericardial edema of zebrafish larvae could be one of the best indicators responding to BPAF exposure.4.The tests were initiated with embryos respectively treated by microinjecting(MI)at blastula stage and dechorionating(DC)at pharyngula stage,and untreated(NT)embryos.During acute toxicity tests,the trend of mortality and malformation rates at different BPAF concentrations were MI-BPAF>NT-1>MI-ZR and DC>NT-2.The 96 h LC50 values of MI-BPAF,NT-1,DC and NT-2 were 1.61,1.68,0.27,1.30 mg/L,respectively.5.The 96 h LC50 values of the MI-BPAF and NT-1 groups are very similar,indicating that the treatment methods by direct exposure and microinjection have the similar results.It is suggested that the use of direct exposure method will be better to avoid the expensive embryonic microinjection method in further research work.6.The chorion acted a bit part at preliminary stage of zebrafish embryonic development and played a more and more important role as an effective barrier with the development of embryos.Meanwhile,zebrafish tended to more sensitive to BPAF exposure with embryos-to-larvae development.7.During subacute toxicity tests,the whole-body TT3,TT4,FT3 and FT4 contents of exposed embryos-to-larvae zebrafish decreased significantly and the expression of the target genes(tshfi,slc5a5,tg,ttr,diol,dio2,tra,tr?)along the hypothalamus-pituitary-thyroid axis disrupted,which were possibly associated with a deterioration of thyroid function.BPAF exposure triggered thyroid endocrine toxicity by altering the whole-body contents of thyroid hormones and changing the transcription of the genes involved in the hypothalamus-pituitary-thyroid axis in embryos-to-larvae zebrafish.8.The BPAF exposure level which can do harm to exposed zebrafish embryos and/or larvae was much higher than the BPAF level exposing in the environment.The zebrafish exposed to the environmental BPAF level(5 ?g/L)by short-term probably do not lead to the thyroid endocrine disruption.The information about toxic effects and thyroid disruption of BPAF on zebrafish,which acquired by carrying out the tests with zebrafish embryos and/or larvae at various development stages exposed to BPAF through different treatments,may provide references to the further research concerning biomonitoring and risk assessment of the treatment efficiency of the wastewater containing BPAF.