Reproduction Impairment And Endocrine Disruption In Adult Zebrafish (Danio Rerio) After Subchronic Exposure To TBOEP

In recent years,the continuous outbreak and spread of fire,has caused great damage of human life and property security.Organic phosphorus flame retardants(organophosphate flame retardants,OPFRs),which as substitutes of polybrominated biphenyl(polychorinated biphenyls,PCBs),polybrominated diphenyl ether(poly real brominated diphenyl ethers,PBDEs),are widely used in electronics,textile,decoration material,transportation and other industries around the world.Tris(2-butoxyethyl)phosphate(TBOEP)is widely used as a typical of OPFRs.Although neurotoxicity,developmental toxicity,reproductive toxicity,and systemic effects of TBOEP have been reported,limited information is currently available on reproduction impairment and the underlying mechanisms of TBEOP.The present study was conducted to evaluate the impact on reproduction function in zebrafish after subchronic exposure to TBEOP.Adult zebrafish pairs were exposed to TBOEP at concentrations of 0 ?g/L,5 ?g/L,50 ?g/L,and 500 ?g/L for 21 days.Reproductive performance and gonadal histology in zebrafish were examined after 21 days exposure.Endpoints of reproduction included exposure endpoint of accumulated eggs production per female fish,hatching and survival rate in offspring and egg diameter,Furthermore,plasma sex hormone levels in zebrafish were detected by ELISA kits.And RT-PCRs were performed to investigate transcription of genes along the hypothalamic-pituitary-gonadal-liver(HPGL)axis.The main results are as follows:1.Significant decreases of average number of accumulated eggs production and egg diameter were found,as well as hatching success and survival rates in offspring were found.2.Histological examination showed the percentages of immature oogonia and previtellogenic oocytes were significantly increased in ovary,while the percentage of mature vitellogenic oocytes and preovulatory were strongly decreased.In males,a significant increase in the percentage of spermatocytes was observed,however the percentage of spermatid was significantly decreased.Histological examination shows inhibition of oocyte maturation in females and retardation spermiation in males,respectively.3.Plasma concentrations of 17?-estradiol were significantly increased in both sexes of fish exposed to TBOEP(500 ?g/L),while increase of testosterone was observed only in male fish.In addition,significant decrease of T/E2 ratio was found in females at highest concentration group(500 ?g/L TBOEP),while significant increase of T/E2 ratio was found in males.4.Transcription levels of genes along the HPGL were significantly influenced by exposure to TBOEP in both male and female fish.Majority of genes in brain of both sex fish were significantly down-regulated,while cyp19 b gene was significantly up-regulated in brain of both sex fish.And most genes in gonad of both sex fish were significantly up-regulated,while cyp19 a gene was significantly down-regulated in brain of male fish.All genes were significantly up-regulated in liver of female fish.In summary,the results demonstrated that TBOEP could disturb the sex hormone balance by disturbing the HPGL axis,inhibit oocyte maturation in females and retardation spermation in males,eventually leading to disruption of reproductive performance and the development of progeny.