Study On Toxic Effects Of New Organophosphate Flame Retardant On Zebrafish (Danio Rerio) And Its Adverse Outcome Pathway (AOP)

Organophosphate flame retardants(OPFRs) as the substitute for polybrominated diphenyl ethers(PBDEs), its amount of usage and concentration detected in the environment is increasing in recent decade,however, the environmental toxicology data are still deficient. Therefore, this study systematically researched the acute, embryo, sub-chronic and reproductive toxicity effects on zebrafish as the model organism and trichloropropylphosphate(TCPP) the representative of OPFRs as the target compound. Also,the ability of endocrine disruption was assessed based on the indicative enzyme aromatase activity and relevant manipulation gene expression analysis. An Adverse Outcome Pathway(AOP) framework related to the decline of fecundity by OPFRs was proposed according to the different biological indicators and available references. The major results were summarized as follows:(1) In acute toxicological test, 96h-LC50 of TCPP to zebrafish and rare minnow were 47.06 and 41.47mg·L-1 respectively whereas that to 2,3-dichloro-propano phosphate(TDCPP) as the comparison were13.13 and 10.24 mg·L-1 respectively. In comparison, the toxicity of TCPP to fish is weaker, but the water solubility is higher than TDCPP's. So it will probably have more risk for environment.(2) The result from embryo toxic tests showed that TCPP inhibited the embryo development under high exposure level, and extended the incubation time led to abnormal larvae after hatch, such as campylorrhachia and pericardial cyst.(3) The results of sub-chonic toxic test showed that the no observed effect concentration(NOEC) of mortality of TCPP to zebrafish is 1.0 mg·L-1 and that of toxicity symptom is 0.2 mg·L-1. In addition, the results from the analysis of aromatase enzymatic activity, VTG concentration and the expression level of hypothalamus-pituitary-gonad axis control genes showed that TCPP has the effects of endocrine disruption,which will lead to the production of VTG from liver of male zebrafish increased and the sex hormone regulation system disordered.(4) From the short term reproduction assay, when exposed to the low concentration of TCPP it was found that the fecundity of zebrafish was declined along with the increase of TCPP concentration.Moreover, from histopathologic examination it was found that TCPP could affect the development of primary oocyte in high concentration.(5) Based on the experimental results set forth in this study and available references as well as combined with computer simulation, it is speculated that the initial action site for OPFRs-AOP possibly located in hypophysis. Whenever TCPP triggered the molecular initial event then key event I occurred viz.the hypophysis could not recognize received manipulating signal or made wrong response thus interrupted the normal functions of whole endocrine system afterwards resulting series biological chain reactions. The normal development of oocyte in ovary was restricted and the number of oocyte decreased, which lead to the decline of fecundity in female. In male, the dysfunction of hypophysis leads to live producing VTG abnormally into the blood. Male fish have feminization tendency and the quality of sperm was affected,which is also one of the factor to decrease fecundity.These results could provide scientific basis for the ecological/environmental assessments and proper management of organophosphate flame retardants. The proposed TCPP adverse outcome pathway framework in this thesis would also provide the direction and new ideas for further research on the toxic mechanisms of OPFRs.