Toxicity Effects On Zebrafish Larvae Follo-Wing Embryonic Exposure To Chlorinated Paraffins And Hexabromocyclododecane

Chlorinated paraffins (CPs) and hexabromocyclododecane (HBCD) are two flame retardants that received much attention recently in the environmental field, and the basic research data about their characteristics of distribution, level of pollution and the possible impacts have been increased. In this study, zebrafish (Danio rerio) embryo was used as an animal model to evaluate the toxic effects of CPs and HBCD, and their potential toxic mechanism on fish were investigated through pathological and optical microscopy methods.Following embryonic exposure to eight commercial chlorinated paraffins(CPs), the result showed chlorinated paraffins could not lead to mortality of embryos after7days embryonic exposure in1.0,5.0,10,20mg/L groups and no significant effects were observed on hatching rate among all groups, while deformity effects of gas bladders of zebrafish larvae were observed in groups of certain kinds of chlorinated paraffins and as the concentration of the chlorinated paraffins increased, deformity of gas bladders of zebrafish larvae increased, with an obvious dose-response relation. Besides, four kinds of non-chlorinated short chain paraffins (C10-13) had no obvious toxicity on zebrafish embryonic development. The data indicated that CPs could cause deformity on the development of gas bladders of zebrafish larvae. Further, the deformity effect on larvae had no relevance with the percent of chlorine and non-chlorinated short-chain paraffins in CPs.The results of zebrafish larvae following embryonic exposure to HBCD showed that the mortality rate of larvae was increased and the hatching of larvae was significantly suppressed as the concentration of HBCD increased. Besides, at168hours post-fertilization (hpf), HBCD could cause zebrafish larvae gas bladder defects, which led to the failure of gas bladder inflation, and the pathological phenomenon of losing the ability of free motility, which can ultimately lead to the death of zebrafish larvae. Meanwhile, the result of HBCD exposure to zebrafish embryos in different developmental period revealed that the phase when HBCD had the most significant influence on zebrafish larvae might be after72hours post-fertilization, which coincided with the initial inflating time of zebrafish gas bladder. In addition, the larvae were exposed to lower concentration of HBCD at120hpf, when normal gas bladders were completely developed. We found that HBCD could cause failure of inflation and significant atrophy in the originally well developed gas bladders.