Bioaccumulation And Toxicity Characteristics Of Polychlorinated Diphenyl Ethers In Zebrafish(Danio Rerio)

Polychlorinated diphenyl ethers(PCDEs)are a class of potential halogenated persistent organic pollutants,and they exist in many environmental samples.However,there is a lack of research on bioaccumulation and toxic effects of PCDEs in aquatic organisms.The enrichment characteristics and toxicity of PCDE in zebrafish are studied.This study mainly uses indoor simulation experiment.The main contents and results are as follows:(1)The acute toxic effects of 12 PCDEs homologues in zebrafish were studied.There was a positive correlation between the zebrafish mortality and PCDEs dose.The 96 h-LC₅₀values were automatically calculated by fitting dose-response curve with nonlinear regression model.The median lethal concentration(96 h-LC₅₀)of zebrafish were 0.050 mg/L(3,3',4,4'-tetra-CDE)to 5.465 mg/L(Deca-CDE),respectively.3,3',4,4'-tetra CDE has the highest toxicity amony them.With the increase of chlorine atoms,the 96 h-LC₅₀ values gradually decreased,that is,the toxic effect of PCDEs to zebrafish gradually increased.The toxicity of PCDEs was highly correlated with its physicochemical characteristics.The LC₅₀value decreased with the increase of n-octanol-water partition coefficient(log K_ow),organic carbon-normalized partitioning coefficients(log K_oc),solubility(-log S_w,l),and 298 K supercooled liquid vapour pressures(-log P_L).(2)The effects of PCDEs homologues on antioxidant defense system,lipid peroxidation and vitellogenin(VTG)levels of zebrafish liver were studied.PCDEs(especially4-mono-CDE and 4,4'-di-CDE)could cause the changes of SOD,CAT and GPx activities,GSH levels and MDA contents in zebrafish liver,which indicates that PCDEs exposure may increase ROS levels and eventually lead to lipid peroxidation and other damages.Moreover,IBR values showed that different PCDEs induced different oxidative stress responses,and 1?g/L 4,4'-di-CDE caused the most serious oxidative damage to zebrafish liver.Five kinds of typical PCDEs exposure could cause the increase of VTG levels in plasma and liver homogenate of male zebrafish,and the order of VTG content is:plasma(10³ ng/m L)>liver(10² ng/m L).These results indicate that PCDEs can produce estrogenic effects,which of PCDEs in some aquatic organisms may be much weaker than that of natural estrogen17?-ethynylestradiol(EE2).(3)The developmental toxicity of PCDEs on zebrafish embryos was studied.The toxicity experiments of 4,4'-di-CDE and 2,3',4,4',5-penta-CDE on zebrafish embryos were carried out and the results showed that these two kinds of PCDEs had obvious lethal effect on zebrafish embryos.The mortality of zebrafish embryos increased in a dose-dependent manner.The 96 h-LC₅₀ values of 4,4'-di-CDE and 2,3',4,4',5-penta-CDE were 0.506 and 0.312 mg/L,respectively.The dose of PCDEs was negatively associated with the hatchability and body length of zebrafish embryos,positively associated with the malformation rate.Developmental malformations mainly included slow hatching,death of embryos,too short larvae,swelling of heart and yolk,and loss or bending of tail.4,4'-di-CDE with higher hatchability(easier to observe morphological changes)was selected to observe the morphological changes of embryos at 24,48,78 and 96 hpf.It was found that with the increase of the dose and time of4,4'-di-CDE,the more abnormal conditions of zebrafish embryo occur,such as slow development and hatching,decreased pigmentation and other toxic effects.The sensitivity of adult zebrafish to 4,4'-di-CDE was much lower than that of embryo,but the tolerance of embryo to 2,3',4,4',5-penta-CDE was much higher than that of adult zebrafish.(4)The enrichment characteristics of 4,4'-di-CDE in zebrafish tissues were studied.The enrichment order of zebrafish tissues was gill>liver>muscle.During the 7-day purification period,the concentration of 4,4'-di-CDE decreased most rapidly from gill tissue and was the slowest in muscle tissue.The enrichment and purification rates of 4,4'-di-CDE in different tissues were different.With the increase of the dose of 4,4'-di-CDE,the absorption rate constant(k₁)of the three tissues decreased significantly(p<0.05),while the purification rate constant(k₂)showed no obvious dose effect.According to the half-life(t_1/2),the half-life of muscle is longer than that of the other two tissues.According to the bioaccumulation factor(BCF)of different doses of 4,4'-di-CDE,the low-dose treatment group(1?g/L)of zebrafish has higher bioaccumulation potential.Under the same dose of 4,4'-di-CDE exposure,the accumulation ability of gill and liver was stronger.