Study On The Toxicity Of Several Typical POPs Exposed To Zebrafish (Danio Rerio) Embryos

In this work,zebrafish(Danio Rerio) embryo-larval toxicity tests were performed to assess the toxicities of some typical persistent organic pollutants(POPs).Basing upon the actuality of worldwide environmental pollution,2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD),pentachlorophenol(PCP) and brominated flame retardants(BFRs) were studied. In order to evaluate their ecological safety,kinds of biological markers,related to the development of zebrafish embryos,were chose to investigate the toxicities and potential mechanisms under solo or combined exposure.Mortality,heart rates,edema severity,CYP1A and regucalcin(RC) gene expressions were investigated to study TCDD-induced toxicity in zebrafish during the early life stage. Results indicated that the 50pg/mL TCDD caused severe and visible developmental toxicity,such as blue sac syndrome,decreased heart rate and increasing mortality. Furthermore,CYP1A mRNA expression was notably induced by TCDD at 96hpf,while fell to the normal at 168hpf.On the other hand,there was no significant difference in RC mRNA expression at each selected time compared to the control.Due to the existing pollution of pentachlorophenol(PCP) in Dongting Lake region and octachlorodibenzo-p-dioxin(OCDD) as one of the important byproducts in the industrial process of PCP,studies were accomplished to assess the combined toxicities of PCP and OCDD.Embryo and larval survival,hatching,morphological development, CYP1A gene expression and activities of SOD and CAT were measured.The results showed that PCP(25μg/L～5mg/L) caused severe and visible developmental toxicity, while no effects were observed at the 250μg/L OCDD respectively.Moreover,zebrafish embryos did not show any effective toxicity under the combined exposure of 250μg/L OCDD and PCP with lower concentration,and simultaneously there were no significant differences in CYP1A expression and activities of SOD and CAT between the co-exposed embryos and the control.In a word,the co-exposure of PCP and OCDD had no remarkable toxicity,while the higher concentration of PCP solo did cause visible developmental toxicity to zebrafish embryos.Still,more investigations on the combined effect of PCP and other dioxin isomers are indispensable.In order to explore the developmental toxicity of BFRs,4,4'-isopropylidenebis (TBBPA) and 1,2,5,6,9,10-hexabromocyclododecane(HBCD) were chosen as the typical BFRs.The results revealed that higher doses of TBBPA(0.75 mg/L and 1.5mg/L) caused obvious malformations and increasing mortality,besides,SOD,MDA and Hsp70 level were induced in TBBPA-treated group,compared to the control.With regard to HBCD, no developmental toxicity can be observed in all range of the concentrations from the lowest 0.002mg/L to the highest 10mg/L,but during its high doses there were significant differences in SOD,MDA and Hsp70 level between the HBCD-treated group and the control.Concretely,the trend of MDA and Hsp70 level were the same with TBBPA,but SOD showed a different trend,which was an initial decrease followed by a decrease. Moreover,higher doses of TBBPA(0.75mg/L and 1.5mg/L) accelerated the hatching of embryos,while relative lower doses of HBCD(0.002mg/L～0.5mg/L) delayed the occurrence of hatching.Thus,it can be concluded that BFRs with different chemical constitutions may have different mechanisms causing toxicities to zebrafish embryos.