Toxic Effects Of PFOA And Its Alternatives HFPO-DA And HFPO-TA On Zebrafish

Perfluorooctanoic acid(PFOA)is one of the typical per-and polyfluoroalkyl substances and exists widely in the environment.Because of its environmental persistence,long-distance migration and bioaccumulation,it has caused a series of environmental problems,and led to a variety of biological toxic effects,which seriously threaten the balance of ecological environment and the safety of organisms.Therefore,the production and application of PFOA are regulated globally and eliminated by more and more countries and regions.However,due to the importance of PFOA in daily life and industrial production,PFOA alternatives have been widely developed and applied.As typical substitutes for PFOA,hexafluoropropylene oxide dimer acid(HFPO-DA)and hexafluoropropylene oxide trimer acid(HFPO-TA)are widely found in water environments around the world,which means that aquatic organisms are at risk of exposure to HFPO-DA and HFPO-TA.However,the current toxicity studies on HFPO-DA and HFPO-TA are mainly focused on terrestrial mammals,and the toxic effects and mechanisms on aquatic organisms are still unclear.In addition,based on the toxicity research status of HFPO-DA and HFPO-TA,it can be found that they are likely to have multiple biological toxicity effects like PFOA,but whether their toxicity to aquatic organisms is lower than PFOA is still unknown.Therefore,based on the study of the toxic effects of PFOA and its alternatives HFPO-DA and HFPO-TA on aquatic organisms,this paper further compared the toxicity of PFOA and these two alternatives.In this study,zebrafish was used as the test organism to study the toxic effects of PFOA and its alternatives HFPO-DA and HFPO-TA on zebrafish adults(28 d)and embryos(120 h)at the same concentration(50 μg/L)from three aspects of oxidative stress,apoptosis and immune function.The toxicity of PFOA and its alternatives HFPO-DA and HFPO-TA to zebrafish was compared by calculating integrated biomarker response index(IBR).This study provides a reliable basis for evaluating the toxic effects of HFPO-DA and HFPO-TA on aquatic organisms and their safety as alternatives to PFOA on aquatic organisms.The main results are as follows:(1)In zebrafish adults,PFOA and HFPO-DA significantly increased reactive oxygen species(ROS)content,antioxidant enzymes(superoxide dismutase,SOD)activity,malondialdehyde(MDA)and 8-hydroxydeoxyguanosine(8-OHd G)content,thereby inducing oxidative stress and causing oxidative damage;HFPO-TA had little effect on ROS and MDA content,but significantly increased SOD activity and 8-OHd G content,resulting in DNA oxidative damage.In embryos,PFOA,HFPO-DA and HFPO-TA significantly increased ROS content and decreased SOD activity and 8-OHd G content,indicating oxidative stress;Except that PFOA had no significant effect on MDA content,HFPO-DA and HFPO-TA significantly increased MDA content,resulting in lipid peroxidation damage.(2)The effects of PFOA,HFPO-DA and HFPO-TA on apoptosis in zebrafish adults and embryos were similar.The expression levels of Caspase 3,Caspase 9 and tumor suppressor gene p53 were down-regulated,and the ratio of Bcl-2/Bax was increased.The expression level of Caspase 8 gene was significantly up-regulated in adults and significantly down-regulated in embryos.This indicated that PFOA and its alternatives HFPO-DA and HFPO-TA inhibited the occurrence of apoptosis in zebrafish adults and embryos,thereby inducing cell proliferation and increasing the risk of tumor and cancer.(3)In zebrafish adults,PFOA significantly down-regulated the expression levels of interleukin-1β(IL-1β)and tumor necrosis factor-α(TNFα)genes,while HFPO-DA significantly up-regulated the expression levels of IL-1β and TNFα genes.HFPO-TA only significantly down-regulated the expression level of TNFα gene,but had no significant effect on the expression of IL-1β.In embryos,PFOA had no significant effect on the expression of IL-1β and TNFα,but both HFPO-DA and HFPO-TA significantly up-regulated the expression levels of IL-1β and TNFα.The above results of adults and embryos experiments indicated that PFOA only caused immune dysfunction in adults,while HFPO-DA and HFPO-TA both destroyed the immune homeostasis in zebrafish adults and embryos,thereby inducing immunotoxicity.(4)The results of IBR showed that the toxicity of HFPO-DA to zebrafish embryos was lower than that of PFOA,but the toxicity of HFPO-DA to adults and HFPO-TA to adults and embryos were higher than that of PFOA,which further indicated that both HFPO-DA and HFPO-TA had higher environmental risks.