Toxicity Of PFOS And Its Three Alternatives To Zebrafish And Comparison

Per-and polyfluoroalkyl substances(PFASs)are a class of man-made fluorinated fine products with good heat resistance,surface activity and chemical stability,which are widely used in commercial and chemical industries,such as: aqueous foams,coating additives,etc.Perfluoroctane sulfonate(PFOS)is a typical per-and polyfluoroalkyl substance,which was listed as a persistent in Annex B(Restriction)of the UNEP Stockholm Convention on Persistent Organic Pollutants(POPs)in 2009 due to its bioaccumulation,toxicity,and ability to persist in the environment and be transported over long distances.Organic pollutants,and subsequently banned or restricted in most countries worldwide.Due to the widespread bans or restrictions on the use of PFOS,new alternatives have been developed,such as Perfluorobutane sulfonate(PFBS),Perfluorohexane sulfonate(PFHx S)and 6:2 fluorotelomer sulfonic acid(6:2 FTSA).With the emergence and extensive use of these alternatives,the environmental aspects of the alternatives are of increasing concern.However,studies on PFBS,PFHx S,and 6:2 FTSA have mostly focused on mammals,and toxicological studies on aquatic organisms are scarce.In addition,further studies on the toxicity of alternatives in relation to PFOS to aquatic organisms are needed.In this study,the aquatic organism zebrafish(Danio rerio)was selected as an indicator organism and PFOS and its three alternatives PFBS,PFHx S and 6:2 FTSA were used as test subjects.The acute toxicity of PFOS and its substitutes to zebrafish embryos and adults was studied.The effects of PFOS and its substitutes on zebrafish embryos(120 h)and adults(28d)were investigated for the oxidative stress markers Reactive oxygen species(ROS),Superoxide dismutase(SOD)and Malondialdehyde(SOD),based on the relevant concentrations of perfluorinated and polyfluoroalkyl substances in the environment(50 μg/L).and malondialdehyde(MDA).The effects of PFOS and its substitutes on the apoptosis gene Caspase-3,the B-lymphoma-2 gene(B-cell lymphoma-2,Bcl-2)and Bcl-2-Associated X protein(Bcl-2 Associated protein X,Bax)in zebrafish embryos and adults.The combined toxicity of PFOS and its alternatives on zebrafish embryos and adults in terms of oxidative stress and apoptosis was assessed using the Integrated biomarker response index(IBR).This study provides a scientific basis for the toxicological study of PFOS alternatives on zebrafish.The main results of this study are as follows:(1)The alternatives PFBS,PFHx S and 6:2 FSTA were less acutely toxic than PFOS to zebrafish embryos and adults in both acute toxicity tests.(2)In terms of oxidative stress,At the zebrafish embryo(120 h)stage,both PFOS and its substitutes inhibited SOD enzyme activity in zebrafish embryos,PFHx S and 6:2FTSA-treated groups significantly increased ROS content in embryos,and PFOS-treated group increased MDA content in embryos.At the adult zebrafish(28 d)stage,PFOS and all three of its alternatives reduced the MDA content in the adults,PFHx S treatment group increased the accumulation of ROS in the adults,PFOS treatment group inhibited the SOD enzyme activity in the adults,and PFBS and PFHx S treatment groups activated the SOD enzyme activity.It was shown that the alternatives PFBS,PFHx S and 6:2 FTSA did not affect lipid peroxidation in zebrafish embryos and that long-term exposure to PFOS and its three alternatives increased resistance in zebrafish adults.(3)In terms of apoptotic gene expression,both PFOS and its alternatives reduced the Bcl-2/Bax ratio in zebrafish embryos and adults,indicating that both PFOS and its alternatives promoted apoptosis in zebrafish embryos and adults.At the zebrafish embryo(120 h)stage,the PFBS and PFHx S treatment groups inhibited Caspase-3 gene expression,with no significant differences between the other treatment groups,indicating that PFBS and PFHx S exposure inhibited apoptosis in embryos in vivo and increased the risk of cell carcinogenesis.At the adult zebrafish(28 d)stage,PFOS,PFBS and PFHx S activated Caspase-3 gene expression and 6:2 FTSA inhibited Caspase-3 gene expression,indicating that PFOS,PFBS and PFHx S promoted the onset of apoptosis in adult fish in vivo while 6:2 FSTA inhibited the onset of apoptosis in adult fish in vivo and increased the the possibility of cell carcinogenesis in adult fish.(4)From the calculation of IBR,it can be concluded that in the comparison of the combined toxicity of PFOS and its three alternatives to zebrafish embryos and adults,the combined toxicity of the PFHx S treatment group to zebrafish embryos and adults was less than that of PFOS,except that the combined toxicity of PFHx S treatment group to zebrafish embryos was comparable to that of PFOS.In summary,this study found that the combined toxicity of the alternatives PFBS,PFHx S and 6:2 FTSA to zebrafish was less than that of PFOS.therefore,it is reasonable that these alternatives are used as consumer products to replace PFOS in terms of the ecotoxic effects of the alternatives PFBS,PFHx S and 6:2 FTSA on zebrafish.