Bioaccumulation And Biotransformation Of Emerging Polyfluoroalkyl Substances(PFASs) In Plant

6:2 fluorotelomer sulfonic acid(6:2 FTSA)and 6:2 fluorotelomer carboxylic acid(6:2 FTCA)are currently used as alternatives to perfluorooctane sulfonate(PFOS)and perfluorooctanoic acid(PFOA),respectively,which have been detected at high level in environmental matrices.Previous investigations demonstrated that they could be degraded to more toxic intermediate products and perfluorocarboxlates(PFCAs)with different carbon chain length through biotic or abiotic pathways.Therefore,it is extremely important to study the bioaccumulation,translocation and biotransformation of 6:2 FTSA and 6:2 FTCA in plant:(1)The uptake,translocation and biotransformation of 6:2 FTSA in pumpkin(Cucurbita maxima L.),and uptake and translocation of perfluoroalkyl acids(PFAAs)were investigated by hydroponic exposure.The root concentration factor(RCF)of 6:2 FTSA was 2.58-24.23 times as high as those of PFAAs of the same or much shorter carbon chain length,demonstrating much higher bioaccumulative ability of 6:2 FTSA in pumpkin roots.Translocation of 6:2 FTSA and PFAAs from root to shoot was negatively correlated with logKow,suggesting that translocation of these compounds in pumpkins is mainly dependent on their hydrophobicity.Six terminal PFCAs metabolites with different carbon chain length were detected in roots and shoots,including perfluoroheptanoic acid(PFHpA),perfluorohexanoic acid(PFHxA),perfluorovaleric acid(PFPeA),heptafluorobutyric acid(PFBA),pentafluoropropionic acid(PFPrA)and trifluoroacetic acid(TFA).PFHpA was the primary metabolite in roots,while PFBA was the major product in shoots.1-aminobenzotriazole(ABT),a Cytochrome P450(CYP450)suicide inhibitor,could decrease the concentrations of PFCAs products with dosedependent relationships in pumpkin tissues,implying the role of CYP450 enzymes involved in plant biotransformation.(2)The uptake,translocation and biotransformation of 6:2 FTCA in pumpkin were investigated by hydroponic exposure.The RCF value of 6:2 FTCA was 2.70-25.17 times as high as those of PFAAs of the same or much shorter carbon chain length,and 1.04 times as high as 6:2 FTSA;the bioconcentration factor(BCF)value of 6:2 FTCA was 2.98 times as high as of 6:2 FTSA,suggesting much higher bioaccumulative ability of 6:2 FTCA in pumpkin seedlings.The translocation capability of 6:2 FTCA from root to shoot depended on its hydrophobicity.Six terminal PFCAs metabolites,including PFHpA,PFHxA,PFPeA,PFBA,PFPrA and TFA,were found in pumpkin roots and shoots.PFHxA and TFA were the primary metabolite in pumpkin root and shoot.To further investigate the transformation mechanism of 6:2 FTCA by enzymes in pumpkin seedlings,inhibition tests of CYP450 and glutathione-Stransferase(GST)were conducted.With the increasing of concentrations of ABT and Ezatiostat hydrochloride(TLK199),which were the inhibitor of CYP450 and GST respectively,significant increasing trends of 6:2 FTCA and significant decreasing trends of metabolites were observed.These results further indicated that CYP450 and GST enzymes were responsible for biotransformation of 6:2 FTCA in pumpkin seedlings.