Bioaccumulation And Biotransformation Mechanism Of Perfluorooctane Sulfonic Acid Precursors (PreFOSs) In Earthworms (Eisenia Fetida)

EtFOSA?N-ethyl perfluorooctyl sulfonamide?and FOSA?perfluorooctyl sulfonamide?are two typical perfluorooctane sulfonic acid?PFOS?precusors?PreFOSs?,which can be biotransformed to PFOS through abiotic and biotic pathways.Transformation of PreFOS is an important indirect source of PFOS in environment and biota.Therefore,it is important to investigate the uptake,elimination and biotransformation of EtFOSA and FOSA in biota.?1?The earthworm-sand system was conducted to investigate the bioaccumulation and elimination of PreFOSs in earthworm.In vivo experiment,earthworms were exposed to EtFOSA and FOSA spiked sands.The bioaccumulation factor?BAF?of EtFOSA and FOSA were 20.4 and 45.8,respectively.The results of the present study demonstrated that earthworms could take up and bioaccumulated PreFOSs from sands.The bioaccumulation ability of FOSA was stronger than that of EtFOSA in earthworms.The elimination rate constants?k_e?of PreFOSs and their metabolites decreased in the order FOSAA(0.130 d^-1)>FOSA(0.118 d^-1)>PFOSA(0.073 d^-1)>PFOS(0.051 d^-1),indicating that the elimination of PFOS is the most difficult.EtFOSA could be biodegraded by microorganisms in sands.to form FOSA and PFOS,while FOSA could be biodegraded to PFOS.?2?The biotransformation mechanisms of PreFOSs in earthworms were investigated after In vivo and In vitro exposure experiments.Three metabolites were observed in the earthworms grown in EtFOSA spiked sand?In vivo?,such as perfluorooctane sulfonamide acetate?FOSAA?,FOSA and PFOS.FOSA exposure tests?In vivo?displayed that the only product was PFOS.In in vitro test,the earthworm homogenates were incubated with PreFOSs.FOSAA,FOSA and PFOS were detected in EtFOSA exposed earthworm homogenates,and PFOS was detected in FOSA exposed homogenates,identifying the above hypothesis in in vivo test.These results further prove that EtOFSA and FOSA can be biotransformed in earthworm.The biotransformation rate?k₀?of EtFOSA calculated with a kinetic first-order decay model,was higher than PFOS.These results proved that the biotransformation of FOSA to PFOS was the limit speed step in earthworms.Thus,it was speculated that the biotransformation pathway of EtFOSA to PFOS via the proposed pathway:EtFOSA was oxidized to FOSAA,FOSAA was metabolized to the major product FOSA by remobal of ethyl and carboxyl group,and futher to form the final produt FPOS by the function of deamination.?3?To research the influence of Phase I and phase II metabolic enzymes,eathworms were exposed to PreFOSs spkied sands.During the period of exposing to EtFOSA and FOSA,significant increases of cytochrome P450?CYP450?and glutathione-s-transferase?GST?activities were found in in vivo earthworms.The results suggested that GST and CYP450might be involved in the metabolism and detoxification of PreFOSs.?4?To further investigate the contribution of metabolizing FOSA by phase I and phase II metabolic enzymes?CYP450 and GST?and intestinal microorganism in earthworm,two tests for inhibition of metabolic enzymes?CYP450 and GST?and degradation of FOSA by gut microbes were conducted.With the increasing of inhibitor concentration,there were significant increasing trends of FOSA and significant decreasing trends of PFOS.The results further indicated that CYP450 and GST enzymes were responsible for biotransformation of FOSA in earthworms.However,the concentrations of FOSA didn't change in inoculated earthworm gut bacteria,suggesting that gut bacteria did not contribute to FOSA biotransformation in earthworm..Therefore,it was concluded that FOSA was biotransformed by enzymes rather than by gut microbes in earthworms.