Biodegradation And Biotransformation Mechanism Of Perfluorooctane Sulfonic Acid Precursors (PreFOSs)

Perfluorooctane sulfonic acid(PFOS)precursors(PreFOSs)can be transformed to PFOS through abiotic and biotic routes,which is an important source of PFOS in environment and biota.N-ethyl perfluorooctyl sulfonamide(N-EtFOSA)and perfluorooctyl sulfonamide(PFOSA)are two typical PreFOSs.Therefore,it is important to investigate the biodegradation characteristics of N-EtFOSA and PFOSA in different biological species.The main research contents and related conclusions of the present study are as follows:(1)A PreFOSs-degrading bacteria PF1,which was able to utilize PreFOSs as sole carbon and energy source for growth,was isolated from the contaminated soil collected from the surroundings of a fluoride factory.According to its morphology and 16 S r DNA gene sequence analysis,strain PF1 was identified as Hyphomicrobium sp..The degradation rates of perfluorooctane sulfonamide(PFOSA)and N-ethyl perfluorooctanesulfonamide(N-Et FOSA)by PF1 were 14.6% and 8.2% within 48 h,respectively,while PF1 was unable to degrade PFOS.PFOSA can be biodegraded to PFOS.N-Et FOSA can be biodegraded to perfluorooctane sulfonamide acetic acid(FOSAA),PFOSA and PFOS,and PFOS was the predominant metabolite.Based on the above analysis,the proposed metabolic pathways of PFOSA and NEtFOSA by strain PF1 was obtained.It was confirmed that the microbial degradation of PreFOSs is an important source of PFOS in the environment.(2)PFOSA was spiked in soil and its biodegradation in soil,uptake and metabolism in wheat(Triticum aestivum L.)and earthworms(Eisenia fetida)were investigated.The results indicated that PFOSA can be biodegraded to highly stable PFOS,which has the same perfluorinated carbon chain length as PFOSA,by microbes in soil.PFOSA can be taken up by wheat root and earthworms from soil with higher bioaccumulation ability than PFOS.In both wheat and earthworms,PFOSA also degraded to PFOS.However,other shorter-chain perfluoroalkanesulfonates(PFSAs),including perfluorohexane sulfonate(PFHx S)and perfluorobutane sulfonate(PFBS),were observed in wheat,but not in soil and earthworms,suggesting that wheat displayed distinctly different degradation mechanisms to PFOSA from soil microbes and earthworms.(3)The present work studied the uptake,translocation and metabolism of N-EtFOSA in wheat(Triticum aestivum L.),soybean(Glycine max L.Merrill)and pumpkin(Cucurbita maxima L.)by hydroponic exposure.Except for parent N-Et FOSA,its metabolites of perfluorooctane sulfonamide acetate(FOSAA),perfluorooctane sulfonamide(PFOSA),PFOS,perfluorohexane sulfonate(PFHxS)and perfluorobutane sulfonate(PFBS)were detected in the roots and shoots of all the three plant species examined.This suggested that plant roots can take up N-EtFOSA from solutions efficiently,and translocate to shoots.A positive correlation was found between root concentration factors(RCFs)of N-EtFOSA and root lipid content.Much higher proportion of N-EtFOSA transformation products in plant tissues than in the solutions,suggested that N-Et FOSA can be in vivo metabolized in plant roots and shoots to FOSAA,PFOSA and PFOS,and other additional shorter-chain perfluoroalkane sulfonates(PFSAs),including PFHxS and PFBS.The results suggested that plants had biotransformation pathways to N-EtFOSA that were different than those from microorganisms and animals.This study provides important information about the uptake and metabolism of PreFOSs in plants.