Study On The Bioavailability Of Perfluoroalkyl Substances(PFASs) In Soil

Perfluoroalkyl substances (PFASs) are a group of synthetic compounds which have been widely applied in a variety of commercial and industrial products, such as surfactants, refrigerants, lubricants, paints, fire fighting foams, cosmetics and so on. PFASs have unique water and oil repelling characteristics due to the hydrophobic fluorinated carbon chain and hydrophilic sulfonate or carboxylate end groups. PFASs are released into the environment during the production, application, transport and disposal of PFAS containing products or by degradation of their precursors, and they are ubiquitous in environmental matrices such as air, water, soil and sewage sludge. PFASs can be bioaccumulated and biomagnified throughout the food chain due to their strong binding potential to proteins and may have dverse effects to individual organisms, food webs and human health. The bioaccumulation of PFASs has become a major concern of the international community.Earthworms were exposed to artificially contaminated soils with ten PFASs to investigate the bioaccumulation and bioavailabiliry of PFASs. All the test PFASs in soil are bioaccumulative to earthworms. The uptake rate coefficients (î–») of PFASs in the range of0.016(perfluorohexanoate, PFHxA)-0.102d-1(perfluorododecanoate, PFDoA) for PFCAs and0.003(perfluorobutane sulfonate, PFBS)-0.030d-1(perfluorooctane sulfonate, PFOS) for PFSAs. The elimination rate coefficients (ke) of PFASs in the range of0.030(PFDoA)-0.187d-1(PFHxA) for PFCAs and0.039(PFOS)-0.072d’1(PFBS) for PFSAs. PFASs with longer perfluorinated carbon chain displayed higher uptake rate coefficients (ku), longer half-life (t1/2) and time to steady-state (tss) but lower elimination rate coefficients (ke) than the shorter ones. Similarly, perfiorosulfonates acids (PFSAs) displayed higher ku, longer t1/2and tss but lower ke than perflurocarboxylic acids (PFCAs) with the same perfluorinated chain length. The results indicate that the uptake of PFASs in the earthworms becomes much easier while the elimination becomes more difficult as the perfluorinated chain length increases and PFCAs are much easier to eliminate from earthworm than PFCAs of equivalent perfluorinated chain length. All the studied PFASs, including those with seven or less perfluorinated carbons, such as PFHxA, perfluoroheptanoate (PFHpA), perfluorooctanoate (PFOA), PFBS and perfluorohexane sulfonate (PFHxS), were bioaccumulated in the earthworms and the biota-to-soil accumulation factors (BSAFs) increased with perfluorinated carbon chain length and were greater for PFSAs than for PFCAs of equal perfluoroalkyl chain length. The BSAFs were found to be dependent on the concentrations of PFASs in soil and decreased as the level of PFASs in soil increased.Wheats were exposed to soils contaminated with11PFASs. Wheat could uptake PFASs from soil by wheat root and translocated to wheat shoot with root concentration factors and bioconcentration factors that decreased as the number of perfluorinated carbons in the molecule increased. And the RCFs of PFASs decreased with the distribution coefficient values between soil and interstitial water (Koc) increased. Translocation factors (TF) of PFCAs in wheat peaked at PFHxA and decreased significantly as the number of carbons increased or decreased. PFHxS produced the greatest TF of the threePFSAs examined. Since PFASs displayed opposite accumulation potentials in earthworms compared to wheat, the accumulation factors of PFASs in earthworms and wheat crossed at around PFHpA, which displayed similar BSAFs in earthworms and BCF in wheat. When the number of perfluorinated carbon is>7, the BSAFs of PFASs in earthworms were larger than their BCFs in plants, while the BSAFs in earthworms were lower than plant BCFs if the number of perfluorinated carbons was<7. The bioaccumulation of PFASs in plant was dependent on the distribution coefficients between soil and interstitial water, ability to cross plant membranes and their water solubility and hydrophobicity.Wheats and earthworms were exposed together to soils contaminated with11PFASs to investigate the mutual impacts of wheat and earthworm on their bioaccumulation of PFASs from soil. Wheat increased the bioaccumulation of all11PFASs in earthworms and earthworms increased the bioaccumulation in wheat of PFCAs containing seven or less perfluorinated carbons, decreased bioaccumulation of PFCAs with more than seven carbons, and decreased bioaccumulation of PFSAs. In general, the co-presence of wheat and earthworms enhanced the bioavailability of PFASs in soil. When earthworms and wheat are both present in soil, they may affect the accumulation of PFASs within each other by competition or by changing the bioavailability of the contaminants.The bioaccumulation and metabolism of N-ethyl perfluorooctane sulfonamidoethanol (N-EtFOSE) and two fluorotelomer alcohols (FTOH, perfluorooctylethanol,(8:2FTOH), perfluorodecylethanol,(10:2FTOH)) in earthworm from soil were investigated. N-EtFOSE in earthworm could be degraded to PFOS via some stable intermediate metabolites, N-EtFOSE->N-ethylperfluorooctane sulfonamide acetate (N-EtFOSAA,52.4%)â†'perfluorooctane sulfonamide acetate (FOSAA,2.0%)â†'perfluorooctane sulfonamide (FOSA,22.4%)â†'PFOS (23.3%). N-EtFOAA was the major metabolite and PFOS was the terminal product of N-EtFOSE. PFOA was the major terminal metabolitesof8:2FTOH and perfluorodecanoate (PFDA) was the major terminal metabolite of10:2FTOH. The results suggested that the biotic degradation of PFAS precursors is an important source of PFCAs and PFSAs in the environment.