Biotransformation of PFOS-precursors (PreFOS) may contribute significantly to the level of perfluorooctanesulfonate (PFOS) in the environment. Perfluorooctane sulfonamide (PFOSA) is one of the major intermediates of higher molecular weight PreFOS. Its further degradation to PFOS could be isomer specific and thereby explain unexpected high percentages of branched (Br-) PFOS isomers observed in wildlife. In this study, isomeric degradation of PFOSA was concomitantly investigated by in vivo and in vitro tests using common carp as an animal model. In the in vivo tests branched isomers of PFOSA and PFOS were eliminated faster than the corresponding linear (n-) isomers, leading to enrichment of n-PFOSA in the fish. In contrast, Br-PFOS was enriched in the fish, suggesting that Br-PFOSA isomers were preferentially metabolized to Br-PFOS over n-PFOSA. This was confirmed by the in vitro test. The exception was 1m-PFOSA, which could be the most difficult to be metabolized due to its α-branched structure, resulting in the deficiency of 1m-PFOS in the fish. The in vitro tests indicated that the metabolism mainly took place in the fish liver instead of its kidney, and it was mainly a Phase I reaction. The results may help to explain the special PFOS isomer profile observed in wildlife.

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Silver nanowires (AgNWs) are being widely utilized in an increasing number of consumer products, which could release silver to aquatic environments during the use or washing process, and have received growing concerns on their potential risks to bio-organisms and humans. The present study demonstrated that AgNWs mainly experienced direct oxysulfidation by reacting with dissolved sulfide species (initial S concentration at 1.6 mg/L) to produce silver sulfide nanostructures under environmentally relevant conditions. Granular AgS nanoparticles were formed on the surface of the nanowires. The sulfidation rate constant (k) of AgNWs was compared with those of silver nanoparticles (AgNPs) at different particle sizes. It was found that the k positively correlated with the specific surface areas of the silver nanomaterials. Natural organic matter (NOM) suppressed the sulfidation of AgNWs to different extents depending on its concentration. Divalent cations (Mg and Ca ions) substantially accelerated the sulfidation rates of AgNWs compared to monovalent cations (Na and K ions). At the same ionic strengths, Ca ions displayed the highest promoting effect among the four metallic ions.

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Carp (Cyprinus carpio) were exposed to perfluoroalkyl acids (PFAAs) including perfluorooctane sulfonate (PFOS) isomers in an artificially contaminated sediment/water microcosm. The uptake constant of PFAAs increased with increasing carbon chain length, whereas the elimination coefficient displayed the opposite trend, suggesting that carbon chain length plays an important role in the bioaccumulation of PFAAs. When the contribution of suspended particulate matter was taken into account, the bioaccumulation factors (BAFs) became lower (3.61-600 L/kg) compared with BAFs derived from only considering the absorption from free PFAAs in water (3.85-97000 L/kg). The results indicate that suspended particulate matter in water constitutes an important source of exposure for aquatic organisms to long-chain PFAAs. Linear (n-)PFOS was preferentially accumulated compared with branched isomers in carp. Among the branched isomers, 1m-PFOS displayed the greatest bioaccumulation, whereas m -PFOS had the lowest. Linear PFOS displayed greater partitioning ability from blood to other tissues over branched PFOS (br-PFOS) isomers, leading to a relatively lower n-PFOS proportion in blood. In summary, suspended particulate matter made a contribution to the accumulation of long-chain PFAAs in aquatic organisms, and n-PFOS was preferentially accumulated compared with br-PFOS isomers. Environ Toxicol Chem 2016;35:3005-3013. © 2016 SETAC.

As one of the most popular carbon-based nanomaterials, graphene oxide (GO) has the potential to be released in aquatic environment and interact with some coexistent organic pollutants, such as perfluorooctanesulfonate (PFOS), which is an emerging persistent organic pollutant. In this study, the adsorption of PFOS on GO in the presence of fulvic acid (FA), the impacts of GO and FA on PFOS toxicokinetics in carp (Cyprinus carpio), and in vitro digestion behaviors were examined. The results indicated that PFOS could be strongly adsorbed on GO with a Freundlich affinity coefficient K of 580 ± 205 (mg/g)/(mg/L), while the adsorption was suppressed by FA due to competitive adsorption. GO significantly enhanced the bioaccumulation of PFOS in blood, kidney, liver, gill, intestine, and muscle of carp, and the corresponding bioaccumulation factor (BAF) was in the range of 2026-53513 L/kg. The enhancement was greatest for liver and intestine, which was 10.3 and 9.33 times of that without GO, respectively. In vivo toxicokinetic and in vitro digestion-absorption experiments indicated that GO could carry PFOS to penetrate the intestine cells. There herein, PFOS absorption, especially via intestine, and the uptake rate coefficient (k) were greatly enhanced, leading to distinctly promoted bioaccumulation of PFOS in fish. However, FA could facilitate the flocculation of GO in the intestine and also accelerate excretion of GO-PFOS complex. Thus, in the presence of FA, PFOS absorption was reduced and the promotion effect of GO on PFOS accumulation was remitted.

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