Influence of coexisting Cr(VI) and sulfate anions and Cu(II) on the sorption of F-53B to soils

Environmental occurrence, bioaccumulation and human risks of emerging fluoroalkylether substances: Insight into security of alternatives

Per- and polyfluoroalkyl substances (PFASs) are widely used due to their unique structure and excellent performance, while also posing threats on ecosystem, especially long-chain perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA). As the control of conventional PFASs, fluoroalkylether substances (ether-PFASs) as alternatives are constantly emerging. Subsequently, the three representative ether-PFASs, chlorinated polyfluoroalkyl ether sulfonic acid (F-53B), hexafluoropropylene oxide-dimer acid (HFPO-DA), and 4,8-Dioxa-3H-perfluorononanoicacid (ADONA) are discovered and have received more attention in the environment and ecosystem. But their security is now also being challenged. This review systematically assesses their security from six dimensions including environmental occurrence in water, soil and atmosphere, as well as bioaccumulation and risk in plants, animals and humans. High substitution level is observed for F-53B, whether in environment or living things. Like PFOS or even more extreme, F-53B exhibits high biomagnification ability, transmission efficiency from maternal to infant, and various biological toxicity effects. HFPO-DA still has a relatively low substitution level for PFOA, but its use has emerged in Europe. Although it is less detected in human bodies and has a higher metabolic rate than PFOA, the strong migration ability of HFPO-DA in plants may pose dietary safety concerns for humans. Research on ADONA is limited, and currently, it is detected in Germany frequently while remaining at trace levels globally. Evidently, F-53B has shown increasing risk both in occurrence and toxicity compared to PFOS, and HFPO-DA is relatively safe based on available data. There are still knowledge gaps on security of alternatives that need to be addressed.

P/Pb transport at the interface of water and Al-substituted ferrihydrite: Effect of P/Pb loading sequence

Sediment mineral such as Al-substituted ferrihydrite plays a critical role for contaminant transport in the river systems. Heavy metals and nutrient pollutants often coexisted in the natural aquatic environment, and they may enter the river at different time frames, altering the fate and transport of each other subsequently discharged into the river. However, most studies focused on the simultaneous adsorption of co-existing pollutants instead of their loading sequence. In this study, the transport of P and Pb at the interface of Al-substituted ferrihydrite and water was investigated under different P and Pb loading sequences. The results showed that preloaded P provided additional adsorption sites for the following adsorption of Pb, with enhanced Pb adsorption amount and accelerated adsorption process. Moreover, Pb preferred to be bounded with the preloaded P to form P-O-Pb ternary complexes rather than directly reacted with Fe-OH. The formation of the ternary complexes effectively prevented the release of Pb once adsorbed. However, the adsorption of P was slightly affected by the preloaded Pb, and most of the P were adsorbed onto Al-substituted ferrihydrite directly with the formation of Fe/Al-O-P. Moreover, the release process of the preloaded Pb was significantly inhibited by the following adsorbed P due to the formation of Pb-O-P. Meanwhile, the release of P was not detected from all P and Pb loaded samples of different adding sequence due to the high affinity between P and the mineral. Thus, the transport of Pb at the interface of Al-substituted ferrihydrite was seriously influenced by the adding sequence of Pb and P, while the transport of P was not sensitive to the adding sequence. The results provided important information for the transport of heavy metal and nutrients in river system with different discharging sequence, and offered new insights to further understand the secondary pollution in multi-contaminated river.

Phytoremediation of fluoroalkylethers (ether-PFASs): A review on bioaccumulation and ecotoxilogical effects

Fluoroalkylethers (ether-PFASs), as alternatives to phased-out per- and perfluoroalkyl substances (PFASs), have attracted mounting attention due to their ubiquitous detection in aquatic environment and their similarity to legacy PFASs in terms of persistence and toxicity. In this review, the sources and distribution of ether-PFASs in soil ecosystem as well as their toxic impacts on soil microbial community are summarized. The plant uptake and bioaccumulation potential of ether-PFASs are presented, and a wide range of the influencing factors for their uptake and translocation is discussed. In response to ether-PFASs, the corresponding phytotoxic effects, such as seed germination, plant growth, photosynthesis, oxidative damage, antioxidant enzymes activities, and genotoxicity, are systematically elucidated. Finally, the current knowledge gaps and future research prospective are highlighted. The findings of this review will advance our understanding for the environmental behavior and implications ether-PFASs in soil-plant systems and help explore the strategies for ether-PFASs remediation to minimize their adverse toxicity.

Interaction mechanism between chlorinated polyfluoroalkyl ether potassium sulfonate (F-53B) and chromium on different types of soil surfaces

The coexistence of per- and polyfluoroalkyl substances (PFASs) and heavy metals have been found in soils. However, the interaction between the combined pollutants in soils remains unclear. In this study, the adsorption processes of single and combined Cr(VI) and chlorinated polyfluoroalkyl ether potassium sulfonate (F-53 B) in red, yellow and black soils were simulated. When compared with the single F-53 B and Cr(VI), the adsorption amount of the combined F-53 B and Cr(VI) on soils changed with the types of soils. The interactions between F-53 B and Cr(VI) in soils affected their adsorption behavior. The adsorption of the combined F-53 B and Cr(VI) best fit second-order kinetics and the Freundlich equation. Moreover, aluminum and iron oxides are highly correlated with adsorption of F-53 B and Cr(VI). Both F-53 B and Cr(VI) can form complexes with aluminum and iron oxides through electrostatic interactions, but PFOS could be bridged with iron oxides to form an inner sphere complex and with aluminum oxides to form an outer sphere complex. The coexistence of F-53 B and Cr(VI) could change the fluorescent group of dissolved organic matter (DOM) in soils due to the complexation between F-53 B and DOM. In addition, F-53 B increased the acid-soluble portion of Cr and decreased its residual form, which promoted the environmental risk of Cr in soils.

Co-occurrence and correlations of PFASs and chlorinated volatile organic compounds (cVOCs) in subsurface in a fluorochemical industrial park: Laboratory and field investigations

Fluorochemical industrial park (FIP) represents an important source of per- and polyfluoroalkyl substances (PFASs) and chlorinated volatile organic compounds (cVOCs). Exploring the co-occurrence and correlations of PFASs and cVOCs is a key step towards the understanding their distributions in the field. In this study, perfluorooctanoic acid (PFOA) was the dominant compound in groundwater and aquifer solids, and elevated concentrations of short-chain perfluoroalkyl carboxylic acids (PFCAs) and hexafluoropropylene oxide oligomers were also detected in the field, suggesting their wide applications as substitutes for PFOA. Correlation analyses between PFASs and cVOCs suggested that cVOCs had a significant influence on the distribution and composition of PFASs in the field. In addition, the presence of cVOCs in the form of dense non-aqueous-phase organic liquids (DNAPL) affected the distribution and migration of PFASs at various depths, as evidenced by the relatively high PFASs concentrations (204 μg/L) and PFOA abundance (85.4%) in the deep aquifer, likely due to DNAPL-water interfaces sorption or partition into bulk DNAPL. The log K_d values, determined in the laboratory, were found to increase in the presence of DNAPL, especially for PFOA, with more than one time higher than those of perfluorobutanoic acid (PFBA) and hexafluoropropylene oxide dimer acid (HFPO-DA). This conclusion further demonstrated that PFOA had a higher potential to participate into DNAPL, which can migrate with DNAPL to the deep aquifer, supporting the higher abundance of PFOA in the deep aquifer mentioned above. However, the log K_d-field values of PFBA and HFPO-DA in the field were higher than that of PFOA, and no significant correlations (p > 0.05) were found between log K_d-field values and the chain-length of PFCAs at various depths, suggesting that the phenomena observed in the field are a result of composite influencing factors.

The Co-Transport of PFAS and Cr(VI) in porous media

PFAS and Cr are present at some sites as co-contaminants. The objective of this research was to investigate the co-transport behavior of per- and polyfluoroalkyl substances (PFAS) and hexavalent chromium (Cr(VI)) in porous media. Miscible-displacement experiments were conducted using two soils and an aquifer sediment with different geochemical properties. Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) were employed as model PFAS. The retardation of PFOS was decreased in the presence of Cr(VI). Conversely, the transport and retardation of PFOA was not affected by the presence of Cr(VI). The reduction of PFOS retardation caused by Cr(VI) is likely due to sorption competition for both organic-carbon and inorganic (metal-oxides and clay minerals) domains. The relative contributions of the three soil constituents to PFOS sorption and the potential for competition between PFOS and Cr(VI) is a function of the geochemical composition of the porous media (i.e., organic carbon, metal-oxides and clay minerals). The PFAS had minimal impact on the retention and transport of Cr(VI). To our knowledge, the results presented herein represent the first reported data for PFOS and Cr(VI) co-transport in porous media. The results of this study indicate that the presence of Cr(VI) has the potential to increase the migration potential of PFOS in soil and groundwater, which should be considered when characterizing electroplating facilities, leather tanning facilities, and other co-contaminated sites.

Effect of Soil Solution Properties and Cu2+ Co-Existence on the Adsorption of Sulfadiazine onto Paddy Soil

Paddy soils are globally distributed and saturated with water long term, which is different from most terrestrial ecosystems. To better understand the environmental risks of antibiotics in paddy soils, this study chose sulfadiazine (SDZ) as a typical antibiotic. We investigated its adsorption behavior and the influence of soil solution properties, such as pH conditions, dissolved organic carbon (DOC), ionic concentrations (IC), and the co-existence of Cu²⁺. The results indicated that (1) changes in soil solution pH and IC lower the adsorption of SDZ in paddy soils. (2) Increase of DOC facilitated the adsorption of SDZ in paddy soils. (3) Cu²⁺ co-existence increased the adsorption of SDZ on organic components, but decreased the adsorption capacity of clay soil for SDZ. (4) Further FTIR and SEM analyses indicated that complexation may not be the only form of Cu²⁺ and SDZ co-adsorption in paddy soils. Based on the above results, it can be concluded that soil solution properties and co-existent cations determine the sorption behavior of SDZ in paddy soils.

First insights into the formation and long-term dynamic behaviors of nonextractable perfluorooctanesulfonate and its alternative 6:2 chlorinated polyfluorinated ether sulfonate residues in a silty clay soil

Per- and polyfluoroalkyl substances (PFAS) are persistent and toxic contaminants that are ubiquitous in the environment. They can incorporate into soil as nonextractable residues (NER) which are not detectable with conventional analytical protocols but are still possible to remobilize with changes of surrounding conditions, and thus will be bioavailable again. Therefore, there is a need to investigate thoroughly the long-term fate of NER-PFAS. In this study, a 240-day incubation of perfluorooctanesulfonate (PFOS) and its alternative 6:2 chlorinated polyfluorinated ether sulfonate (F-53B) in a silty clay topsoil was carried out. Solvent extraction, alkaline hydrolysis and sequential chemical degradation were applied on periodically sampled soil to obtain extractable, moderately bound and deeply bound PFAS, respectively. The results confirmed the formation of NER of both compounds but with different preferences of incorporating mechanisms. NER-PFOS was formed predominantly by covalent binding (via head group) and strong adsorption (via tail group). The formation of NER-F-53B was mainly driven by physical entrapment. Both bound compounds within the incubation period showed three-stage behaviors including an initial period with slight release followed by a (re) incorporating stage and a subsequent remobilizing stage. This work provides some first insights on the long-term dynamic behaviors of nonextractable PFAS and will be conducive to their risk assessment and remediation (e.g. estimating potential NER-PFAS level based on their free extractable level, and selecting remediation methods according to their prevailing binding mechanisms).

Uptake, translocation and toxicity of chlorinated polyfluoroalkyl ether potassium sulfonate (F53B) and chromium co-contamination in water spinach (Ipomoea aquatica Forsk)

Bioaccumulation and toxicity of per-and polyfluoroalkyl substances and metal in plants have been confirmed, however their contamination in soil and plants still requires extensive investigation. In this study the combined effects of chlorinated polyfluoroalkyl ether potassium sulfonate (F53B) and chromium (Cr) on water spinach (Ipomoea aquatica Forsk) were investigated. Compared with each single stress, the combination of F53B and Cr (VI) reduced the biomass and height and increasingly accumulated in the roots and destroyed the cell structure. Besides, the co-contamination led to the immobilization of F53B and Cr (VI) in soil, which affected their migration in soil and transfer to plants. The antioxidant response and photosynthesis of the plant weakened under the single Cr (VI) and enhanced under the single F53B treatment; however the contamination of F53B and Cr (VI) could also reduce this effect, as confirmed by the gene expression of MTa, psbA and psbcL genes. This study provides an evidence of the environmental risks resulting from the coexistence of F53B and Cr (VI).

Efficient sorptive removal of F-53B from water by layered double hydroxides: Performance and mechanisms

Chlorinated polyfluoroalkyl ether sulfonates (trade name F-53B) has been detected in various environmental matrices, and reported to be equally or more toxic than perfluorooctane sulfonate. Efficient sorptive removal of F-53B from water by two types of layered double hydroxides (LDHs), NO₃^--LDH and sodium dodecyl sulfate modified NO₃^--LDH (SDS-LDH), was demonstrated in this study. Both LDHs removed F-53B in several minutes and had sorption capacities of over 860 mg/g. SDS-LDH exhibited a greater F-53B uptake than NO₃^--LDH under the influence of different solution chemistry, including pH 3-11, or in the presence of competing anions or co-contaminants, primarily due to the higher surface areas and the presence of SDS for SDS-LDH. Batch experiments, structural characterization, molecular dynamics simulations, and density functional theory calculations were combined to explore the sorption mechanisms, which mainly include ion exchange (specifically, O-H⋯O/F hydrogen bond), C-F/Cl⋯H hydrogen bond, and micellar sorption (occurring at high initial F-53B concentrations). Accordingly, we propose to improve the sorption performance of LDHs by increasing their surface areas and modifying LDHs to produce more hydrogen bond sites, as well as exfoliating LDHs into two dimensional nanosheets to eliminate the steric hindrance for the micellar formation of F-53B or other per- and polyfluoroalkyl substances.

Accumulation and associated phytotoxicity of novel chlorinated polyfluorinated ether sulfonate in wheat seedlings

Novel alternatives of perfluorooctane sulfonate (PFOS), chlorinated polyfluorinated ether sulfonates (Cl-PFAESs) are increasingly being detected in the aquatic and terrestrial environment. Previous studies mainly focused on aquatic biota; however, the knowledge about the ecotoxicological risk they pose to terrestrial plants was still lacking. In this study, the accumulation of two Cl-PFAES (6:2 and 8:2 Cl-PFAES) and PFOS in wheat seedlings at environmentally relevant levels (50 and 100 μg L^-1) was investigated. Concentrations of Cl-PFAESs in the roots were an order of magnitude higher than those in shoots, indicating that they were primarily accumulated in the roots. The values of root and shoot bioconcentration factor was comparable between 6:2 Cl-PFAES and PFOS. However, these indexes of 8:2 Cl-PFAES were 42-91% higher and 70-76% lower than PFOS, respectively. As a result, 6:2 Cl-PFAES had a similar accumulation pattern as PFOS, whereas 8:2 Cl-PFAES was predominantly restricted to the roots, which might be attributed to their hydrophobicity and carbon chain length. In addition, at 250 mg L^-1 of Cl-PFAESs, plant biomass and pigment content were 24-30% and 0.4-18%, respectively, which were lower than those of PFOS. As compared with PFOS, Cl-PFAESs induced higher levels of root membrane permeability, reactive oxygen species and malondialdehyde content, as well as reduced the activities of antioxidant enzymes and glutathione content. These suggested the occurrence of a severer oxidative damage and the breakdown of the antioxidant defence system in wheat cells. Therefore, we conclude that Cl-PFAESs might pose a higher potential threat to the environment than PFOS.