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Open Access Publications from the University of California

Scholarly Works (7 results)

  • Thesis
  • Peer Reviewed
UC Riverside Electronic Theses and Dissertations (2023)

Per and polyfluoroalkyl substances (PFAS) have been notoriously known for their high environmental persistence. Driven by government regulations, PFAS manufacturers have gradually shifted to relatively short-chain PFAS and emerging PFAS alternatives. Among the developed PFAS treatment technologies, UV/Sulfite (UV/S) process has unique advantages in treating all chain-length PFAS because the reaction occurred in a homogeneous environment. However, the UV/S process still faced challenges from (i) incomplete defluorination (e.g., 40%~70%) after reduction reactions, (ii) relatively slow reaction kinetics, and (iii) unknown feasibilities for the emerging PFAS alternatives.To address the incomplete PFAS defluorination from UV/S reduction (Red) process, we demonstrated for the first time that incorporating the subsequent advanced oxidation (Ox) process further cleaved the residue C−F bonds in reduction products to elevate the overall treatment performance. The integrated Red and Ox process reported >97% defluorination for major PFAS categories (e.g., CnF2n+1−COO−/SO3− and CnF2n+1−CH2CH2−COO−/SO3−). To resolve the relatively slow reaction kinetics for persistent short-chain perfluoroalkyl sulfonate in UV/S, we achieved accelerated PFAS degradation by adding iodide (UV/S+I). The highlight of the UV/S+I system is the substantially improved degradation kinetics (e.g., up to four times increase) and significantly enlarged treatment capacity for concentrated PFAS wastes (e.g., 300 mg/L PFAS mixture), with fewer chemical dosages and shorter reaction time. Using ether-based PFAS (e.g., Nafion-related ether sulfonates, PFESAs) as emerging PFAS alternatives, we further investigated the role of critical structural features (e.g., linear vs. branched and introduction of C−H bond) in PFAS degradation potential in UV/S+I and evaluated the feasibility of integrated Red and Ox process. The results showed that the introduction of branched structure (e.g., −CF3), C−H bond and −COO− group improved PFAS degradation potential. Previously proposed the integrated Red and Ox process achieved >98% defluorination for these emerging PFESAs structures. Finally, we comprehensively evaluated membrane separation performance for a wide spectrum of PFAS compounds. The results showed that perfluoroalkyl sulfonamides (FOSAms) are distinctively different from the other PFAS compounds, with noticeably higher transmission percentages in the permeate solution in NF270 filtration. We also proposed enhancement strategies for FOSAms removal, including switching to “tighter” membrane NF90, elevating solution pH to ~9, and fully peroxidation of FOSAms to the well-rejected PFAS acids.

    • Article
    • Peer Reviewed
    UC Riverside Previously Published Works (2020)
    Per- and polyfluoroalkyl substances (PFASs) have been used for decades within industrial processes and consumer products, resulting in frequent detection within the environment. Using zebrafish embryos, we screened 38 PFASs for developmental toxicity and revealed that perfluorooctanesulfonamide (PFOSA) was the most potent developmental toxicant, resulting in elevated mortality and developmental abnormalities following exposure from 6 to 24 h post fertilization (hpf) and 6 to 72 hpf. PFOSA resulted in a concentration-dependent increase in mortality and abnormalities, with surviving embryos exhibiting a >12-h delay in development at 24 hpf. Exposures initiated at 0.75 hpf also resulted in a concentration-dependent delay in epiboly, although these effects were not driven by a specific sensitive window of development. We relied on mRNA-sequencing to identify the potential association of PFOSA-induced developmental delays with impacts on the embryonic transcriptome. Relative to stage-matched vehicle controls, these data revealed that pathways related to hepatotoxicity and lipid transport were disrupted in embryos exposed to PFOSA from 0.75 to 14 hpf and 0.75 to 24 hpf. Therefore, we measured liver area as well as neutral lipids in 128-hpf embryos exposed to vehicle (0.1% DMSO) or PFOSA from 0.75 to 24 hpf and clean water from 24 to 128 hpf, and showed that PFOSA exposure from 0.75 to 24 hpf resulted in a decrease in liver area and increase in yolk sac neutral lipids at 128 hpf. Overall, our findings show that early exposure to PFOSA adversely impacts embryogenesis, an effect that may lead to altered lipid transport and liver development.
      Cover page: High-content screening in zebrafish identifies perfluorooctanesulfonamide as a potent developmental toxicant
      • Article
      • Peer Reviewed
      UC Riverside Previously Published Works (2024)
      The total oxidizable precursor (TOP) assay has been extensively used for detecting PFAS pollutants that do not have analytical standards. It uses hydroxyl radicals (HO•) from the heat activation of persulfate under alkaline pH to convert H-containing precursors to perfluoroalkyl carboxylates (PFCAs) for target analysis. However, the current TOP assay oxidation method does not apply to emerging PFAS because (i) many structures do not contain C-H bonds for HO• attack and (ii) the transformation products are not necessarily PFCAs. In this study, we explored the use of classic acidic persulfate digestion, which generates sulfate radicals (SO4-•), to extend the capability of the TOP assay. We examined the oxidation of Nafion-related ether sulfonates that contain C-H or -COO-, characterized the oxidation products, and quantified the F atom balance. The SO4-• oxidation greatly expanded the scope of oxidizable precursors. The transformation was initiated by decarboxylation, followed by various spontaneous steps, such as HF elimination and ester hydrolysis. We further compared the oxidation of legacy fluorotelomers using SO4-• versus HO•. The results suggest novel product distribution patterns, depending on the functional group and oxidant dose. The general trends and strategies were also validated by analyzing a mixture of 100000- or 10000-fold diluted aqueous film-forming foam (containing various fluorotelomer surfactants and organics) and a spiked Nafion precursor. Therefore, (1) the combined use of SO4-• and HO• oxidation, (2) the expanded list of standard chemicals, and (3) further elucidation of SO4-• oxidation mechanisms will provide more critical information to probe emerging PFAS pollutants.
        Cover page: Oxidative Transformation of Nafion-Related Fluorinated Ether Sulfonates: Comparison with Legacy PFAS Structures and Opportunities of Acidic Persulfate Digestion for PFAS Precursor Analysis.
        • Article
        • Peer Reviewed
        UC Riverside Previously Published Works (2021)
        Per- and polyfluoroalkyl substances (PFAS) are a large group of manmade chemicals that impose emerging environmental concerns. Among them, short-chain per- and polyfluorinated carboxylic acids represent an important subgroup used as building blocks of biologically active chemicals and functional materials. Some are also considered PFAS alternatives, and some could be byproducts of the physicochemical treatment of PFAS. However, little is known about the environmental fate of short-chain fluorinated carboxylic acids (FCAs) and their defluorination/transformation by microorganisms. To fill the knowledge gap, we investigated the structure-reactivity relationships in the aerobic defluorination of C3-C5 FCAs by activated sludge communities. Four structures exhibited greater than 20% defluorination, with 3,3,3-trifluoropropionic acid being almost completely defluorinated. We further analyzed the defluorination/transformation pathways and inferred the structures susceptible to aerobic microbial defluorination. We also demonstrated that the defluorination was via cometabolism. The findings advance the fundamental understanding of aerobic microbial defluorination and help assess the environmental fate of PFAS. Since some short-chain PFAS, such as 3,3,3-trifluoropropionic acid, are the incomplete defluorination byproducts of advanced reduction processes, their defluorination by activated sludge communities sheds light on the development of cost-effective chemical-biological PFAS treatment train systems.
          Cover page: Structure-Specific Aerobic Defluorination of Short-Chain Fluorinated Carboxylic Acids by Activated Sludge Communities.
          • Article
          • Peer Reviewed
          UC Riverside Previously Published Works (2022)
          The addition of iodide (I-) in the UV/sulfite system (UV/S) significantly accelerated the reductive degradation of perfluorosulfonates (PFSAs, CnF2n+1SO3-) and perfluorocarboxylates (PFCAs, CnF2n+1COO-). Using the highly recalcitrant perfluorobutane sulfonate (C4F9SO3-) as a probe, we optimized the UV/sulfite + iodide system (UV/S + I) to degrade n = 1-7 PFCAs and n = 4, 6, 8 PFSAs. In general, the kinetics of per- and polyfluoroalkyl substance (PFAS) decay, defluorination, and transformation product formations in UV/S + I were up to three times faster than those in UV/S. Both systems achieve a similar maximum defluorination. The enhanced reaction rates and optimized photoreactor settings lowered the EE/O for PFCA degradation below 1.5 kW h m-3. The relatively high quantum yield of eaq- from I- made the availability of hydrated electrons (eaq-) in UV/S + I and UV/I two times greater than that in UV/S. Meanwhile, the rapid scavenging of reactive iodine species by SO32- made the lifetime of eaq- in UV/S + I eight times longer than that in UV/I. The addition of I- also substantially enhanced SO32- utilization in treating concentrated PFAS. The optimized UV/S + I system achieved >99.7% removal of most PFSAs and PFCAs and >90% overall defluorination in a synthetic solution of concentrated PFAS mixtures and NaCl. We extended the discussion over molecular transformation mechanisms, development of PFAS degradation technologies, and the fate of iodine species.
            Cover page: Accelerated Degradation of Perfluorosulfonates and Perfluorocarboxylates by UV/Sulfite + Iodide: Reaction Mechanisms and System Efficiencies.
            • Article
            • Peer Reviewed
            UC Riverside Previously Published Works (2021)
            The UV-sulfite reductive treatment using hydrated electrons (eaq-) is a promising technology for destroying perfluorocarboxylates (PFCAs, CnF2n+1COO-) in any chain length. However, the C-H bonds formed in the transformation products strengthen the residual C-F bonds and thus prevent complete defluorination. Reductive treatments of fluorotelomer carboxylates (FTCAs, CnF2n+1-CH2CH2-COO-) and sulfonates (FTSAs, CnF2n+1-CH2CH2-SO3-) are also sluggish because the ethylene linker separates the fluoroalkyl chain from the end functional group. In this work, we used oxidation (Ox) with hydroxyl radicals (HO•) to convert FTCAs and FTSAs to a mixture of PFCAs. This process also cleaved 35-95% of C-F bonds depending on the fluoroalkyl chain length. We probed the stoichiometry and mechanism for the oxidative defluorination of fluorotelomers. The subsequent reduction (Red) with UV-sulfite achieved deep defluorination of the PFCA mixture for up to 90%. The following use of HO• to oxidize the H-rich residues led to the cleavage of the remaining C-F bonds. We examined the efficacy of integrated oxidative and reductive treatment of n = 1-8 PFCAs, n = 4,6,8 perfluorosulfonates (PFSAs, CnF2n+1-SO3-), n = 1-8 FTCAs, and n = 4,6,8 FTSAs. A majority of structures yielded near-quantitative overall defluorination (97-103%), except for n = 7,8 fluorotelomers (85-89%), n = 4 PFSA (94%), and n = 4 FTSA (93%). The results show the feasibility of complete defluorination of legacy PFAS pollutants and will advance both remediation technology design and water sample analysis.
              Cover page: Near-Quantitative Defluorination of Perfluorinated and Fluorotelomer Carboxylates and Sulfonates with Integrated Oxidation and ReductionCreative Commons 'BY-NC-ND' version 4.0 license
              • Article
              • Peer Reviewed
              UC Riverside Previously Published Works (2023)
              Fluoroalkylether substances (ether PFAS) constitute a large group of emerging PFAS with uncertain environmental fate. Among them, GenX is the well-known alternative to perfluorooctanoic acid and one of the six proposed PFAS to be regulated by the U.S. Environmental Protection Agency. This study investigated the structure-biodegradability relationship for 12 different ether PFAS with a carboxylic acid headgroup in activated sludge communities. Only polyfluorinated ethers with at least one -CH2- moiety adjacent to or a C=C bond in the proximity of the ether bond underwent active biotransformation via oxidative and hydrolytic O-dealkylation. The bioreactions at ether bonds led to the formation of unstable fluoroalcohol intermediates subject to spontaneous defluorination. We further demonstrated that this aerobic biotransformation/defluorination could complement the advanced reduction process in a treatment train system to achieve more cost-effective treatment for GenX and other recalcitrant perfluorinated ether PFAS. These findings provide essential insights into the environmental fate of ether PFAS, the design of biodegradable alternative PFAS, and the development of cost-effective ether PFAS treatment strategies.
                Cover page: Aerobic Biotransformation and Defluorination of Fluoroalkylether Substances (ether PFAS): Substrate Specificity, Pathways, and Applications
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