Yanyan Zhang

The sulfur content in sulfidated nanoscale iron (S-nZVI) alters the degradation efficiency of trichloroethene (TCE), a common groundwater contaminant, but its impact on other chlorinated hydrocarbon contaminants (CHCs) has not been characterized. In this study, the anaerobic degradation of carbon tetrachloride (CT), chloroform (CF), trichloroethane (1,1,1-TCA) and TCE was assessed using S-nZVI at seven S loadings ([S/Fe] = 0.01-0.303). S-nZVI_0.01 yielded the highest degradation rate constants for CT, 1,1,1-TCA, and CF, which were 1.77-10.9 times higher than those of nZVI and other S-nZVI. In contrast, S-nZVI_0.075 yielded the highest rate constant for TCE. S-nZVI_0.01 provides the most rapid electron release, and because CT, 1,1,1-TCA, and CF have higher electron affinity than water, their degradation is the quickest at this [S/Fe]. TCE degradation was faster only at higher [S/Fe], where S-nZVI reactivity to water was diminished and S-nZVI_0.075 provided a 20-fold enhancement in electron selectivity to TCE over H₂O. Although TCE was completely dechlorinated, the other CHCs were only partially dechlorinated. The degradation products dichloromethane and 1,1-dichloroethane were dechlorinated in the presence of their parent CHCs and at specific [S/Fe], although they were not dechlorinated as sole compounds. The results demonstrate that dechlorination rates and extents of CHCs can be optimized by tuning the sulfidation dose.

Polyfluoroalkyl substances (PoFAS) can be oxidized by hydroxyl radicals (^•OH) in both natural and engineered treatment systems, yet a comprehensive understanding of their structure-dependent reactivity and transformation products remains unexplored. Herein, we investigated the ^•OH-mediated transformation of 28 PoFAS among four distinct classes using UV/H₂O₂ and unraveled the mechanisms governing their reactivity and product formation. The second-order rate constants revealed a reactivity order of alkenyl PoFAS (C═C, ∼10⁹ M^-1·s^-1) > PoFAS with H-substitution at the headgroup (-SO₂N-) or α-C (-CH₂-, ∼10⁸ M^-1·s^- 1) ≫ H-substitution at ω-C (H-CF₂-, ∼10⁵ M^-1·s^-1). Transition state theory effectively identified initial ^•OH attacking sites and unraveled how H-substitution patterns, headgroup chemistry, and steric hindrance collectively dictate PFAS reactivity. The experimentally derived rate constants were well described (R² = 0.790, p < 0.01) by the calculated free energy of activation (3.79-14.8 kcal/mol). Analysis of transformation pathways based on products identified revealed the capability of ^•OH to convert diverse nonperfluorinated moieties in PoFAS and their hydroxylated and ketone intermediates into terminal perfluoro(di)carboxylates of varying chain lengths. This study provides the first mechanistic framework linking the PoFAS structure to ^•OH-mediated transformation kinetics and pathways, enabling predictions of environmental persistence, vulnerable oxidation sites, intermediates, and terminal products for novel PoFAS.

Remediation of soils contaminated by the globally concerning per- and polyfluoroalkyl substances (PFAS) is imperative yet challenging. Herein, we identify a PFAS hyperaccumulator, the herbaceous Oenothera rosea, in soil near a fluorochemical facility and demonstrate root-to-shoot translocation factors of 3.07 − 58.6 for 18 distinct PFAS. Comparative hydroponic/pot experiments using conspecifics from non-polluted areas confirm that hyperaccumulation arises from domestication after prolonged PFAS exposure. Root cell wall pectin and hemicellulose are critical PFAS binding sites, significantly affecting root-to-shoot translocation. Subcellular and transcriptomic analyses reveal that the hyperaccumulating O. rosea undergoes minimal cell wall remodeling under PFAS stress, a signature of adaptive evolution. Life cycle assessment further validates the environmental superiority of an integrated strategy combining O. rosea phytoremediation with biomass pyrolysis for PFAS destruction and biochar production, achieving a net-negative carbon footprint (–17.9 kg CO₂/ton soil). Our work provides a comprehensive framework for PFAS remediation, from hyperaccumulator identification to sustainable field application.

The sulfur content in sulfidated nanoscale iron (S-nZVI) alters the degradation efficiency of trichloroethene (TCE), a common groundwater contaminant, but its impact on other chlorinated hydrocarbon contaminants (CHCs) has not been characterized. In this study, the anaerobic degradation of carbon tetrachloride (CT), chloroform (CF), trichloroethane (1,1,1-TCA) and TCE was assessed using S-nZVI at seven S loadings ([S/Fe] = 0.01−0.303). S-nZVI0.01 yielded the highest degradation rate constants for CT, 1,1,1-TCA, and CF, 1.77−10.9 times higher than nZVI and other S-nZVI. In contrast, S-nZVI0.075 yielded the highest rate constant for TCE. S-nZVI0.01 provides the most rapid electron release, and because CT, 1,1,1-TCA, and CF have higher electron affinity than water, their degradation is quickest at this [S/Fe]. TCE degradation was faster only at higher [S/Fe], where S-nZVI reactivity to water was diminished, and S-nZVI0.075 provided a 20-fold enhancement in electron selectivity to TCE over H2O. Although TCE was completely dechlorinated, the other CHCs were only partially dechlorinated. The degradation products dichloromethane and 1,1-dichloroethane were dechlorinated in the presence of their parent CHCs and at specific [S/Fe], although they were not dechlorinated as sole compounds. The results demonstrate that dechlorination rates and extents of CHCs can be optimized by tuning the sulfidation dose.

1,4-Dioxane has emerged as a critical global environmental concern because of its carcinogenic potential, persistence, and ubiquitous occurrence. This review systematically addresses key knowledge gaps in its emission trends, spatiotemporal characteristics on a global scale, and challenges for unified regulatory frameworks. By compiling emission data, we provided the first quantitative global estimates for 1,4-dioxane emissions and revealed a remarkable increase in industrial discharges from 645-1522 tonnes in ca. 2000 to 3868 tonnes in 2023. The emission profile has shifted from direct releases as a chlorinated solvent stabilizer in the 20th century to contemporary unintentional byproduct emissions associated with the production of poly(ethylene terephthalate) and ethoxylated surfactants. The previously overlooked domestic emission was found to contribute 711-832 tonnes annually (2023 estimate), ascribing to the use of household products containing ethoxylated surfactants. Along with shifts in emission patterns, affected environmental matrixes have expanded beyond groundwater to include surface water and drinking water, with rising concentrations observed in nonhistorical production regions. Meanwhile, the environmental persistence and long-range transport capacity of 1,4-dioxane continue to exacerbate legacy contamination issues in historically industrialized regions. However, divergent interpretations of its toxicological mechanisms, particularly regarding the carcinogenic mode of action, have resulted in inconsistent drinking water standards and regulatory approaches worldwide. This review highlights future efforts regarding more accurate emission inventories, enhanced spatiotemporal monitoring of environmental occurrence, and health risks assessment, alongside the need for coordinated regulatory efforts to address the growing concerns of 1,4-dioxane contamination.

Chlorinated polyfluoroalkyl substances (Cl-PFAS) are increasingly detected in contaminated environments, and the relative ease of C-Cl cleavage offers opportunities for defluorination. Herein, we demonstrated, for the first time, the dechlorination of Cl-PFAS by nanoscale zerovalent iron (nZVI), and we revealed that such dechlorination can induce indirect defluorination when Cl is substituted at the middle of the perfluorocarbon chain. The carbanion (-^⊖CF-CF₂-), generated via two successive single-electron transfer steps, is the key intermediate enabling defluorination through β-elimination of F^- to form alkenyl products (-CF═CF-). The extent of defluorination was governed by the competitive reactivity with proton abstraction of carbanion to form hydrogenolysis products (-HCF-CF₂-). Through this novel pathway, an indirect defluorination of up to 25.3% was achieved for the investigated polychlorofluorocarboxylic acids within 120 h using nZVI. The reactivity for dechlorination at varying positions and subsequent β-elimination of F^- can be theoretically described using dissociative electron transfer and transition state theories, respectively. The lack of defluorination in ωCl-PFAS was attributed to the much higher activation energy required for β-elimination from the carbanion (^⊖CF₂-CF₂-) compared with proton abstraction. The alignment of theoretical calculations with experimental results provides a theoretical framework to predict dechlorination and defluorination reactivity of Cl-PFAS, facilitating the design of rapidly degradable alternatives.

The growing regulatory focus on per- and polyfluoroalkyl substances (PFAS) in drinking water raises the urgent need for comprehensive monitoring and effective removal strategies. Herein, we analyzed 81 PFAS in tap water produced from three major water bodies in East China, a global PFAS emission hub. Such systematic quantitative analyses detected 64 PFAS, representing the highest reported number to date and including 28 novel species first quantified in Chinese tap water. Owing to the inefficacy of conventional treatments, PFAS levels and compositions in tap water varied collaboratively with raw water sources and seasonal fluctuations. Consequently, any PFAS contamination in raw water directly translated into tap water, with total concentrations reaching up to 8970.3 ng/L. Source apportionment analysis identified emission sources aligned with local industrial activities, highlighting their critical role in shaping PFAS profiles in tap water. Particularly, household reverse osmosis purifiers demonstrated near-complete removal for most PFAS regardless of perfluorocarbon chain length or contamination levels. Monte Carlo simulations further validated significant reductions in health risks of PFAS in purified waters, with most cases complying with U.S. EPA limits. Our findings provide reference data on novel PFAS occurrences in tap water and offer a practical mitigation strategy to inform management efforts.