Colloidal activated carbon (CAC) is a promising material for in situ remediation of groundwater impacted by per- and polyfluoroalkyl substances (PFAS). However, long-term aging of CAC in the subsurface can trigger particle mobilization, threatening barrier integrity and increasing the risk of CAC-facilitated PFAS transport. Here, we systematically investigate how aging processes influence CAC mobilization from saturated porous media. CAC was subjected to physical, chemical (H2O2, Fenton, acid), and biological aging to mimic wet-dry cycling, oxidation, and biotic transformations relevant to soil-groundwater systems. Physicochemical characterization (surface charge and particle size) showed that most aging treatments increased CAC's negative surface charge and structural fragility. These changes were accompanied by enhanced CAC mobilization in column experiments under stepwise salinity reduction (100 -> 10 -> 0.1 mM). In contrast, the slightly suppressed mobilization of Fenton-aged CAC suggests that dissolved Fe2+ interacts with CAC by neutralizing surface charge and forming iron oxide precipitates, decreasing electrostatic repulsion. Extended Derjaguin-Landau-Verwey-Overbeek (xDLVO) simulations captured how aging-induced changes in surface charge and particle size modify the mobilization energy barrier. These results reveal the critical role of aging in controlling CAC retention in in situ barriers and highlight the utility of interfacial interaction modeling for elucidating colloid mobilization mechanisms.

Abstract Reconstructing the source regions of past atmospheric dust preserved in ice remains a challenge in Antarctic glaciology. Until now, different dust properties were obtained by separate techniques and could not be directly correlated at single particle level limiting the dust characterization. Here we apply a novel technique (single particle Inductively Coupled Plasma-Time of Flight Mass Spectrometry) to characterize millions of individual particles in low-volume (< 2 mL) ice samples. We analyzed more than 2,000,000 individual particles smaller than 2.5 µm in 28 discrete samples from Taylor Glacier, coastal East Antarctica, spanning 44—9 kyr BP. We show a glacial-interglacial shift in particle number and mass concentrations, as well as in the elemental and mineralogical compositions. Our observations suggest a common potential dust source area for central and coastal East Antarctica during the Last Glacial Period, followed by a transition to different dominant sources in coastal sites during the Holocene. These changes likely reflect large-scale variations in dust sources, and environmental conditions in the Southern Hemisphere. We have also identified and measured the elemental composition of thousands of volcanic particles < 2.5 µm, indicating occasional tephra deposition from one of the Victoria Land volcanoes around 14.8 kyr BP.

Advances in robotics and automation enhance workforce safety and increase the speed of environmental site characterization. Accordingly, real-time, robot-deployable sensing methods with sufficient analytical performance are needed to support site management decisions. We evaluated two autonomous approaches for soil total petroleum hydrocarbon (TPH) screening: (1) thermal desorption followed by gas chromatography (TD) and (2) direct sensing using a portable near-infrared (NIR) spectrometer. Soil samples from two crude-oil-impacted sites were analyzed and benchmarked against EPA Method 8015 C (solvent extraction and gas chromatography with FID detection). The TD method achieved high precision and agreed with the EPA reference within 3-27 % across 2270-18,980 ppm TPH but requires complex thermal and gas-handling hardware that would have to be engineered for robustness and to be intrinsically safe. The NIR method enabled rapid, reagent-free analysis, however, it also showed larger deviations (20-40 %) among samples. A prototype robotic platform integrating the NIR module was developed and tested in controlled outdoor conditions, demonstrating the feasibility of autonomous, real-time screening. The present study selected a few soil matrices and a realistic range of TPH concentrations to evaluate analytical trends between the two robot-deployable TPH sensors and compared their potential robotic deployment feasibility. Future work should further expand the number of soils and sites, refine the NIR calibration transferability, and engineer the TD-GC components to achieve fully integrated robotic deployment in field settings.

In situ colloidal activated carbon (CAC) barriers limit the migration of per- and polyfluorinated alkyl substances (PFAS) in groundwater. While the influence of site-specific conditions on equilibrium adsorption has been studied, the kinetics and mechanisms of desorption remain unreported. Here, we quantify the extent of PFAS desorption from CAC using preloaded flow-through columns and explore mechanisms of release. PFAS release after 1600 pore volumes under baseline conditions (1 mM NaHCO3, pH = 7.5) was controlled by chain length and headgroup and varied from <1% for perfluorooctanoic acid (PFOA) to 83% for perfluoropentanoic acid (PFPeA). Release of perfluorobutane sulfonamide (FBSA) (30%) was lower than that of perfluorobutanesulfonic acid (PFBS) (46%), which was attributed to its near-neutral pKa and a fraction of uncharged species with greater sorption stability. Low-molecular-weight (MW) dissolved organic matter (DOM) displaced more PFAS than high-MW DOM. Diesel range organics (DRO 1400 μg/L) led to ∼70% of the total PFOA mass recovered in effluent, which was significant. Elevated ionic strength (100 mM) did not greatly impact the total mass desorbed but did decrease the rate of PFAS mass release. Results demonstrate that previously sequestered PFAS can be released following exposure to DOM and DRO, and that nonequilibrium mass transfer rate-limited processes could impact barrier performance at sites where groundwater retention times in the barrier are below what is required for equilibrium.

Manual polarized light microscopy (PLM) is widely used for asbestos screening in soil, yet the technique remains labor-intensive and susceptible to inter-analyst variability and mineralogical interferences. We developed a chrysotile-focused, deep learning-assisted PLM workflow that links field-of-view (FOV) detections to sample-level screening decisions under regulatory-style sampling designs. The method combines a two-stage instance-segmentation pipeline with rotation-assisted paired imaging and recovery (0°/90°) to mitigate optical extinction and retain auditable optical evidence. FOV-level errors are propagated through slide- and sample-level consensus rules using an occupancy parameter q, defined as the probability that a given FOV contains detectable fibers, together with a dataset-calibrated proxy to approximate mass-fraction interpretation. Under a baseline design (3 slides per sample; 20 FOVs per slide), and assuming a 10% sample-level prevalence, strict consensus supported confirmatory performance near moderate occupancy (q≈0.20; ∼0.05% w/w under the present proxy) under the observed workflow-specific false-positive rate. Sustaining confirmatory performance at lower occupancy required increasing the number of scanned FOVs. Below q ≈ 0.07 (approximately 0.017% w/w under the present proxy calibration), confirmatory performance could not be jointly maintained under the present workflow assumptions and estimated background-error structure. These results are translated into an operational triage framework: samples satisfying the strict consensus criterion support a confirmatory-positive call; samples with only one consensus-positive slide trigger targeted additional scanning and/or complementary analysis; and consensus-negative samples support a negative screen within the protocol's confirmable range are reported as "not detected under this protocol".

For 60 years, the Environmental Science & Technology research community has helped to define the fields of environmental science and engineering. The research topics have evolved over time to respond to the most pressing societal needs, from treatment technologies and pollution control strategies to address severe environmental pollution, to pollution prevention and industrial ecology to help mitigate emissions, and to defining planetary boundaries for sustainability. Since ES&T launched in 1967, it has helped to create a robust global network of researchers, with researchers from 144 countries now contributing to address critical global environmental and human health challenges. Throughout its six decades, ES&T research has remained highly relevant to understanding, addressing, and advancing solutions to both current and emerging challenges and for developing science-based policies to protect the environment and human health. We are optimistic that the ES&T research community will continue to serve to help shape research and action toward a healthier, resilient, and sustainable planet for all of us in the next 60 years.

Colloidal activated carbon (CAC) is an injectable adsorbent that sequesters per- and polyfluoroalkyl substances (PFAS) in the subsurface, serving as an in situ remediation technology for PFAS-impacted sites. However, the effectiveness of the CAC sorptive barrier could change over time due to alterations in its physicochemical properties induced by aging processes. In this study, the effects of CAC aging on surface properties of CAC and resulting impact on the adsorption behaviors of PFAS compounds were determined using four accelerated aging treatments, including wet-dry cycling (W/D), hydrogen peroxide (H), Fenton's reagent (F), and mineral acid (A). Fenton's reagent and mineral acid aging treatments showed a greater impact on the physical structure and chemical composition of CAC than either W/D-CAC and H-CAC. Aging the CAC lowered the CAC specific surface area and anion exchange capacity, increased surface oxygen content, and lowered the point of zero charge, suggesting negative impacts on the capacity of CAC for PFAS removal. This reduction in the sorption capacity was confirmed in batch sorption isotherm experiments. All aged CAC had lower PFAS adsorption in a multisolute system, including six PFAS compounds with different chain lengths (C4-C8) and functional groups (sulfonate or carboxylate), with the only exception being perfluorooctanesulfonic acid (PFOS). The results suggest that the aging process is an important, yet often overlooked, factor in determining the long-term effectiveness of the CAC sorptive barrier for PFAS removal, especially for shorter-chain hydrophilic PFAS. More research is needed to verify the influence of field-scale aging processes on the CAC performance and longevity.

While spICP-MS has been used mainly to measure nanoparticles, it can also be used to measure microparticles. The transport efficiency of nanoparticles is typically independent of their size. However, the transport efficiency of microparticles can be particle size (mass) dependent as well as being dependent on the sample uptake rate and sample introduction system used. To measure both nanoparticles and microparticles a very large linear dynamic range (where signal intensity is linearly proportional to the measured analyte(s) mass within a very short measurement time (∼300 to 500 µs, the width of signals produced by an individual particle)) is needed. Deviations from linearity could occur due to incomplete particle vaporization or from signals that are beyond the instrument's ion detection system linear dynamic range. To characterize and determine the cause of nonlinearity we measured sets of nearly monodisperse engineered SiO2 particles with diameters from 500 to 5000 nm and Au particles with diameters from 60 to 1500 nm. We found that by reducing the sensitivity (up to a factor of 269×) the upper end of the linear dynamic range, in particle size that produced signal intensities that were linearly proportional to the particle (analyte) mass, could be greatly extended. Not surprisingly, reducing the sensitivity increased the minimum size detectable particle. The results are consistent with SiO2 particles as large as 5000 nm being completely vaporized in the ICP.

Urban magnetic dust particles (MDPs) are heterogeneous materials containing elemental iron (Fe0), magnetite (Fe3O4) and trace elements, which potentially pose health risks upon inhalation. The composition of nanoscale MDPs, which have risks of passing the blood brain barrier, has only recently been the subject of quantitative characterization at single-particle level. This study investigates the heterogeneity of hundreds to thousands of MDPs collected from urban parking garages at the individual particle level using both single-particle inductively coupled plasma time-of-flight mass spectrometry (spICP-TOFMS) and scanning transmission electron microscopy coupled with energy-dispersive X-ray microanalysis (STEM-EDX). spICP-TOFMS analysis reveals that only similar to 8.6% of MDPs contain Fe, while STEM-EDX shows Fe in over 99% of particles. The discrepancy is attributed to "Fe-missing particles" enriched with other elements, which, because of their small diameter and low MS response, fall below the spICP-TOFMS detection limit. In contrast, EDX identifies fewer trace-level metals, due to its higher detection limit for metals (0.1%) than TOFMS. Operationally, spICP-TOFMS exhibits higher throughput of particles, while STEM-EDX requires more labor and time-intensive procedures. Three key differences between these methods significantly influence the identification and significance of heterogeneous MDPs: (1) oxygen impacts iron oxidation state interpretation and is detected by X-ray diffraction (XRD) analysis of bulk MDPs or single particle using EDX but not by spICP-TOFMS; (2) spICP-TOFMS exhibits varying detection limits for iron versus potentially catalytic elements (e.g., Cu, Pt, etc.); and (3) spICP-TOFMS has higher particle surveying efficiency compared to EDX. Using both methods reveals complementary insights into the size, shape, composition and potential redox state of MDPs that impact pollution, and potentially respirable particles that lead to adverse human health impacts.

In situ sequestration of per- and polyfluorinated alkyl substances (PFAS) using colloidal activated carbon (CAC) is a growing technology at aqueous film-forming foam (AFFF)-impacted sites, but its long-term effectiveness remains uncertain due to complex groundwater chemistry. Perfluoroalkyl acid (PFAA) adsorption was quantified in four groundwaters collected from AFFF-impacted sites using two CAC materials. PFAA adsorption was inhibited in each groundwater, with short-chain PFAA (<7 perfluorinated carbons) being more impacted than long-chain PFAA (>7 perfluorinated carbons). Groundwater with high concentrations of total organic carbon (TOC) and diesel-range organics (DRO) caused the greatest decrease in adsorption compared to that of the control system (1 mM NaHCO3, pH = 7.5). Correlation analysis confirmed TOC and DRO were most strongly associated with decreased adsorption performance. Addition of individual groundwater solutes to unimpacted groundwater showed TOC has the strongest impact on long-chain PFAA adsorption while an additive effect was observed for short-chain PFAA. CAC with a high point of zero charge (pH(PZC), 9.5) performed better than CAC with a low pH(PZC) (6.7) in every groundwater due to favorable electrostatic interactions, but this advantage was minimized in groundwater with elevated ionic strength. Scientists and practitioners will benefit from the results presented, which will inform future CAC barrier design and implementation.

Elemental mercury and mercury (Hg)-bearing particles may be present in gas and condensate from specific geologic reservoirs and be coproduced with them. In this study, we found that over 70% of the Hg mass in field monoethylene glycol (MEG) is present as 100-200 nm particulate β-HgS, and it is therefore important to understand the decomposition behavior of β-HgS in MEG to determine the partitioning of mercury species in liquid natural gas (LNG) plants. Thermal decomposition studies in MEG and MEG-water solutions showed that β-HgS decomposition to elemental mercury started at around 100 °C, which is significantly lower than the 200 °C required for β-HgS decomposition in an inert gas. Density functional theory calculations supported the experimental observations that β-HgS has a lower decomposition temperature in solvents than its counterpart without a solvent because the solvent interactions decrease the Hg-S bond strength. Thermal decomposition studies at 130 °C showed that increased water content and decreased β-HgS particle size significantly increased the decomposition rate, while some common additives in field MEG did not have a significant effect. Experiment results suggest the decomposition pathway of β-HgS in MEG/water includes dissolution to form dissolved Hg(II) ions, followed by reduction to form elemental mercury by reaction with MEG. This study highlights the strong effect of solvent on the thermal decomposition mechanism of β-HgS, improving our understanding of the fate and species of Hg in petrochemical processing.

Heterogeneous catalysis has the potential to efficiently and sustainably mineralize per- and polyfluoroalkyl substances (PFAS) with low material and energy inputs. However, the implementation of catalytic technologies is hindered by the large variety of PFAS compounds requiring treatment, a limited understanding of catalytic PFAS-degradation mechanisms and pathways, poor catalytic process selectivity towards PFAS over other water constituents, and a lack of appropriate methods to compare catalytic treatment options. Here we recommend strategies to overcome these challenges, including pretreating complex PFAS mixtures to simplify the design space of catalytic treatments, engineering catalytic systems and catalyst surfaces for selectivity, and developing holistic figures of merit that consider defluorination efficiencies and life-cycle costs to push forward the research, development and deployment of catalytic technologies for PFAS mineralization. Research needs to realize these designs and include a better understanding of the reaction mechanisms, catalyst surface engineering and treatment process design. This Perspective proposes strategies to develop and implement heterogeneous catalytic technologies for efficient PFAS mineralization.

Nitrogen fertilizer delivery inefficiencies limit crop productivity and contribute to environmental pollution. Herein, we developed Zn- and Fe-doped hydroxyapatite nanomaterials (ZnHAU, FeHAU) loaded with urea (similar to 26% N) through hydrogen bonding and metal-ligand interactions. The nanomaterials attach to the leaf epidermal cuticle and localize in the apoplast of leaf epidermal cells, triggering a slow N release at acidic conditions (pH 5.8) that promote wheat (Triticum aestivum) growth and increased N uptake compared to conventional urea fertilizers. ZnHAU and FeHAU exhibited prolonged N release compared to urea in model plant apoplast fluid pH in vitro (up to 2 days) and in leaf membranes in plants (up to 10 days) with a high N retention (32% to 53%) under simulated high rainfall events (50 mm). Foliar N delivery doses of up to 4% as ZnHAU and FeHAU did not induce toxicity in plant cells. The foliar-applied ZnHAU and FeHAU enhanced fresh and dry biomass by similar to 214% and similar to 161%, and N uptake by similar to 108% compared to foliar-applied urea under low soil N conditions in greenhouse experiments. Controlled N release by leaf-attached nanomaterials improves N delivery and use efficiency in crop plants, creating nanofertilizers with reduced environmental impact.

ZnO naoparticles (NPs) with a Zn-phosphate shell can modulate the routes of Zn root uptake, translocation and storage mechanisms compared to ZnO NPs. Applying ZnO NPs to roots provides much greater uptake into plants than for foliar application.

Colloidal activated carbon (CAC) is a promising technology for the in situ remediation of groundwater impacted by perfluoroalkyl and polyfluoroalkyl substances (PFAS). The long-term performance of an engineered CAC barrier will depend, in part, on the emplacement and remobilization of CAC particles within aquifer media. We here explored the influence of calcium ions (Ca2+) and Suwanee River natural organic matter (SRNOM) on CAC deposition and remobilization within saturated sand columns. Our results showed that the presence of Ca2+ (e.g., >5 mM) under high ionic strength conditions (100 mM) enhanced CAC deposition and subsequently reduced its remobilization upon the introduction of a low ionic strength solution (i.e., DI water). A combination of cation bridging and electrostatic screening, driven by Ca2+, contributed to the increased retention of CAC in the sand column. In contrast, when SRNOM was present at concentrations above 5 mg/L, CAC exhibited reduced deposition under high ionic strength conditions (100 mM), followed by markedly enhanced remobilization upon flushing with a low ionic strength solution. This behavior is primarily driven by increased electrosteric repulsion at the CAC-sand interface when the sand surfaces are coated by NOM. Atomic force microscopy (AFM) force measurements showed that under the same ionic strength, Ca2+ increased the work of adhesion between CAC and silica surfaces, whereas NOM decreased it. Our work underscores the critical influence of both the presence and concentration of Ca2+ and NOM on the deposition and remobilization behaviors of CAC, providing valuable insights into the engineering design and practical implementation of in situ CAC sorptive barriers for effective PFAS remediation.

ABSTRACT Biological treatment is a recognized approach for removing selenate and selenite oxyanions present in flue gas desulfurization (FGD) wastewater. However, the knowledge of the specific microbial species or communities responsible for reducing water-soluble selenium oxyanions to insoluble elemental selenium remains limited. In addition, the selenium oxyanion reduction genes and pathways have yet to be understood in these wastewaters. This study characterizes selenium oxyanion-reducing bacteria (SeRB) native to FGD wastewater, and the resulting elemental selenium particles formed. By selecting native SeRB microbes in a defined media, a novel resolution of these organisms has been achieved. This research identifies previously unrecognized selenium oxyanion-reducing capabilities in Anaerosolibacter , alongside predominant SeRB from Mesobacillus and Tepidibacillus genera. This work encompasses both 16S and metagenomic techniques to recover novel metagenome-assembled genomes, distinct to this environment. The biogenic selenium produced by these organisms was predominantly of elemental selenium, either amorphous or with a hexagonal structure. This study identifies the SeRB present in FGD wastewater and characterizes their selenium products, offering crucial insights to enhance the efficiency of biological treatment strategies and the potential of selenium recovery from this industrial waste. IMPORTANCE This is the first report on the culturability and recovery of taxonomic and metabolic information of the anaerobic selenium oxyanion-reducing bacteria (SeRB) in flue gas desulfurization (FGD) wastewater. Selenium is a regulated contaminant in FGD wastewater found on average to be 3,130 µg/L that must be removed to meet EPA discharge limits of 16 µg/L (D. B. Gingerich, E. Grol, and M. S. Mauter, Environ Sci Water Res Technol 4:909–925, 2018, https://doi.org/10.1039/C8EW00264A ; also see U.S. EPA EPA-821-R-20-001, 2020). Better understanding of anaerobic SeRB and the microbial community in FGD wastewater is needed to harness their full potential for the bioremediation and recovery of selenium from FGD wastewater. Optimizing the biotreatment strategies for these wastewaters promises to yield cleaner and healthier waterways and ecosystems, even as the United States undergoes a shift in its energy landscape.

Enzyme-catalyzed biodegradation is an emerging green strategy for environmental remediation, although challenged by high cost and poor robustness. Herein, natural biopolymer (cellulose)-derived hydrogels concurrently doped with β-cyclodextrin and montmorillonite nanosheets that are synthesized in one-step demonstrate exceptional pollutant affinity and mechanical strength. Laccase is then stably and effectively assembled onto the hydrogels by a facile strategy based on charge-assisted H-bonding, which can be extended to other enzymes. The advanced laccase-assembled hydrogels display excellent stability and increased degradation activity achieved by strong substrate capture and rapid electron transfer. The laccase-assembled hydrogels exhibit significantly improved removal (62-fold) and degradation (52-fold) performance compared to free laccase for diverse organic pollutants (e.g., polycyclic aromatic hydrocarbons) in real wastewater. This enhanced performance is maintained despite the presence of heavy metals, other organic chemicals or dissolved organic matter. This work provides a practical strategy for designing an advanced and sustainable biodegradation tool for environmental remediation.

Colloidal activated carbon (CAC) is an emerging technology for the in situ remediation of groundwater impacted by per- and polyfluoroalkyl substances (PFAS). In assessing the long-term effectiveness of a CAC barrier, it is crucial to evaluate the potential of emplaced CAC particles to be remobilized and migrate away from the sorptive barrier. We examine the effect of two polymer stabilizers, carboxymethyl cellulose (CMC) and polydiallyldimethylammonium chloride (PolyDM), on CAC deposition and remobilization in saturated sand columns. CMC-modified CAC showed high mobility in a wide ionic strength (IS) range from 0.1 to 100 mM, which is favorable for CAC delivery at a sufficient scale. Interestingly, the mobility of PolyDM-modified CAC was high at low IS (0.1 mM) but greatly reduced at high IS (100 mM). Notably, significant remobilization (release) of deposited CMC-CAC particles occurred upon the introduction of solution with low IS following deposition at high IS. In contrast, PolyDM-CAC did not undergo any remobilization following deposition due to its favorable interactions with the quartz sand. We further elucidated the CAC deposition and remobilization behaviors by analyzing colloid-collector interactions through the application of Derjaguin-Landau-Verwey-Overbeek theory, and the inclusion of a discrete representation of charge heterogeneity on the quartz sand surface. The classical colloid filtration theory was also employed to estimate the travel distance of CAC in saturated columns. Our results underscore the roles of polymer coatings and solution chemistry in CAC transport, providing valuable guidelines for the design of in situ CAC remediation with maximized delivery efficiency and barrier longevity.