Developing a microbial community structure index (MCSI) as an approach to evaluate and optimize bioremediation performance.

Much attention is placed on organohalide-respiring bacteria (OHRB), such as Dehalococcoides, during the design and performance monitoring of chlorinated solvent bioremediation systems. However, many OHRB cannot function effectively without the support of a diverse group of other microbial community members (MCMs), who play key roles fermenting organic matter into more readily useable electron donors, producing corrinoids such as vitamin B12, or facilitating other important metabolic processes or biochemical reactions. While it is known that certain MCMs support dechlorination, a metric considering their contribution to bioremediation performance has yet to be proposed. Advances in molecular biology tools offer an opportunity to better understand the presence and activity of specific microbes, and their relation to bioremediation performance. In this paper, we test the hypothesis that a specific microbial consortium identified within 16S ribosomal ribonucleic acid (rRNA) gene next generation sequencing (NGS) data can be predictive of contaminant degradation rates. Field-based data from multiple contaminated sites indicate that increasing relative abundance of specific MCMs correlates with increasing first-order degradation rates. Based on these results, we present a framework for computing a simplified metric using NGS data, the Microbial Community Structure Index, to evaluate the adequacy of the microbial ecosystem during assessment of bioremediation performance.

Role of Nitrogenous Functional Group Identity in Accelerating 1,2,3-Trichloropropane Degradation by Pyrogenic Carbonaceous Matter (PCM) and Sulfide Using PCM-like Polymers.

Groundwater contamination by 1,2,3-trichloropropane (TCP) poses a unique challenge due to its human toxicity and recalcitrance to degradation. Previous work suggests that nitrogenous functional groups of pyrogenic carbonaceous matter (PCM), such as biochar, are important in accelerating contaminant dechlorination by sulfide. However, the reaction mechanism is unclear due, in part, to PCM's structural complexity. Herein, PCM-like polymers (PLPs) with controlled placement of nitrogenous functional groups [i.e., quaternary ammonium (QA), pyridine, and pyridinium cations (py+)] were employed as model systems to investigate PCM-enhanced TCP degradation by sulfide. Our results suggest that both PLP-QA and PLP-py+ were highly effective in facilitating TCP dechlorination by sulfide with half-lives of 16.91 ± 1.17 and 0.98 ± 0.15 days, respectively, and the reactivity increased with surface nitrogenous group density. A two-step process was proposed for TCP dechlorination, which is initiated by reductive ß-elimination, followed by nucleophilic substitution by surface-bound sulfur nucleophiles. The TCP degradation kinetics were not significantly affected by cocontaminants (i.e., 1,1,1-trichloroethane or trichloroethylene), but were slowed by natural organic matter. Our results show that PLPs containing certain nitrogen functional groups can facilitate the rapid and complete degradation of TCP by sulfide, suggesting that similarly functionalized PCM might form the basis for a novel process for the remediation of TCP-contaminated groundwater.

Low-temperature slow-release permanganate gel for groundwater remediation: Dynamics in saturated porous media.

Due to its adverse health and environmental impacts, groundwater contamination by toxic organic compounds such as chlorinated solvents is a global concern. The slow-release permanganate gel (SRP-G) is a mixture of potassium permanganate (KMnO4) and colloidal silica solution. The SRP-G is designed to radially spread after injection via wells, gelate in situ to form gel barriers containing permanganate (MnO4-), and slowly release MnO4- to treat plumes of chlorinated solvents in groundwater. This study aimed to characterize the effects of temperature on the dynamics of SRP-G in saturated porous media. In gelation batch tests, the viscosity of ambient-temperature (24 °C) SRP-G with 30 g/L-KMnO4 was 21 cP at 70 min, 134 cP at 176 min, and peaked at 946 cP to solidification at 229 min. The viscosity of low-temperature (4 °C) SRP-G with 30 g/L-KMnO4 was 71 cP at 273 min, 402 cP at 392 min, and peaked at 818 cP to solidification at 485 min. A similar pattern, e.g., increased gelation lag time with low-temperature SRP-G, was observed for SRP-Gs with 40 g/L, 50 g/L, and 60 g/L KMnO4. In flow-through tests using a glass column filled with saturated sands, injection rates, spreading rates, and release durations were 0.6 mL/min, 46 mm/min, and 33 h for KMnO4(aq), 0.2 mL/min, 2 mm/min, and 38 h for ambient-temperature SRP-G, and 0.4 mL/min, 16 mm/min, and 115 h for low-temperature SRP-G, respectively. These results indicated that the injectability, injection rate, and gelation lag time of SRP-G and the size, release rate, and release duration of MnO4- gel barriers can be increased at low temperatures. The low-temperature SRP-G scheme can be useful for treating large or dilute dissolved plumes of chlorinated solvents or other pollutants in groundwater.

Polydimethylsiloxane dialysis passive sampler monitoring of chlorinated solvent contaminated sites - A field study.

The complexity of the subsurface contaminated by chlorinated solvents such as trichloroethylene (TCE) makes it challenging to gain a complete understanding of contamination distribution and establish a conceptual site model (CSM). High-resolution vertical contaminant concentration profiling across both the unsaturated zone and the saturated aquifer is desirable for mapping the distribution of contamination. A Fick's law-based polydimethylsiloxane (PDMS) dialysis passive sampler was developed and evaluated on a field scale for its potential application. This study tests the passive sampler at two TCE contaminated sites, and the sampling results were compared with the results from different sampling methods based on the relative percent difference. The PDMS dialysis passive sampler obtained more representative soil gas concentrations in the unsaturated zone than a portable monitoring and sampling device, which caused soil gas flow disturbance by soil gas pumping during sample collection. In the saturated aquifer sampling, the results obtained by the PDMS dialysis passive sampler correlated well with those obtained by a commercial polyethylene passive diffusion bag, and exhibited higher sensitivity under low TCE concentration conditions. Furthermore, the PDMS dialysis passive samplers were densely deployed inside each monitoring well at multiple depths, at two sites, to achieve high-resolution monitoring across the unsaturated zone and saturated aquifer. Based on the PDMS dialysis sampler data, a more comprehensive three-dimensional CSM was systematically established.

Alleviating Chlorinated Alkane Inhibition on Dehalococcoides to Achieve Detoxification of Chlorinated Aliphatic Cocontaminants.

Cocontamination by multiple chlorinated solvents is a prevalent issue in groundwater, presenting a formidable challenge for effective remediation. Despite the recognition of this issue, a comprehensive assessment of microbial detoxification processes involving chloroethenes and associated cocontaminants, along with the underpinning microbiome, remains absent. Moreover, strategies to mitigate the inhibitory effects of cocontaminants have not been reported. Here, we revealed that chloroform exhibited the most potent inhibitory effects, followed by 1,1,1-trichloroethane and 1,1,2-trichloroethane, on dechlorination of dichloroethenes (DCEs) in Dehalococcoides-containing consortia. The observed inhibition could be attributed to suppression of biosynthesis and enzymatic activity of reductive dehalogenases and growth of Dehalococcoides. Notably, cocontaminants more profoundly inhibited Dehalococcoides populations harboring the vcrA gene than those possessing the tceA gene, thereby explaining the accumulation of vinyl chloride under cocontaminant stress. Nonetheless, we successfully ameliorated cocontaminant inhibition by augmentation with Desulfitobacterium sp. strain PR owing to its ability to attenuate cocontaminants, resulting in concurrent detoxification of DCEs, trichloroethanes, and chloroform. Microbial community analyses demonstrated obvious alterations in taxonomic composition, structure, and assembly of the dechlorinating microbiome in the presence of cocontaminants, and introduction of strain PR reshaped the dechlorinating microbiome to be similar to its original state in the absence of cocontaminants. Altogether, these findings contribute to developing bioremediation technologies to clean up challenging sites polluted with multiple chlorinated solvents.

Reviewing the Bioremediation of Contaminants in Groundwater: Investigations over 40 Years Provide Insights into What's Achievable.

Biodegradation and biotransformation of contaminants in groundwater commonly occurs naturally. However, natural biodegradation rates can be slow leading to elongated contaminant plumes and prolonged risks that demand greater remedial intervention. Enhancement of the biodegradation of contaminants in groundwater can be induced by the addition of amendments to change the geochemical conditions to those that are more favorable for indigenous or added biota. Enhancing biodegradation requires collocation of the contaminant of concern with the 'right' microbial communities under the 'right' geochemical conditions, so that the microbiota thrive and bio-transform, degrade or lock up the contaminant of interest. This is most easily achievable at laboratory or bench scale where mixing is easily performed, and mass transfer limitations are minimized. However, inducing such changes at field scale in aquifers is non-trivial - amendments do not easily mix into groundwater because it is a laminar (non-turbulent) and low-energy flow environment. Bioaugmentation of cultured or genetically modified organisms have also been considered to add to groundwater to enhance contaminant degradation rates. Here we provide an overview of research studies over approximately 40 years that highlight the progression of understanding from natural biodegradation of plumes in groundwater to active bioremediation efforts that have been variably successful at field scale. Investigated contaminants providing insights include petroleum hydrocarbons, chlorinated and brominated hydrocarbons, ammonium, metals, munition compounds, atrazine and per- and polyfluorinated alkyl substances. The redox and electron acceptor/donor conditions that are inducive to biodegradation for a range of contaminants are highlighted. Biodegradation is challenged by the availability of electron donors/acceptors in the core of plumes and on plume fringes. Cases for bioaugmentation are identified. A long history of investigations provides examples of the importance of amendment delivery mechanisms, scale-up from laboratory to field, and field-scale demonstration of the effectiveness of groundwater bioremediation technologies. Advantages and disadvantages of remedial approaches are tabulated. The value and contributions of integrative modelling advances are identified. The literature review and example cases provide a deep understanding of what scale of bioremediation might be achievable for groundwater plumes. Limitations to bioremediation strategies outlined here will help direct future efforts. Addressing the sources of groundwater plumes as well as bioremediation of the plume itself will achieve more effective outcomes. Twelve 'lessons learnt' are synthesized from the review.

Remediation of multilayer soils contaminated by heavy chlorinated solvents using biopolymer-surfactant mixtures: Two-dimensional flow experiments and simulations.

To assess the efficiency of remediating dense non-aqueous phase liquids (DNAPLs), here heavy chlorinated solvents, through injection of xanthan solutions with or without surfactant (sodium dodecylbenzenesulfonate: SDBS), we conducted a comprehensive investigation involving rheological measurements, column (1D) and two-dimensional (2D) sandbox experiments, as well as numerical simulations on two-layers sand packs. Sand packs with grain sizes of 0.2-0.3 mm and 0.4-0.6 mm, chosen to represent the low and high permeable soil layers respectively, were selected to be representative of real polluted field. The rheological analysis of xanthan solutions showed that the addition of SDBS to the solution reduced its viscosity due to repulsive electrostatic forces and hydrophobic interactions between the molecules while preserving its shear-thinning behavior. Results of two-phase flow experiments depicted that adding SDBS to the polymer solution led to a reduced differential pressure along the soil and improvements of the DNAPL recovery factor of approximately 0.15 and 0.07 in 1D homogeneous and 2D layered systems, respectively. 2D experiments revealed that the displacement of DNAPL in multilayer zones was affected by permeability difference and density contrast in a heterogeneous soil. Simulation of multiphase flow in a multilayered system was performed by incorporating non-Newtonian properties and coupling the continuity equation with generalized Darcy's law. The results of modeling and experiments are very consistent. Numerical simulations showed that for an unconfined soil, the recovery of DNAPL by injection of xanthan solution can be reduced for more than 50%. In a large 2D experimental system, the combination of injecting xanthan with blocking the contaminated zone led to a promising remediation of DNAPL-contaminated layered zones, with a recovery of 0.87.

Microbial Reductive Dechlorination by a Commercially Available Dechlorinating Consortium Is Not Inhibited by Perfluoroalkyl Acids (PFAAs) at Field-Relevant Concentrations.

Perfluoroalkyl acids (PFAAs) have been shown to inhibit biodegradation (i.e., organohalide respiration) of chlorinated ethenes. The potential negative impacts of PFAAs on microbial species performing organohalide respiration, particularly Dehalococcoides mccartyi (Dhc), and the efficacy of in situ bioremediation are a critical concern for comingled PFAA-chlorinated ethene plumes. Batch reactor (no soil) and microcosm (with soil) experiments, containing a PFAA mixture and bioaugmented with KB-1, were completed to assess the impact of PFAAs on chlorinated ethene organohalide respiration. In batch reactors, PFAAs delayed complete biodegradation of cis-1,2-dichloroethene (cis-DCE) to ethene. Maximum substrate utilization rates (a metric for quantifying biodegradation rates) were fit to batch reactor experiments using a numerical model that accounted for chlorinated ethene losses to septa. Fitted values for cis-DCE and vinyl chloride biodegradation were significantly lower (p < 0.05) in batch reactors containing ≥50 mg/L PFAAs. Examination of reductive dehalogenase genes implicated in ethene formation revealed a PFAA-associated change in the Dhc community from cells harboring the vcrA gene to those harboring the bvcA gene. Organohalide respiration of chlorinated ethenes was not impaired in microcosm experiments with PFAA concentrations of 38.7 mg/L and less, suggesting that a microbial community containing multiple strains of Dhc is unlikely to be inhibited by PFAAs at lower, environmentally relevant concentrations.

Chlorinated solvents source identification by nonlinear optimization method.

In this work, chloride ions were used as conservative tracers and supplemented with conservative amounts of chloroethenes (PCE, TCE, Cis-DCE, 1,1-DCE), chloroethanes (1,1,1-TCA, 1,1-DCA), and the carbon isotope ratios of certain compounds, the most representative on the sites studied, which is a novelty compared to the optimization methods developed in the scientific literature so far. A location of the potential missing sources is then proposed in view of the balances of the calculated mixing fractions. A test of the influence of measurement errors on the results shows that the uncertainties in the calculation of the mixture fractions are less than 11%, indicating that the source identification method developed is a robust tool for identifying sources of chlorinated solvents in groundwater.

Homochiral versus Heterochiral Dimeric Helical Foldamer Bundles: Chlorinated-Solvent-Dependent Self-Sorting.

Aromatic oligoamide sequences programmed to fold into stable helical conformations were designed to display a linear array of hydrogen-bond donors and acceptors at their surface. Sequences were prepared by solid-phase synthesis. Solution 1 H NMR spectroscopic studies and solid-state crystallographic structures demonstrated the formation of stable hydrogen-bond-mediated dimeric helix bundles that could be either heterochiral (with a P and an M helix) or homochiral (with two P or two M helices). Formation of the hetero- or homochiral dimers could be driven quantitatively using different chlorinated solvents-exemplifying a remarkable case of either social or narcissistic chiral self-sorting or upon imposing absolute handedness to the helices to forbid PM species.

Integrated anaerobic-aerobic biodegradation of mixed chlorinated solvents by electrolysis coupled with groundwater circulation in a simulated aquifer.

Chlorinated solvents are widespread subsurface contaminants that are often present as complex mixtures. Complete biodegradation of mixed chlorinated solvents remains challenging because the optimal redox conditions for biodegradation of different chlorinated solvents differ significantly. In this study, anaerobic and aerobic conditions were integrated by electrolysis coupled with groundwater circulation for biodegradation of a mixture of chloroform (CF, 8.25 mg/L), 1,2-dichloroethane (DCA, 7.01 mg/L), and trichloroethylene (TCE, 4.56 mg/L). A two-dimensional tank was filled with field sandy and silty-clayed sediments to simulate aquifer conditions, a pair of electrodes was installed between an injection well and abstraction well, and groundwater circulation transported cathodic H2 and anodic O2 to produce multiple redox conditions. Microbial community analysis demonstrated that the system constructed a habitat suitable for the co-existence of aerobic and anaerobic microbes. After 50 days of treatment, 93.1%, 100%, and 87.3% of CF, 1,2-DCA, and TCE were removed without observed intermediates, respectively. Combined with compound specific isotope analysis, the degradation of 1,2-DCA and CF was mainly attributed to aerobic oxidation and reductive dechlorination, respectively, and TCE was removed by both aerobic and anaerobic biodegradation. Our findings provide a new and efficient strategy for in situ bioremediation of groundwater contaminated by mixed chlorinated solvents.

In silico analysis of soil, sediment and groundwater microbial communities to predict biodegradation potential.

This study examined soil, sediment and groundwater microbial communities for a set of key functional genes important for contaminant biodegradation. This involved PICRUSt2 (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States) predictions based on 16S rRNA gene amplicon datasets from three separate studies with different inocula and incubation conditions, as follows: aerobic soils, oxygen-limited microcosms containing sediments and groundwater, as well as methanogenic microcosms with different inocula. PICRUSt2 predicts functional profiles of microbial communities based on marker gene (16S rRNA gene) data. The relative abundances of genera previously associated with the biodegradation of chlorinated solvents/metabolites and/or 1,4-dioxane were also determined. Predicted values for each functional gene varied between the three datasets. In all, values were high for propane monooxygenase and low for soluble methane monooxygenase. Common phylotypes associated with propane monooxygenase in two of the three datasets included Mycobacterium, Rhodococcus and Pseudonocardia. Toluene monooxygenase predicted values were greater in the oxygen-limited microcosms compared to the other two datasets. The methanogenic microcosms exhibited the highest predicted values for particulate methane/ammonia monooxygenase. The most common genera detected, previously reported as chlorinated solvents/metabolites and/or 1,4-dioxane degraders, included Pseudomonas, Sphingomonas, Rhodococcus and Rhodanobacter. Eighteen of the queried genera were not detected. As expected, more potential anaerobic degrading genera were found in the oxygen-limited and methanogenic microcosms compared to the aerobic soils. The results provide key insights as to which genes and genera may be important for biodegradation over a range of inocula and redox conditions.

Determining effective diffusion coefficients of chlorohydrocarbons in natural clays: Unique results from highly resolved controlled release field experiments.

This study aims to precisely determine the effective diffusion coefficients of chlorohydrocarbons in low permeable units under in-situ field conditions. To this end, two controlled release field experiments using TCE and PCE as dense non-aqueous phase liquids (DNAPLs) were conducted in two natural clayey deposits. Several months to years after the controlled DNAPL release, highly resolved concentration profiles were determined for the chlorohydrocarbons that had diffused into the clayey deposits. Effective diffusion coefficients for TCE and PCE were then determined by calibrating a 3D numerical and 1D analytical model, respectively, to the measured high-resolution concentration profiles. The simulations revealed that the effective diffusion coefficients vary by as much as a factor of four within the same low permeability unit being consistent with observed small-scale heterogeneities. The determined chlorohydrocarbon effective diffusion coefficients were further used to determine the equivalent thickness of DNAPL that would completely dissolve in an idealized, parallel-plate fracture by diffusion transport into clayey deposits for the time periods of the controlled release field experiments. The equivalent TCE and PCE DNAPL film thicknesses ranged between 36 and 581 µm, respectively, comparable and exceeding fracture apertures measured in naturally fractured clay rich deposits. Hence, films of DNAPL initially contained within fractures in clay-rich deposits can completely dissolve away within a few months to a few years due to diffusion. This stored contaminant mass poses a risk to adjacent aquifers if it is re-released due to diffusion out of the matrix after source depletion or remediation.

In Situ Equilibrium Polyethylene Passive Sampling of Soil Gas VOC Concentrations: Modeling, Parameter Determinations, and Laboratory Testing.

The use of low-density polyethylene (PE) sheets as equilibrium passive soil gas samplers to quantify volatile organic compounds (VOCs) such as benzene, toluene, ethylbenzene, and xylenes, and chlorinated solvents (e.g., trichloroethene and tetrachloroethene) in unsaturated subsurface environments was evaluated via modeling and benchtop testing. Two methods were devised to quantify such VOCs in PE. Key chemical properties, including PE-water (KPEw) and PE-air (KPEa) partition coefficients and diffusivities in the PE (Dpe), were determined. These KPEw, KPEa, and Dpe values were consistent with extrapolations of data based on larger compounds. Using these parameter values, field equilibration times of less than 1 day were estimated for such VOCs when using 70-100 µm thick PE sheets. Further, benchtop batch tests carried out in jars filled with VOC-contaminated soils, after 1 or 2 days, showed concentrations in soil air deduced from PE that were consistent with concentrations deduced by analyzing either water or headspace gases recovered from the same tests. Thus, PE-based measurements may overcome inaccuracies from using total soil concentrations and equilibrium partitioning models that may overestimate vapor phase concentrations up to 2 orders of magnitude.

Natural Biodegradation of Vinyl Chloride and cis-Dichloroethene in Aerobic and Suboxic Conditions.

Chlorinated ethene (CE) groundwater contamination is commonly treated through anaerobic biodegradation (i.e., reductive dechlorination) either as part of an engineered system or through natural attenuation. Aerobic biodegradation has also been recognized as a potentially significant pathway for the removal of the lower CEs cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC). However, the role of aerobic biodegradation under low oxygen conditions typical of contaminated groundwater is unclear. Bacteria capable of aerobic VC biodegradation appear to be common in the environment, while aerobic biodegradation of cDCE is less common and little is known regarding the organisms responsible. In this study, we investigate the role of aerobic cDCE and VC biodegradation in a mixed contaminant plume (including CEs, BTEX, and ketones) at Naval Air Station North Island, Installation Restoration Site 9. Sediment and groundwater collected from the plume source area, mid-plume, and shoreline were used to prepare microcosms under fully aerobic (8 mg/L dissolved oxygen (DO)) and suboxic (< 1 mg/L DO) conditions. In the shoreline microcosms, VC and cDCE were rapidly degraded under suboxic conditions (100% and 77% removal in < 62 days). In the suboxic VC microcosms, biodegradation was associated with a > 5 order of magnitude increase in the abundance of functional gene etnE, part of the aerobic VC utilization pathway. VC and cDCE were degraded more slowly under fully aerobic conditions (74% and 30% removal) in 110 days. High-throughput 16S rRNA and etnE sequencing suggest the presence of novel VC- and cDCE-degrading bacteria. These results suggest that natural aerobic biodegradation of cDCE and VC is occurring at the site and provide new evidence that low (< 1 mg/L) DO levels play a significant role in natural attenuation of cDCE and VC.

Improved assessment and performance monitoring of a biowall at a chlorinated solvent site using high-resolution passive sampling.

This study contrasts the use of high-resolution passive sampling and traditional groundwater monitoring wells (GWMW) to characterize a chlorinated solvent site and assess the effectiveness of a biowall (mulch, compost and sand) that was installed to remediate trichloroethene (TCE), the primary contaminant of concern. High-resolution passive profilers (HRPPs) were direct driven hydraulically upgradient, within, and hydraulically downgradient of the biowall and in close proximity to existing GWMWs. Compared with hydraulically upgradient locations, the biowall was highly reducing, there were higher densities of bacteria/genes capable of reductive dechlorination, and TCE was being reductively transformed, but not completely, as cis-1,2-dichloroethene (cis-DCE) was detected within and hydraulically downgradient of the biowall. However, based on the high-resolution data, there were a number of important findings which were not discoverable using data from GWMWs alone. Data from the HRPPs indicate that the biowall was completely transforming TCE to ethene (C2H4) except within a high velocity interval, where the concentrations were reduced, but breakthrough of cis-DCE was apparent. Hydraulically upgradient of the biowall, concentrations of TCE increased with depth where a very low permeability zone exists that will likely remain as a long-term source. In addition, although low concentrations of cis-DCE were present downgradient of the biowall, surfacing into a downgradient stream was not detected. This study demonstrates the advantages of high-resolution passive sampling of aquifers to assess the performance of remediation techniques compared to traditional methods such as GWMWs.

Post-remediation geophysical assessment: Investigating long-term electrical geophysical signatures resulting from bioremediation at a chlorinated solvent contaminated site.

There is a growing need to assess long-term impacts of active remediation strategies on treated aquifers. A variety of biogeochemical alterations can result from interactions of the amendment with the aquifer, conceivably leading to a geophysical signal associated with the long-term alteration of an aquifer. This concept of post-remediation geophysical assessment was investigated in a shallow, chlorinated solvent-contaminated aquifer six to eight years after amendment delivery. Surface resistivity imaging and cross-borehole resistivity and induced polarization (IP) imaging were performed on a transect that spanned treated and untreated zones of the aquifer. Established relationships between IP parameters and surface electrical conductivity were used to predict vertical profiles of electrolytic conductivity and surface conductivity from the inverted cross-borehole images. Aqueous geochemistry data, along with natural gamma and magnetic susceptibility logs, were used to constrain the interpretation. The electrical conductivity structure determined from surface and borehole imaging was foremost controlled by the electrolytic conductivity of the interconnected pore space, being linearly related to fluid specific conductance. The electrolytic conductivity (and thus the conductivity images alone) did not discriminate between treated and untreated zones of the aquifer. In contrast, inverted phase angles and surface conductivities did discriminate between treated and untreated zones of the aquifer, with the treated zone being up to an order of magnitude more polarizable in places. Supporting aqueous chemistry and borehole logging datasets indicate that this geophysical signal from the long-term impact of the remediation on the aquifer is most likely associated with the formation of polarizable, dispersed iron sulfide minerals.

Preventing Parkinson's Disease: An Environmental Agenda.

Fueled by aging populations and continued environmental contamination, the global burden of Parkinson's disease (PD) is increasing. The disease, or more appropriately diseases, have multiple environmental and genetic influences but no approved disease modifying therapy. Additionally, efforts to prevent this debilitating disease have been limited. As numerous environmental contaminants (e.g., pesticides, metals, industrial chemicals) are implicated in PD, disease prevention is possible. To reduce the burden of PD, we have compiled preclinical and clinical research priorities that highlight both disease prediction and primary prevention. Though not exhaustive, the "PD prevention agenda" builds upon many years of research by our colleagues and proposes next steps through the lens of modifiable risk factors. The agenda identifies ten specific areas of further inquiry and considers the funding and policy changes that will be necessary to help prevent the world's fastest growing brain disease.

Evaluation of natural attenuation of 1,4-dioxane in groundwater using a 14C assay.

Monitored Natural Attenuation (MNA) is a preferred remedy for sites contaminated with 1,4-dioxane due to its low cost and limited environmental impacts compared to active remediation. Having a robust estimate of the rate at which biodegradation occurs is an essential component of assessing MNA. In this study, an assay was developed using 14C-labeled 1,4-dioxane to measure rate constants for biodegradation based on accumulation of 14C products. Purification of the 14C-1,4-dioxane stock solution lowered the level of 14C impurities to below 1% of the total 14C activity. This enabled determination of rate constants in groundwater as low as 0.0021 yr-1, equating to a half-life greater than 300 years. Of the 54 groundwater samples collected from 10 sites in the US, statistically significant rate constants were determined with the 14C assay for 24. The median rate constant was 0.0138 yr-1 (half-life = 50 yr); the maximum rate constant was 0.367 yr-1 (half-life = 1.9 yr). The results confirmed that biodegradation of 1,4-dioxane is occurring at 9 of the 10 sites sampled, albeit with considerable variability in the level of activity. The specificity of the assay was confirmed using acetylene and the absence of oxygen to inhibit monooxygenases.

Recent Advances in Sulfidated Zerovalent Iron for Contaminant Transformation.

2021 marks 10 years since controlled abiotic synthesis of sulfidated nanoscale zerovalent iron (S-nZVI) for use in site remediation and water treatment emerged as an area of active research. It was then expanded to sulfidated microscale ZVI (S-mZVI) and together with S-nZVI, they are collectively referred to as S-(n)ZVI. Heightened interest in S-(n)ZVI stemmed from its significantly higher reactivity to chlorinated solvents and heavy metals. The extremely promising research outcomes during the initial period (2011-2017) led to renewed interest in (n)ZVI-based technologies for water treatment, with an explosion in new research in the last four years (2018-2021) that is building an understanding of the novel and complex role of iron sulfides in enhancing reactivity of (n)ZVI. Numerous studies have focused on exploring different S-(n)ZVI synthesis approaches, and its colloidal, surface, and reactivity (electrochemistry, contaminant selectivity, and corrosion) properties. This review provides a critical overview of the recent milestones in S-(n)ZVI technology development: (i) clear insights into the role of iron sulfides in contaminant transformation and long-term aging, (ii) impact of sulfidation methods and particle characteristics on reactivity, (iii) broader range of treatable contaminants, (iv) synthesis for complete decontamination, (v) ecotoxicity, and (vi) field implementation. In addition, this review discusses major knowledge gaps and future avenues for research opportunities.