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Trichloroethylene (TCE) is a prevalent groundwater contaminant detected worldwide, and microbes are sensitive indicators and initial responders to these chemical contaminants causing disturbances to their ecosystem. In this study, microbes isolated from San Marcos River sediment were screened for their TCE degradation potential. Among the twelve isolates (SAN1-12), five isolates demonstrated TCE degradation within 5 days at 25 °C and 40 mg/L of TCE concentration in the following order: SAN8 (87.56%), SAN1 (77.31%), SAN2 (76.58%), SAN3 (49.20%), and SAN7 (3.36%). On increasing the TCE concentration to 80 mg/L, the degradation efficiency of these isolates declined, although SAN8 remained the prominent TCE degrader with 75.67% degradation. The prominent TCE-degrading isolates were identified as Aeromonas sp. SAN1, Bacillus sp. SAN2, Gordonia sp. SAN3, and Bacillus proteolyticus SAN8 using 16S rRNA sequencing. The TCE degradation and cell biomass of Bacillus proteolyticus SAN8 were significantly improved when the incubation temperature was increased from 25 °C to 30 °C. However, both slightly acidic and alkaline pH levels, as well as higher TCE concentrations, lowered the efficacy of TCE degradation. Nevertheless, these conditions led to an increase in bacterial cell biomass. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

AbstractA very small proportion of all chemicals in commerce have occupational exposure limits (OELs) based on quantitative risk assessments which require estimates of exposure-response relationships (XRs). For only 18 of the 94 chemicals declared by NIOSH to be carcinogens were human XRs reported in or calculable from published reports. For the 18 carcinogens, 96 such XRs could be derived (corresponding to chemicals with multiple associated cancer end-points and/or multiple source studies). Twenty-four of 96 XR estimates came directly from reported statistical models (on continuous cumulative exposure), 45 were derived from summary study-population attributes, and 27 came from categorical analyses. Using the 96 XRs, OEL conferring one-per-thousand excess lifetime risk were calculated. OSHA’s OEL, permissible exposure limits (PEL) were then compared to OEL derived from the 96 XRs. For 88 of the 96 calculated OELs (for which a corresponding PEL exists) all but 10 fell below the current PEL. Thirty-four OEL estimates were 10- to 100-fold below the PEL and 21 were greater than 100-fold below the PEL. This same pattern was observed using the different methods for deriving XRs. These findings can guide priorities in setting standards and the method is not limited to carcinogens. [ABSTRACT FROM AUTHOR]

Industrial chlorinated solvents continue to be among the most significant issues in groundwater (GW) pollution worldwide. This study assesses the effectiveness of eight novel oxidation treatments, including persulfate (PS), ferrous sulfate, sulfidated nano-zero valent iron (S-nZVI), and potassium ferrate, along with their combinations, for the potential in situ remediation of GW polluted with chlorinated solvents (1,2-dichloroethylene, trichloroethylene, and tetrachloroethylene). Our bench-scale results reveal that the combined addition of PS and S-nZVI can effectively eliminate trichloroethylene (10 µg/L), achieving removal rates of up to 80% and 92% within 1 h, respectively, when using synthetic GW. In the case of real GW, this combination achieved removal rates of 69, 99, and 92% for cis-1,2-dichloroethylene, trichloroethylene, and tetrachloroethylene, respectively, within 24 h. Therefore, this proposed remediation solution resulted in a significant reduction in the environmental risk quotient, shifting it from a high-risk (1.1) to a low-risk (0.2) scenario. Furthermore, the absence of transformation products, such as vinyl chloride, suggests the suitability of employing this solution for the in situ remediation of GW polluted with chlorinated solvents. [ABSTRACT FROM AUTHOR]

Trichloroethylene (TCE) is a prevalent groundwater contaminant detected worldwide, and microbes are sensitive indicators and initial responders to these chemical contaminants causing disturbances to their ecosystem. In this study, microbes isolated from San Marcos River sediment were screened for their TCE degradation potential. Among the twelve isolates (SAN1-12), five isolates demonstrated TCE degradation within 5 days at 25 °C and 40 mg/L of TCE concentration in the following order: SAN8 (87.56%), SAN1 (77.31%), SAN2 (76.58%), SAN3 (49.20%), and SAN7 (3.36%). On increasing the TCE concentration to 80 mg/L, the degradation efficiency of these isolates declined, although SAN8 remained the prominent TCE degrader with 75.67% degradation. The prominent TCE-degrading isolates were identified as Aeromonas sp. SAN1, Bacillus sp. SAN2, Gordonia sp. SAN3, and Bacillus proteolyticus SAN8 using 16S rRNA sequencing. The TCE degradation and cell biomass of Bacillus proteolyticus SAN8 were significantly improved when the incubation temperature was increased from 25 °C to 30 °C. However, both slightly acidic and alkaline pH levels, as well as higher TCE concentrations, lowered the efficacy of TCE degradation. Nevertheless, these conditions led to an increase in bacterial cell biomass.

Being classified as a suspected carcinogen, 1,4-dioxane (1,4-D) has been one of the most frequently detected organic contaminants in groundwater sites. Due to the common co-occurrence of 1,4-D with chlorinated compounds and a lack of comprehensive health advisory guideline standards established for potable water and other uses on a global scale, a new research emphasis to reflect more realistic situations needs to be placed onto the effects of common co-existing chemicals such as 1,1-dichloroethene, trichloroethylene, cis-1,2-dichloroethylene, and 1,1,1-trichloroethane on the environmental fate of 1,4-D. Additives (e.g., ions, nutrients, enzymes) are also introduced to enhance 1,4-D treatment efficiencies. To the best of our knowledge, however, there is no review article dealing with the removal of 1,4-D in the presence of chlorinated solvents and other interfering substances. Understanding its concurrent removal with the main chlorinated co-contaminants is necessary for more insightful and proper design of effective remediation strategies for 1,4-D. This review article will focus on the behavior, transport, and persistence of 1,4-D in the presence of other pervasive groundwater contaminants and substrates under diverse environmental conditions and treatment technologies. This review will also provide detailed information on currently available remediation technologies for 1,4-D (either individually or co-occurring) and potential key points to be considered for future technologies development. 1,4-dioxane (1,4-D) is an emerging toxic pollutant that is found as a contaminant in soil and groundwater. Despite its harmful nature, there are not many global standards regulating its levels in water. Therefore, finding effective ways to remove harmful pollutants is crucial for safer waters, requiring extended research and time. 1,4-D often exists together with other contaminants such as chlorinated solvents, making water treatment more difficult, costly, and less efficient. This review explains the physical and chemical behaviors of other co-contaminants when combined with 1,4-D as well as the current removal technologies as categorized based on physical, chemical, biological, or combination (hybrid) methods. It is found that each removal technique has its strengths and weaknesses but some failing to eliminate the co-solvents although they successfully removed 1,4-D. Thus, future research is warranted to further elucidate key reaction mechanisms between 1,4-D and other co-contaminants and to test real scale applications. [ABSTRACT FROM AUTHOR]

Industrial chlorinated solvents continue to be among the most significant issues in groundwater (GW) pollution worldwide. This study assesses the effectiveness of eight novel oxidation treatments, including persulfate (PS), ferrous sulfate, sulfidated nano-zero valent iron (S-nZVI), and potassium ferrate, along with their combinations, for the potential in situ remediation of GW polluted with chlorinated solvents (1,2-dichloroethylene, trichloroethylene, and tetrachloroethylene). Our bench-scale results reveal that the combined addition of PS and S-nZVI can effectively eliminate trichloroethylene (10 µg/L), achieving removal rates of up to 80% and 92% within 1 h, respectively, when using synthetic GW. In the case of real GW, this combination achieved removal rates of 69, 99, and 92% for cis-1,2-dichloroethylene, trichloroethylene, and tetrachloroethylene, respectively, within 24 h. Therefore, this proposed remediation solution resulted in a significant reduction in the environmental risk quotient, shifting it from a high-risk (1.1) to a low-risk (0.2) scenario. Furthermore, the absence of transformation products, such as vinyl chloride, suggests the suitability of employing this solution for the in situ remediation of GW polluted with chlorinated solvents.

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. [ABSTRACT FROM AUTHOR]

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 1H 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. [ABSTRACT FROM AUTHOR]

• Poly(lactic acid) (PLA) was insoluble in some industrially important halogenated large-sized solvents. • The α'-type crystals of PLA films changed to α-type crystals during immersion in insoluble solvents. • The α-type crystal structure was stable in these solvents. • The phenomenon did not simply follow the Hansen 3D solubility parameter rules. • The phenomenon was based on the molecular size and electrostatic potential values of the solvents. A circular economy requires that plastic packaging should be recyclable or compostable as well as reusable. Compostable/biodegradable poly(lactic acid) (PLA) is an alternative to conventional packaging materials for films, bags, and containers. Packaging is not only for food and beverages but also for medicine, agricultural chemicals, industrial chemicals, and waste solvents such as chlorinated solvents, which sometimes contain water. This study determined that PLA films were completely soluble in dichloromethane and chloroform, insoluble but strongly swollen in trans-1,2-dichlorocycrohexane, o-dichlorobenzene, and carbon tetrachloride, and insoluble with retained film shape in tetrachloroethylene (TCE), 1,2,4-trichlorobenzene (1,2,4-TCB), and 1-bromonaphthalene (1-BN). The equilibrium mass uptake values of pure insoluble solvents in PLA films were 0.977 ± 0.219 wt% for TCE, 1.716 ± 0.631 wt% for 1,2,4-TCB, and 3.351 ± 1.936 wt% for 1-BN. After sorption of the three insoluble pure solvents, the α'-type crystals of PLA films changed to α-type crystals. This phenomenon was based on the molecular size and electrostatic potential value of the solvents. When insoluble solvents were mixed with water, the water-in-oil mixture enhanced the mass uptake for TCE and 1,2,4-TCB but reduced it for 1-BN. The oil-in-water mixture distinctly reduced the solubility for all solvents. The α-type crystal structure was stable in TCE and 1-BN. If an industrially appropriate method of α-type crystal structure formation could be realized selectively, then PLA could be used as packaging materials for films, bags, and containers for these solvents without any further modification. [Display omitted] [ABSTRACT FROM AUTHOR]

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 (KMnO 4) 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 (MnO 4 −), and slowly release MnO 4 − 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-KMnO 4 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-KMnO 4 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 KMnO 4. 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 KMnO 4 (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 MnO 4 − 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. [Display omitted] • Slow-release permanganate gel (SRP-G) is a mixture of potassium permanganate and colloidal silica solution. • SRP-G solution spreads, gelates, and slowly releases permanganate in saturated porous media. • Cooling increases injectability, gelation lag time, spreading, release rate, and release duration of SRP-G in porous media. • Low-temperature SRP-G can be effective for treating large or dilute plumes of chlorinated solvents in groundwater. • Low-temperature SRP-G scheme can be used with other treatment agents to reduce different pollutants in groundwater. [ABSTRACT FROM AUTHOR]

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.

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. [ABSTRACT FROM AUTHOR]

Bioremediation is an active process for the detoxification of polluted ambient media employing the metabolism of microbes, while natural attenuation relies on physical, chemical and biological processes occurring without human intervention. A shallow aquifer (A0) was treated using a bioremediation approach through the amendment of whey to detoxify the most abundant contaminants: 1,1,2,2- tetrachloroethane (1,1,2,2-TeCA), perchloroethene (PCE) and trichloroethene (TCE). A deeper aquifer (A1), showing lower concentration of the contaminants, was left untreated. In A0, a concomitant decrease of more chlorinated molecules 1,1,2,2-TeCA, PCE and TCE and an increase of less halogenated molecules such as trichloroethane (1,1,2-TCA), cis-dichloroethene (cis-DCE) and vinyl chloride (VC) were observed, suggesting that a reductive dechlorination took place. In contrast, the aquifer A1 did not show a significant decrease of contaminants during this period. A metagenomic approach (shot gun and 16S rRNA gene) was then used to investigate the microbial population of the two aquifers. A massive presence of the dehalogenator Dehalococcoides mccartyi (D. mccartyi) and a spectrum of different Geobacter species were detected in A0, after the treatment. The metagenome assembly of shotgun (SG) data further indicated a significant presence of methanogenic archaea, most likely from class Methanomassiliicoccales, at a level comparable to that of D. mccartyi. Instead, A1 was characterized by the species Burkholderia, Curvibacter and Flavobacterium. These results indicate that the autochthonous microbial consortia reflected the geochemistry of the two aquifers, with a dominant population thriving in an anoxic and nutrient rich environment implicated in reductive dehalogenation in A0 and a more diverse population, not able to decompose the pollutants, in A1. [ABSTRACT FROM AUTHOR]

This study demonstrates a groundwater circulation enhanced electrobioremediation process for 1,2-dichloroethane (1,2-DCA) degradation in a simulated heterogeneous aquifer, in which a pair of electrodes were separately implanted between an injection well and an abstraction well and groundwater circulation carries anodic O2 and cathodic H2 sequentially into the aquifer forming oxidation and reduction regions. A two-dimensional tank was filled with interbedded sandy-clayed sediments to simulate the field aquifer conditions. It is expected that the interbedded clayed sediments could supply bacteria for biological degradation and also supply Fe(II) for chemical oxidation in the presence of O2 due to hydroxyl radical (•OH) production. At a constant circulation flow rate of ∼3.5 PVs/day, 1,2-DCA at an initial concentration of ∼8.07 mg/L was degraded to ∼0.65 mg/L (91.9% removal) after 33-day treatment, in which 80–100 mA current was applied to the electrodes after the initial stage of 8-day circulation. Batch experiments proved that 1,2-DCA degradation was mainly attributed to aerobic biological oxidation, with likely contribution of anaerobic reductive dechlorination in certain areas. Chemical 1,2-DCA oxidation was negligible. This study suggests that coupling groundwater circulation and separated electrolysis is effective for stimulating biological 1,2-DCA degradation in heterogeneous aquifers. [ABSTRACT FROM AUTHOR]

This study investigates the influence of density-driven transport on chlorinated vapor intrusion through modeling and experiments. Density-driven transport involves downward vapor advection, potentially reducing vapor intrusion into buildings. A 1-D steady-state numerical model was developed using COMSOL Multiphysics, considering upward diffusion and downward density-driven advection in the subsoil and in the granular fill layer beneath building's foundations. Source vapor concentration and granular fill layer permeability emerged as the key factors affecting density-driven transport. Regardless of building characteristics, for permeabilities in the granular fill layer exceeding 10−7 m2, density-driven transport is expected to become relevant at vapor concentrations of 1 mg m−3, while for lower soil permeabilities (10−8-10−10 m2), density-driven transport impact is expected for vapor concentrations exceeding 1 g m−3. The results of laboratory column trichloroethylene (TCE) diffusion tests through sand and gravel supported these findings, showing a vertical stratification of TCE vapor concentrations consistent with the model. The trends expected by modeling also align with the findings of different field studies, where the source to building attenuation factors (AF) were found to decrease with increasing source vapor concentration. These outcomes highlight that the common approach adopted for vapor intrusion screening from soil gas data based on default AF values independent of source vapor concentration, may potentially lead to an overestimation of indoor concentrations in the presence of high vapor concentrations and highly permeable soils. Given the use of permeable granular fill layers in building construction, this study underscores the importance of accounting for density-driven transport to improve the accuracy of vapor intrusion risk assessment. [Display omitted] • Density-driven transport influence on chlorinated vapor intrusion was investigated. • TCE vapors diffusion tests were performed in sand and gravel-filled columns. • A numerical model considering density-driven for vapor transport was developed. • Subsurface vapor concentration and soil permeability emerged as determinant factors. • Neglecting density-driven effect may lead to overestimating vapor intrusion risk. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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.

Background: Hypospadias is a male congenital malformation that occurs in ~2 of 1,000 births. The association between hypospadias and fetal exposure to environmental chemicals has been studied, but the results are inconsistent. Although several petroleum and chlorinated solvents are suspected to have teratogenic effects, their role in the occurrence of hypospadias has been little studied and never using biomarkers of exposure. We aimed to evaluate the association between fetal exposure to petroleum and chlorinated solvents measured in meconium and the occurrence of hypospadias.Methods: We conducted a pilot case-control study in the maternity of the University Hospital of Rennes (France). Eleven cases of hypospadias and 46 controls were recruited between October 2012 and January 2014. Data from hospital records and maternal self-reported questionnaires, including socio-demographic characteristics and occupational and non-occupational exposure to chemicals, were collected. Meconium samples were collected using a standardized protocol. Levels of petroleum solvents (toluene, benzene, ethylbenzene, and p, m, and o xylene), certain metabolites (mandelic acid, hippuric acid, methylhippuric acid, S-phenylmercapturic acid, S-benzylmercapturic acid, and phenylglyoxylic acid), and two chlorinated solvents (trichloroethylene and tetrachloroethylene) were measured in meconium by gas and liquid chromatography, both coupled to tandem mass spectrometry. Associations between the concentration of each chemical and the occurrence of hypospadias were analyzed using exact logistic regressions adjusted for maternal age, educational level, pre-pregnancy body mass index, and alcohol, and tobacco consumption during pregnancy. Results are presented with odds ratios (ORs) and their 95% confidence intervals (CIs).Results: Quantification rates for petroleum and chlorinated solvents or metabolites ranged from 2.2% (for methylhippuric acid) to 77.1% (for trichloroethylene) of the meconium samples. We found a significant association between the quantification of phenylglyoxylic acid (metabolite of styrene and ethylbenzene) in the meconium and a higher risk of hypospadias (OR = 14.2, 95% CI [2.5–138.7]). The risk of hypospadias was non-significantly elevated for most of the other solvents and metabolites.Conclusion: This exploratory study, on a limited number of cases, suggests an association between petroleum solvents and hypospadias. Additional studies are needed to confirm these results and identify the determinants for the presence of these solvents in meconium.

The Mineral Trap, or Min‐Trap™, is a monitoring well‐based sampler designed to collect direct physical evidence of reactive mineral formation in situ without collecting soil or rock core samples. The Min‐Trap consists of a nonreactive granular medium (e.g., silica sand) within water‐permeable mesh pillows that are supported inside a slotted polyvinyl chloride housing that is incubated within a conventional monitoring well. The primary objective of the Min‐Trap in this application is to collect reactive minerals that are forming in the aquifer in a retrievable format that can be submitted for laboratory analysis. To evaluate the capability of Min‐Traps to capture reactive iron minerals, both a laboratory tank test and a field test were conducted. Both tests confirmed that iron sulfide minerals form in the Min‐Trap under sulfate reducing conditions within several weeks. Analysis of the precipitated minerals via the AMIBA analysis suite showed that they almost entirely consisted of weak acid soluble (biogenic, microcrystalline) ferrous iron‐based minerals, and at least two thirds of the sulfur‐containing minerals were monosulfides (i.e., mackinawite) at the end of each test. Scanning electron microscopy confirmed the colocation of iron and sulfur in the mineral masses. The dominance of the ferrous iron and reduced sulfur verifies that little to no oxidation of the captured minerals occurred between sample collection and analysis. A subsurface soil core was collected during the field test next to the Min‐Trap‐containing well. AMIBA results were consistent between the native soil and the Min‐Trap except for much higher strong acid soluble (crystalline) ferric iron in the native soil when compared to the silica sand of the Min‐Trap, as expected. This work shows that Min‐Traps are useful for documenting the formation of reactive iron sulfides (FeSx) that can form during in situ anaerobic biostimulation and can drive complementary abiotic treatment of chlorinated volatile organic compounds. Mineralogical data obtained from Min‐Traps can be applied to assess remedial objectives at several stages of the remedial program, including initial characterization, alternatives evaluation, feasibility testing, remedy optimization, and transition from active treatment to passive remedial methods. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • A Fick's Law based PDMS dialysis sampler was developed and tested at a TCE contaminated site. • The sampler can be used for measuring contaminants in the unsaturated zone and saturated aquifers. • The sampler is less susceptible to gas disturbance than other sampling methods. • The sampler exhibits high sensitivity to low contaminant concentrations. • The samplers can be densely deployed inside a monitoring well at multiple depths. [ABSTRACT FROM AUTHOR]

Bioremediation is an active process for the detoxification of polluted ambient media employing the metabolism of microbes, while natural attenuation relies on physical, chemical and biological processes occurring without human intervention. A shallow aquifer (A0) was treated using a bioremediation approach through the amendment of whey to detoxify the most abundant contaminants: 1,1,2,2- tetrachloroethane (1,1,2,2-TeCA), perchloroethene (PCE) and trichloroethene (TCE). A deeper aquifer (A1), showing lower concentration of the contaminants, was left untreated. In A0, a concomitant decrease of more chlorinated molecules 1,1,2,2-TeCA, PCE and TCE and an increase of less halogenated molecules such as trichloroethane (1,1,2-TCA), cis-dichloroethene (cis-DCE) and vinyl chloride (VC) were observed, suggesting that a reductive dechlorination took place. In contrast, the aquifer A1 did not show a significant decrease of contaminants during this period. A metagenomic approach (shot gun and 16S rRNA gene) was then used to investigate the microbial population of the two aquifers. A massive presence of the dehalogenator Dehalococcoides mccartyi (D. mccartyi) and a spectrum of different Geobacter species were detected in A0, after the treatment. The metagenome assembly of shotgun (SG) data further indicated a significant presence of methanogenic archaea, most likely from class Methanomassiliicoccales, at a level comparable to that of D. mccartyi. Instead, A1 was characterized by the species Burkholderia, Curvibacter and Flavobacterium. These results indicate that the autochthonous microbial consortia reflected the geochemistry of the two aquifers, with a dominant population thriving in an anoxic and nutrient rich environment implicated in reductive dehalogenation in A0 and a more diverse population, not able to decompose the pollutants, in A1.

Perchloroethylene (PERC) is the most common solvent used for dry cleaning in the United States. PERC is a reproductive toxicant, neurotoxicant, potential human carcinogen, and a persistent environmental pollutant. The Environmental Protection Agency is evaluating PERC under the Frank R. Lautenberg Chemical Safety for the 21st Century Act, which amended the Toxic Substances Control Act (amended TSCA), and has mandated that PERC dry cleaning machines be removed from residential buildings. Some local and state programs are also requiring or facilitating transitions to alternative cleaning technologies. However, the potential for these alternatives to harm human health and the environment is not well-understood. This review describes the issues surrounding the use of PERC and alternative solvents for dry cleaning while highlighting the lessons learned from a local government program that transitioned PERC dry cleaners to the safest current alternative: professional wet cleaning. Implications for future public health research and policy are discussed: (1) we must move away from PERC, (2) any transition must account for the economic instability and cultural aspects of the people who work in the industry, (3) legacy contamination must be addressed even after safer alternatives are adopted, and (4) evaluations of PERC alternatives are needed to determine their implications for the long-term health and sustainability of the people who work in the industry.

A site in mid-western Sweden contaminated with chlorinated solvents originating from a previous dry cleaning facility, was investigated using conventional groundwater analysis combined with compound-specific isotope data of carbon, microbial DNA analysis, and geoelectrical tomography techniques. We show the value of this multidisciplinary approach, as the different results supported each interpretation, and show where natural degradation occurs at the site. The zone where natural degradation occurred was identified in the transition between two geological units, where the change in hydraulic conductivity may have facilitated biofilm formation and microbial activity. This observation was confirmed by all methods and the examination of the impact of geological conditions on the biotransformation process was facilitated by the unique combination of the applied methods. There is thus significant benefit from deploying an extended array of methods for these investigations, with the potential to reduce costs involved in remediation of contaminated sediment and groundwater. [ABSTRACT FROM AUTHOR]

Petroleum hydrocarbon contaminants in groundwater are among the most impactful environmental problems in oil production in southern Iraq, especially Basra city. Petroleum hydrocarbon contaminants affect related projects surrounding the primary pollution site. Benzene, toluene, and dimethylbenzene are the most toxic pollutants affecting the removal of perchloroethene (Cl2C=CCl2) and trichloroethene (C2HCl3) in groundwater. These pollutants have high solubility in water, leading to their transport over long distances in groundwater and difficult removal. The influence of petroleum hydrocarbons on the chlorine removal of perchloroethene and trichloroethene was studied using a polytetrafluorethylene column packed with zero-valent iron (ZVI). Batch experiments were implemented to investigate the equilibrium supply of mixtures between the aqueous and solid stages in packed column systems. It was designated using the Freundlich isotherm expression, and the result showed that R2 was greater than 0.97 for benzene, toluene, and xylene. The column study noted that the reaction constant was decreased in all columns by approximately 48 % when the pore volume was between 50 and 205, which reflects the dechlorination priority of P-CE over T-CE. These findings indicate that benzene and toluene are more effective for adsorption on the ZVI particle surfaces owing to disparate influences. [ABSTRACT FROM AUTHOR]

Nineteen enantiomer pairs of polychlorinated biphenyls (PCBs) with three or four chloro substituents about the central carbon--carbon bond form a stable subclass of compounds whose biological effects vary with their chirality. Optical rotations for this group ofPCBs were determined from density functional calculations employing extended atomic orbital gauge invariant basis sets. A comparison of these results with the experimental ones found from the literature for 10 of the pairs enabled the identification of their absolute configurations as analytes in gas chromatography studies. Key words: PCB atropisomers, optical rotation, absolute configuration, DFT. Dix-neuf paires d'enantiomeres de biphenyls polychlores (BPC) possedant trois ou quatre substituants chloro autour de la liaison carbone--carbone centrale forment une sous-classe de composes stables dont les effets biologiques varient en fonction de leur chiralite. Nous avons determine les valeurs de rotation optique pour ce groupe de BPC au moyen de calculs de fonctionnelle de la densite en utilisant des bases d'orbitales atomiques invariantes de jauge etendues. En comparant ces resultats aux resultats experimentaux tires de la litterature pour 10 des paires, nous avons ete en mesure d'etablir leur configuration absolue comme analytes dans des etudes de chromatographie en phase gazeuse. [Traduit par la Redaction] Mots-cles : atropisomeres de BPC, rotation optique, configuration absolue, DFT., Introduction Polychlorinated biphenyls (PCB) are a class of well documented environmental pollutants. (1) Because of their carcinogenic, neurotoxic, and endocrine disruption properties, their persistence and bioaccumulation pose a serious threat [...]

An in situ groundwater remediation process, termed EGCW, was developed in this study by integrating in-well groundwater electrolysis into groundwater circulation well. Groundwater circulation carries electrolytically generated O2 and H2 into the impacted aquifer for in situ biodegradation of contaminants. In a two-dimensional tank filled with field sandy sediments, simulated trichloroethylene (TCE)-contaminated groundwater was circulated between an injection well with electrodes inside and a pumping well. Results from a 50-day EGCW experiment show that in-well electrolysis oxygenated most region near the injection well, and 10 mg/L TCE was mainly biodegraded aerobically to about 2.7 mg/L (73% removal) by the indigenous microbes. Aerobic TCE degradation was enhanced by the pulsed addition of acetate. Together with the proofs of stable carbon isotope fractionation (enrichment factor: −0.57‰–−1.53‰) and microbial community variation after EGCW treatment, aerobic cometabolism was proposed to be the most likely mechanism for TCE degradation. It is interesting to find that the intrinsic organic carbon in aquifer matrix could fuel the aerobic TCE degradation, particularly at low TCE concentrations. EGCW treatment is advantageous in terms of supplying appropriate dosages of electron acceptor (O2) and donor (H2) for in situ bioremediation because groundwater electrolysis and circulation are expedient and controllable. [ABSTRACT FROM AUTHOR]

• Simultaneous reduction of trichloroethylene and Cr(VI) demonstrated in a bioelectrochemical reactor (BES). • In the BES, Cr(VI) removal was due to both applied reducing potential and microbial activity. • Cr(VI) exerted partial inhibition on reductive dechlorination in unacclimated dechlorinating consortium. • Previous acclimation period increased both dechlorination performance and removal rate. • Co-contamination microbial consortia adaptation confirmed by a long-term, continuous-flow experiment. A continuous-flow bioelectrochemical reactor was developed in a previous study to address the bioremediation of groundwater contaminated by trichloroethene (TCE). The present report investigated the applicability of the same system in the presence of Cr(VI) and its possible inhibitory effect on dehalorespiring bacterial populations. Preliminary batch tests were performed at the optimal cathodic reducing potential for the reductive dechlorination (RD) of TCE (-0.65 V vs. the standard hydrogen electrode) with two different dechlorinating microorganism consortia. The results demonstrated that Cr(VI) removal efficacy was increased by microorganisms that had been previously acclimatised to Cr(VI). Specifically, Cr(VI) was completely reduced only in the presence of acclimated microorganisms. The presence of chromate negatively affected RD performance, by either (i) limiting the TCE transformation to cis-dichloroethene at lower concentrations, or (ii) completely inhibiting RD at higher concentrations. In contrast, after the acclimation period, RD was extended down to vinyl chloride, which is the main TCE daughter product. Finally, the continuous flow reactor was fed by synthetic groundwater contaminated with TCE (50 μM) and Cr(VI) (45 μM), and the experimental results showed that Cr(VI) was completely reduced under RD conditions. Moreover, TCE removal was complete, with vinyl chloride and ethene as the main intermediates, thus indicating that chromate inhibition was decreased by Cr(VI) removal. [ABSTRACT FROM AUTHOR]

Perchloroethylene is used mainly as a solvent in dry cleaning, cleaning of electrical equipment, and degreasing of metal parts. The authors report a case of acute poisoning with perchloroethylene contracted by a maintenance worker when cleaning an electric transformer. Since perchloroethylene may cause severe poisoning and the International Agency for Research on Cancer has classified it as a probable carcinogen for humans, the authors have revised the main substances that may replace perchloroethylene in the workplace. Med Pr. 2019;70(3):393–5

Groundwater at an abandoned industrial area near Bergamo, Italy, was historically contaminated by tetrachloroethylene (PCE) (>100 µg/L) and, to a lesser extent, by trichlorethylene (TCE), dichloropropane (DP) and 1,1,2,2-tetrachloroethane (R-130). A liquid reagent (EHC® Liquid) was selected for remediation of groundwater at the site. The reagent is provided in two parts: EHC® Liquid Mix (a soluble organo-iron salt), and ELS® Microemulsion (a lecithin-based carbon substrate), and is designed to promote both in situ chemical reduction (ISCR) and enhanced reductive dechlorination (ERD) to destroy chlorinated organic compounds. The two components are mixed with water and injected into the subsurface. Once in groundwater, EHC® Liquid rapidly generates highly reduced conditions, favouring both biotic and abiotic dechlorination reactions. Less than 6 months after the injection of EHC® Liquid in the main source area, concentrations of the target contaminants had reached the site-specific remediation target values (CSC Legislative Decree 152/06) in the main monitoring piezometers present in the area, thus demonstrating the effective establishment of enhanced biotic and abiotic reducing conditions and degradation of the target compounds. [ABSTRACT FROM AUTHOR]

The flash points of binary mixtures of toluene with two chlorinated hydrocarbons (trichloroethylene and dichloromethane) at different concentrations were investigated to evaluate their predictability by existing mixing rules. Measurements were performed using both open and closed cup flash point testers highlighting complex ignition phenomena. Beyond a certain level of concentration in chlorinated compound, no proper flash is observed, in our test conditions when the flame is presented, but specific behaviors are observed that did not allow the definitive determination of a flash point. The observed phenomena can be attributed to the formation of halogenated radicals, presenting flame‐retardant behaviors, by decomposition of the chlorinated vapors at the contact of the flame. Existing mixing rules are based on the consideration of the vapor‐liquid equilibrium defining the amount of flammable vapors above the liquid surface. So, the application of such mixing rule failed predicting this specific phenomenon, more likely related to a specific reactivity problem. This work also confirms that the sole consideration of the flash point to investigate the flammability of such mixtures may lead to an underestimation of their actual hazard. Additional experimental tests should be conducted to investigate deeper the flammability of such liquid mixtures. [ABSTRACT FROM AUTHOR]

At contaminated sites, it is common to observe volatile organic compounds rising from subsurface sources and migrating into overlying buildings through cracks or other openings present in foundation slabs and basement walls. Such process, called vapor intrusion, is usually the most critical exposure pathway at sites contaminated by chlorinated solvents. In this study we present a chlorinated vapor intrusion tool implemented in Microsoft® Excel® using Visual Basic for Applications and integrated within a graphical interface that helps users to visualize two-dimensional (2D) soil gas concentration profiles and indoor air concentration in scenarios involving subsurface vertical heterogeneity. Vertical heterogeneity in soil gas concentration can be induced by a variable soil moisture profile caused by layering (geological barriers) or by the presence of the capillary fringe. This tool can be used in the risk assessment procedure to assess expected indoor air concentrations in conjunction with other lines of evidence, such as the evaluation of the 2D soil gas concentration profiles below and beyond the building footprint. Moreover, this tool allows users to predict indoor air concentration by employing either the traditional perimeter crack entry pathway or the empirical subslab-to-indoor attenuation factor. After a brief description of the developed tool, we show some practical applications to highlight the potential benefits in using this tool compared with the U.S. Environmental Protection Agency (U.S. EPA) tool that implements a simplified form of the Johnson and Ettinger model. Based on our testing, we found that the two-layer approach (capillary fringe and vadose zone) employed in the U.S. EPA tool, can lead to an overestimation of subslab vapor concentrations by more than an order of magnitude. [ABSTRACT FROM AUTHOR]

Vinyl chloride (VC) is a common groundwater contaminant and known human carcinogen. Three major bacterial guilds are known to participate in VC biodegradation: aerobic etheneotrophs and methanotrophs, and anaerobic organohalide-respiring VC-dechlorinators. We investigated the spatial relationships between functional genes representing these three groups of bacteria (as determined by qPCR) with chlorinated ethene concentrations in a surficial aquifer at a contaminated site. We used cryogenic soil coring to collect high-resolution aquifer sediment samples and to preserve sample geochemistry and nucleic acids under field conditions. All samples appeared to be anaerobic (i.e., contained little to no dissolved oxygen). VC biodegradation associated functional genes from etheneotrophs (etnC and/or etnE), methanotrophs (mmoX and/or pmoA), and anaerobic VC-dechlorinators (bvcA and/or vcrA) coexisted in 48% of the samples. Transcripts of etnC/etnE and bvcA / vcrA were quantified in contemporaneous groundwater samples, indicating co-located gene expression. Functional genes from etheneotrophs and anaerobic VC-dechlorinators were correlated to VC concentrations in the lower surficial aquifer (p < 0.05). Methanotroph functional genes were not correlated to VC concentrations. Cryogenic soil coring proved to be a powerful tool for capturing high-spatial resolution trends in geochemical and nucleic acid data in aquifer sediments. We conclude that both aerobic etheneotrophs and anaerobic VC-dechlorinators may play a significant role in VC biodegradation in aquifers that have little dissolved oxygen. Image 1 • Cryogenic coring is a powerful tool for capturing high resolution trends in biogeochemical data. • Geochemical and carbon stable isotope data indicated in situ chlorinated ethene degradation. • Aerobic and anaerobic vinyl chloride-degrading bacteria coexisted in 48% aquifer sediment samples. • Etheneotrophs and VC dechlorinators were correlated to VC concentrations in the lower surficial aquifer. [ABSTRACT FROM AUTHOR]

Chlorinated solvents are toxic and poorly biodegradable pollutants frequently found in contaminated aquifers. Experimental data of chloroform (CF) aerobic cometabolic biodegradation in a sand column with butane as growth substrate were simulated with a system of non‐stationary second‐order partial differential equations with non‐linear kinetic terms. A MATLAB optimization code based on the Gauss‐Newton method and coupled with the Comsol Multiphysics finite elements solver was developed to calibrate the model. For each experimental phase, the best‐fit quality was evaluated by an innovative multi‐variable model adequacy test. The proposed code solved systems of up to 5 partial differential equations and optimized up to 6 unknown parameters, leading to statistically acceptable best‐fits. The optimization of the butane/oxygen pulsed feed led to an 82 % CF biodegradation and to a 0.27 gCF/gbutane transformation yield. When the substrate/pollutant ratio was minimized, the standard model of aerobic cometabolism initially tested required additional terms aimed at taking into account the depletion of reducing energy, in order to attain a statistically acceptable best‐fit. This is the first work in which a model of aerobic cometabolism taking into account reducing energy availability was applied to a continuous‐flow process. The proposed optimization code can be used for model calibration in a wide range of physical problems described by non‐stationary, non‐linear partial differential equations, a task that no commercial software can perform. The developed code is made available in the Supplementary Material. [ABSTRACT FROM AUTHOR]

Abstract The objective of this research was to evaluate slow-release permanganate and unactivated persulfate for in situ treatment of dioxane and associated chlorinated solvents. Laboratory batch studies with unactivated persulfate in deionized water or in soil and groundwater demonstrated dioxane removal with pseudo second-order rate constants ranging from 10−5 to 10−3 M−1 s−1. Flow-through column studies demonstrated over 99% dioxane removal with slow-release unactivated persulfate but not with slow-release permanganate. The slow-release permanganate cylinders became coated with a rind that limited oxidant mass transfer and dioxane oxidation. A field study was conducted with slow-release persulfate cylinders transverse to groundwater flow. Over 99% removal of dioxane and chlorinated solvents was observed 2.5 m downgradient of the cylinders. Density-driven flow associated with the released persulfate was observed and was attributed to a low horizontal hydraulic gradient. Thus, most of the contaminant and persulfate flux was thought to be isolated to a deep aquifer zone that was bound by an underlying silt aquitard. Contaminant reductions were also observed in shallow groundwater samples, albeit at a lesser extent. The longevity of the persulfate oxidant cylinders was estimated to be 6–12 months. Results of this study demonstrate that dioxane and co-mingled chlorinated solvents can be effectively treated using slow-release persulfate cylinders. Careful consideration to cylinder placement during the design phase is essential to prevent the contaminant plume from bypassing and not coming into contact with the released oxidant. Highlights • Persulfate without added activators and permanganate promoted dioxane and chlorinated solvent destruction. • A rind formed around slow-release permanganate cylinders limited permanganate release, resulting in poor dioxane destruction. • 99% removal of dioxane and chlorinated solvents was observed in a field study using slow-release persulfate cylinders. • Density-driven flow was observed and was attributed to a low horizontal gradient at the site. [ABSTRACT FROM AUTHOR]

Abstract Groundwater status in highly urbanized areas is particularly affected by anthropogenic influence due to diffuse pollution deriving from many sources. This makes very often challenging to determine whether the observed groundwater conditions are the result of localized pollutant sources (PS-Point Sources). In the EU legislative framework it is accepted that, when Natural Background Levels (NBLs) of undesirable elements are proven to be higher than specific Groundwater Quality Standards (GQSs), NBLs should be assumed as GQSs. No procedure is instead defined when anthropogenic Diffuse Pollution Background levels (DBPLs) are higher than GQSs and make unfeasible any remediation strategy. Among the many contaminants affecting groundwater, the chlorinated solvents, tetrachloroethylene (PCE), trichloroethylene (TCE) and trichloromethane (TCM) among the organics and hexavalent chromium, among the inorganics, having been widely used in several industries all over Europe, are very often the most prevalent contaminants in soil and groundwater. Aim of this paper is to discuss a multivariate statistical approach to address the issue of identification of anthropogenic Diffuse Pollution Background Levels. With such aim, an area of about 1600 km2, including the Functional Urban Area of Milan, was considered and 10 independent geochemical datasets, provided by local and regional agencies, and covering the period 2003–2014 were merged into a single database after homogenization and multiple quality checks. A total of 618,258 chemical analyses from 3477 sampling wells were considered, being all samples collected and analyzed through internally consistent protocols. The analysis enabled to identify five main clusters, having specific hydrogeological characteristics, different temporal profiles and pollutant background concentration levels, which were also found to respond differently to meteo-climatic changes. This study offers a robust knowledge basis for drafting a diffuse pollution management plan of the area. Graphical abstract Unlabelled Image Highlights • Knowledge of diffuse pollution is needed for the management groundwater remediation • Groundwater chemistry after decades of urbanization is investigated in the Milan area. • Temporal and spatial patterns of groundwater diffuse pollution were documented • Diffuse pollution background levels may be determined based on the observed patterns [ABSTRACT FROM AUTHOR]

Subgrade biogeochemical reactors (SBGRs) are an in situ remediation technology shown to be effective in treating contaminant source areas and groundwater hot spots, while being sustainable and economical. This technology has been applied for over a decade to treat chlorinated volatile organic compound source areas where groundwater is shallow (e.g., less than approximately 30 feet below ground surface [ft bgs]). However, this article provides three case studies describing innovative SBGR configurations recently developed and tested that are outside of this norm, which enable use of this technology under more challenging site conditions or for treatment of alternative contaminant classes. The first SBGR case study addresses a site with groundwater deeper than 30 ft bgs and limited space for construction, where an SBGR column configuration reduced the maximum trichloroethene (TCE) groundwater concentration from 9,900 micrograms per liter (μg/L) to <1 μg/L (nondetect) within approximately 15 months. The second SBGR is a recirculating trench configuration that is supporting remediation of a 5.7‐acre TCE plume, which has significant surface footprint constraints due to the presence of endangered species habitat. The third SBGR was constructed with a new amendment mixture and reduced groundwater contaminant concentrations in a petroleum hydrocarbon source area by over 97% within approximately 1 year. Additionally, a summary is provided for new SBGR configurations that are planned for treatment of additional classes of contaminants (e.g., hexavalent chromium, 1,4‐dioxane, dissolved explosives constituents, etc.). A discussion is also provided describing research being conducted to further understand and optimize treatment mechanisms within SBGRs, including a recently developed sampling approach called the aquifer matrix probe. [ABSTRACT FROM AUTHOR]

• Analysis of injection of xanthan with/without SDBS on DNAPL recovery in layered soils. • Repulsive electrostatic forces and hydrophobic interactions in xanthan-SDBS mixture. • Impact of permeability and density contrasts on DNAPL displacement in layered system. • Role of confinement of contaminated soil on displacement of DNAPL. • Modeling of two-phase flow (non-Newtonian fluid and DNAPL) in multilayer system. 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. [Display omitted] [ABSTRACT FROM AUTHOR]

The aim of this work was to gain insights about the feasibility of chlorinated solvents removal through biostimulated and bioaugmented biological processes in laboratory-scale permeable reactive barriers (PRBs) under anaerobic and aerobic conditions. The experimental plant consisted of two Plexiglas cylindrical columns filled with silica sand and fed with real groundwater contaminated by chlorinated solvents (mainly 1,2-dichloroethane, 1,2-DCA, at a concentration of 20 mg l−1). Column A simulated a PRB containing poly-β-hydroxybutyrate (PHB) powder as electron donor and worked under anaerobic conditions; in Column B an inlet air flow rate ensured aerobic conditions. Both columns were inoculated with dechlorinating bacterial consortia obtained by enrichment cultures from the same contaminated groundwater. Results from Column A showed that PHB can be fermented and used as a slow-releasing carbon source for sustaining reductive dechlorination, as revealed by acetate production up to 267 mg l−1 and 100% 1,2-DCA removal. The microbial community detected in Column A at the end of the experimental period was mainly enriched in sulfate reducing bacteria that could act as both fermenting and dechlorinating agents. Column B showed a slight lower 1,2-DCA removal efficiency (98%) likely related to the establishment of aerobic (co)metabolic processes. [Display omitted] • 98–100% (an)aerobic 1,2-DCA removal from a real contaminated groundwater in PRB. • PHB used as slow-release acetate source for anaerobic reductive dechlorination, 267 mg l−1. • Establishment of direct or cometabolic oxidative biodegradation in aerobic PRB. • Biodegradation confirmed by metagenomic detection of dehalogenating bacteria. • Feasibility of a bioremediation approach using bioaugmented and biostimulated PRBs. [ABSTRACT FROM AUTHOR]