1,4-Dioxane pollution at contaminated groundwater sites in western Germany and its distribution within a TCE plume

Groundwater quality and associated health risks in the Eastern Region of Ghana

In the Eastern Region of Ghana, 95 % of residents have access to boreholes. However, approximately 30 % of these boreholes are characterized by unpleasurable taste, odour, oily scum and particulate matter. Thus, this study aimed to assess water quality, predict the sources of groundwater contaminants, evaluate the human health risk and to generate spatial distribution and health risk maps. In achieving this, the water quality of 136 boreholes in the region was evaluated through Water Quality Index (WQI) and Groundwater Pollution Index (GPI) analyses. Multivariate statistical procedures, namely, principal component and correlation analyses were employed to define the major groundwater pollutants and their possible sources. Non-carcinogenic health risk to infants, children and adults through nitrates, iron, manganese and fluorides ingestion was also assessed. The results revealed that groundwater in the region is generally slightly acidic with a mean pH of 6.30. WQI analysis grouped 68 % of the groundwater samples under the 'excellent' and 'good' water types with the remaining percent categorized under 'poor', 'very poor' and 'unsafe' drinking water types. GPI analysis classified 95 %, 2.21 % and 2.79 % of the boreholes as 'insignificant', 'low' and 'highly' polluted zones. From the multivariate analyses, the dominant pollutants were iron, manganese, chlorides, sodium, fluorides, potassium, turbidity, total suspended and dissolved solids, hardness, alkalinity, sulphates, nitrates and phosphates. The sources of these contaminants are primarily from rock-water interactions and fertilizers. Health risk assessment for nitrates, fluorides, iron and manganese ingestion revealed that 23, 17 and 15 boreholes in the region are likely to pose non-carcinogenic health risk to infants, children and adults respectively. Health risk maps indicated that the most vulnerable districts were Atiwa East, Fanteakwa North, Achiase, Birim South, Akwapim, Suhum and Ayensuano. From these findings, it is imperative that appropriate groundwater remediation measures are implemented in the region to protect public health.

France-Wide Monitoring of 1,4-Dioxane in Raw and Treated Water: Occurrence and Exposure Via Drinking Water Consumption

In recent years, 1,4-dioxane has emerged as a pollutant of increasing concern following widespread detection in the aquatic environment of several countries. This persistent contaminant with specific physical and chemical properties can be rapidly dispersed and transported to river banks, groundwater and drinking water. Given the limited data on its occurrence in France, it was considered necessary to assess the potential exposure of the French population to this compound in drinking water. An analytical method based on solid-phase extraction (SPE) combined with gas chromatography tandem mass spectrometry (GC-MS/MS) was developed and validated during this study with a limit of quantification (LOQ) of 0.15 µg/L. Recoveries in natural water matrices ranged from 113 to 117% with a relative bias not exceeding 17%. This method was used for a nationwide campaign at almost 300 sites, evenly distributed over 101 French départements (administrative units), including some that were overseas. Of the 587 samples analysed, only 8% had a concentration that was greater than or equal to the LOQ. 1,4-Dioxane was detected mainly (63%) in raw and treated water from sites associated with historical industrial practices related to the use of chlorinated solvents. Concentrations of 1,4-dioxane ranging from 0.19 to 2.85 µg/L were observed in the raw water and from 0.18 to 2.46 µg/L in the treated water. Drinking water treatment plants using ozonation, granular activated carbon and chlorination have limited effectiveness in the removal of 1,4-dioxane. The results of this study are the first step towards bridging the knowledge gap in the occurrence of 1,4-dioxane in France.

Fabrication of Curcumin-Based Electrochemical Nanosensors for the Detection of Environmental Pollutants: 1,4-Dioxane and Hydrazine

This work reports the development of novel curcuminoid-based electrochemical sensors for the detection of environmental pollutants from water. In this study, the first set of electrochemical experiments was carried out using curcumin-conjugated multi-walled carbon nanotubes (MWCNT-CM) for 1,4-dioxane detection. The MWCNT-CM/GCE showed good sensitivity (103.25 nA nM-1 cm-2 in the linear range 1 nM to 1 µM), with LOD of 35.71 pM and LOQ of 108.21 pM. The second set of electrochemical experiments was carried out with bisdemethoxy curcumin analog quantum dots (BDMCAQD) for hydrazine detection. The BDMCAQD/GCE exhibited good sensitivity (74.96 nA nM-1 cm-2 in the linear range 100 nM to 1 µM), with LOD of 10 nM and LOQ of 44.93 nM. Thus, this work will serve as a reference for the fabrication of metal-free electrochemical sensors using curcuminoids as the redox mediator for the enhanced detection of environmental pollutants.

Ubiquitous occurrence of 1,4-dioxane in drinking water of China and its ecological and human health risk

The occurrence and distribution of 1,4-dioxane was investigated in 280 source and finished drinking water samples from 31 Chinese cities, based on which its ecological and health risks were systematically evaluated. The findings demonstrated that 1,4-dioxane was detected in about 80.0 % samples with values ranging from n.d. to 7757 ng/L in source water and n.d. to 2918 ng/L in drinking water. 1,4-Dioxane showed limited removal efficiency using conventional coagulation-sedimentation-filtration processes (14 % ± 48 %), and a removal efficiency of 35 % ± 44 % using ozonation-biological activated carbon advanced treatment processes. Relatively higher concentrations, detection frequency and environmental risk were observed in Taihu Lake, Yellow River, Yangtze River, Zhujiang River, and Huaihe River mainly in the eastern and southern regions, where there are considerable industrial activities and comparatively high population densities. The widespread presence as by-products during manufacturing consumer products e.g., ethoxylated surfactants, suggested municipal wastewater discharges were the dominant source for the ubiquitous occurrence of 1,4-dioxane, while industrial activities, e.g. resin manufacturing, also contribute considerably to the elevated concentrations of 1,4-dioxane. The estimated risk quotients were in the range of <1.5 × 10-4 for ecological risk, <5.0 × 10-3 by oral exposure and < 5.0 × 10-2 by inhalation exposure for health risk, illustrating limited ecological harm to water environment or chronic toxicity to human health. For carcinogenic risk, 1,4-Dioxane presented a mean risk of 1.8 × 10-6 by oral exposure, which slightly surpassed the recommended acceptable levels of U.S. EPA (<10-6), and risk from inhalation exposure could be negligible. The pervasiveness in drinking water, low removal efficiencies during water treatment processes, and suspected health impacts, highlighted the necessity to set related water quality standards of 1,4-dioxane in order to improve water environment in China.

Tracking groundwater pollution plumes at landfill sites using borehole hydrochemical and hydrodynamic profile (BHHP) method

Groundwater pollution at landfill sites poses a significant risk to human health and ecological security. However, efficiently tracking pollution plumes in a polluted aquifer with variable pollutants remains challenging. In order to track groundwater pollution plumes at landfill sites, an in-situ borehole hydrochemical and hydrodynamic profile (BHHP) method was developed. Total dissolved solids (TDS), oxidation-reduction potential (ORP), and ammonia nitrogen were selected as the hydrochemical indicators. Meanwhile, the hydrodynamic indicators included flow direction and flow velocity of groundwater. Among the three hydrochemical indicators, TDS and ORP were analyzed to be the prior alternative ones for the BHHP application. The BHHP method was successfully applied to track groundwater pollution plumes at a typical valley-type landfill site and its neighboring downstream zone. Consequently, four groundwater pollution plumes of different types and different scales were identified in both horizontal and vertical directions within the depth of 0-50 m, and the various pollution sources for the detected pollution plumes were revealed. Furthermore, the BHHP method was validated using sampling test results of groundwater chloride and chemical oxygen demand at the surveyed landfill site.

Formation of corrosion-based ZVMg nanoparticles for reductive degradation of high-level trichloroethylene in aqueous solution

This study discovered that nanosized zero valent magnesium (nZVMg) could be formed during the electrochemical corrosion of microsized ZVMg (mZVMg) in aqueous solution. It is observed that the nZVMg particle sizes were less than 50 nm with the specific surface area of 54.63 m2/g after it was corroded for 96 h (ZVMg96) at the expense of losing about 60 wt% Mg0. However, the XPS characterization indicated the thickness of Mg(OH)2 layer over ZVMg96 being less than 5 nm, accompanied by the faster electron transfer rate but slower corrosion rate than mZVMg. Most importantly, the removal efficiency of 82 % under high-level trichloroethylene (TCE) at 100 mg/L was achieved by ZVMg96 within one hour relative to 48 % by mZVMg. The rate constant normalized by surface area was 3.11 × 10-2 L/m2/h by ZVMg96 due to the high surface energy of nanoparticles. The degradation products were dependent on the initial TCE concentrations, with environmentally friendly and biodegradable degradation products being generated via hydrodechlorination, hydrogenation and polymerization pathways according to the density functional theory calculations. ZVMg corroded for 14 days illustrated a long-term chemical stability and excellent degradation performance, demonstrating significant application potential in remediating the TCE plumes in groundwater.

Biodegradation of 1,4-dioxane by a native digestate microbial community under different electron accepting conditions

The potential of a native digestate microbial community for 1,4-dioxane (DX) biodegradation was evaluated under low dissolved oxygen (DO) concentrations (1-3 mg/L) under different conditions in terms of electron acceptors, co-substrates, co-contaminants and temperature. Complete DX biodegradation (detection limit of 0.01 mg/L) of initial 25 mg/L was achieved in 119 days under low DO concentrations, while complete biodegradation happened faster at 91 and 77 days, respectively in nitrate-amended and aerated conditions. In addition, conducting biodegradation at 30 ˚C showed that the time required for complete DX biodegradation in unamended flasks reduced from 119 days in ambient condition (20-25 °C) to 84 days. Oxalic acid, which is a common metabolite of DX biodegradation was identified in the flasks under different treatments including unamended, nitrate-amended and aerated conditions. Furthermore, transition of the microbial community was monitored during the DX biodegradation period. While the overall richness and diversity of the microbial community decreased, several families of known DX-degrading bacteria such as Pseudonocardiaceae, Xanthobacteraceae and Chitinophagaceae were able to maintain and grow in different electron-accepting conditions. The results suggested that DX biodegradation under low DO concentrations, where no external aeration was provided, is possible by the digestate microbial community, which can be helpful to the ongoing research for DX bioremediation and natural attenuation.

Development of a New Polar Organic Chemical Integrative Sampler for 1,4-dioxane Using Silicone Membrane as a Diffusion Barrier

Efficient monitoring methods must be developed for 1,4-dioxane, which is suspected to be carcinogenic to humans and is highly mobile in aquatic environments. In this regard, polar organic chemical integrative samplers (POCIS) have been utilized extensively as passive samplers for determining time-weighted average concentrations of hydrophilic organic compounds. However, POCIS are difficult to apply to extremely hydrophilic known organic compounds with negative log octanol-water partition coefficient (K_ow ) values due to their limited kinetic sampling time. Using an activated carbon-based sorbent with a high adsorption capacity and a bilayer of silicone and polyethersulfone membranes that inhibit mass transfer to the sorbent, we developed a POCIS device to measure 1,4-dioxane (log K_ow -0.27) in the present study. Permeation and field calibration tests demonstrated that the use of silicone membranes effectively reduces the water-to-sorbent mass transfer rate. The sampling rate and kinetic sampling period determined by field calibration tests were 1.4 ml day^-1 and >14 days, respectively. Finally, the developed POCIS device was applied to a landfill treatment plant to determine the 1,4-dioxane concentrations. Environ Toxicol Chem 2023;42:296-302. © 2022 SETAC.

Remedial strategies for abating 1,4-dioxane pollution-special emphasis on diverse biotechnological interventions

1,4-dioxane is a heterocyclic ether used as a polar industrial solvent and are released as waste discharges. 1,4-dioxane deteriorates health and quality, thereby attracts concern by the environment technologists. The need of attaining sustainable development goals have resulted in search of an eco-friendly and technically viable treatment strategy. This extensive review is aimed to emphasis on the (a) characteristics of 1,4-dioxane and their occurrence in the environment as well as their toxicity, (b) remedial strategies, such as physico-chemical treatment and advanced oxidation techniques. Special reference to bioremediation that involves diverse microbial strains and their mechanism are highlighted in this review. The role of macronutrients, stimulants and other abiotic cofactors in the biodegradation of 1,4-dioxane is discussed lucidly. We have critically discussed the inducible enzymes, enzyme-based remediation, distinct instrumental method of analyses to know the fate of intermediates produced from 1,4-dioxane biotransformation. This comprehensive survey also tries to put forth the different toxicity assessment tools used in evaluating the extent of detoxification of 1,4-dioxane achieved through biotransforming mechanism. Conclusively, the challenges, opportunities, techno-economic feasibility and future prospects of implementing 1,4-dioxane through biotechnological interventions are also discussed.

In vivo effects of 1,4-dioxane on genotoxic parameters and behavioral alterations in Drosophila melanogaster

1,4-Dioxane (DXN) is used as solvent in different consumer products including cosmetics, paints, surfactants, and waxes. In addition, DXN is released as an unwanted contaminating by-product as a result of some reactions including ethoxylation of alcohols, which occurs with in personal care products. Consequently, DXN pollution was detected in drinking water and is considered as an environmental problem. At present, the genotoxicity effects attributed to DXN are controversial. The present study using an in vivo model organism Drosophila melanogaster aimed to determine the toxic/genotoxic, mutagenic/recombinogenic, oxidative damage as evidenced by ROS production, phenotypic alterations as well as behavioral and developmental alterations that are closely related to neuronal functions. Data demonstrated that nontoxic DXN concentration (0.1, 0.25, 0.5, or 1%) induced mutagenic (1%) and recombinogenic (0.1, 0.25, or 0.5%) effects in wing spot test and genotoxicity in hemocytes using comet assay. The nontoxic concentrations of DXN (0.1, 0.25, 0.5, or 1%) significantly increased oxidative stress, climbing behavior, thermal sensivity and abnormal phenotypic alterations. Our findings show that in contrast to in vitro exposure, DXN using an in vivo model Drosophila melanogaster this compound exerts toxic and genotoxic effects. Data suggest that additional studies using other in vivo models are thus warranted.

Implementation of initial emission mitigation measures for 1,4-dioxane in Germany: Are they taking effect?

Since our comprehensive investigation of finished drinking water in Germany obtained from managed aquifer recharge systems in the period 2015-2016, which revealed widespread contamination with 1,4-dioxane, mitigation measures (integration of AOP units, shutdown or alteration of production processes) have been implemented at some sites. In this study, we conducted follow-up tests on surface water concentrations and associated finished drinking water concentrations in 2017/2018, to evaluate the effectiveness of these measures. Our findings demonstrate that the emission mitigation measures had considerably reducing effects on the average 1,4-dioxane drinking water concentrations for some of the previously severely affected areas (Lower Franconia: -54%, Passau: -88%). Conversely, at notoriously contaminated sites where neither monitoring nor mitigation measures were introduced, the drinking water concentrations stagnated or even increased. Drinking water concentrations determined via a modified US EPA method 522 ranged from below LOQ (0.034 μg/L) up to 1.68 μg/L in all drinking water samples investigated. In river water samples, the maximum concentration exceeded 10 μg/L. Effluents of wastewater treatments plants containing 1,4-dioxane (5 μg/L-1.75 mg/L) were also analyzed for other similar cyclic ethers by suspected target screening. Thus, 1,3-dioxolane and three other derivatives were tentatively identified in effluents from the polyester processing or manufacturing industry. 1,3-Dioxolane was present in concentrations >1.2 mg/L at one site, exceeding up to sevenfold the 1,4-dioxane concentration found there. At another site 2-methyl-1,3-dioxolane was still found 13 km downstream of the discharge point, indicating that ethers analogous to 1,4-dioxane should be further considered regarding their occurrence and fate in wastewater treatment and the aquatic environment.

Transmembrane penetration mechanism of cyclic pollutants inspected by molecular dynamics and metadynamics: the case of morpholine, phenol, 1,4-dioxane and oxane

The presence of industrially produced chemicals in water is often not monitored, while their passive transport and accumulation can cause serious damage in living cells. Molecular dynamics simulations are an effective way to understand the mechanism of the action of these pollutants. In this paper, the passive membrane transport of 1,4-dioxane, phenol, oxane and morpholine was investigated and analyzed thoroughly from structural and energetic points of view. Free energy profiles for pollutant and water penetration into the bilayer were obtained from well-tempered metadynamics (WT-MD) simulations and a mass density-based approach. It was found that all four investigated compounds can penetrate biological membranes and affect the free energy profile of water penetration. Out of the investigated species, oxane has the thermodynamically most preferred position in the bilayer center, leading to a lower free energy barrier of water molecules by 3 kJ mol-1, resulting in 5 times more water molecules in the bilayer center. The concentration dependence of free energy was tested at two different phenol concentrations using WT-MD, and it was found that the higher phenol concentration lowers the main barrier by 3 kJ mol-1. Density-based free energy calculations were found to reproduce the results of WT-MD within the limits of chemical accuracy.

Treatment of 1,4-dioxane-containing water using carriers immobilized with indigenous microorganisms in landfill leachate treatment sludge: A laboratory-scale reactor study

1,4-Dioxane (DX) is a contaminant of emerging concern in aquatic environments, and is frequently found in landfill leachate. As a biological method applicable to landfill leachate treatment facilities, the feasibility of DX treatment using carriers immobilized with microorganisms indigenous to landfill leachate treatment sludge was explored through laboratory-scale reactor experiments by introducing carriers prepared via microorganism immobilization in the aeration tank of a leachate treatment facility. Three different carrier materials were used to immobilize microorganisms, and a model DX-containing water (10 mg/L) was treated under continuous feeding. Biological DX removal to < 0.5 mg/L was achieved using all carrier types, thereby adhering to the effluent standard for landfill leachate in Japan, which confirms the usefulness of the proposed method. However, weaker aeration and enhanced DX loading drastically impaired the DX removal performance depending on the carrier materials. This suggests the importance of carrier selection and control of the operational variables to ensure stable and effective DX removal. Microbial community analyses revealed that Pseudonocardia with thm genes may largely contribute to the initial oxidation of DX, irrespective of the carrier type, suggesting the importance of this population for the continuous treatment of low DX concentrations with mixed microbial consortia.

Cometabolic degradation of 1,4-dioxane by a tetrahydrofuran-growing Arthrobacter sp. WN18

1,4-Dioxane (dioxane), an emerging groundwater contaminant, is frequently detected in landfill leachates with its structural analog, tetrahydrofuran (THF). Along with undesirable leakage of landfill leachates, dioxane and THF inevitably percolate into groundwater leading to a broader region of contamination. Cometabolic bioremediation is an effective approach to manage commingled THF and dioxane pollution. In this study, a newly isolated bacterium Arthrobacter sp. WN18 is able to co-oxidize dioxane with THF as the primary substrate. Meanwhile, the THF-induced thmADBC gene cluster was responsible for the dioxane degradation rate indicating THF monooxygenase is the essential enzyme that initializing α-hydroxylation of THF and dioxane. Further, γ-butyrolactone and HEAA were characterized as the key metabolites of THF and dioxane, respectively. In addition, WN18 can tolerate the inhibition of trichloroethylene (5.0 mg/L) as a representative of co-existing leachate constituent, and sustain its activity at various pH (5-11), temperatures (15-42 °C), and salinities (up to 4%, as NaCl wt). Like other Arthrobacter species, WN18 also exhibited the capability of fixing nitrogen. All this evidence indicates the feasibility and advantage of WN18 as a thmADBC-catalyzed inoculator to bioremediate co-contamination of THF and dioxane.

Removal of 1,4-dioxane during on-site wastewater treatment using nitrogen removing biofilters

The presence and release of 1,4-dioxane to groundwater from onsite-wastewater treatment systems (OWTS), which represent 25% of the total wastewater treatment in the U.S., has not been studied to date. In this study we monitored 1,4-dioxane in six septic tank effluents (STE) and receiving OWTS installed at residences on Long Island (LI), NY, for a period of 15 months. We specifically evaluated the performance of Nitrogen Removing Biofilters (NRBs) as an innovative/alternative-OWTS, consisting of a top sand layer and a bottom woodchip/sand layer, to simultaneously remove nitrogen and 1,4-dioxane. 1,4-Dioxane levels in STE (mean: 1.49 μg L^-1; range: 0.07-8.45 μg L^-1; n = 37) were on average > 15 times higher than tap water from these residences, demonstrating that 1,4-dioxane primarily originated from the use of household products. NRBs were effective in removing both 1,4-dioxane and total nitrogen with an overall removal efficiency of 56 ± 20% and 88 ± 12%, respectively. The majority of 1,4-dioxane removal (~80%) occurred in the top oxic layer of the NRBs. The detection of functional genes (dxmB, prmA, and thmA), which encode for metabolic and co-metabolic 1,4-dioxane degradation, in NRBs provides the first field evidence of aerobic microbial degradation of 1,4-dioxane occurring in a wastewater system. Given that there are ~500,000 conventional OWTS on LI, the 1,4-dioxane discharge to groundwater from residential wastewater was estimated at 195 ± 205 kg yr ^-1, suggesting high risk of contamination to shallow aquifers. The results also demonstrate that installation of NRBs can reduce 1,4-dioxane to levels even lower than the NY State drinking water standard of 1 μg L^-1.

Combinatorial Analysis of Sparse Experiments on Photocatalytic Performance of Cement Composites: A Route toward Optimizing Multifunctional Materials for Water Purification

Blending TiO₂ and cement to create photocatalytic composites holds promise for low-cost, durable water treatment. However, the efficiency of such composites hinges on cross-effects of several parameters such as cement composition, type of photocatalyst, and microstructure, which are poorly understood and require extensive combinatorial tests to discern. Here, we report a new combinatorial data science approach to understand the influence of various photocatalytic cement composites based on limited datasets. Using P25 nanoparticles and submicron-sized anatase as representative TiO₂ photocatalysts and methyl orange and 1,4-dioxane as target organic pollutants, we demonstrate that the cement composition is a more influential factor on photocatalytic activity than the cement microstructure and TiO₂ type and particle size. Among the various cement constituents, belite and ferrite had strong inverse correlation with photocatalytic activity, while natural rutile had a positive correlation, which suggests optimization opportunities by manipulating the cement composition. These results were discerned by screening 7806 combinatorial functions that capture cross-effects of multiple compositional phases and obtaining correlation scores. We also report ^•OH radical generation, cement aging effects, TiO₂ leaching, and strategies to regenerate photocatalytic surfaces for reuse. This work provides several nonintuitive correlations and insights on the effect of cement composition and structure on performance, thus advancing our knowledge on development of scalable photocatalytic materials for drinking water treatment in rural and resource-limited areas.

Managed aquifer recharge implementation criteria to achieve water sustainability

Depletion of groundwater is accelerated due to an increase in water demand for applications in urbanized areas, agriculture sectors, and energy extraction, and dwindling surface water during changing climate. Managed aquifer recharge (MAR) is one of the several methods that can help achieve long-term water sustainability by increasing the natural recharge of groundwater reservoirs with water from non-traditional supplies such as excess surface water, stormwater, and treated wastewater. Despite the multiple benefits of MAR, the wide-scale implementation of MAR is lacking, partly because of challenges to select the location for MAR implementation and identify the MAR type based on site conditions and needs. In this review, we provide an overview of MAR types with a basic framework to select and implement specific MAR at a site based on water availability and quality, land use, source type, soil, and aquifer properties. Our analysis of 1127 MAR projects shows that MAR has been predominantly implemented in sites with sandy clay loam soil (soil group C) and with access to river water for recharge. Spatial analysis reveals that many regions with depleting water storage have opportunities to implement MAR projects. Analyzing data from 34 studies where stormwater was used for recharge, we show that MAR can remove dissolved organic carbon, most metals, E. coli but not efficient at removing most trace organics, and enterococci. Removal efficiency depends on the type of MAR. In the end, we highlight potential challenges for implementing MAR at a site and additional benefits such as minimizing land subsidence, flood risk, augmenting low dry-season flow, and minimizing salt-water intrusion. These results could help identify locations in the water-stressed regions to implement specific MAR for water sustainability.

A Synergistic Platform for Continuous Co-removal of 1,1,1-Trichloroethane, Trichloroethene, and 1,4-Dioxane via Catalytic Dechlorination Followed by Biodegradation

Groundwater co-contaminated with 1,4-dioxane, 1,1,1-trichloroethane (TCA), and trichloroethene (TCE) is among the most urgent environmental concerns of the U.S. Department of Defense (DoD), U.S. Environmental Protection Agency (EPA), and industries related to chlorinated solvents. Inspired by the pressing need to remove all three contaminants at many sites, we tested a synergistic platform: catalytic reduction of 1,1,1-TCA and TCE to ethane in a H₂-based membrane palladium-film reactor (H₂-MPfR), followed by aerobic biodegradation of ethane and 1,4-dioxane in an O₂-based membrane biofilm reactor (O₂-MBfR). During 130 days of continuous operation, 1,1,1-TCA and TCE were 95-98% reductively dechlorinated to ethane in the H₂-MPfR, and ethane served as the endogenous primary electron donor for promoting 98.5% aerobic biodegradation of 1,4-dioxane in the O₂-MBfR. In addition, the small concentrations of the chlorinated intermediate from the H₂-MPfR, dichloroethane (DCA) and monochloroethane (MCA), were fully biodegraded through aerobic biodegradation in the O₂-MBfR. The biofilms in the O₂-MBfR were enriched in phylotypes closely related to the genera Pseudonocardia known to biodegrade 1,4-dioxane.

Combined method of 3H/3He apparent age and on-site helium analysis to identify groundwater flow processes and transport of perchloroethylene (PCE) in an urban area

Urban groundwater management requires a thorough and robust scientific understanding of flow and transport processes. ³H/³He apparent ages have been shown to efficiently help provide important groundwater-related information. However, this type of analysis is expensive as well as labor- and time-intensive, and hence limits the number of potential sampling locations. To overcome this limitation, we established an inter-relationship between ³H/³He apparent groundwater ages and ⁴He concentrations analyzed in the field with a newly developed portable gas equilibrium membrane inlet mass spectrometer (GE-MIMS) system, and demonstrated that the results of the simpler GE-MIMS system are an accurate and reliable alternative to sophisticated laboratory based analyses. The combined use of ³H/³He lab-based ages and predicted ages from the ³H/³He-⁴He age relationship opens new opportunities for site characterization, and reveals insights into the conceptual understanding of groundwater systems. For our study site, we combined groundwater ages with hydrochemical data, water isotopes (¹⁸O and ²H), and perchloroethylene (PCE) concentrations (1) to identify spatial inter-aquifer mixing between artificially infiltrated groundwater and water originating from regional flow paths and (2) to explain the spatial differences in PCE contamination within the observed groundwater system. Overall, low PCE concentrations and young ages occur when the fraction of artificially infiltrated water is high. The results obtained from the age distribution analysis are strongly supported by the information gained from the isotopic and hydrochemical data. Moreover, for some wells, fault-induced aquifer connectivity is identified as a preferential flow path for the transport of older groundwater, leading to elevated PCE concentrations.

Degradation of 1,4-Dioxane by Xanthobacter sp. YN2

1,4-Dioxane is a highly toxic and carcinogenic pollutant found worldwide in groundwater and soil environments. Several microorganisms have been isolated by their ability to grow on 1,4-dioxane; however, low 1,4-dioxane tolerance and slow degradation kinetics remain obstacles for their use in 1,4-dioxane bioremediation. We report here the isolation and characterization of a new strain, Xanthobacter sp. YN2, capable of highly efficient 1,4-dioxane degradation. High degradation efficiency and high tolerance to 1,4-dioxane make this new strain an ideal candidate for the biodegradation of 1,4-dioxane in various treatment facilities. The maximum degradation rate of 1,4-dioxane was found to be 1.10 mg-1,4-dioxane/h mg-protein. Furthermore, Xanthobacter sp. YN2 was shown to grow in the presence of higher than 3000 mg/L 1,4-dioxane with little to no degradation inhibition. In addition, Xanthobacter sp. YN2 could grow on and degrade 1,4-dioxane at pH ranges 5 to 8 and temperatures between 20 and 40 °C. Xanthobacter sp. YN2 was also found to be able to grow on a variety of other substrates including several analogs of 1,4-dioxane. Genome sequence analyses revealed the presence of two soluble di-iron monooxygenase (SDIMO) gene clusters, and regulation studies determined that all of the genes in these two clusters were upregulated in the presence of 1,4-dioxane. This study provides insights into the bacterial stress response and the highly efficient biodegradation of 1,4-dioxane as well as the identification of a novel Group-2 SDIMO.

Framework, method and case study for the calculation of end of life for HWL and parameter sensitivity analysis

Mass construction and operation of hazardous waste landfill infrastructure has greatly improved China’s waste management and environmental safety. However, the deterioration of engineering materials and the failure of landfill may lead to the release of untreated leachate rich in persistent toxic pollutants to the soil and shallow groundwater. Accordingly, we develop the framework and process model to predict landfill life by coupling the landfill hydrological performance model and material degradation model. We found that the decrease rate of the concentration of persistent pollutants in leachate was significantly slower than the deterioration rate of the landfill engineering materials. As a result, when the materials failed, the leachate with high concentrations of persistent pollutants continued to leak, resulting in the pollutants concentration in surrounding groundwater exceeding the acceptable concentration at around 385 a, which is the average life of a landfill. Further simulation indicated that hydrogeological conditions and the initial concentration of leachate will affect landfill lifespan. The correlation coefficients of concentration, the thickness of vadose zone and the thickness of aquifer are − 0.79, 0.99 and 0.72 respectively, so the thickness of vadose zone having the greatest impact on the life of a landfill. The results presented herein indicate hazardous waste landfill infrastructure reinvestment should be directed toward long-term monitoring and maintenance, waste second-disposal, and site restoration.

Enhanced reactivity and mechanisms of mesoporous carbon supported zero-valent iron composite for trichloroethylene removal in batch studies

Ordered mesoporous carbon (CMK-3) supported nanoscale zero-valent iron (nZVI) composites were synthesized and used for the removal of trichloroethylene (TCE). The nZVI/CMK-3 composites exhibited high TCE removal efficiency in a batch study, which was 2.5 times that of nZVI alone. They also displayed excellent reusability, with 65.2% removal efficiency after three treatments. Dechlorination dominated the process of TCE removal (75.3%-79.4%), whereas adsorption accounted for 20.6%-24.7%. CMK-3 enhanced the dechlorination rate and efficiency of TCE by nZVI, and the enhancement was favored with the increase in CMK-3 content. The Tafel analysis and H₂ evolution experiments indicated the mechanisms of CMK-3 action in nZVI/CMK-3 composites for TCE removal. CMK-3 serves as a direct electron transfer, whereas CO was identified as the functional group involved; the other involved the acceleration of redox reaction of atomic hydrogen owing to the superior hydrogen adsorption capacity of CMK-3. The present study provides new perspectives for seeking more efficient nZVI to reinforce the dechlorination process; however, more studies are warranted in the long-term performance of nZVI/CMK-3 in the aquifer condition.

1,4-Dioxane contamination of German drinking water obtained by managed aquifer recharge systems: Distribution and main influencing factors

1,4-Dioxane, a cyclic ether that has been classified as a class 2B carcinogen by the US-EPA, is a substance of growing environmental concern because of its abundant occurrence in surface waters worldwide. Its high polarity and low biodegradability hamper its retardation in aquifer systems. Previous investigations in Germany have shown that 1,4-dioxane is already widely distributed in rivers and can be found in groundwater at contamination sites. Therefore, the present study shall provide an overview of the Germany-wide distribution of 1,4-dioxane in finished drinking water (FDW) obtained by managed aquifer recharge (MAR) systems. Thus, we investigated the 1,4-Dioxane levels in FDW obtained by MAR, such as river bank filtration (RBF) or artificial groundwater recharge (AGR), in regions that are supplied by surface water bodies (mainly rivers) with already known 1,4-dioxane contaminations. In total, 125 FDW samples and 33 samples of corresponding surface waters were analyzed for 1,4-dioxane content using solid phase extraction followed by gas chromatography-mass spectrometry (SIM-mode) using a slight modification to US-EPA method 522. About 80% of the investigated FDW samples contained 1,4-dioxane at levels exceeding the limit of quantification (0.034 μg/L); the maximum value was 2.05 μg/L. However, a maximum concentration of 3 μg/L was obtained in the surface water samples. Three main factors were associated with elevated levels of 1,4-dioxane in the FDW: A significant 1,4-dioxane contamination of the associated surface water, the application of RBF instead of AGR, and the proportion of available unpolluted groundwater and/or reservoir water blended in the individual waterworks. The results show that 1,4-dioxane should be critically monitored during FDW production by means of MAR not only in Germany. The findings are also of relevance to neighboring countries depending on the same river systems and for research in the field of small mobile substances in drinking water production in general.

Removal of 1,4-dioxane from landfill leachate by a rotating advanced oxidation contactor equipped with activated carbon/TiO2 composite sheets

A rotating advanced oxidation contactor (RAOC) equipped with activated carbon (AC)/TiO₂ composite sheets for 1,4-dioxane removal from biologically treated landfill leachate (BTLL) was developed. The performance of the RAOC in 1,4-dioxane removal was compared to that of a TiO₂ slurry reactor by evaluating the removal efficiencies in pure water (PW) and the BTLL. In the TiO₂ slurry reactor, 1,4-dioxane was hardly degraded in the BTLL during 66 h of treatment because of strong inhibition by coexisting substances in the BTLL. In contrast, the RAOC successfully removed 1,4-dioxane from the BTLL by 89% through adsorption and by 81% through photocatalysis during treatment for 66 h. The ratio of the rate constants for degrading 1,4-dioxane in the BTLL and PW by the RAOC was two orders of magnitude higher than that for a TiO₂ slurry reactor. This shows that the RAOC greatly mitigated the inhibition by coexisting substances in the BTLL. The electrical energy required for 1,4-dioxane degradation in the BTLL by the RAOC was much lower than that required for degradation by the TiO₂ slurry reactor. The results show that the RAOC equipped with AC/TiO₂ composite sheets effectively removed 1,4-dioxane from BTLL.

Potential application of mixed metal oxide nanoparticle-embedded glassy carbon electrode as a selective 1,4-dioxane chemical sensor probe by an electrochemical approach

Here, low-dimensional mixed metal oxide (ZnO/NiO/MnO2) nanoparticles (NPs) were prepared to develop a selective, efficient and ultra-sensitive 1,4-dioxane sensor by using the wet-chemical method (co-precipitation) in alkaline medium at low temperature. Detailed characterization of the prepared calcined NPs was achieved via conventional methods, including X-ray diffraction, field emission scanning electron microscopy, and X-ray photoelectron, UV-vis, Fourier-transform infrared and energy dispersive X-ray spectroscopies. To develop a thin layer of nanomaterial on the fabricated electrode, a slurry of prepared NPs was used to coat the glassy carbon electrode (GCE) with conductive Nafion (5% in ethanol) binder. The fabricated electrochemical sensor showed good sensitivity (1.0417 μA μM-1 cm-2), a wide linear dynamic range (0.12 nM to 1.2 mM), lower detection limit (9.14 ± 4.55 pM), short response time, good reproducibility, and long-term stability to selectively detect 1,4-dioxane in the optimized buffer system. Thus, this work presents a reliable alternative approach over existing methods to selectively detect hazardous chemicals in large scale for safety in the environmental and healthcare fields.

1,4-Dioxane as an emerging water contaminant: State of the science and evaluation of research needs

1,4-Dioxane has historically been used to stabilize chlorinated solvents and more recently has been found as a contaminant of numerous consumer and food products. Once discharged into the environment, its physical and chemical characteristics facilitate migration in groundwater, resulting in widespread contamination of drinking water supplies. Over one-fifth of U.S. public drinking water supplies contain detectable levels of 1,4-dioxane. Remediation efforts using common adsorption and membrane filtration techniques have been ineffective, highlighting the need for alternative removal approaches. While the data evaluating human exposure and health effects are limited, animal studies have shown chronic exposure to cause carcinogenic responses in the liver across multiple species and routes of exposure. Based on this experimental evidence, the U.S. Environmental Protection Agency has listed 1,4-dioxane as a high priority chemical and classified it as a probable human carcinogen. Despite these health concerns, there are no federal or state maximum contaminant levels for 1,4-dioxane. Effective public health policy for this emerging contaminant requires additional information about human health effects, chemical interactions, environmental fate, analytical detection, and treatment technologies. This review highlights the current state of knowledge, key uncertainties, and data needs for future research on 1,4-dioxane.

Dioxanes and dioxolanes in source waters: Occurrence, odor thresholds and behavior through upgraded conventional and advanced processes in a drinking water treatment plant

Over the last years, the human probable carcinogen 1,4-dioxane and alkyl-1,3-dioxanes and dioxolanes have been detected and identified as the cause of several pollution episodes in the Llobregat River (Catalonia, NE Spain) and its aquifer. It is an issue of major concern to study these compounds which are released to the environment by resin manufacturing plants' spills and wastewater discharges spread along rivers and reach drinking water treatment plants (DWTPs) in order to protect the environment and public health. In this study four seasonal sampling campaigns were carried out over a year to determine the removal efficiency of the dioxanes and dioxolanes at each step of a DWTP including ozonation, granular activated carbon filters, ultrafiltration and reverse osmosis step's treatments. Additionally, a weekly sampling monitoring of 1,4-dioxane and alkyl-1,3-dioxanes and dioxolanes in raw water, groundwater and finished water was performed at a DWTP over more than two years. Aqueous odor concentration thresholds (OTCs) were established by the three-alternative forced choice method (3-AFC). Following a previous published methodology, samples were analyzed and results showed that the advanced treatment (Ultrafiltration followed by reverse osmosis) line removes more efficiently 1,4-dioxane, alkyl dioxanes and dioxolanes (80 ± 6% for 1,4-dioxane, 97 ± 7% for 5,5-DMD and 100 ± 0% for 2,5,5-TMD) than the upgraded conventional treatment line (ozonation followed by granular activated carbon filters) (-12 ± 50%, 25 ± 62% and 50 ± 51% respectively), where some desorption processes were eventually observed. From the monitoring study, results suggest that the presence of 1,4-dioxane is not only due to spills, but also from other sources of contamination. Whereas dioxolanes almost completely disappeared in time, 1,4-dioxane's concentrations remained low and fluctuant. A background concentration of 1,4-dioxane in surface waters (∼1 μg/L) has been determined with a relevant concentration up to 11.6 μg/L of 1,4-dioxane in groundwater. The perception values for some of the studied compounds were extremely low (few ng/L only), which confirms the relevancy of this group of compounds as malodorous agents in waters.

Development of highly sensitive 1,4-dioxane sensor with semiconductor NiO-doped Nd2O3 nanostructures by electrochemical approach

In this approach, selective and sensitive 1,4-dioxane sensor probe was developed based on facile NiO@Nd₂O₃ nanocomposites embedded GCE for the safety management of environment and health care fields at a large scale.

Fabrication of 1,4-dioxane sensor based on microwave assisted PAni-SiO2 nanocomposites

In this study, conducting polyaniline (PAni) and silicon dioxide (SiO₂) nanocomposites (NCs) were synthesized for chemical sensing applications by microwave assisted reaction technique. Facile synthesis and characterization of the PAni-SiO₂ nanocomposites were investigated in details and discussed in this report. For the potential application, 1,4-dioxane chemical sensor was fabricated with the PAni-SiO₂ nanocomposites deposited onto glassy carbon electrode (GCE). A very thin uniform film was deposited onto GCE with nanocomposite by using conducting 5% nafion binder at room conditions. To evaluate the sensor analytical performances, a calibration plot such as current versus concentration of 1,4-dioxane was drawn and calculated the analytical parameters from the slope of calibration curve. Results are found as sensitivity (0.5934 µAµmol^-1 L^-2 cm^-2), detection limit (16.0 ± 0.8 pmol L^-1), and quantification limit (LOQ; 53.3 ± 1.5 pmol L^-1) in this observation. Considering the linear region in calibration plot, the linear dynamic range of 1,4-dioxane chemical sensor was found (0.12 nmol L^-1 ∼ 1.2 mmol L^-1). Besides this, the proposed 1,4-dioxane chemical sensor was exhibited good reproducibility, long-term stability, high accuracy in detecting of 1,4-dioxane in real environmental samples. This research is to develop of a selective and an efficient electrochemical sensor. It might be a simple and easy way by applying electrochemical method to ensure the safe and sustainable green environment.