Global diagnosis of nitrate pollution in groundwater and review of removal technologies

Techno-economic assessment of distributed wellhead RO water treatment for nitrate removal and salinity reduction: A field study in small disadvantaged communities

Techno-economic analysis of distributed wellhead water treatment and desalination (DWTD) systems was carried out based on a three-year field study in three small, disadvantaged communities (DACs) to evaluate the reliability and affordability of upgrading their impaired well water. The local water supplies of the three study DACs, located in Salinas Valley, California, were contaminated with nitrate at levels (∼ 12-87 mg/L NO3--N) above the California maximum contaminant level (MCL) of 10 mg/L NO3--N, and had elevated water salinity (∼600-1,600 mg/L total dissolved solids(TDS)) above its secondary MCL (SMCL) of 500 mg/L TDS. Well water nitrate removal and salinity reduction were accomplished via reverse osmosis (RO) based DWTD systems that operated autonomously, supported by remote monitoring and supervisory cyberinfrastructure. Reliable DWTD operation provided treated water quality, with respect to nitrate and salinity, in the range of 0.5-6.3 mg/L NO3--N and 57-161 mg/L TDS, respectively, which were well below the respective MCL and SMCL. The levelized cost of water treatment was in the range of ∼$2/m3- $2.9/m3 which aligns with typical residential water costs in California and in the study region, and monthly residential water costs ($39-$74/residential unit/month) were also within the range in California. The study showcased the DWTD approach as a viable and potentially scalable solution for upgrading impaired local potable water supply of communities lacking centralized water delivery infrastructure. However, streamlined permitting processes and standardized regulatory frameworks are critical to promoting wider adoption and maximizing the socio-economic benefits of the DWT approach. Moreover, DACs are likely to require government subsidies in order to cover the CapEx of DWTD systems in addition to upgrade of site infrastructure.

Importance of isotope fractionation in SIAR model for quantifying NO3- sources in groundwater of China

Quantifying NO3- sources by the combination of dual nitrate isotopes (δ15N-NO3- and δ18O-NO3-) with Stable Isotope Analysis in R (SIAR) models is crucial for mitigating NO3- pollution in groundwater. However, isotope fractionation effects during denitrification lead to significant uncertainties when quantifying groundwater NO3- sources using the SIAR model. In this study, hydrochemical data, water isotopes (δD-H2O and δ18O-H2O), and dual nitrate isotopes of groundwater at the West Lake watershed, East China were measured to estimate the isotope fractionation effect of denitrification in groundwater and assess its impact on quantifying NO3- source contributions using the SIAR model. The significant spatial (εN: -6.9 ‰ and εO: -3.1 ‰ in G1; εN: -15.1 ‰ and εO: -10.0 ‰ in G2) and temporal (εN: -17.0 ‰ and εO: -4.1 ‰ in spring; εN: -4.9 ‰ and εO: -2.5 ‰ in summer; εN: -7.2 ‰ and εO: -6.0 ‰ in autumn) variations in isotope fractionation effects of denitrification in groundwater at the West Lake watershed were observed. By incorporating these respective isotope fractionation enrichment factors into the SIAR model, more accurate NO3- source apportionments for G1 and G2 were obtained, confirming that the isotope fractionation effect of denitrification is an important parameter for quantifying NO3- sources in groundwater using the SIAR model. Furthermore, the national δ15N-NO3- and δ18O-NO3- observations of groundwater were compiled and the SIAR model integrated with isotope fractionation effect of denitrification were used to quantify NO3- sources in groundwater of China. It was found that regional differences in human activities directly influenced spatial variations of δ15N-NO3- and δ18O-NO3- values. The SIAR model outputs on a national scale revealed that sewage/manure (22.9-42.1 %) and chemical fertilizers (23.0-42.7 %) were the main NO3- sources in groundwater of China, attributable to large populations and extensive agricultural cultivation areas. These results provide direct evidence for formulating suitable policies and measures to control and reduce groundwater NO3- in China.

In situ bioelectrochemical remediation of contaminated soil and groundwater: A review

Contamination of the subsurface environment poses a serious hazard to the environment and human health. Recently, the bioelectrochemical system (BES) has drawn great attention in soil and groundwater remediation as it does not necessitate the addition of chemicals and exhibits minimal energy consumption to facilitate microbial degradation of pollutants. However, the complexity of the subsurface environment and the design parameters of the BES significantly affect the remediation performance and the current literature on BES primarily concentrates on its application in wastewater treatment, with a lack of summary of that in the subsurface environment. Therefore, the purpose of this review was to provide the current status, challenges, and outlooks of BES in situ treatment of pollutants from soil and groundwater. Firstly, the principles and efficacies of BES in treating the typical pollutants from the subsurface environment were discussed. Secondly, the factors that impact the BES treatment efficiencies, especially soil properties, the distinctive and pivotal factors for BES in situ application, were discussed specifically. Finally, the challenges and outlooks of BES for the in situ remediation of the contaminated soil and groundwater were addressed. BES is a green and sustainable in situ remediation technology and future advancements may necessitate the integration with complementary technologies and innovative system configurations to advance the practical implementation of BES.

CuO/Bi2CuO4 Heterostructured Electrocatalyst for the Efficient Reduction of Nitrate to Ammonia

The electrochemical reduction of nitrate to ammonia (NH3) not only provides an effective approach to balance the perturbed nitrogen cycle for addressing environmental issues but also provides a potential technology for green NH3 synthesis. However, the process is limited by the produced intermediate-nitrite that tends to accumulate on cathode surfaces and multiple competing reactions. Herein, CuO/Bi2CuO4-450 heterostructures are reported as efficient electrocatalysts for the nitrate reduction reaction with extraordinary catalytic activities and selectivities for NH3 production. The optimized catalyst achieves a remarkable Faradaic efficiency (96.49%) and exceptional NH3 yield rate (9.17 mg h-1 mgcat.-1) at -0.5 V versus RHE, surpassing most of the reported Cu-based catalytic systems. The characterization results and theoretical evidence reveal that the interface effect originating from the strong interaction between Bi2CuO4 and CuO tunes the electronic structures of the Cu and Bi active sites for optimized intermediate adsorption and lowers the rate-determining step reaction barriers, resulting in improved catalytic performance. This work offers a strategy to flexibly develop catalysts to promote electrocatalytic techniques for NH3 production by electrochemical nitrate reduction.

Microfluidic-electrochemical sensor utilizing statistical modeling for enhanced nitrate detection in surface water towards environmental monitoring

The presence of nitrate (NO3-) in surface water and groundwater used for potable supply needs to be closely monitored since in elevated amounts it can adversely affect aquatic life and human health by causing hypoxia and methemoglobinemia. Many of the existing EPA-certified sensors used for environmental monitoring are expensive, bulky, and labor-intensive. To address these concerns, we have successfully developed a low-cost microfluidic electrochemical impedimetric sensor, consisting of a nitrate-binding nickel complex within a polyaniline/carbon nanocomposite (Ni@Pani/C) enabling nitrate monitoring in field samples. Under optimized conditions, our sensor demonstrated a high sensitivity of 2.31 ± 0.09 Ω ppm-1 cm-2 across a wide nitrate concentration range (0.6-10 ppm). It also showed a desirable low detection limit of 0.015 ppm and a swift response time under 20 seconds. It maintained repeatability over a wide temperature range (5-65 °C) and exhibited consistent performance over an extended period (∼1 month). The sensor exhibited high specificity towards nitrate when tested against potential interferences (SO42-, C2H3O2-, HCO3-, NH4+, Cl-) and showed good reproducibility for test water samples collected from various streams in Maryland, U.S.A. A statistical model was used to confirm the sensor's accuracy, which yielded a maximum standard deviation of ±0.6 ppm (absolute value). Our sensor was also benchmarked against a commercial SUNA device resulting in comparable performance.

Nitrate pollution index and age wise health risk appraisal for the Pambar River basin in south India

Water and human healthcare are common concerns for everyone, resonating with the sustainable development goal. In Pambar River basin, south India, groundwater samples were obtained in 100 locations from open and bore wells to assess the quality of groundwater based on hydrochemical constituents like pH (Hydrogen Ion Concentration), CO₃2- (carbonate), Ca2⁺ (calcium), HCO₃- (bicarbonate), Cl- (chloride), Mg2⁺ (magnesium), SO₄2- (sulfate), K⁺ (potassium), Na⁺ (sodium), TDS (Total Dissolved Solids) with a special focus on NO₃- (nitrate) enrichment in groundwater and health risk computed from consumption of nitrate enriched water by different age categories of people, and acceptableness of water for consumption depends on the range of NPI (Nitrate Pollution Index). The nitrate content in subsurface water samples falls from 0.7 to 187.5 mg/L. Out of 100 samples, 31 samples surpassed the WHO, 2017 recommended limit for drinking purpose (> 45 mg/L). The calculated nitrate pollution index (NPI) values of samples  represent clean class (n = 43), light pollution class (n = 26), moderate pollution class (n = 9), significant class (n = 11) and very significant class (n = 11). The correlation matrix explains nitrate is weakly correlated with pH, magnesium, calcium, and potassium, and negatively associated with TDS, sodium, bicarbonate, chloride, and sulfate. The human health risk assessment computed from oral intake and dermal contact indicated that 36%, 34%, 31%, 36%, and 31% of samples for children, younger women, elder women, younger men, and elder men respectively, had a total hazard index (THI) > 1, indicating potential health risks. The nitrate enrichment in the subsurface water is caused by human-induced factors like fertilizers usage for agriculture, and leaching of animal waste. The health risk and water quality study suggest regular monitoring and managing the quality of groundwater for making the healthy society.

Two-dimensional Monte Carlo simulation coupled with multilinear regression modeling of source-specific health risks from groundwater

Effective protection of groundwater requires an accurate health risk assessment of contaminants; however, the diversity of pollution sources, variability, and uncertainties in exposure parameters present significant challenges in this assessment. In this study, groundwater risk estimates associated with NO3-, and F-, along with fourteen heavy metal(loid)s (V, Cr, Mn, Fe, Ni, Cu, As, Co, Cd, Se, Pb, Hg, Zn, and Al) in an agricultural area were optimized by implementing positive matrix factorization (PMF), multilinear regression, and two-dimensional Monte Carlo simulations to characterize source-specific health risks. Groundwater pollution was analyzed considering regional variations, including differences in elevation, land use and land cover, and soil types. Three pollution sources were identified: agricultural practices, traffic, and natural processes. Moreover, the results revealed NO3- from an agricultural source as the primary control contaminant. Additionally, both adults and children in the study area face significant non-carcinogenic health risks. To mitigate these risks, this study recommends maximum consumption levels of 1.44 L/day for adults and 0.35 L/day for children. Furthermore, adults weighing > 68.1 kg and children weighing > 15.9 kg are likely to be at reduced risk of experiencing adverse health effects. Compared to deterministic health risk assessment and one-dimensional Monte Carlo simulation of health risks, two-dimensional Monte Carlo simulation showed improved performance, providing better accuracy and higher precision in health risk assessment results. Thus, this research is expected to enhance the understanding of health risk assessment related to groundwater and to provide valuable guidance for managing groundwater pollution.

Breaking Linear Scaling Relation Limitations on a Dual-Driven Single-Atom Copper-Tungsten Oxide Catalyst for Ammonia Synthesis

Electrocatalytic reduction of nitrate (NO3 -, NO3RR) on single-atom copper catalysts (Cu-SACs) offers a sustainable approach to ammonia (NH3) synthesis using NO3 - pollutants as feedstocks. Nevertheless, this process suffers from inferior NO3RR kinetics and nitrite accumulation owing to the linear scaling relation limitations for SACs. To break these limitations, a single-atom Cu-bearing tungsten oxide catalyst (Cu1/WO3) was developed, which mediated a unique dual-driven NO3RR process. Specifically, WO3 dissociated water molecules and supplied the Cu1 site with ample protons, whereas the Cu1 site in an electron-deficient state converted NO3 - to NH3 efficiently. The Cu1/WO3 delivered an impressive NH3 production rate of 1274.4 mgN h-1 gCu -1, a NH3 selectivity of 99.2%, and a faradaic efficiency of 93.7% at -0.60 V, surpassing most reported catalysts. Furthermore, an integrated continuous-flow system consisting of a NO3RR cell and a vacuum-driven membrane separator was developed for NH3 synthesis from nitrate-contaminated water. Fed with the Yangtze River water containing ∼22.5 mg L-1 of NO3 --N, this system realized an NH3 production rate of 325.9 mgN h-1 gCu -1 and a collection efficiency of 98.3% at energy consumption of 17.11 kwh gN -1. This study provides a new dual-driven concept for catalyst design and establishes a foundation for sustainable NH3 synthesis from waste.

Cobalt-copper dual-atom catalyst boosts electrocatalytic nitrate reduction from water

Electrochemical nitrate reduction reaction (NO3RR) presents a promising approach for sustainable water denitrification. Yet its practical implementation is hindered by sluggish reaction kinetics. Herein, we develop a nitrogen-doped carbon supported cobalt-copper dual-atom catalyst (CoCu-NC DAC) to significantly enhance the electro-catalytic NO3RR performance. The optimized CoCu-NC DAC demonstrates exceptional activity, achieving a faraday efficiency of 95.3 % and a high NH4+ yield rate of 2.41 mg h-1 cm-2 at -0.6 VRHE, surpassing the performance of conventional Cu/Co single-atom catalysts. In-situ analysis and density functional theory calculations confirm that the synergistic effects arising from (1) optimized electronic structure for balanced intermediate adsorption, and (2) enhanced surface H concentration facilitating NOx hydrogenation. This work not only provides fundamental insights into the DACs, but also offers a practical solution for groundwater nitrate remediation, opening new avenues for the application of atomically dispersed catalysts.

Seasonal variations in groundwater chemistry and quality and associated health risks from domestic wells and crucial constraints in the Pearl River Delta

Groundwater quality is strongly compromised by polluted surface water recharge in rapidly developing urban regions. However, gaps still remain in the understanding of the critical contaminants controlling water quality and the health risks associated with groundwater consumption, particularly considering seasonal and climate changes in rainfall. This work focused on changes in groundwater quality and critical contaminants in domestic wells in the fast-developing Pearl River Delta (PRD) from the wet season to the dry season. The stable isotope δD and δ18O values indicated that groundwater was largely impacted by precipitation and has experienced strong evaporation. The groundwater generally exhibited oxidizing and slightly alkaline properties and was predominantly of the Ca-HCO3 type. Owing to the dominant water type of Ca-HCO3 and the high concentrations of Ca, concerns related to hard water arose, particularly during the wet season, which promotes the need for water softening before groundwater use. Although the heavy metal pollution index (HPI) and water quality index (WQI) indicated excellent or good water quality, 34% and 47% of the groundwater samples presented elevated concentrations of arsenic and nitrate, respectively, compared with the WHO recommended levels, and the contamination level was elevated during the dry season. To our knowledge, this study is the first to report the fluoride concentrations in the PRD groundwater, with median values below 0.5 mg L-1, underscoring the need for dietary fluoride supplementation. Health risk assessment confirmed the presence of both noncarcinogenic risks from arsenic and nitrate and cancer risk from arsenic in local populations resulting from groundwater consumption in the PRD region. This research emphasizes the importance of critical contaminants that constrain groundwater quality from different seasons with large variations in rainfall. Our work highlights the urgent need for the construction of adequate sanitation systems and for the control of agricultural nonpoint source pollution in rapidly urbanizing areas to safeguard both surface water and groundwater resources.

Inorganic bioelectric system for nitrate removal with low N2O production at cold temperatures of 4 and 10 °C

Groundwater, essential for ecological stability and freshwater supply, faces escalating nitrate contamination. Traditional biological methods struggle with organic carbon scarcity and low temperatures, leading to an urgent need to explore efficient approaches for groundwater remediation. In this work, we proposed an inorganic bioelectric system designed to confront these challenges. At 10 and 4 °C, the system achieved total nitrogen (TN) removal efficiencies of 95.4 ± 2.7% and 90.9 ± 1.9% at 2 h hydraulic retention time (HRT), while maximum TN removal rates were recorded as 206.0 ± 6.3 and 178.3 ± 9.4 g N·m-3·d-1 at 1 h HRT. The microbial analysis uncovered shifts in dominant genera across temperatures, with Dechloromonas prevalent at 10 °C and Chryseobacterium at 4 °C, highlighting adaptability to cold-tolerant species. Gene analysis on narG, napA, nirS, nirK, norB, nosZI, nosZII, and nifA examined the nitrate reduction processes, and analysis on mtrC and omcA hinted at electrotrophic processes. Additionally, we demonstrated system resilience to disruptions of power outage and short periods without flow through. These findings establish a foundational understanding of electricity-driven nitrate bioreduction in cold environments, crucial in groundwater remediation strategies and paving the way for future optimization and upscaling efforts.

An empirical and statistical investigation on decarbonizing groundwater using industrial waste-based biochar: Trading-off zero-waste management and zero-emission target

This study recommended a trade-off between zero-waste management of a brewery industry and zero-aim target of the drinking water sector. This study mainly aimed to decrease the carbon dioxide (CO2) emissions resulting from groundwater treatment using biochar derived from malt sprout (MS) which is a waste by-product of a brewery industry. Also, CO2 resulting from groundwater treatment was collected and gas adsorption was performed to define the CO2 adsorption capacity of each biochar. Data Envelopment Analysis (DEA) was performed to determine the effect of groundwater quality on CO2 emissions. In the result of experimental and computational analysis, a new carbon capture indicator (CCIB) was derived depending on biochar adsorption process, in this study. The results revealed that averagely 28.98 % of reduction on CO2 emission from groundwater treatment was reported using the mixture of three malt sprout derived biochar. MS1 had the highest carbon capture capacity which was derived at 300 °C. According to (DEA) results, the optimum total organic carbon (TOC) should be 3.2 mg/L for the minimum CO2 emission. Also, optimum biochar dose, contact time and gas flow were 8 g, 10 min and 965 mL/d, respectively for the maximum CO2 adsorption by biochar according to Box-Behnken design method.

Influencing factors of groundwater 238U, 232Th, 40K, and rare earth element contamination: Insights from the two-dimensional Monte Carlo simulation of radiological risks

Ionizing radiation from naturally occurring radioactive materials (NORM) can pose significant health risks to humans, particularly when contaminating groundwater. As a vital resource, groundwater is essential for drinking, irrigation, and industrial processes in many regions worldwide. Therefore, this study developed a comprehensive and innovative method for groundwater source-specific radiological risk assessment, integrating multivariate statistical analysis, the two-dimensional Monte Carlo simulation (2D MCS), and a geographic information system (GIS) for mapping. Groundwater samples from an agricultural region were analyzed for radionuclides, including 238U, 232Th, and 40K, alongside sixteen rare earth elements (REE). Using the positive matrix factorization model, three pollution sources were identified: geogenic processes, weathering of REE-rich rocks, and agricultural activities. The results of source-specific radiological risk assessment revealed that adults were more vulnerable to radiological risk than children, and agricultural activities as the dominant contributor to risks. It was concluded that exposure frequency (EF), ingestion rate (IR), and 40K concentration were the exposure parameters with the greatest impact on radiological risk. Modeling these parameters established their critical values as 190 days/year, 2 L/day, and 415 ng/L, respectively, to ensure that the radiological risk for adults remains within the safety limit. Additionally, the incorporation of the 2D MCS into the risk assessment process significantly enhanced the accuracy and precision of the results, in comparison with the deterministic and one-dimensional Monte Carlo simulation (1D MCS) models. This research provides practical guidance for the sustainable management of water resources and presents an innovative methodology that can be applied to similar regions globally.

Kuala Gula Bird Sanctuary, Perak, Malaysia: Status, challenges and future for migratory shorebirds population in the East-Asian Australian Flyway

Birds are an excellent bio-indicator of biodiversity changes. Migratory shorebirds in particular cover a large distances traversing different types of habitats, from the tundra region in the most northern part of the world, to tropical and temperate areas in the southern most area. Kuala Gula, a sanctuary for more than 200 bird species is part of an Important Bird and Biodiversity Areas (IBAs) along the East-Asian Australian Flyway. Despite its importance, the area including its coastline is continuously pressured by anthropogenic activity. As such, there is a need to critically review Kuala Gula's environmental status to highlight its potential, along with understanding the issues and threats particularly to the migratory shorebirds population in the long run. This is important not just to maintain Kuala Gula's relevance as part of the important IBA in the Southeast Asia, but also to ascertain its qualification to meet its recognition's goal. Throughout this review, we found that there are several issues that need to be addressed urgently, particularly ones related to pollution activity. Furthermore, the studies done so far are not coordinated well enough and lack continuity. As such, certain important information is still lacking making the protection and conservation of the area a big challenge. It is concluded that, the stability and sustainability of Kuala Gula's habitats and its coastline is at stake, and there is a hope that this review will help related stakeholders to understand the current issues, and work together effectively to conserve the area.

Nitrate induced hepatic fibrosis in tadpoles of Bufo gargarizans by mediating alterations in toll-like receptor signaling pathways

The nitrate pollution has become an increasingly serious environmental problem worldwide, and the toxic effects of elevated nitrate levels in the environment on aquatic animals remain to be elucidated. The purpose of the present study was to investigate the mechanisms of liver injury to tadpoles after exposure to nitrate from embryonic to metamorphic climax and to assess the recovery process of liver function after cessation of exposure. In the group with continuous nitrate exposure, the livers and thyroid of tadpoles showed remarkably histological lesions, of this with structural disorganization of the hepatocytes, cellular atrophy, and fibrosis, as well as significant reduction in the follicular and colloidal area of the thyroid. Meanwhile, the expression levels of genes related to inflammatory signaling pathways, such as TLR2, TLR6 and NF-κB, were significant elevated. After termination of exposure at Gs23, liver damage (histologic, ultrastructural, and molecular levels) was almost completely recovered, whereas thyroid gland damage was irreversible. Overall, this study shed light on the harmful effects of nitrate pollution on amphibian health and emphasizes the importance of controlling nitrate emissions in the environment.

TET1 mitigates prenatal fluoride-induced cognition impairment by modulating Bcl2 DNA hydroxymethylation level

Fluoride exposure during pregnancy commonly compromises fetal neurodevelopment and largely results in a broad spectrum of cognitive deficiencies in the adult offspring. However, the precise mechanisms underlying these effects remain to be fully elucidated. Herein, we investigate the impacts of fluoride on neural excitability and apoptosis, synaptic plasticity, and cognitive function, as well as possible underlying mechanisms. Our results indicated that exposure to a high sodium fluoride (100 mg/L) during pregnancy in the mouse can cause the cognitive deficits of their offspring, accompanied by a decrease in the expression of Tet-eleven translocation protein 1 (TET1), an enzyme responsible for DNA hydroxymethylation. Additionally, there is a reduction in the dendritic spine density and the expression of postsynaptic density protein-95 (PSD95) in the hippocampal regions of male offspring. Furthermore, in vitro fluoride treatment significantly exacerbates neuronal apoptosis and reduces the frequency of spikes in spontaneous action potential. More significantly, we also found that TET1 could directly bind to the promotor region of Bcl2, altering its DNA hydroxymethylation and Bcl2 expression. Intriguingly, Tet1 knock-out mice exhibited cognitive deficits similar to those observed in male animals exposed to high levels of fluoride. Furthermore, the down-regulation of TET1 protein, along with the consequent alteration in Bcl2 hydroxymethylation and increased neuronal apoptosis, are likely mechanisms underlying the impact of prenatal fluoride exposure on the neurodevelopment of male offspring. These findings provide novel insights into the molecular mechanisms by which fluoride exposure induces neurodevelopmental impairment of the male offspring.

Groundwater Safety and Availability Index (GSAI) and its association with salinity indicators

This study assesses the quality of groundwater in the Odra River Basin in Poland, focussing on environmental health risks, temporal variability, and their association with salinity indices. A new indicator, the Groundwater Safety and Availability Index (GSAI), was developed to evaluate groundwater resources by integrating health risk and resource quantity factors, providing a novel tool for ranking water resources and informing environmental and administrative decision-making. Groundwater samples were collected between 2005 and 2021 and analysed in accordance with national standards. The results demonstrate an improvement in groundwater quality over time, indicated by a reduction in Health Index (HI) values, particularly in Lower Silesia, Lubusz, and Silesia. Significant correlations were found between HI and NO₃- (τ-Kendall = 0.40) and arsenic (τ-Kendall = 0.55). GSAI values varied across regions, with West Pomerania showing the highest groundwater safety and availability, while Silesia had the lowest. Elevated concentrations of contaminants such as arsenic and nitrates were found to significantly impact water safety, particularly during hydrogeological droughts. These findings support the need for region-specific management strategies to ensure sustainable groundwater use and mitigate health risks, with the GSAI serving as a valuable tool for policymakers and environmental planners.

Geochemistry of some fluoride and nitrate enriched water resources from the Oriental Basin: a prospective health risk hotspot from eastern-central Mexico

In attention to the Sustainable Development Goal 6, the quality evaluation of water resources in Mexico is limited compared to other regions. This study provided new data from Oriental Basin, an important socio-economic region with up to 20% population growth over the last decade by assessing groundwater from the Libres-Oriental aquifer (Ca-Mg-HCO3 facies; F-: 2.5-9.9 mg/L; NO3-: up to 75.3 mg/L) and water from the Totolcingo Lake (Na-Cl facies; F-: 12.7-13.2 mg/L; NO3-: < 0.75 mg/L). Fluoride content grouped about 80% groundwater samples as promotor of dental and skeletal fluorosis. Nitrate Pollution Index suggested moderate pollution in 20% and very significant pollution in 10% groundwater samples. Possible exposure of older adults and elderly pregnant women to fluorosis from all the groundwater samples (Hazard Quotient > 1) from the Oriental Basin and 55% of them might also be causing fluorosis in infants suggest a potential health risk hotspot in the eastern-central Mexico. Even though all the groundwater samples did not contain enough NO3- to cause methemoglobinemia, their boiling for drinking could enhance nitrate content beyond the WHO limit. Thus, the mitigation techniques might diminish the health risks in consuming population.

Palladium Membrane Applications in Hydrogen Energy and Hydrogen-Related Processes

In recent years, increased attention has been paid to environmental issues and, in connection with this, to the development of hydrogen energy. In turn, this requires the large-scale production of ultra pure hydrogen. Currently, most hydrogen is obtained by converting natural gas and coal. In this regard, the issue of the deep purification of hydrogen for use in fuel cells is very relevant. The deep purification of hydrogen is also necessary for some other areas, including microelectronics. Only palladium membranes can provide the required degree of purification. In addition, the use of membrane catalysis is very relevant for the widely demanded processes of hydrogenation and dehydrogenation, for which reactors with palladium membranes are used. This process is also successfully used for the single-stage production of high-purity hydrogen. Polymeric palladium-containing membranes are also used to purify hydrogen and to remove various pollutants from water, including organochlorine products, nitrates, and a number of other substances.

Periodic Table Exploration of MXenes for Efficient Electrochemical Nitrate Reduction to Ammonia

Applying electrochemical nitrate reduction reaction (NO3RR) to produce ammonia offers a sustainable alternative to the energy-intensive Haber-Bosch process, which is crucial for clean energy and agricultural applications. While 2D MXenes hold great promise as electrocatalysts for NO3RR, their application for ammonia production remains underexplored. This study combines experimental and theoretical approaches to evaluate the catalytic performance of a series of MXenes with different central metal atoms for NO3RR. Among the materials studied (Ti3C2Tx, Ti3CNTx, Ti2CTx, V2CTx, Cr2CTx, Nb2CTx, and Ta2CTx), Ti3-based MXenes exhibit superior faradaic efficiency, ammonia yield rate, and stability. Density functional theory calculations offer further insights explaining the structure-activity-based observations. This research establishes a foundation for future studies aimed at leveraging MXenes for electrochemical nitrate reduction for green synthesis of ammonia.

2D copper-iron bimetallic metal-organic frameworks for reduction of nitrate with boosted efficiency and ammonia selectivity

Electrocatalytic reduction of nitrate to ammonia has been considered a promising and sustainable pathway for pollutant treatment and ammonia has significant potential as a clean energy. Therefore, the method has received much attention. In this work, Cu/Fe 2D bimetallic metal-organic frameworks were synthesized by a facile method applied as cathode materials without high-temperature carbonization. Bimetallic centers (Cu, Fe) with enhanced intrinsic activity demonstrated higher removal efficiency. Meanwhile, the 2D nanosheet reduced the mass transfer barrier between the catalyst and nitrate and increased the reaction kinetics. Therefore, the catalysts with a 2D structure showed much better removal efficiency than other structures (3D MOFs and Bulk MOFs). Under optimal conditions, Cu/Fe-2D MOF exhibited high nitrate removal efficiency (87.8%) and ammonium selectivity (89.3%) simultaneously. The ammonium yielded up to significantly 907.2 µg/(hr·mgcat) (7793.8 µg/(hr·mgmetal)) with Faradaic efficiency of 62.8% at an initial 100 mg N/L. The catalyst was proved to have good stability and was recycled 15 times with excellent effect. DFT simulations confirm the reduced Gibbs free energy of Cu/Fe-2D MOF. This study demonstrates the promising application of Cu/Fe-2D MOF in nitrate reduction to ammonia and provides new insights for the design of efficient electrode materials.

Anthropogenic impacts on the terrestrial subsurface biosphere

The terrestrial subsurface is estimated to be the largest reservoir of microbial life on Earth. However, the subsurface also harbours economic, industrial and environmental resources, on which humans heavily rely, including diverse energy sources and formations for the storage of industrial waste and carbon dioxide for climate change mitigation. As a result of this anthropogenic activity, the subsurface landscape is transformed, including the subsurface biosphere. Through the creation of new environments and the introduction of substrates that fuel microbial life, the structure and function of subsurface microbiomes shift markedly. These microbial changes often have unintended effects on overall ecosystem function and are frequently challenging to manage from the surface of the Earth. In this Review, we highlight emerging research that investigates the impacts of anthropogenic activity on the terrestrial subsurface biosphere. We explore how humans alter the constraints on microbial life in the subsurface through drilling, mining, contamination and resource extraction, along with the resulting impacts of microorganisms on resource recovery and subsurface infrastructure.

Modeling Study on Optimizing Water and Nitrogen Management for Barley in Marginal Soils

Water and N availability are key factors limiting crop yield, particularly in marginal soils. This study evaluated the effects of water and N stress on barley grown in marginal soils using field trials and the AgroC model. Experiments from 2020 to 2022 in Lithuania with spring barley cv. KWS Fantex under two N fertilization treatments on sandy soil provided data for model parameterization. The AgroC model simulated barley growth to assess yield potential and yield gaps due to water and N stress. Potential grain yields (assuming no water or N stress) ranged from 4.8 to 6.02 t DW ha-1, with yield losses up to 54.4% assuming only N stress and 59.2% assuming only water stress, even with the N100 treatment (100 kg N ha-1 yr-1). A synthetic case study varying N fertilization from 0 to 200 kg N ha-1 yr-1 showed that increasing N still enhanced yield, but the optimal rate of 100-120 kg N ha-1 yr-1 depended on climatic conditions, leading to uncertainty in fertilization recommendations. This study underscores the importance of integrating advanced modeling techniques with sustainable agricultural practices to boost yield potential and resilience in marginal soils. Incorporating remote sensing data to capture soil and crop variability is recommended for improving simulation accuracy, contributing to sustainable agriculture strategies in the Baltic-Nordic region.

Role of Mass Transfer Phenomena in Electrochemical Nitrate Reduction: A Case Study Using Ti and Ag-Modified Ti-Hollow Fiber Electrodes

Decentralized electrochemical reduction of nitrate into ammonium is explored as a viable approach to mitigate nitrate accumulation in groundwater. In this study, tubular porous electrodes made of titanium (termed hollow fiber electrodes or HFEs) were successfully modified with silver (Ag) nanoparticles through electrodeposition. Under galvanostatic control and in acidic electrolyte, Ag deposition on Ti HFE resulted in an increase in the Faradaic efficiency for ammonium formation from low concentrations of nitrate (50 mM), but only under reaction conditions of restricted mass transport. For conditions of favorable transport, facilitated by an inert gas flow (Ar) exiting the pores, a higher nitrate conversion but an increase in hydroxylamine selectivity at the expense of the ammonium selectivity are observed for Ti/Ag hollow fiber electrodes. For Ti/Ag electrodes, it is concluded that ammonium formation is prevented by effective removal of surface intermediates. Remarkably, for unmodified Ti hollow fiber electrodes, the Faradaic efficiency to ammonium is significantly improved when operated at high current densities and in conditions of high mass transport. The selectivity to liquid products even surpasses the selectivity of Ti/Ag electrodes. These findings indicate that nitrate reduction to ammonium at Ti and Ti/Ag hollow fiber electrodes can be achieved at comparable rates but under distinctly different process conditions. In fact, for Ti electrodes, operation at a lower applied potential compared to Ti/Ag electrodes is feasible, ultimately resulting in reduced energy consumption. This study thus highlights the importance of controlling the interfacial electrode environment, particularly when comparing and evaluating the effectiveness of electrode materials in electrochemical nitrate reduction. The study also reveals that transport phenomena affect electrode material-dependent activity-selectivity correlations and must be considered in ongoing material development efforts.

Synergistic Effect of Boron Doping and Porous Structures on Titanium Dioxide for Efficient Photocatalytic Nitrate Reduction to Nitrogen in Pure Water

Photocatalytic reduction of nitrate to N2 holds great significance for environmental governance. However, the selectivity of nitrate reduction to N2 is influenced by sacrificial agents and the kinds of cocatalysts (such as Pt and Ag). The presence of unconsumed sacrificial agents can aggravate environmental pollution, while noble metal-based cocatalysts increase application costs. Herein, the porous boron-doped TiO2 (B-TiO2) was successfully synthesized by using the sol-gel method with Amberlite IRA-900 as a template. The incorporation of 33% boron into TiO2 (33% B-TiO2) achieved a 100% nitrate (20 ppm) conversion rate and 94.5% N2 selectivity without the need for sacrificial agents and cocatalysts during the nitrate reduction process. The catalyst's unique multistage porous structure not only enhances the light absorption ability but also significantly provides abundant surface adsorption sites. Additionally, theoretical studies show that boron doping effectively modulates the band structure of TiO2 and increases the electron density at the Ti surface active sites, both of which are essential for achieving a high nitrate reduction efficiency. This work emphasizes the synergistic effect between morphology control and electronic structure regulation in promoting the photocatalytic reduction of nitrate to nitrogen, providing valuable insights for the photocatalytic treatment of nitrate wastewater.

Impact of climate change and land management on nitrate pollution in the high plains aquifer

High concentrations of nitrate in groundwater pose risks to human and environmental health. This study evaluates the potential impact of climate change, land use, and fertilizer application rates on groundwater nitrate levels in the High Plains Aquifer under four Shared Socioeconomic Pathway (SSP) scenarios. A random forest model, with predictors such as fertilizer application rates, cropland coverage, and climate variables from six Coupled Model Intercomparison Project models, is used to project future nitrate concentrations. Results show increases across all scenarios, with nitrate levels rising by 4% under SSP5-8.5 and up to 13% under SSP2-4.5 when accounting for climate change effects. Fertilizer application rates are identified as the primary driver of projected changes. The northern and central regions of the aquifer exhibited the most pronounced increases. The projected changes in nitrate levels, observed across both low- and high-greenhouse gas emission pathways, highlight the need to develop integrated management strategies that consider shared socioeconomic scenarios and water resource protection constraints.

Tracing nitrate contamination sources and dynamics in an unconfined alluvial aquifer system (Velika Gorica well field, Croatia)

Nitrate ions (NO3-) are one of the most common contaminants in the groundwater of the Zagreb alluvial aquifer, which hosts strategic groundwater reserves of the Republic of Croatia and supplies drinking water to one million inhabitants of the capital city. To better understand the origin and the dynamics of NO3- in the unsaturated and saturated zones, the stable isotopes of nitrogen (δ15N) and oxygen (δ18O) in dissolved nitrate, combined with physico-chemical, hydrogeochemical and water stable isotope data, were used in the current work, together with statistical tools and mixing models. The study involved monthly sampling of groundwater, surface water, precipitation and soil water samples. Additionally, the isotopic composition of total nitrogen (δ15Nbulk) was determined in solid samples representing the local nitrate sources. The combination of a nitrous oxide isotopic analyzer and the titanium(III) reduction method provides reliable measurements of δ15NNO3 and δ18ONO3, with optimal stability achieved under specific conditions. Nitrate in the study area predominantly originates from organic sources, with nitrification as the main biogeochemical process, while denitrification was identified at sampling sites under specific anaerobic conditions. Although statistical analysis can be a valuable tool, it should be applied with caution if NO3- originates from multiple sources. The isotopic composition of water showed that groundwater is predominantly recharged by the Sava River but its contribution varied spatially. The results also show the existence of a different recharge source in the southern part of the aquifer. Our findings highlighted the importance of employing a diverse range of analytical methods to obtain reliable and comprehensive understanding of nitrate contamination. By integrating multi-method approaches, stakeholders can better understand the complexities of groundwater contamination and implement more targeted measures to safeguard the water supplies for future generations.

Groundwater denitrification using electro-assisted autotrophic processes: exploring bacterial community dynamics in a single-chamber reactor

Nitrate, a major groundwater pollutant from anthropogenic activities, poses serious health risks when present in drinking water. Denitrification using bio-electrochemical reactors (BER) offers an innovative technology, eco-friendly solution for nitrate removal from groundwater. BER use electroactive bacteria to reduce inorganic compounds like nitrate and bicarbonate by transferring electrons directly from the cathode. In our work, two batch BER were implemented at 1V and 2V, using anaerobic digestate from a full-scale wastewater treatment plant as inoculum. Nitrate, nitrite, sulfate, total ammoniacal nitrogen, and 16S rRNA analysis of bacterial community, were monitored during BER operation. The results showed effective nitrate removal in all BERs, with denitrification rate at 1V and 2V higher than the Control system, where endogenous respiration drove the process. At 1V, complete nitrate conversion to N2 occurred in 4 days, while at 2V, it took 14 days. The slower rate at 2V was likely due to O2 production from water electrolysis, which competed with nitrate as final electron acceptor. Bacterial community analysis confirmed the electroactive bacteria selection like the genus Desulfosporosinus and Leptolinea, confirming electrons transfer without an electroactive biofilm. Besides, Hydrogenophaga was enhanced at 2V likely due to electrolytically produced H2. Sulfate was not reduced, and total ammoniacal nitrogen remained constant indicating no dissimilatory nitrite reduction of ammonia. These results provide a significant contribution to the scaling up of electro-assisted autotrophic denitrification and its application in groundwater remediation, utilizing a simple reactor configuration-a single-chamber, membrane-free design- and a conventional power source instead of a potentiostat.

Environmental justice issues in drinking water contaminant exposure in a European context

Previous studies have documented ethnic and sociodemographic disparities in exposure to drinking water (DW) contaminants. A majority were conducted in the U.S., with fewer studies conducted in other regions. This research aims to assess available evidence regarding environmental justice (EJ) issues in Europe, identify contaminants and potential drivers. A Scoping Review was conducted, exploring the existing European studies from 1990 to 2022. The review encompasses types of DW contaminants studied in relation to EJ, research designs, and potential drivers contributing to inequalities in exposure to specific contaminants. In addition, a case study was conducted in Ille-et-Vilaine, France, focusing on contaminants identified in the review and using a national monitoring database. Inequalities in contaminants' exposure were assessed using a composite deprivation index, FDep, at the census tract level (IRIS) applied in multilevel models and geographically weighted regression models, accounting for the rural-urban heterogeneity. Results show a limited number of primary studies focusing on EJ and DW contaminants exposure in Europe (n = 16). Various chemical contaminants such as nitrates, trihalomethanes (THMs), heavy metals, fluoride and pesticides have been assessed. Case study findings suggest some association between FDep and contaminants, with a different level of correlation depending on the contaminant. THMs show a negative correlation with deprivation, while lead displays a positive correlation related to the FDep. Disparities in exposure were also found according to the spatial scale of analysis. In rural areas, higher deprivation levels were associated with higher levels of nitrate (OR: 1.47; 95%CI: 1.02, 2.15) and lower level of fluoride (OR: 0.16; 95%CI: 0.07, 0.30) or THMs (OR: 0.73; 95%CI: 0.55, 0.98) in tap water. This study emphasizes the need for comprehensive research on EJ and DW contaminants exposure on a larger scale. Understanding complex interactions between contaminant distribution, socioeconomic factors, and exposure is essential for addressing EJ in drinking water.

Revealing nitrate sources seasonal difference between groundwater and surface water in China's largest fresh water lake (Poyang Lake): Insights from sources proportion, dynamic evolution and driving forces

Tracing the source of nitrate is the key path to solve the problem of nitrogen pollution. However, the seasonal difference of nitrate sources in groundwater and surface water and its dynamic evolution process and mechanism in large fresh water lake area are still not clear. In this study, 126 water samples were collected from groundwater and surface water in China's largest fresh water lake (Poyang Lake) region from 2022 to 2023. Bayesian stable isotope mixing model, absolute principal component score-multiple linear regression, ion ratio coefficients and uncertainty index (UI90) were used to investigate the nitrate sources variation in groundwater and surface water as well as its uncertainty in Poyang Lake area. Results showed that anthropogenic influence had significant influence on nitrate sources, which was mainly affected by chemical fertilizer (CF), soil nitrogen (SN) and manure and sewage input (M&S). Specifically, from 2022 to 2023, CF contributed 16.6 % to 32.4 %, SN contributed 26.0 % to 38.1 %, M&S contributed 26.5 % to 48.2 % to groundwater. CF contributed 38.8 % to 43.9 %, SN contributed 37.6 % to 40.6 %, M&S contributed 12.3 % to 18.6 % to surface water. The sources and proportion of nitrate in groundwater and surface water exhibited obvious difference. Temporal heterogeneity, land use type, population density and vegetation cover type had influence on nitrate sources. UI90 results showed that there was uncertainty in nitrate sources tracing process, with SN (mean 0.78), CF (mean 0.64), M&S (mean 0.35) and AD (mean 0.09), respectively. These results will provide vital references for understanding nitrate sources variation, controlling and removing nitrate surplus in groundwater-surface water system in the similar large fresh water lake areas.

Key factors affecting groundwater nitrate levels in the Yinchuan Region, Northwest China: Research using the eXtreme Gradient Boosting (XGBoost) model with the SHapley Additive exPlanations (SHAP) method

Groundwater is a vital natural resource that has been extensively used but, unfortunately, polluted by human activities, posing a potential threat to human health. Groundwater in the Yinchuan Region is contaminated with NO3-, which is harmful to the local population. This study utilized the eXtreme Gradient Boosting (XGBoost) model with the SHapley Additive exPlanations (SHAP) method to identify the key factors influencing groundwater nitrate pollution in the Yinchuan Region. The SHAP feature dependence plots revealed the intricate relationship between NO3- levels and TDS, Mn2+, TFe, and pH in complex groundwater systems. The results indicate that the high levels of groundwater NO3- are primarily caused by the combined effect of irrigation water from the Yellow River, shallow groundwater depth, unfavorable drainage, water recharge, overuse of fertilizers, and geological factors such as weathering nitrogen-bearing rocks. Hydrochemical parameters such as Mn2+, Fe2+, and pH create a strong reducing groundwater environment, resulting in lower NO3- concentrations in this region. Well depth and soil organic carbon at a depth of 80-100 cm have a negative impact on NO3- concentrations; conversely, sand in soil depths 0-20 cm and 100-150 cm and climatic factors such as precipitation have a weak but positive effect on the level of NO3- in groundwater in the region. The recommendation is to quickly and extensively implement a farming water-conservancy transformation project, reducing water-intensive crops, promoting groundwater use for irrigation in areas where soil salinization is a concern are proposed. This research could provide local agencies with a scientific foundation for sustainable management of farming and groundwater in the Yinchuan Region, ultimately benefiting the entire Yinchuan Plain.

An integrated computational and graphical approach for evaluating the geochemistry and health risks of nitrate-contaminated water for six age groups

Nitrate contamination in drinking water poses significant health risks, particularly in rapidly urbanizing areas of developing countries. This study presents an integrated computational and graphical approach to evaluate the geochemistry and health risks of nitrate-contaminated water for six age groups in Southeast, Nigeria. The research employed a detailed methodology combining water nutrient pollution index (WNPI), nitrate pollution index (NPI), water pollution index (WPI), geochemical plotting techniques, stoichiometry, and health risk computations. Water samples from several locations were analyzed for physicochemical parameters and nitrate concentrations. Results revealed predominantly acidic conditions and varying levels of nitrate contamination. Geochemical analysis indicated that silicate weathering and ion exchange processes were the primary influences on water chemistry. The WPI identified 14.29% of samples as "extremely polluted" (WPI > 1), while the WNPI classified 7.14% of samples as "moderately polluted" (WNPI > 1). However, the NPI categorized the samples as safe, indicating low nitrate inputs from anthropogenic sources. Health risk assessments indicated low-moderate risks, with the highest total hazard index of 0.839 for the 6-12 months age group; thus, higher vulnerability for infants. Oral exposure was found to be the dominant pathway, contributing over 99.90% to the total risk. This research provides crucial insights for achieving the Sustainable Development Goals (SDGs) related to water quality and public health protection. The integrated approach offers a robust framework for water resource management and interventions in risk-prone areas. Future research should focus on expanding the spatial coverage, incorporating sensitivity analyses, and exploring advanced technologies for real-time monitoring and predictive modeling of water quality.

Unraveling the synergistic interplay of sulfur and wheat straw in heterotrophic-autotrophic denitrification for sustainable groundwater nitrate remediation

Nitrate pollution in groundwater is a global environmental issue that poses significant threats to human health and ecological security. This study focuses on elucidating the mechanisms of heterotrophic-autotrophic cooperative denitrification (HAD) by employing wheat straw and elemental sulfur as electron donors in varying proportions. The research initially underscores that heterotrophic denitrification (HD) accelerates the denitrification process due to its high-energy metabolism. However, as readily degradable organic matter diminished, reliance on more complex substrates such as lignocellulose posed a challenge to HD. This marks a pivotal transition towards autotrophic denitrification (AD), which, despite a slower initial rate, exhibits a more sustained denitrification performance. A low proportion of heterotrophic denitrification layer (e.g., 3:1) at the bottom facilitating efficient and sustainable denitrification. HD is capable of simultaneous removal of nitrates and nitrites, whereas AD demonstrates a higher affinity for nitrates, with nitrite accumulation reaching 100% at high influent nitrate concentrations (100 mg/L). HD not only provides the necessary alkaline environment for AD but also reduces sulfate production, whereas AD utilizes the residual organic carbon and ammonia produced by HD. The heterotrophic layer is characterized by a diverse community, whereas the autotrophic layer is predominantly composed of Thiobacillus. By delineating the interactive mechanisms and characteristics of HAD, this study highlights the importance of balancing heterotrophic and autotrophic activities for the effective remediation of groundwater nitrates.

Study on the remediation of groundwater nitrate pollution by pretreated wheat straw and woodchips

Groundwater nitrate contamination poses a threat to both the ecological environment and human health. This study investigated the potential of using saturated Ca(OH)2 to pretreat wheat straw and woodchips, aiming to enhance their efficacy as carbon sources for denitrification. The optimization of pretreatment conditions, and the elucidation of underlying mechanisms were explored. The pretreatment process involved the dissolution of lignin and hemicellulose, exposure of the cellulose structure, reduction of hydrogen bonds within cellulose, hydrolysis of polymerized cellulose, and the formation of cracks and hierarchical structures on the surface of the carbon source. These alterations improved the attachment and utilization of microorganisms. The maximum enzymatic reducing sugar yields for wheat straw and woodchips were achieved at solid-liquid ratios of 1:40 and soaking times of 5 and 2 days, respectively. The response surface predicted the optimal pretreatment conditions for wheat straw to be a solid-liquid ratio of 1:88.1 and a soaking time of 8.2 h. Alkaline treatment increased the denitrification rate of woodchips by fivefold and prevented the initial organic matter leaching rate of wheat straw, thereby reducing the risk of secondary pollution. The predominant microbial communities in all samples exhibited functions related to lignocellulose degradation and denitrification. The community composition of solid-phase carbon sources was found to be richer than that of liquid-phase carbon sources, and the pretreatment increased the abundance of lignocellulose degradation and denitrification functional microorganisms. The pretreatment liquid of wheat straw achieved the highest denitrification rate constant (0.43 h-1). Our result validated the feasibility of using the pretreatment liquid as a denitrification carbon source and presenting a novel approach for waste resource utilization.

Nitrate sources and transformation in surface water and groundwater in Huazhou District, Shaanxi, China: Integrated research using hydrochemistry, isotopes and MixSIAR model

Global water resources affected by excessive nitrate (NO3-) have caused a series of human health and ecological problems. Therefore, identification of NO3- sources and transformations is of pivotal significance in the strategic governance of widespread NO3- contaminant. In this investigation, a combination of statistical analysis, chemical indicators, isotopes, and MixSIAR model approaches was adopted to reveal the hydrochemical factors affecting NO3- concentrations and quantify the contribution of each source to NO3- concentrations in surface water and groundwater. The findings revealed that high groundwater NO3- concentration is concentrated in the southwestern region, peaking at 271 mg/L. NO3- concentration in the Wei River and Yuxian River exhibited an increase from upstream to downstream, but in the Shidi River and Luowen River, its concentration was highest in the upstream. Groundwater NO3- has noticeable correlation with Na+, Ca2+, Mg2+, Cl-, HCO3-, TDS, EC, and ORP. In surface water, NO3- level is significantly correlated with NH4+ and ORP. Major sources of NO3- in surface and groundwater comprise manure & sewage and soil nitrogen. Source contribution for surface water was calculated by MixSIAR model to obtain soil nitrogen (57.7%), manure & sewage (23.8%), chemical fertilizer (12%), and atmospheric deposition (6.4%). In groundwater, soil nitrogen and manure & sewage accounted for 19% and 63.8% of nitrate sources, respectively. Both surface water and groundwater exhibited strong oxidation, with nitrification the primary process. It is expected that this study will provide insights into the dynamics of NO3- and contribute to the development of effective strategies for mitigating NO3- contaminant, leading to sustainable management of water resources.

Innovative approaches to electrochemical oxidation of Bisphenol B in synthetic and complex water environments

The substitution of Bisphenol A (BPA) with Bisphenol B (BPB) has raised concerns due to BPB's increased environmental presence and its potential hazards. Despite the frequent detection in water environments, effective removal methods for BPB are still limited. This study hypothesizes that electrochemical oxidation (EO) can effectively degrade BPB and its by-products. To test this, EO was applied under various conditions, analyzing the role of anode material, current density, pH, and BPB concentration. The results revealed that BPB degradation followed pseudo-first-order kinetics, with boron-doped diamond (BDD) anode showing a rate constant 27 times higher than iridium oxide electrodes. After 180 min, BDD achieved 81.8 % mineralization of BPB. The remaining organic load was associated to easily biodegradable short-chain carboxylic acids. Additionally, the EO process was evaluated in different matrices, including drinking water, tap water, simulated municipal wastewater, and synthetic urine, to assess the impact of matrix complexity. Electrogenerated oxidants, such as hydroxyl radicals, sulfate radicals, and active chlorine, significantly enhanced BPB degradation rates in real water matrices. Energy consumption varied from 5.32 kWh m-3 in drinking water to 2.28 kWh m-3 in synthetic urine, demonstrating the role of matrix composition in EO efficiency. These findings show that EO is a promising technology for removing BPB and similar chemicals in real-world water matrices.

Remediation of Cr(VI) Polluted Groundwater Using Zero-Valent Iron Composites: Preparation, Modification, Mechanisms, and Environmental Implications

The extensive application of chromium (Cr) in many industries has inevitably resulted in the release of Cr(VI) into the groundwater environment, thus posing damage to the ecosystem and human health. Nano zero-valent iron (nZVI) has been widely studied and applied in the remediation of Cr(VI)-contaminated water as an ideal material with high reductive capacity, which enables the transformation of teratogenic and carcinogenic Cr(VI) into less toxic Cr(III). This review comprehensively summarizes the preparation and modification methods of nZVI Cr(VI) removal performance and mechanisms by nZVI and modified nZVI materials. The field applications of nZVI-based materials, such as combining the injection well and the permeable reactive barrier (PRB) to remove Cr(VI) in groundwater, have been reported. Subsequently, the potential toxicity of nZVI-based materials to organisms during environmental application has been highlighted in the current study. Finally, the review outlines potential improvements and explores future directions for the use of nZVI-based materials in groundwater contamination remediation.

Groundwater nitrate contamination in China: Spatial distribution, temporal trend, and driver analysis

China's groundwater is facing a significant threat from nitrate pollution. Here we analyzed 2348 regional surveys of groundwater nitrate levels in China from 1990 to 2020, examining distribution, trends, and drivers. This study uncovers a concerning rise in nitrate pollution, with estimated median nitrate levels climbing from 3.84 mg/L in 1990 to 6.94 mg/L in 2020. A stark contrast is observed between regions: the northern areas have a median nitrate concentration of 8.54 mg/L, significantly higher than the southern regions, where the median is just 7.15 mg/L. From 1990 to 2020, agricultural activity consistently emerges as the dominant driver of changes in groundwater nitrate concentrations, while groundwater exploitation, domestic pollution, and industrial production also contribute to varying degrees. This analysis highlights the urgency for region-specific policies and interventions to address the escalating nitrate pollution in China's groundwater.

Self-Reconstruction Induced Electronic Metal-Support Interaction for Modulated Cu+ Sites on TiO2 Nanofibers in Electrocatalytic Nitrate Conversion

The Cu+ active sites have gained great attention in electrochemical nitrate reduction, offering a highly promising method for nitrate removal from water bodies. However, challenges arise from the instability of the Cu+ state and microscopic structure over prolonged operation, limiting the selectivity and durability of Cu+-based electrodes. Herein, a self-reconstructed Cu2O/TiO2 nanofibers (Cu2O/TiO2 NFs) catalyst, demonstrating exceptional stability over 50 cycles (12 h per cycle), a high NO3 --N removal rate of 90.2%, and N2 selectivity of 98.7% is reported. The in situ electrochemical reduction contributes to the self-reconstruction of Cu2O/TiO2 nanofibers with stabilized Cu+ sites via the electronic metal-support interaction between TiO2 substrates, as evidenced by in situ characterizations and theoretical simulations. Additionally, density functional theory (DFT) calculations also indicate that the well-retained Cu+ sites enhance catalytic capability by inhibiting the hydrogen evolution reaction and optimizing the binding energy of *NO on the Cu2O/TiO2 NFs heterostructure surface. This work proposes an effective strategy for preserving low-valence-state Cu-based catalysts with high intrinsic activity for nitrate reduction reaction (NO3RR), thereby advancing the prospects for sustainable nitrate remediation technologies.

Investigating the efficiency of fixed bed column containing Fe3O4-ZIF8@eggshell membrane matrix in concurrent adsorption of arsenic and nitrate from water

In the current work, the behavior of a fixed bed column (FBC) containing an innovative nanocomposite, Fe3O4-ZIF8@eggshell membrane matrix (F-ZIF8@EMM), was investigated in the concurrent elimination of arsenic and nitrate, as two potentially harmful elements (PHEs) in drinking water. Flow rate (6-10 mL/min), column height (10-20 cm), reaction time (30-180 min), pH (5-10), primary content of arsenic (25-100 µg/L), primary content of nitrate (100-200 mg/L), and nanocomposite dose (0.25-1 mg/L) were examined as different operational effects on the simultaneous uptake of arsenic and nitrate from actual water via the as-fabricated novel nanocomposite through various experiments. Characteristics of F-ZIF8@EMM were analyzed via X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), and Brunauer-Emmett-Teller (BET) analyses. The consequences illustrated that the optimal parameters were: flow rate (6 mL/min), primary content of arsenic (100 µg/L), primary content of nitrate (150 mg/L), bed height (20 cm), and pH (7). The simultaneous elimination efficiency of nitrate and arsenic was 90 % under optimal conditions. The FBC fed with water containing arsenic and high nitrate could operate for 440 min with a qm of 226 mg/g. After fitting, different models were identified, with the concurrent uptake of nitrate and arsenic was the optimum fit with the Thomas model (R2 = 0.9998). Analysis of the cost of the process displayed that it should be estimated to be approximately 0.005$ per liter of safe drinking water. This study demonstrates the stability and high efficiency of the newly structured adsorbent after 10 consecutive adsorption cycles. It also validates the significant capacity of the as-made composite F-ZIF8@EMM in the concurrent uptake of nitrate and arsenic. Consequently, the application of FBC technology has shown promise in enhancing this process.

Mapping key areas to protect high-value and high-vulnerability groundwater from pollution load: Method for management

Severe groundwater pollution has necessitated prioritizing the prevention and control of groundwater pollution (PCGP). The fundamental strategy of PCGP involves identifying priority areas. Vulnerability assessment, such as DRASTIC, and its extension, pollution risk assessment, have been developed to guide PCGP. However, managers find it struggling to implement these results in PCGP due to a lack of consideration for practical management demands. This study establishes a management-oriented method to map key areas for groundwater protection and PCGP, considering water sources, pollution source load, vulnerability, and function value, to facilitate management implementation. The key area includes the protection area aimed at protecting water sources and the control area focused on preventing and controlling pollution load in high-value and high-vulnerability groundwater. The effectiveness and practicality of this method are demonstrated through a case study in a large district reliant on groundwater, enabling the key area and corresponding suggestions to directly guide local management. This method offers a practical tool for PCGP worldwide and is expected to guide the sustainable development plan.

A novel electrochemical membrane filtration system operated with periodical polarity reversal for efficient resource recovery from nickel nitrate laden industrial wastewater

The economical and efficient removal of nickel nitrate from industrial wastewater remains a challenge. Herein, we developed an innovative electrochemical membrane filtration system that used a periodic polarity reversal process to adjust the acid-base environment near membrane interface for the recovery of nickel (II) and ammonia. The Ru based electrocatalytic layer could boost the selective reduction of nitrate to ammonia by generating atomic hydrogen, resulting in the precipitation of Ni2+ by the increasing pH at the membrane interface. Then, the precipitation of Ni(OH)2 could be effectively stripped and collected under the periodic polarity reversal process. In-situ interfacial measurements demonstrated that the polarity reversal process enabled a reversible transformation between strongly acidic (pH < 2) and alkaline (pH > 13) environments within a 200 µm range at the membrane interface. In continuous flow operation treating real industrial wastewater containing 96.7 mg-N L-1 nitrate and 135.0 mg L-1 Ni2+, the system demonstrated the capability to achieve 92.5 ± 2.6 % nitrate removal (with a recovery efficiency of 15.1 ± 1.9 g-NH3 kWh-1) and 99.7 ± 0.1 % Ni²⁺ removal (with a recovery efficiency of 24.9 ± 2.4 g-Ni kWh-1). Additionally, the specific treatment cost was approximately $0.17 m-3, attributed to the recovery of Ni(OH)₂ and ammonia. Furthermore, this system could deliver a significant economic benefit ($1.64 per m3) for treating a high concentration real wastewater (331.5 mg-N L-1 nitrate and 1496.3 mg L-1 Ni2+), outperforming traditional alkali precipitation and biological nitrification/denitrification processes. Overall, our study presents an economical and sustainable method for recovering valuable chemicals from wastewater containing heavy metals and inorganic nitrogen, potentially advancing cost-effective water treatment technologies.

A multidisciplinary approach using hydrogeochemistry, δ15NNO3 isotopes, land use, and statistical tools in evaluating nitrate pollution sources and biochemical processes in Costa Rican volcanic aquifers

Nitrate pollution threatens the Barva and Colima multi-aquifer system, the primary drinking water source in the Greater Metropolitan Area of Costa Rica. In addressing nitrate contamination dynamics, this study proposes an integrated approach by combining multivariate statistical analyses, hydrochemical parameters, sewage discharge, and regional land-use and land-cover patterns to assess the extent and degree of contamination, dominant biogeochemical processes, and refine the interpretation of nitrate sources previously derived solely from δ15NNO3 information. Over seven years (2015-2022), 714 groundwater samples from 43 sites were analyzed for nitrate and major ions, including two sampling campaigns for dissolved organic and inorganic carbon, nitrite, ammonium, FeTotal, MnTotal, and δ15NNO3 analyses. The findings presented elevated nitrate concentrations in urban and agricultural/urban areas, surpassing the Maximum Concentration Levels on several occasions, and oxidizing conditions favoring mineralization and nitrification processes in unconfined Barva and locally confined Upper Colima/Lower Colima aquifers. Similar nitrate contents and spatial patterns in agricultural and urban zones in the shallow Barva aquifer suggest comparable contributions from nitrogen fertilizers and urban wastewaters despite the gradual increase in urban land cover and the reduction of agricultural areas. Isotopic analyses and dissolved organic carbon (DOC) indicate a shift in nitrate sources from agricultural to urban areas in both Barva and Colima aquifers. Principal Component and Hierarchical Cluster Analyses link land use, nitrate sources, and water quality. Three distinct sample clusters aligned with forest/grassland, agricultural/urban, and urban land use, emphasizing the impact of anthropogenic activities on groundwater quality, even in the deeper Colima aquifers. The study challenges nitrate isotope mixing models, enhancing accuracy in identifying pollution sources and assessing the spatial extent of contamination by incorporating DOC and other hydrochemical parameters. Similar outcomes, with and without the use of nitrate isotopes, reinforce the usefulness of the integrated approach, providing a practical and cost-effective alternative.

Laser-Induced Graphene-Based Sensors in Health Monitoring: Progress, Sensing Mechanisms, and Applications

The rising global population and improved living standards have led to an alarming increase in non-communicable diseases, notably cardiovascular and chronic respiratory diseases, posing a severe threat to human health. Wearable sensing devices, utilizing micro-sensing technology for real-time monitoring, have emerged as promising tools for disease prevention. Among various sensing platforms, graphene-based sensors have shown exceptional performance in the field of micro-sensing. Laser-induced graphene (LIG) technology, a cost-effective and facile method for graphene preparation, has gained particular attention. By converting polymer films directly into patterned graphene materials at ambient temperature and pressure, LIG offers a convenient and environmentally friendly alternative to traditional methods, opening up innovative possibilities for electronic device fabrication. Integrating LIG-based sensors into health monitoring systems holds the potential to revolutionize health management. To commemorate the tenth anniversary of the discovery of LIG, this work provides a comprehensive overview of LIG's evolution and the progress of LIG-based sensors. Delving into the diverse sensing mechanisms of LIG-based sensors, recent research advances in the domain of health monitoring are explored. Furthermore, the opportunities and challenges associated with LIG-based sensors in health monitoring are briefly discussed.

Long-term spatiotemporal changes in nitrate contamination of municipal groundwater resources after sewerage network construction in the Hungarian Great Plain

Over the last decades, as a consequence of wastewater discharges and other anthropogenic sources, severe nitrate (NO3-) pollution has developed in municipal environment causing global concern. Thus, eliminating the potential sources of pollution is one of the major challenges of the twenty-first century, whereby sanitation services are essential for ensuring public health and environmental protection. In the present study, long-term monitoring (2011-2022) of shallow groundwater NO3- contamination in municipal environment was carried following the construction of the sewerage network (2014) in the light of the pre-sewerage situation. Our primary aim was to assess the long-term effects of sewerage on nitrate NO3- levels in the shallow groundwater and evaluate the efficiency of these sanitation measures over time. Based on the results, significant pollution of the shallow groundwater in the municipality was identified. During the pre-sewer period, NO3- concentrations exceeded the 50 mg/L limit in the majority of monitoring wells significantly, upper quartile values ranged between 341 and 623 mg/L respectively. Using Nitrate Pollution Index (NPI) and interpolated NO3- pollution maps, marked spatial north-south differences were detected. In order to verify the presence of wastewater discharges in the monitoring wells, the isotopic ratio shifts (δ) for 18O and D(2H) were determined, confirming municipal wastewater effluent. Variations in NO3-/Cl- molar ratios suggest also contamination from anthropogenic sources, including septic tank effluent from households and the extensive use of manure. Data series of 7 years (2015-2022) after the investment indicate marked positive changes by the appearance of decreasing trends in NO3- values confirmed by Wilcoxon signed rank test and ANOVA. By comparing the pre- and post-sewerage conditions, the mean NO3- value decreased from 289.7 to 175.6 mg/L, with an increasing number of monitoring wells with concentrations below the limit. Our results emphasise the critical role of sanitation investments, while also indicating that the decontamination processes occur at a notably slow pace. Detailed, long-term monitoring is therefore essential to ensure accurate follow-up of the ongoing changes. The results can provide information for local citizens and authorities to improve groundwater management tools in the region.

What should we do for water security? A technical review on more yield per water drop

Water scarcity is a global challenge. A severe gap between water supply and demand will arise. Consequently, a large part of the world could face water shortage issues in the near future. Increasing cultivated areas and rapid population growth will intensify water consumption, which may lead to a "drink or grow" situation in many countries. Promoting more yield per water drop (MYWD) ideology for water secure development is critically important because the agriculture sector is the largest water consumer by 70%. In lower-middle and low-income countries, water use in agriculture ranges from 80-90%. Advanced water-saving technologies can reduce water consumption by 35-65%, but adoption is less than 20% of the total irrigated area in most countries. Mission 2050 in agricultural countries would be to cover at least 75% and 85% of land under water-saving technologies, which receive surface and groundwater, respectively. The water-saving technologies can decrease farm-scale water consumption, thus alleviating pressure on water resources. In the water scarcity mitigation agenda, the increasing cultivated area under the water-saving technologies should be mapped well since some researchers believe that the water-saving technologies are increasing cultivated area, thereby jeopardizing the "water-saving goal." This comprehensive review navigated the MYWD concept, discussed strategies, sketched a hydrological model to conserve resources, and highlighted economic feasibility, environmental benefits of water-saving technologies, and further improvements. This study can contribute significantly to the future water policy and measures worldwide.

Differential interaction modes of As(III)/As(V) with microbial cell membrane induces opposite effects on organic contaminant biodegradation in groundwater

Arsenic, a widespread toxic metalloid in groundwater, derives both from natural geological environment and industrial discharge, is extensively detected to be coexisting with organic contaminants, such as 2,4,6-trichlorophenol (TCP), a prior concerned pollutant. During biological remediation of groundwater, arsenic potentially intervenes microbial behaviors. This study found an opposite interference of arsenic in its two different valences (III and V) on the degradation of TCP by the functional bacteria, Sphingomonas fennica K101. As(III) inhibited TCP degradation in a concentration-dependent manner (from 0.1-10 mg/L), with a maximum inhibition rate of 35.5%, whereas As(V) exhibited promoting effects by 13.8% and 33.2% at 1 mg/L and 10 mg/L, respectively. Employing field emission transmission electron microscopy, quantum chemical calculations, fourier-transform ion cyclotron resonance mass spectrometry and metabolomic analysis, we unveil distinct interactions between cell membranes and arsenic in two valence states. Exposure to As(III) led to significant accumulation of As(III) in the cytoplasm, followed by interaction with intracellular ferritin (ferritin heavy chain 1), releasing iron ions and generating ROS. Subsequently, it induced ferroptosis and disrupted bacterial basal metabolism, thereby inhibiting TCP biodegradation. Oppositely, As(V) bound to a critical component sphingosine and triggered sphingosine polymerization, increasing membrane permeability, which was evidenced by measuring lactate dehydrogenase release. This process facilitated TCP transmembrane permeation by reducing membrane or extracellular secretion resistance. As(V) concurrently upregulated energy metabolism and accelerated TCP degradation. Our study elucidates the influence of prevalent arsenic on biodegradation efficacy, particularly amidst changing redox conditions associated with varying arsenic valences.

Coherent NiS2@SnS2nanosheet for accelerating electrocatalytic nitrate reduction to ammonia

The development of an effective and selective catalyst is the key to improving the multi-electron transfer nitrate reduction reaction (NO3-RR) to ammonia. Here, we synthesized a coherent NiS2@SnS2nanosheet catalyst loaded on carbon cloth via one-step solvothermal method. Experimental data reveals that the integration of NiS2and SnS2can enhance the NO3-RR performance in terms of high NH3yield rate of 408.2μg h-1cm-2and Faradaic efficiency of 89.61%, as well as satisfying cycling and long-time stability.

Structure properties and industrial applications of anion exchange resins for the removal of electroactive nitrate ions from contaminated water

The presence of nitrates in lakes, rivers, and groundwater is common. Anion exchange resins (AER) are polymeric structures that contain functional groups as well as a variety of particle sizes that are used for removing nitrate ions from solutions. This article provides a concise review of the types and properties of AER, synthesis methods, characterization, and environmental applications of AER. It discusses how different factors affect the adsorption process, isotherm and kinetic parameters, the adsorption mechanism, and the maximum adsorption capacities. Additionally, the present review addresses AER's regeneration and practical stability. It emphasizes the progress and proposes future strategies for addressing nitrate pollution using AER to overcome the challenges. This review aims to act as a reference for researchers working in the advancement of ion exchange resins and presents a clear and concise scientific analysis of the use of AER in nitrate adsorption. It is evident from the literature survey that AER is highly effective at removing nitrate ions from wastewater effluents.

Nitrate recovery from groundwater and simultaneous upcycling into single-cell protein using a novel hybrid biological-inorganic system

Nitrate pollution in groundwater is a serious problem worldwide, as its concentration in many areas exceeds the WHO-defined drinking water standard (50 mg/L). Hydrogen-oxidizing bacteria (HOB) are a group of microorganisms capable of producing single-cell protein (SCP) using hydrogen and oxygen. Furthermore, HOB can utilize various nitrogen sources, including nitrate. This study developed a novel hybrid biological-inorganic (HBI) system that coupled a new submersible water electrolysis system driven by renewable electricity with HOB fermentation for in-situ nitrate recovery from polluted groundwater and simultaneously upcycling it together with CO2 into single-cell protein. The performance of the novel HBI system was first evaluated in terms of bacterial growth and nitrate removal efficiency. With 5 V voltage applied and the initial nitrate concentration of 100 mg/L, the nitrate removal efficiency of 85.52 % and raw of 47.71 % (with a broad amino acid spectrum) were obtained. Besides, the HBI system was affected by the applied voltages and initial nitrogen concentrations. The water electrolysis with 3 and 4 V cannot provide sufficient H2 for HOB and the removal of nitrate was 57.12 % and 59.22 % at 180 h, while it reached 65.14 % and 65.42 % at 5 and 6 V, respectively. The nitrate removal efficiency reached 58.40 % and 50.72 % within 180 h with 200 and 300 mg/L initial nitrate concentrations, respectively. Moreover, a larger anion exchange membrane area promoted nitrate removal. The monitored of the determination of different forms of nitrogen indicated that around 60 % of the recovered nitrate was assimilated into cells, and 40 % was bio-converted to N2. The results demonstrate a potentially sustainable method for remediating nitrate contaminant in groundwater, upcycling waste nitrogen, CO2 sequestration and valorization of renewable electricity into food or feed.