Does the groundwater nitrate pollution in China pose a risk to human health? A critical review of published data

Identification of hydrochemical fingerprints, quality and formation dynamics of groundwater in western high Himalayas

Identifying hydrochemical fingerprints of groundwater is a challenge in areas with complex geological settings. This study takes the Gilgit-Baltistan, a complex geological area in west high Himalayas, Pakistan, as the study area to get insights into the hydrochemcial genesis and quality of groundwater in complex geological mountainous regions. A total of 53 samples were collected across the area to determine the hydrochemical characteristics and formation of groundwater. Results revealed groundwater there is characterized by slightly alkaline and soft fresh feature. Groundwater is dominated by the hydrochemical facies of HCO3·SO4-Ca·Mg type. The factor method yields three components (PCs) of principal component analysis, which together explain 75.71% of the total variances. The positive correlation of EC, TDS, Ca2+, SO42-, K+ in PC1, and NO3-, Cl- in PC2 indicate that a combination of natural and anthropogenic activities influences groundwater hydrochemistry. Water-rock interaction is the main mechanism governing the natural hydrochemistry of groundwater. The negative correlation of Cl-, SO42-, Ca2+, and Na+ with NDVI attributes to inorganic salt uptake by plant roots. Groundwater chemical composition is also affected by the type of land use. Groundwater is characterized as excellent and good water quality based on the entropy-weighted water quality index assessment, and is suitable for drinking purposes except for very few samples, while aqueous fluoride would pose potential health threats to water consumers in western high Himalayas, and infants are most at risk compared to other populations. This study will help to deepen the hydrochemial formation mechanism and exploitation suitability of groundwater resources in the mountainous areas that undergone the combined actions of nature and human activities, and provide insights into the characteristics of water environmental quality in western Himalayas area.

Probabilistic modelling is superior to deterministic approaches in the human health risk assessment: an example from a tribal stretch in central India

This case drew national attention in 2018. About 100 people died and more than 300 hospitalized in a span of few years in a village of 1200 people in a tribal stretch in central India. Medical teams visiting the area reported severe renal failure and blamed the local eating and drinking habits as causative factors. This human health assessment based on geochemical investigations finds nitrate (NO3-) and fluoride (F-) pollution as well in village's groundwater. Both deterministic and probabilistic techniques are employed to decipher the contamination pathways and extent of contamination. Source apportionments of NO3- and F- and their relationship with other ions in groundwater are carried out through chemometric modelling. Latent factors controlling the hydrogeochemistry of groundwater too are explored. While hazard quotients ([Formula: see text]) of the chemical parameters ([Formula: see text] and [Formula: see text]) identify ingestion as the prominent pathway, the calculated risk certainty levels (RCL) of the hazard index (HI) values above unity are compared between the deterministic and probabilistic approaches. Deterministic model overestimates the HI values and magnify the contamination problems. Probabilistic model gives realistic results that stand at infants ([Formula: see text] = 34.03%, [Formula: see text] = 24.17%) > children ([Formula: see text] = 23.01%, [Formula: see text] = 10.56%) > teens ([Formula: see text] = 13.17%, [Formula: see text] = 2.00%) > adults ([Formula: see text] = 11.62%, [Formula: see text] = 1.25%). Geochemically, about 90% of the samples are controlled by rock-water interaction with Ca2+-Mg2+-HCO3- (~ 56%) as the dominant hydrochemical facies. Chemometric modelling confirms Ca2+, Mg2+, HCO3-, F-, and SO42- to originate from geogenic sources, Cl- and NO3- from anthropogenic inputs and Na+ and K+ from mixed factors. The area needs treated groundwater for human consumption.

Temporal groundwater quality, health risks and source point management zonation of multi-aquifers in Jilin Qian'an, Northeastern China

Jilin Qian'an, located in Northeastern China's Songnen Plain, relies almost exclusively on groundwater for drinking. The quaternary phreatic aquifer (Q3) is distinguished by high geogenic fluoride and arsenic concentrations, which necessitates reliance on quaternary confined (Q1) and neogene confined (N) aquifers (deeper aquifers) as source point management (SPM) alternatives. However, deeper aquifers are contaminated, necessitating temporal monitoring and unique management strategies. Using 165 samples, this study investigated the appropriateness of deeper restricted aquifers as a continuous SPM alternative by assessing the spatiotemporal groundwater quality and human health risk of the multi-aquifers in Jilin Qian'an from the 1980s to the 2010s. In addition, a source point management zonation (SPMZ) was implemented to define the specific intervention necessary in various portions of the study area. Results indicate water quality parameters were within recommended limits for most samples except fluoride, while arsenic was the most significant heavy metal pollutant. Mean groundwater mineralization in all the aquifers increased with time. Deeper aquifers are still a better alternative to the shallow phreatic aquifer as groundwater quality in the study is of the order N > Q1 > Q3 in the respective aquifers. Cancer risk assessment (CR) shows increases from 2001 to the 2010s in all aquifers except in Q3. SPMZ delineated: High As and high F zones; high As and low F zones; high As zones; high F zones; low F zones; and safe zones. Localized intervention based on SPMZ is recommended, along with the use of alternative water sources.

Tracking anthropogenic nitrogen-compound sources of surface and groundwater in southwestern Nile Delta: hydrochemical, environmental isotopes, and modeling approach

This research aims to assign the specific and potential sources that control migration and transformation mechanisms of ammonium/nitrate contaminants of surface and groundwater systems in the southwestern Nile Delta, Egypt. To achieve that, an integration of hydrogeochemistry, multiple environmental stable isotopes (δ²H-H₂O, δ¹⁸O-H₂O, δ¹⁵N-NH₄, and δ¹⁵N-NO₃) coupled with three-dimensional nitrogen transport numerical model (MODFLOW-MT3D) was done. A set of representative water samples (20 canals and drainage water) and 14 groundwater samples were collected and analyzed for physical, chemical, and stable isotope analysis. NH₄⁺ and NO₃^- concentrations in surface water samples varied from 0.29 to 124 mg/l and 0.52 to 39.67 mg/l, respectively. For groundwater samples, NH₄⁺ and NO₃^- concentrations varied from 0.21 to 1.75 mg/l and 0.33 to 32.8 mg/l, respectively. Total risk quotient (THQ) level of nitrate (oral and dermal effects) from drinking water exceeds unity for all water samples indicating a potential noncancer risk for the southwestern Nile Delta residents. The potential sources of nitrogen compound pollution are water from sewage treatment plants used for irrigation, sludge and animal manure, septic tanks, soil nitrogen, and artificial fertilizers according to results of δ¹⁵N values. Results of ammonium/nitrate modeling in shallow groundwater aquifers are compared with observed concentrations and are found to be in good agreement. Some recommendations are given to decrease nitrogen loads in the study area through suggested a need for adoption of N-fertilizer management practices and treatment of sewage water before to application in agricultural activities.

Groundwater characterization and non-carcinogenic and carcinogenic health risk assessment of nitrate exposure in the Mahanadi River Basin of India

Agriculture is the mainstay of India's economy and chemical fertilizers have been extensively used to meet increasing demands. Anthropogenic interventions at the soil surface, especially the application of nitrogenous fertilizers in agricultural fields, provide essential nutrients but become major pollutant sources in terrestrial ecosystems and aquatic environments. Groundwater samples from phreatic aquifers of the Mahanadi River Basin, Chhattisgarh, India, showed that the Ca²⁺-Mg²⁺-HCO₃^- freshwater type dominates, followed by the Ca²⁺-Mg²⁺-Cl- and Na⁺-HCO₃^- types. Increasing trends in the ionic ratios of (NO₃-+Cl-)/HCO₃- over TDS and of NO₃-/Cl- over Cl- indicated the significant impact of anthropogenic pollution on groundwater contamination. Deterministic and probabilistic approaches were used to assess the non-carcinogenic and carcinogenic health risks of nitrate to children and adults. Both approaches produced the same results and indicated children were more prone to non-carcinogenic health risk than adults. An excess gastric cancer risk (ER) exposure model showed that approximately 42% of the groundwater samples had a non-negligible ER (1.00 × 10^-4 to 1.00 × 10^-5). Sensitivity analysis indicated groundwater nitrate concentration, ingestion rate, and the percentage of nitrite from nitrate were the most significant variables in determining HI and ER. It is suggested to adopt proper management of control policies for reducing the elevated groundwater nitrate concentration in the present study area.

Rapidly achieving partial denitrification from nitrate wastewater in a alkaline fermentation system with primary sludge as inoculated sludge and fermentable substrate

In order to promote practical engineering application of anaerobic ammonium oxidation(anammox) process, reduction of primary sludge(PS) in wastewater treatment plants(WWTPs) and removal of nitrate contaminant, a single-stage simultaneous alkaline fermentation coupled with partial denitrification(SAFPD) system was established successfully in this study. Nitrite production was rapidly achieved from nitrate wastewater with PS as inoculated sludge and fermentable substrate under anaerobic and anoxic operating conditions. During the stable operation period, the primary sludge reduction(PSR) and productivity of organic matters were 27.9% and 483.8mgCOD/gVSS, with nitrate removal of 90.7%, NO₃^- to NO₂^- transformation ratio(NTR) of 80.0%. After 125 days of acclimation, the relative abundance of Thauera, Dechloromonas and Candidatus_Competibacter increased from 0.17%, 0.02% and 0.05% to 11.58%, 4.28% and 5.6% respectively. Above results showed that this SAFPD system not only realized the reduction of PS and nitrate removal, but also laid a solid foundation for anammox process with its high nitrite production.

Groundwater quality evaluation and human health risks assessment using the WQI, NPI and HQnitrate models: case of the Sfax intermediate aquifer, Sahel Tunisia

Groundwater is a vital natural resource required to satisfy the domestic and agricultural needs. In general, human health is linked to the quality of the consumed water. For instance, long-term exposure to high nitrate levels in groundwater may cause problems. Hence, the present study was conducted to assess the nitrate contamination of groundwater as well as its related health risks for the inhabitants of the Sfax region, Sahel Tunisia. Irrigation groundwater suitability has been evaluated with sodium content (%Na), electrical conductivity (EC), magnesium hazard (MH), sodium adsorption ratio (SAR), permeability index (PI), Kelly's ratio (KR) and soluble sodium percent (SSP). The results indicate that the selected groundwater is characterized by low to moderate quality for irrigation. Furthermore, the drinking water quality index (DWQI) was assessed using potential of hydrogen (pH), total dissolved solids (TDS), magnesium (Mg²⁺), calcium (Ca²⁺), sodium (Na⁺), chloride (Cl^-), sulfate (SO₄^2-), potassium (K⁺), bicarbonate (HCO₃^-) and nitrate (NO₃^-). The results indicate that 3.63% of samples have good quality of water, while 41.82% have poor to very poor water quality and the rest (54.55%) are unfit for drinking. The nitrate pollution index (NPI) model revealed that about 42% of the samples present significant to very significant type of pollution. Based on human health risk assessment, the children are at higher risks compared to the other affected groups. The obtained results could be used as a basic document for realistic management of groundwater quality and to provide an overview for decision-making authorities to take necessary actions.

The Role of Iodine for Thyroid Function in Lactating Women and Infants

Iodine is a micronutrient needed for the production of thyroid hormones, which regulate metabolism, growth, and development. Iodine deficiency or excess may alter the thyroid hormone synthesis. The potential effects on infant development depend on the degree, timing, and duration of exposure. The iodine requirement is particularly high during infancy because of elevated thyroid hormone turnover. Breastfed infants rely on iodine provided by human milk, but the iodine concentration in breast milk is determined by the maternal iodine intake. Diets in many countries cannot provide sufficient iodine, and deficiency is prevented by iodine fortification of salt. However, the coverage of iodized salt varies between countries. Epidemiological data suggest large differences in the iodine intake in lactating women, infants, and toddlers worldwide, ranging from deficient to excessive intake. In this review, we provide an overview of the current knowledge and recent advances in the understanding of iodine nutrition and its association with thyroid function in lactating women, infants, and toddlers. We discuss risk factors for iodine malnutrition and the impact of targeted intervention strategies on these vulnerable population groups. We highlight the importance of appropriate definitions of optimal iodine nutrition and the need for more data assessing the risk of mild iodine deficiency for thyroid disorders during the first 2 years in life.

Effect of Different Fertilizations on the Plant-Available Nitrogen in Soil Profile (0-100 cm): A Study on Chinese Cabbage

The aim of this study is to analyze the variations in the plant-available nitrogen (PAN) concentrations in the soil profile. Different fertilizers were applied for Chinese cabbage plantation (CCP) in the experimental fields of the Shunyi region. The treatments used for the comparative analysis are (i) no fertilizer and plantation (NVP), (ii) no fertilizer with CCP (CTP), (iii) fertilization as urea (URP), and (iv) potassium nitrate (KNP) and chicken manure (CMP) with CCP. It was concluded that the yield was significantly high in URP, CMP, and KNP as compared to CTP. In URP, maximum PAN in soil layers 0-60 cm was recorded during crop production and in 60-100 cm after harvesting as compared to other treatments. Significant variations in soil pH and electrical conductivity (EC) for the soil profile (0-100 cm) from the initial values with respect to time and treatments were observed. CMP showed maximum ammonium in the upper layers of 0-60 cm throughout the season, whereas minimum PAN was observed in NVP but increased in lower layers of 60-100 cm. In general, all fertilizers raised the PAN below the soil 60-100 cm which indicates their potential for nitrate leaching (NL).

High efficient bio-denitrification of nitrate contaminated water with low ammonium and sulfate production by a sulfur/pyrite-based bioreactor

Sulfur-based autotrophic denitrification (SAD) and pyrite-based autotrophic denitrification (PAD) are important technologies that address nitrate pollution, but high sulfate production and low denitrification efficiency, respectively, limit their application in engineering. A bio-denitrification reactor with sulfur and pyrite as filler materials was studied to remove NO₃^--N from nitrate contaminated water. At an influent NO₃^--N concentration of 50 mg/L, NO₃^--N removal efficiency of the sulfur/pyrite-based bioreactor was 99.2%, producing less NH₄⁺-N and SO₄^2- than the sulfur-based bioreactor, even after long-term operation. Denitrification performance was significantly related to environmental variable, especially dissolved oxygen. Proteobacteria and Epsilonbacteraeota were the predominant phyla in the sulfur/pyrite-based bioreactor, and fewer dissimilatory nitrate reductions to ammonia process-related bacteria were enriched compared to those in the sulfur-based bioreactor. Sulfur-pyrite bio-denitrification provides an efficient alternative method for treatment of nitrate contaminated water.

A critical review of existing mechanisms and strategies to enhance N2 selectivity in groundwater nitrate reduction

The pollution of nitrate (NO3-) in groundwater has become an environmental problem of general concern and requires immediate remediation because of adverse human and ecological impacts. NO3- removal from groundwater is conducted mainly by chemical, biological, and coupled methods, with the removal efficiency of NO3- considered the sole performance indicator. However, in addition to the harmless form of N2, the reduced NO3- could be transformed into other intermediates, such as nitrite (NO2-), nitrous oxide (N2O), and ammonia (NH4+), which may have direct or indirect negative impacts on the environment. Therefore, increasing N2 selectivity is a significant challenge in reducing NO3- in groundwater, which seriously impedes the large-scale implementation of available remediation technologies. In this work, we comprehensively overview the most recent advances in N2 selectivity regarding the understanding of emerging groundwater NO3- removal technologies. Mechanisms of by-product production and strategies to enhance the selective reduction of NO3- to N2 are discussed in detail. Furthermore, we proposed topics for further research and hope that the total environmental impacts of remediation schemes should be evaluated comprehensively by quantifying all potential intermediate products, and promising strategies should be further developed to enhance N2 selectivity, to improve the feasibility of related technologies in actual remediation.

Nitrates in the environment: A critical review of their distribution, sensing techniques, ecological effects and remediation

Nitrate pollution is eminent in almost all the developing nations as a result of increased natural activities apart from anthropogenic pollution. The release of nitrates in more than critical quantities into the water bodies causes accretion impacts on living creatures, environmental receptors, and human vigour by accumulation through the food chain. Nitrates have recently acquired researchers' huge attention and extend their roots in environmental contamination of surface and groundwater systems. The presence of nitrate in high concentrations in surface and groundwater triggers several health problems, for instance, methemoglobinemia, diabetes, eruption of infectious disorders, harmfully influence aquatic organisms. Sensing nitrate is an alternate option for monitoring the distribution of nitrate in different water bodies. Here we review electrochemical, spectroscopic, and electrical modes of nitrate sensing. It is concluded that, among the various sensors discussed in this review, FET sensors are the most desirable choice. Their sensitivity, ease of use and scope for miniaturisation are exceptional. Advanced functional materials need to be designed to satiate the growing need for environmental monitoring. Different sources of nitrate contamination in ground and surface water can be estimated using different techniques such as nitrate isotopic composition, co contaminants, water tracers, and other specialized techniques. This review intends to explore the research work on remediation of nitrate from wastewater and soil using different processes such as reverse osmosis, chemical denitrification, biological denitrification, ion exchange, electrodialysis, and adsorption. Denitrification proves as a promising alternative over previously reported techniques in terms of their nitrate removal because of its high cost-effectiveness.

Investigating sources, driving forces and potential health risks of nitrate and fluoride in groundwater of a typical alluvial fan plain

Groundwater of alluvial fan plains is the foremost water source, especially in arid/semiarid regions. Its contaminants are big issues for water supply and public health concern. To reveal the groundwater chemistry, contaminants sources and health threats in alluvial aquifers, 81 groundwaters were collected from a typical alluvial fan plain of northern China for nitrogen, fluoride and major ions analysis. Statistical analysis and hydrochemical diagrams as well as human health risk assessment were performed. Nitrate is widely distributed and 53% of groundwaters exceed the permissible limit with the maximum concentration up to 326 mg/L. The distributions of nitrite, ammonia and fluoride contaminants are sporadic in spatial, and the concentrations of fluoride in groundwaters are slightly beyond the permissible limit of 1 mg/L. The hydrochemical facies shift from HCO₃-Ca or Mixed HCO₃-Na·Ca type to Mixed Cl-Mg·Ca and ClCa type with the increase of nitrate content. Two factors (Factor-1 and Factor-2) are extracted by factor analysis and account 63% of the total variances. The positive loading of F^- and negative loading of NO₃^- on Factor-2 reveal geogenic and anthropogenic origins, respectively. The significant positive loadings of TDS, TH, SO₄^2-, Cl^-, Ca²⁺, Mg²⁺ on Factor-1 reveal the governing mechanisms on groundwater chemistry by intermixed sources of geogenic origins and anthropogenic inputs. Hydrogeochemical evolution in the study area is driven by both water-rock interaction and anthropogenic forces. Anthropogenic inputs/influences are the dominated forces increasing groundwater nitrate content and salinity in the piedmont zone and the residential and industrial zone of the southeastern lower parts, and would pose potential non-carcinogenic risks to various populations via oral intake pathway. Rational measures should be taken to protect groundwater quality out of the threats of anthropogenic pollution. The geogenic fluoride in groundwater would threat the health of children through oral pathway and should be also concerned. CAPSULE: The driving forces of groundwater chemistry in alluvial fan plains were revealed using integrated approach of factor analysis and geostatistical modelling.

Evaluation of Groundwater Suitability for Irrigation and Drinking Purposes in an Agricultural Region of the North China Plain

Groundwater is an irreplaceable resource for irrigation and drinking in the North China Plain, and the quality of groundwater is of great importance to human health and social development. In this study, using the information from 59 groups of groundwater samples, groundwater quality conditions for irrigation and drinking purposes in an agricultural region of the North China Plain were analyzed. The groundwater belongs to a Quaternary loose rock pore water aquifer. The depths of shallow groundwater wells are 20–150 m below the surface, while the depths of deep groundwater wells are 150–650 m. The sodium adsorption ratio (SAR), sodium percentage (%Na), residual sodium carbonate (RSC), magnesium hazard (MH), permotic index (PI) and electrical conductivity (EC) were selected as indexes to evaluate the shallow groundwater suitability for irrigation. What’s more, the deep groundwater suitability for drinking was assessed and the human health risk of excessive chemicals in groundwater was studied. Results revealed that SAR, Na% and RSC indexes indicated the applicability of shallow groundwater for agricultural irrigation in the study area. We found 57.1% of the shallow groundwater samples were located in high salinity with a low sodium hazard zone. The concentrations of fluorine (F−) in 79.0% of the deep groundwater samples and iodine (I−) in 21.1% of the deep groundwater samples exceeded the permissible limits, respectively. The total hazard quotient (HQ) values of fluorine in over half of the deep groundwater samples exceeded the safety limits, and the health risk degree was ranked from high to low as children, adult females and adult males. In addition to natural factors, the soil layer compression caused by groundwater over-exploitation increased the fluorine concentration in groundwater. Effective measures are needed to reduce the fluorine content of the groundwater of the study area.

Human health risk assessment of groundwater nitrate at a two geomorphic units transition zone in northern China

To assess groundwater nitrate contamination and its human health risks, 489 unconfined groundwater samples were collected and analyzed from Zhangjiakou, northern China. The spatial distribution of principle hydrogeochemical results showed that the average concentrations of ions in descend order was HCO₃^-, SO₄^2-, Na⁺, Ca²⁺, Cl^-, NO₃^-, Mg²⁺ and K⁺, among which the NO₃^- concentrations were between 0.25 and 536.73 mg/L with an average of 29.72 mg/L. In total, 167 out of 489 samples (~ 34%) exceeded the recommended concentration of 20 mg/L in Quality Standard for Groundwater of China. The high NO₃^- concentration groundwater mainly located in the northern part and near the boundary of the two geomorphic units. As revealed by statistical analysis, the groundwater chemistry was more significantly affected by anthropogenic sources than by the geogenic sources. Moreover, human health risks of groundwater nitrate through oral and dermal exposure pathways were assessed by model, the results showed that about 60%, 50%, 32% and 26% of the area exceeded the acceptable level (total health index>1) for infants, children, adult males and females, respectively. The health risks for different groups of people varied significantly, ranked: infants> children> adult males>adult females, suggesting that younger people are more susceptible to nitrate contamination, while females are more resistant to nitrate contamination than males. To ensure the drinking water safety in Zhangjiakou and its downstream areas, proper management and treatment of groundwater will be necessary to avoid the health risks associated with nitrate contamination.

Cultivation of aerobic granular sludge coupled with built-in biochemical cycle galvanic-cells driven by dual selective pressure and its denitrification characteristics

Dual selective pressure was applied as the driving condition to cultivate an enhanced aerobic granular sludge (AGS) with Fe(0)-based biochemical cycle galvanic-cells (BCGC) as the core. The BCGC-AGS coupled micro-electrolysis with synergistic autotrophic-heterotrophic denitrification to enhance nitrogen removal. COD and total nitrogen removal of 91.8% and 95.9% were achieved, respectively. The formation of circulation channel between Fe³⁺ and Fe²⁺ provided a solid foundation for the biochemical cycle of galvanic-cells with low consumption. The existence of micro-electrolysis selective pressure in BCGC-AGS was also confirmed. Facultative aerobic bacteria Methylocystis and Azospirillum were the most abundant genera. Facultative iron redox bacteria and autotrophic denitrifying bacteria Geobacter, Thiobacillus, Aquabacterium, Thauera and Azospirillum showed high abundance, affirming the success culture of EAGS system. Load shock test verified BCGC-AGS possessed excellent load shock resistance. Obtaining the advantages of fast-cultivation, high-efficiency and low galvanic-cells consumption, BCGC-AGS showed significant potential for practical application.

Hydrochemistry, quality and potential health risk appraisal of nitrate enriched groundwater in the Nanchong area, southwestern China

Assessments for groundwater quality and potential health risk are significant for better utilization and exploitation. In the present study, seventy groundwater samples were collected from domestic tube wells and public water-supply wells in the Nanchong area, southwestern China. The integration of statistical analysis, ion correlation, geomodelling analysis, entropy water quality index and health risks assessment were compiled in this study. Statistical analysis indicated the cations followed the concentration order as Ca²⁺ > Na⁺ > Mg²⁺ > K⁺, while anions' concentrations were HCO₃^- > SO₄^2- > Cl^- > NO₃^- > F^- based on Box and Whisker plot. Piper triangle diagram proposed the hydrochemical type was characterized as Ca-HCO₃. Correlations of ions and geomodelling revealed the concentrations of major ions were mainly determined by calcite dissolution and ion exchange process and NO₃^- concentrations were controlled by agriculture activities. Entropy water quality index computation demonstrated that 96% of groundwater samples possessed the EWQI values of 29-95, and thus were suitable for drinking purpose. The HI_Total values for 66% groundwater samples exceeded the acceptable limit for non-carcinogenic risk (HI =1) for infants, followed by 41% for children, 37% for adult males, and 30% for adult females. The non-carcinogenic human health risk of different population groups followed the order of infants > children > adult males > adult females. In future, targeted measures for human health risks of NO₃^- will focus on the improvements for agricultural activities, including reducing the use of nitrogenous fertilizer, changing irrigation pattern, etc. Our study provides the vital knowledge for groundwater management in the Nanchong and development of the Cheng -Yu Economic Circle.

Anthropogenic Organic Pollutants in Groundwater Increase Releases of Fe and Mn from Aquifer Sediments: Impacts of Pollution Degree, Mineral Content, and pH

In many aquifers around the world, there exists the issue of abnormal concentrations of Fe and Mn in groundwater. Although it has been recognized that the main source of this issue is the release of Fe and Mn from aquifer sediments into groundwater under natural environmental conditions, there lacks enough reliable scientific evidence to illustrate whether the pollutants imported from anthropogenic activities, such as organics, can increase this natural release. On the basis of time series analysis and comparative analysis, the existence of an increasing effect was verified through laboratorial leaching test, and the impacts of aquatic chemical environment conditions, such as pH, on the effect were also identified. The results showed that the increase of organics in groundwater made the release of Fe and Mn more thorough, which was favorable for the increase of groundwater concentrations of Fe and Mn. The higher the contents of Fe- and Mn-bearing minerals in aquifer sediments, the higher the concentrations of Fe and Mn in groundwater after the release reaches kinetic equilibrium. Lower pH can make the leaching more thorough, but the neutral environment also increases the amount of Mn. It can be deduced that the pollutants such as organics imported by anthropogenic activities can indeed increase the releases of Fe and Mn from aquifer sediments into groundwater, thus worsening the issue of groundwater Fe and Mn pollution. The findings provide a deeper insight into the geochemical effects of Fe and Mn in the natural environment, especially in the groundwater system.

Water quality evaluation and non-cariogenic risk assessment of exposure to nitrate in groundwater resources of Kamyaran, Iran: spatial distribution, Monte-Carlo simulation, and sensitivity analysis

Water is exceptionally vital for all living beings and socio-economic development. This study aimed to investigate the groundwater suitability for drinking in rural areas of Kamyaran city, Kurdistan province, Iran, by using the water quality index (WQI) and evaluating the non-carcinogenic health risk caused by nitrate from the drinking route. Forty-five groundwater samples were collected (2019) from operated dug-wells, and twelve parameters (TDS, pH, TH, EC, HCO3 -, K+, Na+, Mg2+, Ca2+, Cl-, SO4 2-, and NO3 -) were measured to the calculation of WQI. Hazard Quotient (HQ) and sensitivity analysis (SA) using the Monte-Carlo Simulation technique with 10,000 iterations were employed to determine the non-carcinogenic effects of Nitrate in different exposed groups (Infant, children, teenagers, and adults). The results of WQI showed that 74% of groundwater samples fall within the excellent water quality class, and 26% of rural areas fall in the category of good water type. The nitrate concentration in drinking water ranged from 22.42 ± 11.44 mg/L. The HQ mean for infants, children, teenagers, and adults were 0.5606, 0.7288, 0.5606, and 0.438, respectively. Probability estimation showed the HQ values for the 5th, and 95th percentile in infants, children, teenagers, and adult groups were (0.25-1.81), (0.13-1.08), (0.13-0.97), and (0.07-0.51), respectively. The SA showed that the most significant parameter of non-carcinogenic risk in all exposed populations was nitrate concentration. Generally, nitrate concentration in the study area was relatively high, and remarkably in agriculture and fertilizer management required more attention.

An experimental investigation on engineering properties of undisturbed loess under acid contamination

Even though soil acidification can cause significant destabilizing effects on various geotechnical issues, studies have rarely been conducted to determine the influence of soil structure on the impact of acid-contaminated soil. The current work aims to understand the effect of acid fluids on engineering behavior of undisturbed loess through laboratory tests. The sampling site is in a typical region of Loess Plateau, China. The variations in particle size distribution, Atterberg limits, uniaxial compression strength, and permeability were investigated with the help of microstructure for a better understanding of the governing mechanism of undisturbed loess subjected to acid fluids. It was found that exposure to acid fluids can improve the particle size distribution of loess. In contrast, the experimental results indicated that acid fluids can decrease Atterberg limits and strength and permeability of loess, although Atterberg limits and strength of loess are considerably increased in a highly sulfuric acid environment. Then, analyzing the engineering response in the light of microstructure revealed that the face-to-face contacts primarily exist in loess prepared with hydrochloric acid and nitric acid, respectively, whereas the mosaic structure is indeed active in sulfur-contaminated loess. Furthermore, a micro-conceptual structure was proposed based on the experiment led to the conclusion that the cementitious salt and structural characteristics play a dominant role in governing the engineering behavior of loess under acidic conditions.

Hydrogeochemical Features and Genesis of Confined Groundwater and Health Perspectives for Sustainable Development in Urban Hengshui, North China Plain

Groundwater in confined aquifers is the preferred water resource worldwide, and its hydrochemical quality is the premise for sustainable development. A systematic hydrogeochemical research was conducted to get insight into the hydrochemical characteristics, genesis, and potential health threats of confined groundwater, based on analytical data of 45 groundwater samples collected from the urban area of Hengshui, Central North China Plain (NCP). The results showed most groundwater had desirable hydrochemical quality with a nearly neutral to slightly alkaline nature and dominantly soft-fresh Cl-Na face. Solute chemistry was governed by rock-water interaction including minerals dissolution and ion exchange, but out of the anthropogenic influences. All nitrogen pollutants and Zn were within the desirable limit, while F−, Mn, and Fe were beyond the desirable limit recommended by WHO in 28.9%, 15.6%, and 68.9% of samples. Overall chronic health risk from these toxic elements was identified in terms of various populations and mainly contributed by F−. Infants were more prone to the health risks of aqueous pollutants. Differential water supplies based on hydrochemical quality are recommended, and water improvement measures are suggested to be conducted aiming at the harmful fluoride in confined groundwater. The present research could provide valuable references for the health sustainability of confined groundwater utilization in sedimentary plains like NCP worldwide.

Groundwater fluoride chemistry and health risk assessment of multi-aquifers in Jilin Qianan, Northeastern China

Groundwater from deep confined aquifers is often recommended for use because of it's low fluoride health risk. Thus, this study appraised groundwater fluoride hydrochemistry in a multi-aquifer system in Jilin Qianan to determine the non-carcinogenic health risk liable from exploiting the respective aquifers. 124 samples collected from the tertiary confined aquifer (N), quaternary confined aquifer (Q₁), and quaternary phreatic aquifer (Q₃) during surveys in 2001 and 2017 was analyzed using hydrochemical, statistical, spatial, and health risk assessment methods. Results show that the dominant water facies in the respective aquifer layers was Na+K-HCO₃+CO₃ except in Q_1, where Ca+Mg - HCO₃ + CO₃ was marginally dominant. Fluoride concentrations outside the recommended guideline occurred in all the aquifers except N, where concentrations were optimum. The mean fluoride concentration of groundwater in the aquifers was of the order Q₃ (2017) > Q₃ (2001) > Q₁ > N ( mean 2.09, 2.03, 1.41 and 0.75 mg/L with 51.85%, 57.44%, 36.36% and 0% occurring beyond recommended guideline values respectively). Silicate weathering, cation exchange, and fluorite dissolution in an alkaline environment were the significant fluoride contributing processes. Evaporation and MgF⁺ complex additionally influenced Q₁ and Q₃ (2017). The total hazard quotient (THQ) from oral and dermal pathways shows fluoride health risks in the order: infant > children > adult. The associated risks likely from using water in the respective aquifer layers is of the order Q₃ (2017) > Q₃ (2001) > Q₁ > N. The mean groundwater fluoride in 2017 was marginally higher than that of 2001 ( 2.09>2.03 mg/L respectively) although the percentage of age group members disposed to fluoride risk from using water from Q₃ decreased from 2001 to 2017. Knowledge of local hydrogeology in exploiting deep groundwater free of fluoride pollution and on-site defluoridation treatment of groundwater was recommended in the study area and other areas with similar characteristics.

Spatiotemporal evolution of groundwater nitrate nitrogen levels and potential human health risks in the Songnen Plain, Northeast China

As one of the most widespread pollutants worldwide, nitrogen has long been a concern in the environment, including groundwater. However, due to the limitations of investigations and study progress, there is still a poor understanding of groundwater nitrogen pollution and its potential effects on human health in many areas, particularly in developing countries. The spatiotemporal evolution of groundwater nitrate nitrogen levels and potential human health risks in the Songnen Plain, Northeast China were comprehensively studied based on both our own test data and available published data that were collected by us over a study period from 1995 to 2015. Groundwater nitrate nitrogen concentrations exhibited significant temporal and spatial differences: there was an increasing trend with time; and the distribution of high concentration areas expanded from the central and western areas to the east with time. The similar pattern existed in the potential health risks posed to the residents considering the two exposure pathways including drinking water and dermal contact. The effects of groundwater nitrate nitrogen on human health depend on the nitrate concentration but there were also age differences, namely, in the order of infants > children > adult females ≈ adult males, according to the hazard quotient (HQ) used in the human health risk assessment (HHRA) model. The spatiotemporal evolution of groundwater nitrate nitrogen levels and potential human health risks indicate that the issue of nitrogen pollution in groundwater in the study area is worsening and needs further attention. The drivers that increased nitrate nitrogen concentrations in the groundwater of the study area were the increased fertilizer use due to the increased cultivated land area and implementation of a land fertility policy by the local government. It should be acknowledged that the results have uncertainties that not only come from the layout of sampling points and selection of spatial interpolation methods but also come from the parameter settings in the assessment model and assumptions of drinking water scenarios. However, the conclusions still have important reference value for groundwater pollution control and management and human health risk supervision and early warning.

Effects of drought on environmental health risk posed by groundwater contamination

This publication presents a comparison of the content of pollutants in groundwater samples taken at 117 measurement points in four regions of Poland during a drought period and in the reference period without drought. Based on the chemical analyses of water, an assessment of the health risk resulting from the use of underground water for consumption was carried out. The study aimed to determine whether drought affects the increase in health risk exposure of the population. It was found that despite the occurrence of drought, the expected increase in the concentration of pollutants in water does not take place in all locations. This study found that in some cases the occurrence of drought did not cause an increase in the non-cancerogenic threat expressed by the hazard index. There were also no clear changes in excess lifetime cancer risk values except for selected measurement points. On the other hand, the statistical analysis of all data collected in the regions where the research was conducted showed a general trend of increasing environmental health risk caused by changes in groundwater pollution during drought.

Health risk assessment of groundwater nitrogen pollution in Songnen Plain

Access to safe drinking water is one of the fundamental human rights and an important part of healthy living. This study considered various land use methods, used geostatistical analysis, and triangular random model to explore nitrogen pollution and estimate its potential risk to human health for local populations in Songnen Plain of Northeast China and recognize parameter uncertainties. Nitrate concentrations in groundwater ranged from 0.01 to 523.45 mg/L, more than 72.35% of the samples exceeded Grade III threshold (20 mg/L of N) as per China's standard, and nitrate nitrogen content is greater than 20 mg/L accounted for around 60% of the research area, mainly distributed in the eastern and central high plain area. The nitrate-nitrogen content of groundwater in the town land was significantly higher than that of agricultural land, and the ammonia nitrogen content was conversely. The townland's risk value was two times that of agricultural land, considering different land use methods would avoid overestimating or underestimating regional risk value. Non-carcinogenic risks (HI) of two land use were above the safety level (i.e., HI > 1), suggesting that groundwater nitrate would have significant health effects on the age groups, and further threaten children. There was a wide range of fluctuations in the uncertainty of nitrogen concentration and model evaluation parameters; triangular random model was more sensitive to data changes, which could reduce the uncertainty. The contribution rate of nitrate-nitrogen concentration to risk was above 90%, which explained the need for random sampling to improve the evaluation results reliability. The findings in this paper will provide new insight for solving uncertainties in water safety management.

Comprehensive Understanding of Groundwater Geochemistry and Suitability for Sustainable Drinking Purposes in Confined Aquifers of the Wuyi Region, Central North China Plain

Confined groundwater is important for the domestic water supply in arid and semiarid regions that have salty phreatic water. A systematic investigation was conducted in the Wuyi region, a typical central area of the North China Plain (NCP), regarding the confined groundwater geochemistry. A total of 59 samples were collected from confined aquifers across the region for in situ parameter determination and laboratory analysis. The results showed the confined groundwater was neutral to slightly alkaline, and dominantly soft fresh. The moderately hard brackish water and very hard brackish water accounted for 1.69% and 6.78% of the total samples, respectively. The hydro-chemical faces are mainly SO4·Cl–Na type with a few of the HCO3–Na type. The entropy-weighted water quality index assessment demonstrated that 21.3% of the groundwater samples came under the medium to extremely poor quality, and were unsuitable for drinking purposes due to the high content of major ions. Various populations are at a chronic health risk at some local sites by high levels of F- and Fe in groundwater, with susceptibility in the order of adult females < adult males < children < infants. The poor groundwater quality and health threats result from the natural water–rock interactions (including mineral dissolution and cation exchange) rather than anthropogenic inputs. This research can provide references for groundwater resource development and management in the NCP and other similar regions worldwide.

Use of environmental isotopes to assess groundwater pollution caused by agricultural activities

This work applied environmental isotope techniques to validate the results of previous studies on recharge sources in a rural area in central Chile (34.3° S and 71.3° W) and discern the origin of nitrate contamination in wells. Stream water and groundwater samples were taken during three surveys, two during spring snowmelt and one in low-water conditions. Chemical analyses included major cations and anions, isotope analyses included ¹⁸O-H₂O; ²H-H₂0; ³H-H₂0; ¹⁸O-NO₃ ^- and ¹⁵N-NO₃ ^-. The stable isotope data show that surface water and deep groundwater present depleted isotope values associated with recharge from the Andes Mountains and that shallow groundwater has more enriched isotope values that reflect the contribution of local recharge from rainwater infiltration. Depleted isotope values observed in shallow groundwater show the effect of recirculated river water used for irrigation. These results are consistent with the conceptual groundwater model developed in previous studies. Some wells have nitrate concentrations above the allowable limit for drinking water. The stable nitrogen isotopes indicate that nitrate is associated mainly with urea and ammoniacal fertilizers, and nitrate is attenuated by denitrification. The results of this study are relevant to improving management of groundwater resources used for drinking water.

Investigation of Groundwater Contamination and Health Implications in a Typical Semiarid Basin of North China

Groundwater chemistry and its potential health risks are as important as water availability in arid and semiarid regions. This study was conducted to determine the contamination and associated health threats to various populations in a semiarid basin of north China. A total of 78 groundwater samples were collected from the shallow unconfined aquifers. The results showed that the phreatic water was slightly alkaline, hard fresh water with ions in the order of Ca2+ > Na++K+ > Mg2+ and HCO3− > SO42− > Cl−. Four hydrochemical elements, NO3−, F−, Mn and Zn, exceeded the permissible limits. NO3− and F− contaminants may pose health risks to local residents, while the risks of Mn and Zn are negligible. Dermal exposure is safe for all populations, while the oral pathway is not. Minors (i.e., infants and children) are susceptible to both NO3− and F− contaminants, and adults only to NO3−. The susceptibility of various populations is in the order of infants > children > adult males > adult females. Anthropogenic activities are responsible for the elevated levels of NO3−, Zn, Total dissolved solids (TDS), while F− and Mn are from geogenic sources. Thus, differential water supplies, strict control of waste, and rational irrigation practices are encouraged in the basin.

Nitrate contamination of water in dug wells and associated health risks of rural communities in southwest Bangladesh

Consumption of drinking water with high nitrate may pose a serious health hazard. This study examined nitrate concentration in the water of dug wells at the Jashore district of Bangladesh. A total of 58 water samples were collected from dug wells which are currently in use for drinking water. Concentrations of nitrate in the water range from 0.05 to 430 mg/l and from 0.24 to 206 mg/l respectively in the wet and dry seasons. About 17% and 14% of the samples during the wet and dry seasons respectively showed nitrate concentration above the WHO guideline value of 50 mg/l. The wells with high nitrate concentration showed health risks for adults and children. About 17% of the samples showed a health hazard index (HQ_nitrate) values above the acceptable limit (HQ_nitrate values > 1) for adults, in both the wet and dry seasons, whereas 26% and 33% of the water samples in the wet and dry seasons respectively showed HQ_nitrate values > 1 for children. Therefore, children are more likely to be affected by intaking nitrate-contaminated dug well water. Health risks of elevated nitrate concentration in the dug wells require proper attention to ensure reliable water supply.

Combined microbial and isotopic signature approach to identify nitrate sources and transformation processes in groundwater

Nitrate (NO₃^-) pollution is a serious problem worldwide. Identification of NO₃^- sources and transformation processes in aquifers is a key step in effectively controlling and mitigating NO₃^- contamination. In this study, hydrochemical, microbial, and dual isotopic approaches were integrated to elucidate the sources and processes influencing NO₃^- contamination in the Pearl River Delta, China. The results showed a severe NO₃^- contamination, with 75% of the samples having NO₃^--N concentrations above the WHO standard of 10 mg L^-1. The δ¹⁵NNO₃^- and δ¹⁸ONO₃^- values and a multivariate statistical analysis of hydrochemical data both revealed that manure and sewage were mainly responsible for NO₃^- contamination. Biological indicators further demonstrated that, manure and sewage had greater impacts on groundwater quality during the rainy season than during the dry season. Based on the significant relationships of δ¹⁵NNO₃^- and δ¹⁸ONO₃^- with the logarithmic NO₃^- concentration (Ln(NO₃^-)), denitrification was confirmed to occur in the discharge zone during the rainy season. Proteobacteria, Bacteroidetes, and Planctomycetes were identified as the dominant phyla, and Dechloromonas, Flavobacterium, and Nitrospira were dominant among the denitrifying bacteria in groundwater. The abundance of denitrifying bacteria had significant positive correlations with δ¹⁵NNO₃^- and NO₂^--N during the rainy season, further confirming the occurrence of denitrification during the rainy season. This study showed that dual isotope techniques combined with microbial data can be a powerful tool for identifying the sources and microbial processes affecting NO₃^- in groundwater. Moreover, the results can provide useful insights for environmental managers to verify groundwater pollution and better apply remediation solutions.

Environmental health risk posed by contamination of the individual water wells

This paper presents the results of analyzes of water samples taken from individual water wells intended for supplying households in non-urbanized areas with low population and infrastructure density. Relatively high concentrations of harmful pollutants were found in ground waters of the examined spots located in the suburban areas which may increase the risk of health incidents in exposed populations. Based on long-term measurements carried out in individual spots and toxicological data, the individual health risks related to carcinogenic effects in humans were assessed, resulting from direct ingestion of such water and from dermal contact. Non-carcinogenic hazard levels were determined, as well. In this work a novel approach to health risk assessment was proposed. It consists of determining the risks that range between minimum and possible maximum values. In the case of limited traceability of a pollutant the maximum and minimum risk values were derived from the limit of quantification (LOQ). Thus, for the minimum risk, zero concentration was applied, while for calculation of the maximum risk, LOQ was used as the possible highest pollutant content in water. The calculations proved that using untreated water for consumption and bathing is likely to cause an increase of both mutagenic and toxic risk in humans concerned. Depending on the site, the calculated non-carcinogenic hazard level expressed by the hazard index HI ranges between 0.6 and 3.6 while the excess lifetime cancer risk ELCR is of the order of 10^-4.

Groundwater nitrate contamination and associated human health risk assessment in southern districts of Punjab, India

Consumption of high NO₃ containing water may pose serious health hazard especially in children (< 5 years). The source of NO₃ in groundwater includes surface leaching from wastewater and waste dump sites, animal excreta disposal, industrial effluents, and N-based fertilizers, etc. This study aimed to investigate the concentration of NO₃ in groundwater of 14 intensively cultivated districts of Malwa Punjab, India, and its possible health hazards in local residents. The sampling of 76 sites revealed the concentration of NO₃ in ranges of 38.45-198.05 mgL^-1, and over 92% sites showed the high level of it than the safe limits as decided by the Bureau of Indian standards (45 mg L^-1) and World Health Organization (50 mg L^-1). The possible health hazards of high NO₃ intake was estimated using USEPA human health risk assessment (HHRA) model for both adult and children. Results of this study suggested the chronic daily intake (CDI) in the ranges of 1.09-5.65 and 2.56-13.20 in adult and children population of this region, respectively. The hazard quotient (HQ_nitrate) value was > 1 in most sampling locations ranging 1.09-5.65 for the adult and 2.56-13.20 for children population of Malwa. This study indicates that 93.42% adult and 100% young population of the Malwa are at higher risk of chronic toxicity by excess NO₃ intake. The HHRA results suggested a high vulnerability of a local community to NO₃ toxicity in this region; therefore, there is an instant need to take preventive measures to safeguard the health of local residents.

Progress, opportunities, and key fields for groundwater quality research under the impacts of human activities in China with a special focus on western China

Groundwater quality research is extremely important for supporting the safety of the water supply and human health in arid and semi-arid areas of China. This review article was constructed to report the latest research progress of groundwater quality in western China where groundwater quality is undergoing fast deterioration because of fast economic development and extensive anthropogenic activities. The opportunities brought by increasing public awareness of groundwater quality protection were also highlighted and discussed. To guide and promote further development of groundwater quality research in China, especially in western China, ten key groundwater quality research fields were proposed. The review shows that the intensification of human activities and the associated impacts on groundwater quality in China, especially in western China, has made groundwater quality research increasingly important, and has caught the attention of local, national, and international agencies and scholars. China has achieved some progress in groundwater quality research in terms of national and regional laws, regulations, and financial supports. The future of groundwater quality research in China, especially in western China, is promising reflected by the opportunities highlighted. The key research fields proposed in this article may also inform groundwater quality protection and management at the national and international level.