Nitrate contamination in groundwater of some rural areas of Rajasthan, India

Emerging nitrate contamination in groundwater: Changing phase in a fast-growing state of India

The consumption of nitrate-contaminated groundwater is often associated with potential health risks, particularly in children. This study aimed to assess the hydrochemistry and nitrate contamination in groundwater of Kerala state, India for the years 2010 and 2018 and evaluate the potential human health risks due to nitrate exposure in adults, and children through oral ingestion and dermal contact pathways. Nitrate-contaminated zones were identified by spatial mapping of nitrate concentration based on groundwater quality data of 324 wells. Groundwater is typically acidic to slightly alkaline, and the electrical conductivity (EC) varied from 33 to 1180 μS/cm in 2010 and 34.6-2500 mg/L in 2018 indicating a noticeable increase over the years. Most samples fall within low salt enrichment category. The nitrate concentration in groundwater varied from 0 to 173 mg/L with a mean of 15.4 mg/L during 2010 and 0 to 244 with a mean of 20.3 mg/L during 2018. Though nitrate concentrations show uneven spatial distributions due to both natural and anthropogenic sources, the spatial clustering of higher concentrations remains almost same in both periods. In 2010, non-carcinogenic risk, as measured by Health Index Total (HITotal) values in groundwater for the investigated region, ranged from 0.005 to 4.170 (mean of 0.349) for males, 0.005 to 4.928 (mean of 0.413) for females, and 0.008 to 7.243 (mean of 0.607) for children, while in 2018, the corresponding values varied from 0.001 to 5.881 (mean of 0.501) for males, 0.002 to 6.950 (mean of 0.592) for females, and 0.003 to 10.215 (mean of 0.870) for children, indicating a substantial increase in risk, for females and children. Greater health risk is observed in children during both the periods. The findings emphasize the need for proper water quality management, especially in regions with higher vulnerability to nitrate pollution, to safeguard human health and well-being.

Nitrate electro-bioremediation and water disinfection for rural areas

Nitrate-contaminated groundwater is a pressing issue in rural areas, where up to 40 % of the population lacks access to safely managed drinking water services. The high costs and complexity of centralised treatment in these regions exacerbate this problem. To address this challenge, the present study proposes electro-bioremediation as a more accessible decentralised alternative. Specifically, the main focus of this study is developing and evaluating a compact reactor designed to accomplish simultaneous nitrate removal and groundwater disinfection. Significantly, this study has established a new benchmark for nitrate reduction rate within bioelectrochemical reactors, achieving the maximum reported rate of 5.0 ± 0.3 kg NO3- m-3NCC d-1 at an HRTcat of 0.7 h. Furthermore, thein-situ generation of free chlorine was effective for water disinfection, resulting in a residual concentration of up to 4.4 ± 1.1 mg Cl2 L-1 in the effluent at the same HRTcat of 0.7 h. These achievements enabled the treated water to meet the drinking water standards for nitrogen compounds (nitrate, nitrite, and nitrous oxide) as well as pathogens content (T. coliforms, E. coli, and Enterococcus). In conclusion, this study demonstrates the potential of the electro-bioremediation of nitrate-contaminated groundwater as a decentralised water treatment system in rural areas with a competitive operational cost of 1.05 ± 0.16 € m-3.

The impacts of climate change on groundwater quality: A review

Groundwater has been known as the second largest freshwater storage in the world, following surface water. Over the years, groundwater has already been under overwhelming pressure to satisfy human needs for artificial activities around the world. Meanwhile, the most noticeable footprint of human activities is the impact of climate change. Climate change has the potential to change the physical and chemical properties of groundwater, thereby affecting its ecological functions. This study summarizes existing research affiliated with the possible effects of a changing climate on the quality of groundwater, including changes in water availability, increased salinity and pollution from extreme weather events, and the potentiality of seawater intrusion into coastal aquifers. Previous works dealing with groundwater-induced responses to the climate system and climate impacts on groundwater quality through natural and anthropogenic processes have been reviewed. The climate-induced changes in groundwater quality including pH, dissolved oxygen level, salinity, and concentrations of organic and inorganic compounds were assessed. Some future research directions are proposed, including exploring the potential changes in the occurrences and fate of micropollutants in groundwater, examining the relationship between the increase of microcystin in groundwater and climate change, studying the changes in the stability of metals and metal complexation, and completing studies across different regional climate regions.

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.

Groundwater hydrogeochemistry and non-carcinogenic health risk assessment in major river basins of Punjab, India

The Indian Punjab state is drained by the four rivers, along with a well-connected network of canals, and is now dealing with a slew of water quality issues and problems. In this study, basin-wise hydrogeochemical modelling of 323 groundwater samples and identification of NO3- and F- enrichment pathways in aquifer systems of Punjab were studied using different plots and multivariate statistics. To evaluate the groundwater quality and human health risks, an entropy-based water quality index and Monte Carlo simulation were used, respectively. Spatial distribution of NO3- indicated that its very high values were prominent in parts of southwestern Punjab falling under LSRB, along with few pockets in eastern and northeastern Punjab falling under MSRB and GRB. High NO3- values (> 45.0 mg/L) were found in 15.0% of Ravi River Basin (RRB) groundwater samples, 22.86% of Beas River Basin (BRB), 23.52% of Middle Sutlej River Basin (MSRB), 36.9% of Lower Sutlej River Basin (LSRB), and 21.31% of Ghaggar River Basin (GRB). The spatial distribution of NO3- revealed elevated concentrations (> 100 mg/L) in the southwestern part of Punjab, particularly in LSRB and localized pockets in the eastern and northeastern areas of Punjab within MSRB and GRB. High F- concentration (> 1.5 mg/L) was observed in 15.12% and 21.31% groundwater samples of LSRB and GRB, respectively. Spatially southern parts falling under LSRB and GRB reflected high F- content (> 1.5 mg/L) in groundwater. In LSRB, evaporative and anthropogenic processes influence the groundwater quality. The results of interionic relationships and statistical analysis revealed that NO3- has anthropogenic origin and that is being aggravated by leaching, the evaporation processes, animal excreta, septic tanks and irrigation return flows in LSRB and GRB, while F- is geogenic in nature. Hazard index (HI) values in 14.63%, 22.2%, 24.6%, 49.58%, and 34.42% samples for adults and 21.95%, 27.7%, 42.0%, 72.3%, and 52.46% samples for children were higher than unity in RRB, BRB, MSRB, LSRB, and GRB, respectively. The basin-wise demarcation of various groundwater quality parameter and assessment of human health risk would be of significance for the management of water resources.

Effects of elevated arsenic and nitrate concentrations on groundwater resources in deltaic region of Sundarban Ramsar site, Indo-Bangladesh region

An attempt has been adopted to predict the As and NO₃^- concentration in groundwater (GW) in fast-growing coastal Ramsar region in eastern India. This study is focused to evaluate the As and NO₃^- vulnerable areas of coastal belts of the Indo-Bangladesh Ramsar site a hydro-geostrategic region of the world by using advanced ensemble ML techniques including NB-RF, NB-SVM and NB-Bagging. A total of 199 samples were collected from the entire study area for utilizing the 12 GWQ conditioning factors. The predicted results are certified that NB-Bagging the most suitable and preferable model in this current research. The vulnerability of As and NO₃^- concentration shows that most of the areas are highly vulnerable to As and low to moderately vulnerable to NO₃. The reliable findings of this present study will help the management authorities and policymakers in taking preventive measures in reducing the vulnerability of water resources and corresponding health risks.

Assessment of groundwater potability and health risk due to fluoride and nitrate in groundwater of Churu District of Rajasthan, India

The availability of potable drinking water is a tough challenge particularly in arid and semiarid regions as it is closely linked to human health. Fluoride and nitrate are widely reported concern in different districts of Rajasthan. Therefore, this study was engaged in the Churu District of Rajasthan to appraise the water quality especially in reference to fluoride and nitrate and health risk associated with its consumption. The overall potability of water was evaluated using water quality index and PCA indicated major sources responsible for water contamination. A total of 515 groundwater samples were collected from different locations of Churu District and16 water quality parameters were analyzed as per the standard protocol of APHA. The results showed that the values for all analyzed water quality parameters were greater than the prescribed limit of WHO and BIS. F^- levels in 191 samples and nitrate levels in 147 samples were found to be over than BIS-acceptable limit. The results of the fluoride and nitrate risk assessment revealed that the Hazard Index value was greater than one of 393 groundwater samples for males, 403 groundwater samples for females, and 397 groundwater samples for children, indicating that drinking groundwater poses a significant health risk in the study area. Only 46.02 percent of groundwater samples may be utilized for drinking, according to the water quality index (WQI), while the remaining are unfit for drinking purpose without treatment. The huge number of variables impacting the overall quality and chemistry of groundwater were reduced using principal component analysis (PCA), which identified four key components that account for 69.11 percent of variance in the dataset. The PCA indicated that both geogenic and anthropogenic factors significantly influenced the water quality of the study region.

Fluoride and nitrate in groundwater: a comprehensive analysis of health risk and potability of groundwater of Jhunjhunu district of Rajasthan, India

Groundwater contamination is a major concern in front of the scientific community because it is directly related to human health, especially in arid and semi-arid regions. Therefore, a comprehensive study was engaged to evaluate the water quality, potability, and human health risk assessment due to the consumption of fluoride- and nitrate-contaminated water in Jhunjhunu district of Rajasthan. In order to assess the water quality, samples were collected from 87 locations in the study region, and a total of 16 parameters were analyzed as per the standard methods. The results showed that the value of the number of quality parameters consisting of pH, EC, TDS, fluoride, chloride, nitrate, sulfate, total hardness, calcium, magnesium, and total alkalinity was higher than the recommended limit of BIS and WHO. The fluoride in 11% and nitrate in 6% of samples were observed to exceed the permissible limit of WHO. The results of risk assessment due to fluoride and nitrate revealed that hazard index values of 71% of groundwater samples for males, 78% of groundwater samples for females, and 75% of groundwater samples for children were greater than 1, indicating the significant health hazard due to consumption of groundwater. The water quality index (WQI) found that 39% of groundwater samples belong to categories that cannot be used for drinking purposes. Principal component analysis (PCA) reduced the large number of variables affecting the overall quality and chemistry of groundwater and determined four major components which account for 69.50% variance in the data. PCA concluded that both geogenic and anthropogenic sources of contamination influenced the groundwater of the study area.

Nitrogen use efficiency-a key to enhance crop productivity under a changing climate

Nitrogen (N) is an essential element required for the growth and development of all plants. On a global scale, N is agriculture's most widely used fertilizer nutrient. Studies have shown that crops use only 50% of the applied N effectively, while the rest is lost through various pathways to the surrounding environment. Furthermore, lost N negatively impacts the farmer's return on investment and pollutes the water, soil, and air. Therefore, enhancing nitrogen use efficiency (NUE) is critical in crop improvement programs and agronomic management systems. The major processes responsible for low N use are the volatilization, surface runoff, leaching, and denitrification of N. Improving NUE through agronomic management practices and high-throughput technologies would reduce the need for intensive N application and minimize the negative impact of N on the environment. The harmonization of agronomic, genetic, and biotechnological tools will improve the efficiency of N assimilation in crops and align agricultural systems with global needs to protect environmental functions and resources. Therefore, this review summarizes the literature on nitrogen loss, factors affecting NUE, and agronomic and genetic approaches for improving NUE in various crops and proposes a pathway to bring together agronomic and environmental needs.

Nitrate Controls on the Extent and Type of Metal Retention in Fine-Grained Sediments of a Simulated Aquifer

Aquifer groundwater quality is largely controlled by sediment composition and physical heterogeneity, which commonly sustains a unique redox gradient pattern. Attenuation of heavy metals within these heterogeneous aquifers is reliant on multiple factors, including redox conditions and redox-active species that can further influence biogeochemical cycling. Here, we simulated an alluvial aquifer system using columns filled with natural coarse-grained sediments and two domains of fine-grained sediment lenses. Our goal was to examine heavy metal (Ni and Zn) attenuation within a complex aquifer network and further explore nitrate-rich groundwater conditions. The fine-grained sediment lenses sustained reducing conditions and served as a sink for Ni sequestration─in the form of Ni-silicates, Ni-organic matter, and a dominant Ni-sulfide phase. The silicate clay and sulfide pools were also important retention mechanisms for Zn; however, Ni was associated more extensively with organic matter compared to Zn, which formed layered double hydroxides. Nitrate-rich conditions promoted denitrification within the lenses that was coupled to the oxidation of Fe(II) and the concomitant precipitation of an Fe(III) phase with higher structural distortion. A decreased metal sulfide pool also resulted, where nitrate-rich conditions generated an average 20% decrease in solid-phase Ni, Zn, and Fe. Ultimately, nitrate plays a significant role in the aquifer's biogeochemical cycling and the capacity to retain heavy metals.

Nitrate transport velocity data in the global unsaturated zones

Nitrate pollution in groundwater, which is an international problem, threatens human health and the environment. It could take decades for nitrate to transport in the groundwater system. When understanding the impacts of this nitrate legacy on water quality, the nitrate transport velocity (v_N) in the unsaturated zone (USZ) is of great significance. Although some local USZ v_N data measured or simulated are available, there has been no such a dataset at the global scale. Here, we present a Global-scale unsaturated zone Nitrate transport Velocity dataset (GNV) generated from a Nitrate Time Bomb (NTB) model using global permeability and porosity and global average annual groundwater recharge data. To evaluate GNV, a baseline dataset of USZ v_N was created using locally measured data and global lithological data. The results show that 94.50% of GNV match the baseline USZ v_N dataset. This dataset will largely contribute to research advancement in the nitrate legacy in the groundwater system, provide evidence for managing nitrate water pollution, and promote international and interdisciplinary collaborations.

Nitrate contamination in water resources, human health risks and its remediation through adsorption: a focused review

The level of nitrate in water has been increasing considerably all around the world due to vast application of inorganic nitrogen fertiliser and animal manure. Because of nitrate's high solubility in water, human beings are getting exposed to it mainly through various routes including water, food etc. Various regulations have been set for nitrate (45-50 mgNO₃^-/L) in drinking water to protect health of the infants from the methemoglobinemia, birth defects, thyroid disease, risk of specific cancers, i.e. colorectal, breast and bladder cancer caused due to nitrate poisoning. Different methods like ion exchange, adsorption, biological denitrification etc. have the ability to eliminate the nitrate from the aqueous medium. However, adsorption process got preference over the other approaches because of its simple design and satisfactory results especially with surface modified adsorbents or with mineral-based adsorbents. Different types of adsorbents have been used for this purpose; however, adsorbents derived from the biomass wastes have great adsorption capacities for nitrate such as tea waste-based adsorbents (136.43 mg/g), carbon nanotube (142.86 mg/g), chitosan beads (104 mg/g) and cetyltrimethylammonium bromide modified rice husk (278 mg/g). Therefore, a thorough literature survey has been carried out to formulate this review paper to understand various sources of nitrate pollution, route of exposure to the human beings, ill effects along with discussing the key developments as well as the new advancements reported in procuring low-cost efficient adsorbents for water purification.

Hydrogeochemical and health risk assessment in and around a Ramsar-designated wetland, the Ganges River Basin, India: Implications for natural and human interactions

Wetlands are the most productive and dynamic ecosystems, which have continuously been influenced by social and economic development. As a result, the pollution of wetland surface water and groundwater in adjacent regions has become an emerging global issue that requires constant monitoring and assessment. The current study investigates the natural and anthropogenic processes that influence surface and groundwater chemistry in and around Saman wetland (a Ramsar site) in the Ganges River Basin, India. Various physicochemical parameters are analyzed, and different hydrochemical indices are utilized to evaluate surface and groundwater quality for domestic and irrigation purposes. It is observed that the waters are alkaline in nature and dominated by moderately hard to hard types. An increase in the concentration of nitrate (NO₃^-) in Saman wetland water is noted, which is possibly due to the leaching of nitrogen ions primarily from fertilizers, pesticides, animal and human waste, and wastewater drained from brick and other factories. The elevated fluoride (F^-) content in studied groundwater samples is mainly governed by geogenic processes. Furthermore, surface and groundwater chemistry are mainly controlled by weathering reaction (rock-water interaction), excluding a few wetland surface water samples that are placed outside the boomerang-shaped boundaries of Gibb's diagram, which suggests evaporated dominance. Water Quality Index (WQI) estimation suggests that around 57% of groundwater samples have poor groundwater quality for drinking purposes. Estimation of irrigation water quality indices suggests that surface water of Saman wetland is permissible for irrigation purposes; however, none of the samples have excellent and good class as per sodium (alkali) hazard. Furthermore, health risk assessment showed that NO₃^- and F^- levels in the groundwater pose noncarcinogenic health effects, preferably to children, and thus is unfit for drinking purposes. For long-term water resource management and conservation of the Saman wetland, this study suggests proper awareness, appropriate remedial measures, and regular monitoring of the surface as well as groundwater quality monitoring in the study region.

Nitrate concentration analysis and prediction in a shallow aquifer in central-eastern Tunisia using artificial neural network and time series modelling

Agricultural activities have become a major source of groundwater nitrate contamination. In this context, this study aims to analyse nitrate concentrations in a shallow aquifer of Mahdia-Kssour Essef in central-eastern Tunisia, identify the assignable sources, and predict the future levels using artificial neural network (ANN) and autoregressive integrated moving average (ARIMA) models. The results showed that nitrate concentrations measured in 21 pumping wells across the plain ranged from 17 to 521 mg L^-1. A total of 67% of the monitoring points greatly exceed the standard guideline value of 50 mg L^-1. The main relevant anthropogenic and natural factors, such as soil texture, land use, fertilizers application rates, livestock waste disposal, and groundwater table, are positively correlated with groundwater nitrate concentration. The ANN model showed good fitting between measured and simulated results with coefficient of determination (R²), root-mean-square error (RMSE), and mean absolute error (MAE) values of 0.88, 53.95, and 39.64, respectively. The ARIMA applied on annual average nitrate concentrations from 1998 to 2017 revealed that the best fitted model (p, d, q) is (1, 2, 1). The R² value is approximately 0.36, and the Theil inequality coefficient and bias proportion values are small and close to zero. These results proved the ARIMA model's adequacy in forecasting annual average nitrate concentrations of 116 mg L^-1 in 2025. These findings may be useful in making groundwater management decisions, particularly in rural and semi-arid areas, and the proposed ARIMA model could be used as a managed tool to monitor and reduce the nitrate intrusion into groundwater.

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.

Source apportionment and health risk assessment of nitrate in foothill aquifers of Western Ghats, South India

The present research reports the level of nitrate (NO₃^-), associated health risks and possible sources of contamination in groundwater from south India. Many samples (32%) are above or approaching the recommended level of NO₃^- for safe drinking water. The correlation analysis indicates different sources of NO₃^- contamination in different regions rather than a common origin. The isotopic measurements provide information about potential nitrogen sources contributing NO₃^- to the groundwater. Based on isotope analysis, the sources of NO₃^- in the groundwater of this region are likely to be from (a) septic sewage (b) organic nitrogen (animal and livestock excreta) (c) sewage (domestic & chemical fertilizers). Among the sample analyzed sewage, manure and septic sewage contribute 46%, 23% and 31% NO₃^- to groundwater. The HQ > 1 indicates non-carcinogenic health risk due to consumption of high NO₃^- in drinking water. Among the studied age groups, infants are exposed to higher risk than children and adults. Results indicate that groundwater of this region is polluted with NO₃^- due to anthropogenic activities. Continuous consumption of such water may pose serious health risk to the residents.

Preliminary Evaluation of the Possible Occurrence of Pesticides in Groundwater Contaminated with Nitrates—A Case Study from Southern Poland

This paper addresses groundwater pollution and the potential presence of pesticides within the catchment areas of two reservoirs that are sources of drinking water. The two reservoirs are Goczałkowice and Kozłowa Góra, both in Southern Poland. Agricultural and rural areas dominate both catchments. Archival data showed local groundwater contamination with nitrates. This indicated the possible presence of pesticides in shallow groundwater. In total, 13 groundwater samples from shallow sandy aquifers were collected. All the samples were tested for the presence of 35 organophosphate pesticides and 28 organochlorine pesticides. Additionally, in order to determine the current groundwater conditions, physicochemical parameters were measured in the field, and water samples were subjected to analysis of their chemical composition (incl. the determination of nitrates). The research outcomes showed that pesticides were not detected above the detection limits in any of the samples. Due to variations in the persistence and degradation rates of pesticides, the occurrence of these substances in the groundwater environment and the possibility of their migration to aquifers should not be completely excluded. Natural processes and factors (e.g., sorption, biodegradation, hydrolysis and redox conditions) may gradually reduce the pesticide concentrations in groundwater. The chemical analyses revealed high concentrations of nitrates in the groundwater. This suggests the possible influence of agriculture and fertilizer application on groundwater quality; however, a proportion of NO3- ions may be connected with improper sewage management within the two catchments. The absence of pesticides in groundwater impacted by agriculture may result from processes occurring in the aquifer and the rapid degradation of these compounds due to photolysis and prevailing weather conditions. In the vicinity of dwellings, nitrates also originate from domestic wastewater. Thus, the occurrence of pesticides in groundwater contaminated with NO3 cannot always be expected.

Fluoride and nitrate in groundwater of rural habitations of semiarid region of northern Rajasthan, India: a hydrogeochemical, multivariate statistical, and human health risk assessment perspective

In arid and semiarid regions, groundwater is required for the drinking, agriculture, and industrial activities due to scarcity of surface water. Groundwater contaminated with high concentrations of fluoride and nitrate can severely affect human health in these regions. Twenty-eight groundwater samples from rural habitations of Jhunjhunu district, Rajasthan, India, were collected in March 2018 and subjected to analysis for water quality parameters. Fluoride and nitrate concentrations in groundwater varied from 0 to 5.74 mg/L and 10.22-519.64 mg/L, respectively. Nitrate content of about 86% samples and fluoride content of about 54% exceeded the permissible limit of Bureau of Indian Standards (IS:10,500) as well as World Health Organization standards. All groundwater samples belonged to poor to unfit drinking water quality index. Principle component analysis elucidates the anthropogenic contribution to high nitrate concentrations observed in this area. Noncarcinogenic human health risk evaluated from high nitrate and fluoride in drinking water for children, men, and women points to the fact that noncarcinogenic risk is exceeding the allowable limit to human health. The predominating hydrochemical facies in the area is Na⁺-HCO₃^--Cl^- followed by Na⁺-Mg²⁺-HCO₃^--Cl^-. The Gibbs plot and bivariate ionic cross-plots suggest the noncarbonate weathering (rock dominance), evaporation dominance, and ion exchange process to be the predominating geochemical mechanisms governing the evolution of groundwater hydrogeochemistry. Giggenbach diagram shows the immature character, i.e., incomplete equilibration of the groundwater.

Faecal and nitrate contamination in the groundwater of Mardan district, Pakistan

This study aimed to determine the status of groundwater contamination with faecal coliform and nitrate in the rural areas of Mardan district, Pakistan. Both analytes require regular monitoring according to the National Environmental Quality Standards (NEQS) of Pakistan. Groundwater samples (n = 100) were collected from 25 villages across four zones. Samples were analysed for physicochemical parameters including pH, electrical conductivity (EC), Escherichia coli (E. coli) contamination, nitrite, and nitrate ([Formula: see text] and [Formula: see text]). Whilst the average concentrations of [Formula: see text] in the water samples were within the permissible limits of 50 mg L^-1 set by the World Health Organisation (WHO) and NEQS two villages exceeded the safety limits. Non-carcinogenic health risks of [Formula: see text] were estimated in terms of average daily dose (ADD) and hazard quotient (HQ). The HQ values for [Formula: see text] were > 1 for children signifying potential health risks; however, the adult population had HQ < 1 which indicates no risk. Groundwater samples tested positive for E. coli contamination in 13 villages, suggesting that residents may be living at risk of various microbial diseases due to drinking of contaminated water. The findings of this study provide valuable baseline data for groundwater researchers, policymakers, and the local public health department.

Investigation of health risks related with multipath entry of groundwater nitrate using Sobol sensitivity indicators in an urban-industrial sector of south India

In the present study, we used a variance decomposition based global sensitivity index to evaluate the sensitivity of input variables and their contribution for non-carcinogenic health risks via intake and dermal pathways. Groundwater samples were collected from an industrial sector (Tiruppur region) of south India during the month of January 2020. These samples were analysed for nitrate, which varied from 10 to 290 mg L^-1 having the mean of 87 mg L^-1. Nearly 58% of the samples surpassed the permissible limit (45 mg L^-1) defined by the World Health Organization. Total hazard index (THI) ranged from 0.29 to 8.52 for children, 0.28 to 8.26 for women, and 0.24 to 6.99 for men. The first-order effect (FOE) and second-order effect (SOE) were derived for the three different age groups using Sobol sensitivity approach. The FOE scores showed that nitrate concentration in groundwater is the most sensitive parameter followed by exposure frequency for children, men and women via oral pathway. The SOE scores showed that nitrate concentration along with ingestion rate had greater sensitiveness in the oral input model. The higher SOE was obtained for the interaction of nitrate with skin surface area for children via dermal pathway, but it was not significant for women and men. These results suggest that epidemiology due to nitrate risk should be studied taking into account of concentration of nitrate, exposure frequency, fraction of contact and body weight. Additionally, ingestion rate and skin surface area were considered for the assessment of health risks for children.

Chronic nitrate exposure cause alteration of blood physiological parameters, redox status and apoptosis of juvenile turbot (Scophthalmus maximus)

Nitrate (NO₃^-) is one of the common inorganic nitrogen compound pollutants in natural ecosystems, which may have serious risks for aquatic organisms. However, its toxicological mechanism remains unclear. In the current study, juvenile turbot (Scophthalmus maximus) were exposed to different concentrations of NO₃^- (CK- 3.57 ± 0.16, LN - 60.80 ± 1.21, MN - 203.13 ± 10.97 and HN - 414.16 ± 15.22 mg/L NO₃-N) for 60 d. The blood biochemical assays results revealed that elevated NO₃^- exposure significantly increased the concentrations of plasma NO₃^-, NO₂^-, MetHb, K⁺, cortisol, glucose, triglyceride, lactate, while significantly decreased the concentrations of plasma Hb, Na⁺ and Cl^-, which meant that NO₃^- caused hypoxic stress and further affected the osmoregulation and metabolism in fish. Besides, exposure to MN and HN induced a significant decrease in the level of antioxidants, including SOD (Point: 60th day, MN, HN v.s. CK: 258.36, 203.73 v.s. 326.95 U/mL), CAT (1.97, 1.17 v.s. 2.37 U/mL), GSH (25.38, 20.74 v.s. 37.00 μmol/L), and GPx (85.32, 71.46 v.s. 129.36 U/mL), and a significant increase of MDA (7.54, 9.73 v.s. 5.27 nmol/L), suggesting that NO₃^- exposure leading to a disruption of the redox status in fish. Also, further research revealed that NO₃^- exposure altered the mRNA levels of p53 (HN: up to 4.28 folds) and p53-regulated downstream genes such as Bcl-2 (inferior to 0.44 folds), caspase-3 (up to 2.90 folds) and caspase-7 (up to 3.49 folds), indicating that NO₃^- exposure induced abnormal apoptosis in the fish gills. Moreover, IBRv2 analysis showed that the toxicity of NO₃^- exposure to turbot was dose-dependent, and the toxicity peaked on the 15th day. In short, NO₃^- is an environmental toxicological factor that cannot be ignored, because its toxic effects are long-term and could cause irreversible damage to fish. These results would be beneficial to improve our understanding of the toxicity mechanism of NO₃^- to fish, which provides baseline evidence for the risk assessment of environmental NO₃^- in aquatic ecosystems.

Assessment of Groundwater Quality beneath Agriculturally Advanced Region of Northern Alluvial Plain, India

In the present study, groundwater suitability for domestic and irrigation purposes was analyzed in the alluvial aquifers of the Bist-Doab region of Punjab, India, using various indices such as WQI, WAWQI, MCDA, RSC, SAR, PI, %Na, KR, MH, PS, K, and Ka. Since it is difficult to assess the suitability of groundwater for irrigation based on various indices individually, a composite groundwater quality index for irrigation (CGQII) was used in the study which transforms nine indices to a single value for each sample. Results reveal that the groundwater of a few blocks was found unsuitable for domestic use due to chemical leaching from fertilizers, pesticides, and agricultural and industrial wastes. Whereas, the groundwater of mainly southwestern parts was found unsuitable for irrigation due to long-term water accumulation in aquifers and continuous use of sodium-ion-rich groundwater. The findings conclude that anthropogenic activities have played a significant role in making groundwater unfit for domestic and irrigation purposes in the study area. The present study also emphasizes continuous monitoring and evaluation of groundwater quality, which will help in strategic planning and management for the conservation of groundwater resources in the region.

Anthropogenic nitrate in groundwater and its health risks in the view of background concentration in a semi arid area of Rajasthan, India

An increased nitrate (NO₃^-) concentration in groundwater has been a rising issue on a global scale in recent years. Different consumption mechanisms clearly illustrate the adverse effects on human health. The goal of this present study is to assess the natural and anthropogenic NO₃^- concentrations in groundwater in a semi arid area of Rajasthan and its related risks to human health in the different groups of ages such as children, males, and females. We have found that most of the samples (n = 90) were influenced by anthropogenic activities. The background level of NO₃^- had been estimated as 7.2 mg/L using a probabilistic approach. About 93% of nitrate samples exceeded the background limit, while 28% of the samples were beyond the permissible limit of 45 mg/L as per the BIS limits. The results show that the oral exposure of nitrate was very high as compare to dermal contact. With regard to the non-carcinogenic health risk, the total Hazard Index (HI_Total) values of groundwater nitrate were an average of 0.895 for males, 1.058 for females, and 1.214 for children. The nitrate health risk assessment shows that about 38%, 46%, and 49% of the samples constitute the non-carcinogenic health risk to males, females, and children, respectively. Children were found to be more prone to health risks due to the potential exposure to groundwater nitrate.

Groundwater hydro-geochemistry, quality, microbiology and human health risk assessment in semi-arid area of Rajasthan, India: a chemometric approach

The present investigation focused on groundwater hydro-geochemistry of Alsisar block of Jhunjhunu district, India, aims on evaluating the quality of groundwater for drinking and irrigation purposes and assessing the human health risk from ingestion of groundwater. The groundwater of Alsisar block is neutral to alkaline, brackish and very hard in nature. Total dissolved solids, total hardness, Na⁺, Mg²⁺, HCO₃^-, F^- and NO₃^- in majority of the groundwater samples were exceeding the World Health Organization and Bureau of Indian Standards recommended limits. The drinking water quality index ranged from 111.53 to 492.84. None of the sample belonged to excellent and good categories of drinking water quality. Fluoride varied from 0.018 to 4.176 mg L^-1, and nitrate varied from 0.34 to 520.66 mg L^-1 in groundwater. The non-carcinogenic risk assessment for children, men and women owing to ingestion of fluoride and nitrate-enriched groundwater indicates human health risks in the entire study area. Irrigation with groundwater of Alsisar block is liable to cause salinity and magnesium hazard to agricultural crops grown in the area. Source apportionment using principal component analysis suggests the geogenic origin of fluoride and anthropogenic origin of nitrate. Na⁺-Mg²⁺-Cl^- followed by Na⁺-Mg²⁺-HCO₃^- are the predominant hydrochemical facies in the groundwater of Alsisar block. Silicate rock weathering, ion exchange and evaporation are the predominating processes governing ionic concentrations in the groundwater. Biochemical and molecular tests demonstrated the presence of Brevibacillus borstelensis strain DSM 6347 16s rRNA and Bacillus paramycoides strain MCCC 1A04098 16s rRNA in the groundwater of the area.

Exposure and health risk assessment of nitrate contamination in groundwater in Coimbatore and Tirupur districts in Tamil Nadu, South India

Anthropogenic factors are contaminating crystalline aquifers more rapidly than natural sources and affecting human health in many states in India. Since a large population depends on untreated groundwater, identifying the sources of this contamination and assessing the related human health risk are essential to ensure a good-quality water supply. Nitrate is one of the most widespread means of groundwater contamination in many parts of India. Coimbatore and Tirupur districts are the most rapidly growing industrial urban areas in southern India. This paper deals with nitrate contamination and possible health risks for children and adults in the Coimbatore and Tirupur districts based on 93 groundwater samples. To achieve this goal, classical hydrochemical and deterministic hazard identification methods coupled with spatial mapping technologies were applied. A wide variation in nitrate concentration, between 1 and 415 mg/L, was observed, with 37% of the samples exceeding the WHO permissible limit of 50 mg/L. The distinct concentrations of nitrate and other ions observed spatially can be attributed to the diverse geochemical and land use settings in the study area. The bivariate plots of NO3 with other ions suggested that the principal origin of nitrate in this study is related to the excess application of fertilizers and sewages. The spatial variation of NO3, in comparison with the land use map, confirmed these results. The values of hazard quotient (HQ) via ingestion exceeded the critical value, one in 40% in males, 42% in females, and 45% in children. However, HQ values via oral pathways are within one and pose no exposure risk. Thus, the hazard index corresponds to HQingestion only. The health risk was in the increasing order of male>female>children, and shows that body weight is the most critical factor that is influencing the health impact to children as compared to adults. The spatial variation of hazard index values showed that groundwater quality is highly polluted with NO3 in the north and northeastern parts of the study area, mainly due to intensive agricultural practices, and poses critical health concerns. Considering the increasing population and higher dependencies on groundwater, immediate and sufficient measures are proposed.

Potential risk assessment of groundwater to address the agricultural and domestic challenges in Ordos Basin

The safety of groundwater has been a great concern for irrigation and drinking purposes in recent decades due to the increasing impacts of anthropogenic activities. There are several standards to evaluate the groundwater quality for different utilization purposes. In this paper, 804 samples covering the entire Ordos Basin across five provinces were used to evaluate the irrigation suitability and human health risks. The results showed that the sequence of cationic concentration was Na⁺ > Ca²⁺ > Mg²⁺ > K⁺ > NH₄ ⁺, and the anion concentration was HCO₃ ^- > SO₄ ^2- > Cl^- > NO₃ ^- > F^- > NO₂ ^-. For drinking purposes, TDS, Na⁺, SO₄ ^2-, F^-, TH and NO₃ ^- exceed seriously the regulated standard in the study area. For irrigating purposes, 80% of the water in the study area belongs to "good water" according to the evaluation of salinity and alkalinity. Saline water which is not suitable for irrigation accounts for about 9%. High health risks of fluoride ions are mainly observed to the samples representing the western part of the study area, while the health risks of nitrates spread throughout the study area. Health risk is not only related to location, but also varies with age, and it is found that children suffer more threats than adults.

Appraisal of Groundwater Quality with Human Health Risk Assessment in Parts of Indo-Gangetic Alluvial Plain, North India

Groundwater contamination in the Indo-Gangetic alluvial plain has reportedly been affected by various factors, such as mineral dissolution, overexploitation, precipitation, and ion exchange. This study was designed to interpret the hydrochemical fluctuations in the groundwater sources of a rural area in Raebareli district. Groundwater is slightly alkaline and affected by the issues of fluoride, salinity, hardness, and nitrate. The Pollution Index of Groundwater significantly categorize 57% and 79% of the samples under the "insignificant pollution" category during pre-monsoon and post-monsoon periods. The Health risk assessment indicated the high susceptibility of children toward health risks. It also indicated that fluoride had greater impact than nitrate in the study area. The multivariate statistical analysis indicates that anthropogenic activities, such as agricultural practices, including excessive fertilizer application and improper domestic and cattle waste management, are probable causes of groundwater contamination through NO₃^-, Cl^-, Na⁺, and K⁺. Furthermore, the base exchange index classified 71.43% samples in pre-monsoon and 78.57% in post-monsoon as Na-HCO₃ type. The meteoric genesis index suggested that 78.57% and 85.71% of the samples belong to shallow meteoric water percolation type during pre- and post-monsoon periods, respectively. The Piper plots revealed that HCO₃-Ca·Mg and SO₄·Cl-Na + K type are the prominent facies in the area, with dominance of alkalis and weak acids. According to Gibbs plot, majority of the samples fall under "rock dominance" suggesting that "rock-water" interaction was the dominant natural process controlling the groundwater chemistry.

Groundwater quality and non-carcinogenic health risk assessment of nitrate in the semi-arid region of Punjab, India

Groundwater is the main source of water in the study area (Rupnagar District, Punjab), and its quality is essential since it is the primary determinant of the suitability of groundwater for drinking and irrigation purposes. In this study, data from 28 years have been used to evaluate the adequacy of groundwater for domestic and irrigation purposes and assess the potential human health impacts of nitrate contaminants. Results of sodium adsorption ratio, percentage sodium, magnesium hazard ratio, Kelley ratio, and residual sodium carbonate illustrate that most of the sampling locations were suitable for irrigational purposes and drinking water quality of the region mostly belonged to the 'good' class. The maximum nitrate concentration was observed in the northern and north-east parts of the area. Among the three age groups, children > female > male was found to be more prone to health risks with oral ingestion of nitrate. Uncertainties in the risk estimates were quantified using Monte Carlo simulation and sensitivity analyses. Thus, a proper management plan should be adopted by the decision-makers to improve the quality of drinking water in this area to avoid major health problems in the near future.

Drinking-water nitrate and cancer risk: A systematic review and meta-analysis

BACKGROUND

Nitrate is an inorganic compound that occurs naturally in all surface and groundwater, although higher concentrations tend to occur only where fertilizers are used on the land. The regulatory limit for nitrate in public drinking water supplies was set to protect against infant methemoglobinemia, but other health effects were not considered. Risk of specific cancers and congenital disabilities may be increased when the nitrate is ingested, and nitrate is reduced to nitrite, which can react with amines and amides by nitrosation to form N-nitroso compounds which are known animal carcinogens. This study aims to evaluate the association between nitrate ingested through drinking water and the risk of developing cancers in humans.

METHODS

We performed a systematic review following PRISMA and MOOSE guidelines. A literature search was performed using PubMed, EMBASE, the Cochrane Library databases, Web of Science and Google Scholars in the time-frame from their inception to January 2020, for potentially eligible publications. STATA version 12.0 was used to conduct meta-regression and a two-stage meta-analysis.

RESULTS

A total of 48 articles with 13 different cancer sites were used for analysis. The meta-regression analysis showed stomach cancer had an association with the median dosage of nitrate from drinking water (t = 3.98, p = 0.0001, and adjusted R-squared = 50.61%), other types of cancers didn't show any association. The first stage of meta-analysis showed there was an association only between the risk of brain cancer & glioma (OR = 1.15, 95% CI: 1.06, 1.24) and colon cancer (OR = 1.11, 95% CI: 1.04, 1.17) and nitrate consumption in the analysis comparing the highest ORs versus the lowest. The 2^nd stage showed there was an association only between the risk colon cancer (OR = 1.14, 95% CI: 1.04, 1.23) and nitrate consumption in the analysis comparing all combined higher ORs versus the lowest.

CONCLUSION

This study showed that there is an association between the intake of nitrate from drinking water and a type of cancer in humans. The effective way of controlling nitrate concentrations in drinking water is the prevention of contamination (water pollution). Further research work on this topic is needed.

Distinct functional microbial communities mediating the heterotrophic denitrification in response to the excessive Fe(II) stress in groundwater under wheat-rice stone and rock phosphate amendments

Denitrifying microbial community can be utilized for eliminating nitrate and Fe(II) combined contamination in groundwater, while excessive amount of Fe(II) limit the process. Natural mineral can be additional substrate for the microbial growth, whereas how it influences the microbial community that mediating the denitrification coupling with Fe(II) oxidation and balancing inhibition of excessive Fe(II) on denitrification remain unclear. In the present study, we conducted a series of microcosm experiments to explore the denitrification and Fe(II) oxidation kinetic, and used RNA-based qPCR and DNA-based high-throughput sequencing to elucidate microbial diversity, co-occurrence and metabolic profiles amended by wheat-rice stone and rock phosphate. The results showed that both minerals could extensively improve and double the denitrification rates (2.0 ± 0.03 to 2.12 ± 0.13 times), decrease the nitrite accumulation and trigger the high resistance of the denitrifiers from the stress of Fe(II), whereas only wheat-rice stone with higher surface area increased the oxidation of Fe(II) (<10%). The addition of both minerals enhanced the microbial alpha-diversity, shaped the beta-diversity and co-occurrence network, and recovered the transcription of nitrate and nitrite reductase (Nar, Nap, NirS, NirK) from the Fe(II) inhibition. Accordingly, heterotroph Methyloversatilis sp., Methylotenra sp. might contribute to the denitrification under wheat-rice stone amendment, Denitratisoma sp. contribute to the denitrification for rock phosphate, and Fe oxidation was partially catalyzed by Dechloromonas sp. or abiotically by the nitrite/nitrous oxide. These findings would be helpful for better understanding the bioremediation of nitrate and Fe contaminated groundwater.

Controlling factors and mechanism of groundwater quality variation in semiarid region of South India: an approach of water quality index (WQI) and health risk assessment (HRA)

The study region comprises fractured granitic, basaltic and lateritic aquifer system constituted by Precambrian rocks. Groundwater is the primary source for drinking and household needs. Its quality is a big issue in the three aquifers, which are mostly of human health concern. Many developing regions suffer from lack of safe drinking water, thereby health problems arise in many parts of the regions, and Telangana state is one of them. For this reason, 194 groundwater samples were collected and analyzed for fluoride, nitrate, chloride and other physicochemical parameters. The concentrations of fluoride (F^-), nitrate (NO₃^-), magnesium (Mg²⁺), total dissolved solids and total hardness are above the acceptable limits for drinking purposes, prescribed by the World Health Organization. The higher concentrations of fluoride and nitrate in drinking water cause health hazards, and above 50% of the groundwater samples are not suitable for drinking purposes with respect to fluoride and nitrate. Weathering of rocks and dissolution of fluoride-bearing minerals can be a cause for higher fluoride concentrations, while anthropogenic sources are one of the major reasons for higher nitrate concentrations in the study area. Groundwater suitability for irrigation suggests that more than 90% of the groundwater sampling locations are suitable for irrigation. In addition, health risk assessments were evaluated by using the United States Environmental Protection Agency model, to determine the non-carcinogenic risk of fluoride and nitrate in drinking water for adults (females and males) and children. The ranges of hazard index in all sampling locations are varied from 0.133 to 8.870 for males, 0.146 to 10.293 for females and 0.419 to 29.487 for children, respectively. The health risk assessment results indicated that children were more exposed to health risk, due to the intake of high contaminated drinking water with respective of nitrate and fluoride in the study region.

Assessment of denitrification potential for coastal and inland sites using groundwater and soil analysis: the multivariate approach

In an effort to determine the reason behind excellent nitrate remediation capacity at Kelantan region, a multivariate approach is employed to evaluate extent to which the influence of sea on soil geochemical composition affect variation pattern of groundwater quality. The results obtained from geochemical analysis of paleo-beach soil in coastal site at Bachok revealed multiple redox activity at different soil strata, involving both heterotrophic and autotrophic denitrification. In soil and water analysis, eight of the fourteen hydro-geochemical parameters (conductivity, temperature, soil texture, oxidation reduction potential, pH, total organic carbon, Fe, Cu, Mn, Cl^-, SO₄^2-, NO₂^-, NO₃^- and PO₄^3-) measured using standard procedures were subjected to multivariate analysis. Evaluation of general variation pattern across the area reveals that the principal component analysis (PCA), hierarchical cluster analysis (HCA) and linear discriminant analysis (LDA) are in consonance with one another on apportioning three parameters (SO₄^2-, Cl^- and conductivity) to the coastal sites and two parameters (Fe and NH₄⁺ or NO₃^-) to inland sites. The step forward analysis of LDA reveals four parameters in order of decreasing significance as Cl^-, Fe and SO₄^2-, while the two-way HCA identifies three clusters on location basis, respectively. In addition to the significant data reduction obtained, the results indicate that proximity to sea and location/geological-based influence are more significant than temporal-based influence in denitrification. By extension, the research reveals that influence of labile portion of natural resources is explorable for broader application in other remediation strategies.

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.

Multi-scaled response of groundwater nitrate contamination to integrated anthropogenic activities in a rapidly urbanizing agricultural catchment

Anthropogenic activities have a significant contribution to groundwater nitrate contamination at multiple spatial scales in urbanizing agricultural catchments, while how to derive the optimal researching scale and explore the relative importance among anthropogenic activities for groundwater nitrate contamination still remains challenging. In this study, 165 perched groundwater and 120 shallow groundwater samples were collected in two urbanizing agricultural catchments, to explore anthropogenic activity effects on groundwater nitrate contamination crossing multiple spatial scales, integrating the probability kriging, multi-scale comparison at spatial scales of 100 to 1900 m with an increment of 200 m at the block scales, and variance partitioning analysis. Probability of perched and shallow groundwater nitrate concentration > 3 mg L^-1 exhibited strong spatial autocorrelation, with effective ranges of 1091 m and 3743 m from semivariogram, respectively. Relationships between perched and shallow groundwater nitrate concentrations were more significant and robust (r = 0.30-0.52, p < 0.001) at the block scale from 300 to 1100 m, indicating that perched groundwater nitrate closely related to shallow groundwater nitrate. The responses of groundwater nitrate contamination on anthropogenic drivers presented strongly scaling correlation and had the highest correlation at the spatial scale of 1100 m, suggesting the optimal scale for exploring anthropogenic activity effects on groundwater nitrate contamination. The three categories of anthropogenic drivers (urbanization, agriculture intensification, and demographic driver) contributed to 31.0-84.0% part of the total variations in groundwater nitrate contamination at the spatial scale of 1100 m. Particularly, agriculture intensification was the most influential driver for groundwater nitrate contamination, while the urbanizing process and population growth played important roles surrounding urban cores. Our findings highlighted the importance of incorporating multi-scale comparisons on regional groundwater quality evaluation, and provided technical support to the groundwater resource management strategy development in urbanizing agricultural regions.

Impacts of Emerging Agricultural Practices on Groundwater Quality in Kahe Catchment, Tanzania

This paper assesses the impacts of farmers’ intensive use of agrochemicals (fertilizers and pesticides) on groundwater quality in the Kahe catchment. Samples were collected during the wet and dry seasons of the year 2018 and analyzed for the presence of agrochemicals in the water. Groundwater chemistry was dominated by magnesium-sodium-bicarbonate (Mg-Na-HCO3−). The cations levels were in the trend of Mg2+ >Na+ > Ca2+ > K+, whereas anions were HCO3− > Cl− > SO42− for both seasons. The NO3− had an average value of about 18.40 ± 4.04 and 7.6 ± 1.7 mg/L in the wet and dry season, respectively. Elevated levels of nitrate, sulfate, phosphate, and ammonium were found in water samples collected near the large-scale sugarcane plantation in the catchment. For both seasons, Pb, Cd, Fe, Mn, Zn and Cu concentrations averaged approximately 0.08 ± 0.03, 0.11 ± 0.03, 0.16 ± 0.02, 0.11 ± 0.01, 0.46 ± 0.05, and 0.55 ± 0.02 mg/L, respectively. On the other hand, the concentrations were higher in shallow wells than in the deep boreholes. Pesticides’ residues were below the detection limit in all sampled groundwater. The findings from this study provide important information for intervention in groundwater quality management in Kahe Catchment, Tanzania.

Predicting uncertainty of machine learning models for modelling nitrate pollution of groundwater using quantile regression and UNEEC methods

Although estimating the uncertainty of models used for modelling nitrate contamination of groundwater is essential in groundwater management, it has been generally ignored. This issue motivates this research to explore the predictive uncertainty of machine-learning (ML) models in this field of study using two different residuals uncertainty methods: quantile regression (QR) and uncertainty estimation based on local errors and clustering (UNEEC). Prediction-interval coverage probability (PICP), the most important of the statistical measures of uncertainty, was used to evaluate uncertainty. Additionally, three state-of-the-art ML models including support vector machine (SVM), random forest (RF), and k-nearest neighbor (kNN) were selected to spatially model groundwater nitrate concentrations. The models were calibrated with nitrate concentrations from 80 wells (70% of the data) and then validated with nitrate concentrations from 34 wells (30% of the data). Both uncertainty and predictive performance criteria should be considered when comparing and selecting the best model. Results highlight that the kNN model is the best model because not only did it have the lowest uncertainty based on the PICP statistic in both the QR (0.94) and the UNEEC (in all clusters, 0.85-0.91) methods, but it also had predictive performance statistics (RMSE = 10.63, R² = 0.71) that were relatively similar to RF (RMSE = 10.41, R² = 0.72) and higher than SVM (RMSE = 13.28, R² = 0.58). Determining the uncertainty of ML models used for spatially modelling groundwater-nitrate pollution enables managers to achieve better risk-based decision making and consequently increases the reliability and credibility of groundwater-nitrate predictions.

Co-occurrence of geogenic and anthropogenic contaminants in groundwater from Rajasthan, India

Northwest India suffers from severe water scarcity issues due to a combination of over-exploitation and climate effects. Along with concerns over water availability, endemic water quality issues are critical and affect the usability of available water and potential human health risks. Here we present data from 243 groundwater wells, representing nine aquifer lithologies in 4 climate regions that were collected from the Northwestern Indian state of Rajasthan. Rajasthan is India's largest state by area, and has a significant groundwater reliant population due to a general lack of surface water accessibility. We show that the groundwater, including water that is used for drinking without any treatment, contains multiple inorganic contaminants in levels that exceed both Indian and World Health Organization (WHO) drinking water guidelines. The most egregious of these violations were for fluoride, nitrate, and uranium; 76% of all water samples in this study had contaminants levels that exceed the WHO guidelines for at least one of these species. In addition, we show that much of the groundwater contains high concentrations of dissolved organic carbon (DOC) and halides, both of which are risk factors for the formation of disinfectant byproducts in waters that are treated with chemical disinfectants such as chlorine. By using geochemical and isotopic (oxygen, hydrogen, carbon, strontium, and boron isotopes) data, we show that the water quality issues derive from both geogenic (evapotranspiration, water-rock interactions) and anthropogenic (agriculture, domestic sewage) sources, though in some cases anthropogenic activities, such as infiltration of organic- and nitrate-rich water, may contribute to the persistence and enhanced mobilization of geogenic contaminants. The processes affecting Rajasthan's groundwater quality are common in many other worldwide arid areas, and the lessons learned from evaluation of the mechanisms that affect the groundwater quality are universal and should be applied for other parts of the world.

Fe-exchanged nano-bentonite outperforms Fe3O4 nanoparticles in removing nitrate and bicarbonate from wastewater

Nitrate (NO₃^-) and bicarbonate (HCO₃^-) are harmful for the water quality and can potentially create negative impacts to aquatic organisms, crops and humans. This study deals with the removal of NO₃^- and HCO₃^- from contaminated wastewater using Fe-exchanged nano-bentonite and Fe₃O₄ nanoparticles. X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, surface area measurement and particle size analysis revealed that the adsorbents fall under the nano-scale size range with high specific surface area, and Fe was successfully exchanged in the nano-bentonite clay. The kinetics of adsorption was well defined by pseudo-first order and pseudo-second order kinetic models for both NO₃^- and HCO₃^-. The Fe-exchanged nano-bentonite was a better performing adsorbent of the oxyanions than Fe₃O₄ nanoparticles. According to the Sips isothermal model, the Fe-exchanged nano-bentonite exhibited the highest NO₃^- and HCO₃^- adsorption potential of 64.76 mg g^-1 and 9.73 meq g^-1, respectively, while the respective values for Fe₃O₄ nanoparticles were 49.90 mg g^-1 and 3.07 meq g^-1. Thus, inexpensiveness and easy preparation process of Fe-exchanged nano-bentonite make it attractive for NO₃^- and HCO₃^- removal from contaminated wastewater with significant environmental and economic benefits.

Hydrogeochemical Characteristics and Quality Assessment of Groundwater in an Irrigated Region, Northwest China

Groundwater is one of the most important sources of water for drinking and irrigation in arid and semi-arid regions of the world. In this study, 50 groundwater samples were collected and analyzed for various chemical constituents (pH, TDS, Na+, K+, Ca2+, Mg2+, SO42−, Cl−, HCO3−, NO3−, and F−) to identify the hydrogeochemical characteristics, and to evaluate its suitability for drinking and irrigation uses in Zhongning area of Northwest China. Results showed that groundwater was slightly alkaline in nature. Fluoride and nitrate concentrations in the groundwater of the study region were much higher than its prescribed limits for drinking purposes. A factor analysis (FA) was implemented to understand the contamination source of groundwater in the region, and the results indicated that rock–water interaction, geogenic, and human-induced contamination were the major factors influencing groundwater chemistry. An entropy-weighted water quality index (EWQI) was employed to evaluate the water quality for drinking purpose. Mg2+, Ca2+, SO42-, HCO3−, and TDS played the leading roles in influencing the groundwater quality with high weights. Forty-eight percent of groundwater samples were unfit for drinking purpose in the study area, due to poor quality. Elevated concentrations of SO42−, Cl− and NO3−-N in groundwater caused poor quality and extremely poor quality water, which may be attributed to human activities. According to the calculation of sodium percentage (Na%), sodium adsorption ration (SAR), and permeability index (PI), the majority of the groundwater samples were suitable for irrigation. However, it should be noted that 26% of the samples were unfit for irrigation because of the high salinity in the groundwater. This is mainly attributed to the intense evaporation and the intensified irrigation activities in the region. The findings in this study contribute to a better understanding of groundwater sustainability for supporting water management and protection in the future.

Nitrate in drinking water and vegetables: intake and risk assessment in rural and urban areas of Nagpur and Bhandara districts of India

The study focuses on the estimation of health risk from nitrate present in the drinking water and vegetables in Nagpur and Bhandara districts in the state of Maharashtra, India. Drinking water samples from 77 locations from the rural as well as urban areas and 22 varieties of vegetable were collected and analyzed for the presence of nitrate for a period of 1 year (two seasons). The daily intake of nitrate from these water and vegetable samples was then computed and compared with standard acceptable intake levels to assess the associated health risk. The mean nitrate concentration of 59 drinking water samples exceeded the Bureau of Indian Standards limit of 45 mg/L in drinking water. The rural and urban areas were found to have mean nitrate concentration in drinking water as 45.69 ± 2.08 and 22.53 ± 1.97 mg/L, respectively. The estimated daily intake of drinking water samples from 55 study sites had nitrate concentration far below the safety margin indicating serious health risk. The sanitation survey conducted in 12 households reported contaminated source with positive E. coli count in 20 samples as the major factor of health risk. The average nitrate concentration was maximum in beetroot (1349.38 mg/kg) followed by spinach (1288.75 mg/kg) and amaranthus (1007.64 mg/kg). Among the samples, four varieties of the vegetables exceeded the acceptable daily intake (ADI) with an assumption of 0.5 kg consumption of vegetables for an average of a 60-kg individual. Therefore, irrigation of these locally grown vegetables should be monitored periodically for nitrogen accumulation by the crop above the ADI limit. The application of nitrogenous fertilizers should also be minimized in the rural areas to help protect the nitrate contamination in groundwater sources.

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.