Contamination of nitrate in groundwater and its potential human health: a case study of lower Mae Klong river basin, Thailand

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

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

Genomic insights of a native bacterial consortium for wheat production sustainability

The use of plant growth-promoting bacteria as bioinoculants is a powerful tool to increase crop yield and quality and to improve nitrogen use efficiency (NUE) from fertilizers in plants. This study aimed to bioprospecting a native bacterial consortium (Bacillus cabrialesii subsp. cabrialesii TE3T, Priestia megaterium TRQ8, and Bacillus paralicheniformis TRQ65), through bioinformatic analysis, and to quantify the impact of its inoculation on NUE (measured through 15N-isotopic techniques), grain yield, and grain quality of durum wheat variety CIRNO C2008 grown under three doses of urea (0, 120, and 240 kg N ha-1) during two consecutive agricultural cycles in the Yaqui Valley, Mexico. The inoculation of the bacterial consortium (BC) to the wheat crop, at a total N concentration of 123-225 kg N ha-1 increased crop productivity and maintained grain quality, resulting in a yield increase of 1.1 ton ha-1 (6.0 vs. 7.1 ton ha-1, 0 kg N ha-1 added, 123 kg N ha-1 in the soil) and of 2.0 ton ha-1 (5.9 vs. 7.9 ton ha-1, 120 kg N ha-1 added, 104 kg N ha-1 in the soil) compared to the uninoculated controls at the same doses of N. The genomic bioinformatic analysis of the studied strains showed a great number of biofertilization-related genes regarding N and Fe acquisition, P assimilation, CO2 fixation, Fe, P, and K solubilization, with important roles in agroecosystems, as well as genes related to the production of siderophores and stress response. A positive effect of the BC on NUE at the studied initial N content (123 and 104 kg N ha-1) was not observed. Nevertheless, increases of 14 % and 12.5 % on NUE (whole plant) were observed when 120 kg N ha-1 was applied compared to when wheat was fully fertilized (240 kg N ha-1). This work represents a link between bioinformatic approaches of a native bacterial inoculant and the quantification of its impact on durum wheat.

A multi-model study for understanding the contamination mechanisms, toxicity and health risks of hardness, sulfate, and nitrate in natural water resources

Several water quality contaminants have attracted the attention of numerous researchers globally, in recent times. Although the toxicity and health risk assessments of sulfate and water hardness have not received obvious attention, nitrate contamination has gained peculiar research interest globally. In the present paper, multiple data-driven indexical, graphical, and soft computational models were integrated for a detailed assessment and predictive modeling of the contamination mechanisms, toxicity, and human health risks of natural waters in Southeast Nigeria. Majority of the tested physicochemical parameters were within their satisfactory limits for drinking and other purposes. However, total hardness (TH), SO₄, and NO₃ were above stipulated limits in some locations. A nitrate health risk assessment revealed that certain areas present a chronic health risk to children, females, and males due to water intake. However, the dermal absorption route was found to have negligible health risks. SO₄ in some locations was above the 100 mg/L Nigerian limit; thus, heightening the potential health effects due to intake of the contaminated water resources. Most samples had low TH values, which exposes users to health defects. There are mixed contamination mechanisms in the area, according to graphical plots, R-mode hierarchical dendrogram, factor analysis, and stoichiometry. However, geogenic mechanisms predominate over human-related mechanisms. Based on the results, a composite diagrammatic model was developed. Furthermore, predictive radial basis function (RBF) and multiple linear regression (MLR) models accurately predicted the TH, SO₄, and NO₃, with the RBF outperforming the MLR models. Insights from the RBF and MLR models were useful in validating the results of the hierarchical dendrogram, factor, stoichiometric, and graphical analyses.

Evaluating groundwater nitrate and other physicochemical parameters of the arid and semi-arid district of DI Khan by multivariate statistical analysis

Nitrate as an important water pollutant, causing eutrophication was analyzed in Pakistan at different water sources (hand pump (HP), bore hole (BH) and tube well (TW)) to assess the contamination level caused by NO₃^-. NO₃^- concentrations in the HP water samples were 31 mg L^-1 to 59 mg L^-1, in BH 20 mg L^-1 to 79 mg L^-1 while in TW water samples it was between 29 to 55 mg L^-1. The association of NO₃^- with other selected parameter in groundwater can be determined by using statistical approaches. Different physicochemical parameters (pH, electrical conductivity (EC), temperature and dissolved oxygen (DO)) were studied in groundwater samples of the research district. The Pearson correlation coefficient (r) for groundwater characteristics were calculated. Hierarchical Cluster Analysis (HCA) was used to categorize samples based on their groundwater quality similarities and to find links between groundwater quality factors. The key relationship of the groundwater for HP samples on EC and TDS (r = 1) had a great correlation, while all other parameters correlations were lower (r = 0.40), BH's parameters on WT and WSD (r = 0.57), WT and pH (r = 0.57), EC and DO (r = 0.50), DO and TDS (0.50), EC and TDS (r = 1) had a quite high correlation, while all other parameters correlations were less than (r = 0.40), on the other hand, tube well parameters on TDS and EC (r = 1) had a perfect correlation, DO and pH (r = 0.75) parameters correlations were less than (r = 0.40).

Distinguishing and quantifying the fate of nitrate in irrigation water and nitrate produced by ammonium nitrification

When the sources of nitrogen include not only ammonium (NH₄⁺) fertilizer (ANF) but also nitrate (NO₃^-) from groundwater and rainfall (NRI), if the proportions of various types of NO₃^- are still based on the amount of ANF, the corresponding calculation method may be complicated. This paper established a water flow-nitrogen migration transformation model for the unsaturated zone in grain-planting and vegetable-planting areas, and studied the migration and transformation of NH₄⁺ and NO₃^- in the unsaturated zone when ANF and NRI coexist. This paper proposed for the first time the proportional coefficient method (PCM) and hypothetical assignment method (HAM) to distinguish and quantify the fate proportions of NO₃^- from NO₃^- produced by NH₄⁺ nitrification (NNR) and NRI. The results showed that the PCM was more practical than the HAM in quantifying the fate of NO₃^- from different sources. If only the root absorption ratio was used to evaluate the degree of nutrient supply to crops, the ratios of root absorption were as high as 40% (44.75-50.85%). NRI provided more nutrients in grain-growing areas than those in vegetable-growing areas. If the sum of the proportion of other fates was regarded as the degree of groundwater NO₃^- mitigation through irrigation in the unsaturated zone, except for the ratio of NO₃^- leaching to groundwater, the proportion of NO₃^- pollution mitigation was as high as 57.89% (57.89-92.99%), and the mitigation ability of groundwater NO₃^- pollution in grain-growing areas was higher than that in vegetable-growing areas.

Assessing the Effect of Intensive Agriculture and Sandy Soil Properties on Groundwater Contamination by Nitrate and Potential Improvement Using Olive Pomace Biomass Slag (OPBS)

The relationship between agricultural activities, soil characteristics, and groundwater quality is critical, particularly in rural areas where groundwater directly supplies local people. In this paper, three agricultural sandy soils were sampled and analyzed for physicochemical parameters such as pH, water content, bulk density, electrical conductivity (EC), organic matter (OM), cation exchange capacity (CEC), and soil grain size distribution. Major and trace elements were analyzed by inductively coupled plasma-optical emission spectrometry (ICP/OES) to determine their concentrations in the fine fraction (FF) of the soils. Afterward, the elemental composition of the soils was identified by X-ray powder diffraction (XRD) and quantified by X-ray fluorescence (XRF). The surface soil characteristics were determined by the Brunauer–Emmett–Teller (BET) method, whereas the thermal decomposition of the soils was carried out using thermogravimetric analysis and differential scanning calorimetric (TGA-DSC) measurements. The morphological characteristics were obtained by scanning electron microscopy (SEM). Afterward, column-leaching experiments were conducted to investigate the soil’s retention capacity of nitrate (NO−3). Parallelly, a chemical and physical study of olive pomace biomass slag (OPBS) residue was carried out in order to explore its potential use as a soil additive and improver in the R’mel area. The OPBS was characterized by physicochemical analysis, assessed for heavy metals toxicity, and characterized using (XRD, XRF, SEM, and BET) techniques. The results show that the R’mel soils were slightly acidic to alkaline in nature. The soils had a sandy texture with low clay and silt percentage (<5% of the total fraction), low OM content, and weak CEC. The column experiments demonstrated that the R’mel irrigated soils have a higher tendency to release large amounts of nitrate due to their texture and a higher degree of mineralization which allows water to drain quickly. The OPBS chemical characterization indicates a higher alkaline pH (12.1), higher water content (7.18%), and higher unburned carbon portion (19.97%). The trace elements were present in low concentrations in OPBS. Macronutrients in OPBS showed composition rich in Ca, K, and Mg which represent 10.59, 8.24, and 1.56%, respectively. Those nutrients were quite low in soil samples. Both XRD and XRF characterization have shown a quasi-dominance of SiO2 in soil samples revealing that quartz was the main crystalline phase dominating the R’mel soils. Oppositely, OPBS showed a reduced SiO2 percentage of 26,29% while K, Ca, and P were present in significant amounts. These results were confirmed by XRF analysis of OPBS reporting the presence of dolomite (CaMg, (CO3)2), fairchildite (K2Ca (CO3)2), and free lime (CaO). Finally, the comparison between the surface characteristic of OPBS and soils by BET and SEM indicated that OPBS has a higher surface area and pore volume compared to soils. In this context, this study suggests a potential utilization of OPBS in order to (1) increase soil fertility by the input of organic carbon and macronutrients in soil; (2) increase the water-holding capacity of soil; (3) increase soil CEC; (4) stabilize trace elements; (5) enhance the soil adsorption capacity and porosity.

Nitrate removal by combining chemical and biostimulation approaches using micro-zero valent iron and lactic acid

The occurrence of nitrate is the most significant type of pollution affecting groundwater globally, being a major contributor to the poor condition of water bodies. This pollution is related to livestock-agricultural and urban activities, and the nitrate presence in drinking water has a clear impact on human health. For example, it causes the blue child syndrome. Moreover, the high nitrate content in aquifers and surface waters significantly affects aquatic ecosystems since it is responsible for the eutrophication of surface water bodies. A treatability test was performed in the laboratory to study the decrease of nitrate in the capture zone of water supply wells. For this purpose, two boreholes were drilled from which groundwater and sediments were collected to conduct the test. The goal was to demonstrate that nitrate in groundwater can be decreased much more efficiently using combined abiotic and biotic methods with micro-zero valent iron and biostimulation with lactic acid, respectively, than when both strategies are used separately. The broader implications of this goal derive from the fact that the separate use of these reagents decreases the efficiency of nitrate removal. Thus, while nitrate is removed using micro-valent iron, high concentrations of harmful ammonium are also generated. Furthermore, biostimulation alone leads to overgrowth of other microorganisms that do not result in denitrification, therefore complete denitrification requires more time to occur. In contrast, the combined strategy couples abiotic denitrification of nitrate with biostimulation of microorganisms capable of biotically transforming the abiotically generated harmful ammonium. The treatability test shows that the remediation strategy combining in situ chemical reduction using micro-zero valent iron and biostimulation with lactic acid could be a viable strategy for the creation of a reactive zone around supply wells located in regions where groundwater and porewater in low permeability layers are affected by diffuse nitrate contamination.

Environmental and Health Risks Posed by Heavy Metal Contamination of Groundwater in the Sunan Coal Mine, China

Groundwater is often used for domestic and irrigation purposes, even in mining areas. Mine drainage, rainfall, and infiltration cause heavy metal enrichment, adversely affecting the groundwater and harming human health. In this study, water samples (October 2021) in the Suzhou southern coal mining area were analyzed for the heavy metals As, Cr, Cu, Fe, Mn, Pb, and Zn to determine potential effects of heavy metal contamination on environmental quality and human health. It was found that 22% and 31% of the sampling sites had “excellent” and “good” water quality, respectively. Excessive concentrations of Fe and Mn were detected in 47% and 72% of the samples, respectively. The non-carcinogenic health risk values of As, Cr, Cu, Fe, Mn, Pb, and Zn were below the negligible levels of health risk set by various environmental agencies. Content ranking was as follows: Fe > Mn > Cr > Cu > Pb > Zn > As, with Fe accounting for 43%. All sampling points exceeded the maximum acceptable level of Cr recommended by the agencies. Chromium, the major carcinogenic factor in the study area, contributed to 95.45% of the total health risk. Therefore, the authorities in this region must closely monitor three heavy metal elements—Fe, Mn, and Cr.

Consumption of water contaminated by nitrate and its deleterious effects on the human thyroid gland: a review and update

Nowadays, the nitrates have been established as carcinogenic components due to the endogenous formation of N-nitroso compounds, however, the consumption of water contaminated with nitrates has only been strongly related to the presence of methemoglobinemia in infants, as an acute effect, leaving out other side effects that demand attention. The thyroid gland takes relevance because it can be altered by many pollutants known as endocrine disruptors, which are agents capable of interfering with the synthesis of hormones, thus far, it is known that nitrates may disrupt the amount of iodine uptake causing most of the time hypothyroidism and affecting the metabolic functions of the organism in all development stages, resulting in an important health burden for the exposed population. Here, this review and update highlighted the impact of consumption of water contaminated with nitrates and effects on the thyroid gland in humans, concluding that nitrates could act as true endocrine disruptor.

Subclinical Hypothyroidism in Families Due to Chronic Consumption of Nitrate-Contaminated Water in Rural Areas with Intensive Livestock and Agricultural Practices in Durango, Mexico

Nitrate is a widely disseminated water pollutant and has been linked to health disorders, including hypothyroidism. Here, we evaluated the relationship between thyroid function and chronic exposure to nitrates in rural zone families, in addition to the genetic and autoimmune factors. Exposure and effect biomarkers, thyroid hormones, and autoantibodies of tiroperoxidase were measured, as well the presence of two FOXE1 polymorphisms (rs965513, rs1867277). Pearson’s correlation, principal component analysis, Kruskal–Wallis, and chi-squared tests were used for statistical analysis. A total of 102 individuals were analyzed; 45% presented subclinical hypothyroidism, a negative correlation was observed between methemoglobin and the total T3 (r = −0.43, p = 0.001) and free T3 levels (r = −0.34, p = 0.001), as well as between TSH and the free T4 (r = −0.41, p = 0.0001) and total T4 (r = −0.36, p = 0.0001). A total of 15.7% had positive antithyroid ab-TPO, while the polymorphic genotype (AA) represented only 3% (rs965513) and 4% (rs1867277) among subjects with subclinical hypothyroidism. The high frequency of subclinical hypothyroidism in the population under study could be related, mainly, to chronic exposure through the consumption of nitrate-contaminated water.

Comparative health risk assessment of nitrate in drinking groundwater resources of urban and rural regions (Isfahan, Iran), using GIS

Infantile methemoglobinemia, thyroid disorders, and probably some carcinogenic effects are health concerns associated with dietary nitrate. Isfahan province has a dry and semi-arid desert climate such that the main source of various applications in this province is groundwater resources. This study evaluated spatial analysis of the groundwater NO3- concentrations and its possible health risk to residents. Method 8171 Hach was used for nitrate measurement of 1319 groundwater samples from March 2018 to February 2019. Non-carcinogenic risk due to NO3- exposure through consumption of drinking water was assessed, and the associated zoning maps were presented using geographic information system (GIS). Nitrate concentrations in the rural and urban areas were within 0.4-137 mg/L NO3- and 2.9-209 mg/L NO3-, respectively. Also, 226 (25%) and 104 (24%) of samples in the rural and urban areas, respectively, were detected above the Iran and WHO guideline NO3- values of 50 mg/L. The highest levels of NO3-, which were found in the western and central groundwater resources, occurred in the agricultural and residential areas. The NO3- concentrations were higher in urban than rural areas in the many studied counties. Also, nitrate was higher in wet seasons than in dry ones. Infants' non-carcinogenic risks were higher than the other groups. Infants (HQ > 1) were the most vulnerable group compared with the other groups in some counties. Thus, there are potential risks of methemoglobinemia, especially for infants. It is critical to adopt specific strategies to reduce the nitrate concentration in the studied groundwater.

Interactions of microalgae-bacteria consortia for nutrient removal from wastewater: A review

Nitrogen and phosphorus pollution can cause eutrophication, resulting in ecosystem disruption. Wastewater treatment systems employing microalgae-bacteria consortia have the potential to enhance the nutrient removal efficiency from wastewater through mutual interaction and synergetic effects. The knowledge and control of the mechanisms involved in microalgae-bacteria interaction could improve the system's ability to transform and recover nutrients. In this review, a critical evaluation of recent literature was carried out to synthesize knowledge related to mechanisms of interaction between microalgae and bacteria consortia for nutrient removal from wastewater. It is now established that microalgae can produce oxygen through photosynthesis for bacteria and, in turn, bacteria supply the required metabolites and inorganic carbon source for algae growth. Here we highlight how the interaction between microalgae and bacteria is highly dependent on the nitrogen species in the wastewater. When the nitrogen source is ammonium, the generated oxygen by microalgae has a positive influence on nitrifying bacteria. When the nitrogen source is nitrate, the oxygen can have an inhibitory effect on denitrifying bacteria. However, some strains of microalgae have the capability to supply hydrogen gas for hydrogenotrophic denitrifiers as an energy source. Recent literature on biogranulation of microalgae and bacteria and its application for nutrient removal and biomass recovery is also discussed as a promising approach. Significant research challenges remain for the integration of microalgae-bacteria consortia into wastewater treatment processes including microbial community control and process stability over long time horizons.

Influence of regional climatic on the hydrogeochemistry of a tropical river basin-a study from the Walawe river basin of Sri Lanka

The Walawe river basin is one of the important watersheds in Sri Lanka subjected to water scarcity due to intensive exploitation for irrigation and domestic purposes. The groundwater resource in the basin is under-explored for its capacity to sustain a continuous supply of water for future demand while facing the growing climate change challenges. The objective of this study was to identify the behavior of groundwater in the Walawe river basin that flows through two major climatic zones in Sri Lanka. The study approach includes hydrogeochemical and stable isotope analysis in order to differentiate the geochemical evolution of groundwater in the basin with respect to climatic factors. Water samples from thirty-eight (38) deep wells (> 20 m), 25 shallow wells, and 14 surface water bodies were collected and measured for their major ions, and isotope ratios of δ²H and δ¹⁸O. The results indicated a clear difference in the geochemistry of groundwater between the two climatic zones of the basin. The dry zone area was characterized by a higher content of dissolved minerals as compared to that in the wet zone area. Silicate weathering, calcite dissolution, and ion exchange processes were found to be the main control of groundwater geochemistry in the basin. The Ca-HCO₃-type water was found to be the predominant water type. The isotope data suggested that the groundwater in the study area is recharged mainly from the northeast monsoon rain. Isotope characteristics also suggested that direct infiltration is prominent in the wet zone regions, whereas modifications of shallow groundwater by evaporation were dominated in the dry zone areas. The findings of the study suggest that water quality management in the dry zone areas of the basin is critical for the future sustainability of the water resource of the basin.

Groundwater quality evolution based on geochemical modeling and aptness testing for ingestion using entropy water quality and total hazard indexes in an urban-industrial area (Tiruppur) of Southern India

This study used geochemical modeling to understand the chemical evolution of groundwater, entropy water quality index to assess the aptness of groundwater for human consumption, and total hazard index to determine the possible non-carcinogenic risks among children, women, and men in an urban-industrial area (Tiruppur region) of southern India. For the above purposes, 40 groundwater samples were collected from tube and dug wells, and they were tested for various physicochemical parameters. Fluoride and nitrate levels ranged from 0.10 to 2.70 mg/l and 10 to 290 mg/l, respectively. Nearly, 50% of the fluoride samples and 58% of the nitrate samples exceeded the WHO limits of 1.5 and 45 mg/l, respectively. The majority of the groundwater samples (22.5%) represented Ca²⁺-Na⁺-Cl^- water type while the remaining samples exhibited mixed water types. Approximately, 85% of the samples indicated high levels of salinization since they had Revelle index > 0.5 meq/l. The saturation index (SI) revealed that mineral weathering; dissolution of halite, gypsum, and anhydrite; and precipitation of calcite and dolomite contributed to groundwater chemistry. Based on the entropy water quality index (EWQI), none of the groundwater samples was characterized as excellent or good water quality while 57.5% of the samples had medium water quality, and 32.5% and 10% of the samples exhibited poor and extremely poor water qualities, respectively. The last two categories are designated as unfit for consumption. The cumulative health risk (nitrate and fluoride together) ranged from 0.97 to 11.16 for children, 0.60 to 10.54 for women, and 0.39 to 6.92 for men. These values represent health risks among 88%, 80%, and 73% of the groundwater samples for children, women, and men, respectively. Therefore, proper measures should to be done to reduce the health risks associated with high nitrate and fluoride in the groundwater of the study area, which is used for drinking purposes.

Human health risks associated with multipath exposure of groundwater nitrate and environmental friendly actions for quality improvement and sustainable management: A case study from Texvalley (Tiruppur region) of India

The present research was attempted to examine the human health risks due to nitrate contamination in the groundwater of Texvalley (Tiruppur region) of southern India. Groundwater samples (n = 40) were picked up from open wells (shallow aquifer) and tube wells (deep aquifer) during January 2020, and laboratory examination was conducted for various major physicochemical constituents. Nitrate concentration varied from 10 to 290 mg/l with a mean of 83.45 mg/l. About 58% (n = 23) of the wells exceeded the recommended limit (>45 mg/l) of World Health Organisation, which spread over an area of 335.16 km². Among this, 45% of the samples (n = 18) represented shallow aquifers (depth < 15 m), and 13% of them (n = 5) represented deep aquifers (depth > 15 m). Synthetic fertilizers, cow dung and sheep manure, industrial discharge, septic tank leakage and municipal solid waste disposal are the major sources of nitrate pollution in this region. The USEPA health risk assessment model was applied in this study to assess hazard quotients (HQ) according to the NO₃^- exposure in various age groups of inhabitants through two different pathways such as drinking (HQ_oral) and skin contact (HQ_dermal). Eventually, total hazard index (THI) was obtained for all the groundwater samples for different age groups. According to THI, 87%, 78%, 66%, 60%, 56% and 48% of the samples contain health risks (THI >1) for infants, kids, children, teens, adults and aged people, respectively. The study finally recommended seven environmental friendly actions for the groundwater quality improvements and for the sustainable health management.

Impact of land use on shallow groundwater quality characteristics associated with human health risks in a typical agricultural area in Central China

Groundwater pollution seriously threatens water resource safety due to high-intensity land use throughout the world. However, the relationship between groundwater pollution characteristics and land use in alluvial plains is still unclear. In this study, the effects of land use on shallow groundwater quality and human health risk were investigated via two sampling campaigns in a typical alluvial plain, namely, Jianghan Plain, China. Results show that the shallow groundwater in this area was polluted by nitrogen (with average concentrations of 5.12 mg/L in the dry season and 4.46 mg/L in the rainy season) and phosphorus (0.29 and 0.13 mg/L in the two seasons, respectively). The nutrient concentrations during the dry season were significantly higher than those during the rainy season (p < 0.05). Correlation analysis indicated that the concentration of nutrients was significantly positively correlated with cultivated land and negatively correlated with water and residence, suggesting that land use patterns can affect the groundwater quality. The best buffer where land use patterns affect the total N concentration was about 1000 m for cultivated land and water, while the optimal ranges for ammonium N were about 1000 and 2500 m for the areas, respectively. For the total phosphorus, a radius of 2000 m leads to the best fitting effect on both areas. Human health risk assessment showed that the total health risk indexes in about 75% of the samples were higher than 1, indicating the potential risk of the shallow groundwater in this area to human health. The results indicate that land use patterns will greatly affect the shallow groundwater quality. Thus, adjusting the land use pattern can improve the water quality and reduce health risks. Identification and selection of appropriate management solutions for the groundwater protection should be based on not only water quality problems but also surface land use patterns.

Hydrogeological and Hydrochemical Regime Evaluation in Flamouria Basin in Edessa (Northern Greece)

Groundwater quality deterioration and overexploitation constitute two critical environmental issues worldwide. In this study, with the aim to achieve a groundwater sustainability purpose, a preliminary hydrogeochemical survey is conducted in the Flamouria basin, Pella prefecture, Northern Greece using available and collected data. For this purpose, chemical analyses of groundwater, springs, and surface water were collected and analyzed with three electrical resistivity tomographies (ERTs). A Groundwater Quality Index (GQI), along with a nitrate susceptibility assessment is applied within the porous aquifer. The water quality analysis along with GQI application showed excellent water quality for potable and irrigation use however highlighted future issue for irrigation utilization as the high alkalinity and total dissolved solid (TDS)could generate excessive soil salinization. Moreover, the application of a methodology for the identification of “Nitrate Vulnerable Zone” called the Protection from Natural and Anthropogenic sources (PNA) highlighted the natural susceptibility to nitrate pollution of the porous aquifer, especially in the central part of the area where most agricultural activity is localized. The work further confirmed how the proposed elaboration could represent an easy and widely applicable hydrological assessment where there is also limited data available.

Applying Membrane Distillation for the Recovery of Nitrate from Saline Water Using PVDF Membranes Modified as Superhydrophobic Membranes

In this study, a flat sheet direct contact membrane distillation (DCMD) module was designed to eliminate nitrate from water. A polyvinylidene fluoride (PVDF) membrane was used in a DCMD process at an ambient pressure and at a temperature lower than the boiling point of water. The electrical conductivity of the feed containing nitrate increased, while the electrical conductivity of the permeate remained constant during the entire process. The results indicated that the nitrate ions failed to pass through the membrane and their concentration in the feed increased as pure water passed through the membrane. Consequently, the membrane was modified using TiO₂ nanoparticles to make a hierarchical surface with multi-layer roughness on the micro/nanoscales. Furthermore, 1H,1H,2H,2H-Perfluorododecyltrichlorosilane (FTCS) was added to the modified surface to change its hydrophobic properties into superhydrophobic properties and to improve its performance. The results for both membranes were compared and reported on a pilot scale using MATLAB. In the experimental scale (a membrane surface area of 0.0014 m², temperature of 77 °C, nitrate concentration of 0.9 g/Kg, and flow rate of 0.0032 Kg/s), the flux was 2.3 Kgm⁻²h⁻¹. The simulation results of MATLAB using these data showed that for the removal of nitrate (with a concentration of 35 g/Kg) from the intake feed with a flow rate of 1 Kg/s and flux of 0.96 Kgm⁻²h⁻¹, a membrane surface area of 0.5 m² was needed.

Assessment of the Vulnerability to Agricultural Nitrate in Two Highly Diversified Environmental Settings

A significant rise of groundwater pollution has been registered worldwide, where nitrate has been recognized as the most widespread pollutant. In this context, the groundwater vulnerability assessment and more specifically the delineation of “Nitrate Vulnerable Zones” represents a reliable cost-effective tool for groundwater management. In this study, the Agricultural Nitrate Hazard Index (ANHI) method was applied to two case histories in southern Italy: the Lete River catchment and the eastern sector of the Campania Plain. The first area is characterized by agricultural activities and a low anthropic influence while the eastern part of the Campania Plain, around Caserta city, is strongly urbanized and developed on an extensive alluvial plain filled with volcaniclastic deposits. The parametric method applied suggests moderate hazard for the more natural setting highlighting how the intensive crop farming and livestock activities that characterized the area negatively influenced the results. For the eastern part of the Campania Plain, where a strong urbanization and widespread industrial crops are dominant, a low to very low hazard has been identified. The groundwater quality value, in contrast with the methodology results underlines the importance of further risk evaluations based on accurate aquifer characterization. A multiple year assessment based on land use change and climate variation could further highlights the difference between the study areas.

Source characterization of nitrate in groundwater using hydrogeochemical and multivariate statistical analysis in the Muling-Xingkai Plain, Northeast China

The source characterization of nitrate (NO₃^-) in groundwater of Muling-Xingkai Plain (MXP) and the influence of NO₃^- on the water environment were studied by hydrogeochemical and multivariate statistical analysis. A total of 164 groundwater samples were collected, and the samples were classified into three clusters by using hierarchical cluster analysis. Cluster 1 (C1), accounting for 13% of total samples, was mainly located in local residential zones where the top soils were the medium-textured sediments. Cluster 2 (C2) and cluster 3 (C3) were mainly located in farmlands and residential zones where the clay sediments were overlaying the aquifers. The soil media covering the aquifers was an important factor controlling the concentration of NO₃^- in groundwater, which determined the infiltration rate of wastewater and the redox environment of aquifers. Only the samples in C1 exceeded the WTO standards for NO₃^- (50 mg/L), and the samples in C2 and C3 had low NO₃^- concentration (less than 10 mg/L). The excessive NO₃^- in groundwater was observed in the shallow groundwater under local residential zones, and it was closely related to the anthropogenic activities since the 1950s. The domestic sewage was responsible for the elevated NO₃^- contents in the MXP. Then, it was still necessary to construct the sewage disposal system in rural areas to further protect the groundwater resource to avoid the formation of extensive nitrogen pollution. At present, NO₃^- in the groundwater mainly shows a fertilizer and natural rainwater origin and is not demonstrating the significant deterioration of groundwater qualities and water environment.

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.

A lumped-parameter model for investigation of nitrate concentration in drinking water in arid and semi-arid climates and health risk assessment

PURPOSE

This study was conducted to assess the capability of the lumped parameter model (LPM), an efficient model due to its analytical nature and the limited data requirements, to estimate health risks from nitrate in groundwater in arid and semi-arid climates.

METHODS

To assess the capability of LPM, two scenarios were established: one for estimation of hazard quotient (HQ) via monitoring nitrate concentration in groundwater and the other using the LPM. After nitrate was monitored in 148 randomly-selected wells, a modified LPM was used to estimate water volume and nitrate concentration, which ultimately led to the development of a model for estimating HQ. The performances of LPM were assessed using the coefficient of determination, percentage standard deviation, and root mean square error. To compare health risk maps Kriging, Spline, Inverse distance weighted, and natural neighbor models were run using geographical information system (GIS).

RESULTS

Linear analysis revealed a strong correlation between HQ values estimated in LPM and monitoring scenarios in arid climate compared to semi-arid (r = 0.962, n = 22, p = 0.00), suggesting that the LPM was more accurate in predicting nitrate concentration in the arid climate. Uncertainty analysis showed that LPM outputs were sensitive to several parameters, especially leakage from cesspits, which are involved in the sources and sinks of nitrate in the groundwater. In addition, it was found that the natural neighbor was the most appropriate model with the lowest errors for preparing health risk maps from nitrate.

CONCLUSIONS

The obtained results revealed that LPM can be effectively used to estimate nitrate concentration in groundwater in arid climates and thereby LPM is an appropriate model to estimate health risk from nitrate in this climate.

Sonocatalytic reduction of nitrate using magnetic layered double hydroxide: Implications for removal mechanism

In this study, magnetic layered double hydroxides (mag-LDHs) were synthesized through compositing magnetite with three different metals (Mg, Cu and Al) under ultrasound (US, 100 kHz frequency and 50 W power). For the first time, mag-LDHs were applied to sonocatalytic reduction of nitrate (NO₃^-) and the reduction mechanism were determined by conducting kinetic tests and various spectroscopic analyses. Based on the kinetic data, NO₃^- reduction and the selectivity for N₂ highly depends on the ratio between Mg/Al, solution pH and sonication frequency. The best condition for sonocatalytic denitrification was found to be pH 7 operated under 100 kHz (50% power) using the catalyst with lowest amount of Al (mag-LDH-Al_0.3Mg_1.5). As a proposed mechanism, NO₃^- is initially reduced to NO₂^- by Cu⁰, and then further reduced to N₂/NH₄⁺ by Mg⁰. Hypothetically Al⁰ could provide sorption sites for hydrogen radicals (·H) dissociated from ultrasound, hence served as reducing sites in denitrification process. The XPS analysis showed an increased peak of Cu⁰ after the sonocatalytic reduction when catalyst has lower amount of Al. The excessive hydrogen adsorbed on Al⁰ might spill-over to the adjacent Cu, thus reducing the CuO into Cu⁰ at high temperature created by the implosion of the microbubbles. Without the use of consumable reducing agents (i.e. H₂ gas), sonocatalytic reduction could be a potential candidate of remediation method to treat NO₃^- polluted water with high N₂ selectivity and easy magnetic recovery.

Pollutant source analysis and tempo-spatial analysis of pollutant discharge intensity in a transboundary river basin

From the perspective of river basin refined management and pollution control of water bodies, a transboundary river basin and its regional pollutant sources are identified and the typical status of discharging processes of different pollutant sources are screened. Then organic connection which can comprehensively reflect and dynamically characterize the discharge of transboundary water pollutants is constructed. In addition, the integrated prediction (IP) model of the transboundary river basin and its regional water pollutants discharge is established. Finally, the dynamic simulation of typical status characteristics of the transboundary river basin and its regional pollutant sources discharge as well as the tempo-spatial changing pattern of pollutant discharge intensity is conducted in this paper. This paper selected the Songhua River basin as an example where planting, industry, household (urban living and rural living), and livestock and poultry are the main pollutant sources. The dynamic simulation of water pollution discharge in Songhua River basin during the 13th Five-year Plan and its tempo-spatial changing trend analysis are conducted by employing the established IP model of transboundary river basin water pollution discharge. The results show that during the 13th Five-year Plan, through comprehensive management and control of pollutant sources in Songhua River basin, the discharge amounts of different pollutant sources (planting, industry, household, livestock, and poultry) present an overall decreasing trend and the main pollutants discharge intensity decreases significantly year by year. It is demonstrated that pollution discharge in Songhua River basin is controlled effectively.

Optimal strategies for bioremediation of nitrate-contaminated groundwater and microalgae biomass production

Optimizing the mono-cultivation and mixed cultivation of Chlamydomonas reinhardtii, Chlorella vulgaris, and an Ettlia sp. was evaluated for treating nitrate-contaminated groundwater and biomass production. Ettlia sp. showed the highest nutrient assimilation and growth rate among the three microalgae during bioremediation. Light-dark cycle was the effective condition for nutrient removal and COD mitigation by microalgae. Mixed microalgae with a larger presence of the Ettlia sp. exhibited the highest biomass productivity, nitrate-nitrogen, and phosphate-phosphorus removal rates of 0.21 g/L/d, 16.6, and 3.06 mg/L/d, respectively. An N:P mass ratio of 5 was necessary to increase the mixed-microalgal performance. The settling efficiency of the mixed microalgae increased up to 0.55 when using pH modulation during 30 min. Therefore, applying an Ettlia sp.-dominant consortium was the optimum strategy for the bioremediation of nitrate-contaminated groundwater in 3 days.

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.

Discontinuous permeable adsorptive barrier design and cost analysis: a methodological approach to optimisation

The following paper presents a method to optimise a discontinuous permeable adsorptive barrier (PAB-D). This method is based on the comparison of different PAB-D configurations obtained by changing some of the main PAB-D design parameters. In particular, the well diameters, the distance between two consecutive passive wells and the distance between two consecutive well lines were varied, and a cost analysis for each configuration was carried out in order to define the best performing and most cost-effective PAB-D configuration. As a case study, a benzene-contaminated aquifer located in an urban area in the north of Naples (Italy) was considered. The PAB-D configuration with a well diameter of 0.8 m resulted the best optimised layout in terms of performance and cost-effectiveness. Moreover, in order to identify the best configuration for the remediation of the aquifer studied, a comparison with a continuous permeable adsorptive barrier (PAB-C) was added. In particular, this showed a 40% reduction of the total remediation costs by using the optimised PAB-D.

Living in uncertainty due to floods and pollution: the health status and quality of life of people living on an unhealthy riverbank

BACKGROUND

People living on the banks of polluted rivers with yearly flooding lived in impoverished and physically unhealthy circumstances. However, they were reluctant to move or be relocated to other locations where better living conditions were available. This study aimed to investigate the health status, quality of life (QoL), happiness, and life satisfaction of the people who were living on the banks of one of the main rivers in Jakarta, Indonesia, the Ciliwung.

METHODS

Respondents were 17 years and older and recruited from the Bukit Duri community (n = 204). Three comparison samples comprised: i) a socio-demographically matched control group, not living on the river bank (n = 204); ii) inhabitants of Jakarta (n = 305), and iii) the Indonesian general population (n = 1041). Health status and QoL were measured utilizing EQ-5D-5L, WHOQOL-BREF, the Happiness Scale, and the Life Satisfaction Index. A visual analogue scale question concerning respondents' financial situations was added. MANOVA and multivariate regression analysis were used to analyze the differences between the Ciliwung respondents and the three comparison groups.

RESULTS

The Ciliwung respondents reported lower physical QoL on WHOQOL-BREF and less personal happiness than the matched controls but rated their health (EQ-5D-5L) and life satisfaction better than the matched controls. Similar results were obtained by comparison with the Jakarta inhabitants and the general population. Bukit Duri inhabitants also perceived themselves as being in a better financial situation than the three comparison groups even though their incomes were lower.

CONCLUSIONS

The recent relocation to a better environment with better housing might improve the former Ciliwung inhabitants' quality of life and happiness, but not necessarily their perceived health, satisfaction with life, and financial situations.

Adsorption of nitrate onto biochar derived from agricultural residuals

To develop low-cost adsorbents for aqueous nitrate, biochars were prepared from three types of agricultural residuals at different pyrolysis temperatures (300 °C, 450 °C, and 600 °C). The corncob biochar produced at 600 °C (CC600) was the best nitrate adsorbent of all the tested biochars. Characterization results showed that CC600 had good thermal stability, porous structure, and abundant surface functional groups. Findings from batch adsorption experiments demonstrated that CC600 showed relatively fast adsorption kinetics to nitrate in aqueous solutions. In addition, the Langmuir adsorption capacity of CC600 to nitrate was 14.46 mg/g, comparable to that of other biochar-based adsorbents. Therefore, CC600 showed promising potential to be used as a low-cost adsorbent for the treatment of nitrate in water.

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.