Severe Nitrate Pollution and Health Risks of Coastal Aquifer Simultaneously Influenced by Saltwater Intrusion and Intensive Anthropogenic Activities

Seasonal dynamics of dissolved inorganic nitrogen in groundwater: Tracing environmental controls and land use impact

High levels of dissolved inorganic nitrogen (DIN) in groundwater pose challenges for regions like northern Anhui Province, China, where groundwater is a crucial domestic resource. This study utilized modern geostatistics to explore the spatial and temporal dynamics of DIN in groundwater. Significant seasonal influences on DIN concentrations were identified: ammonium peaks during wet season driven by agricultural activities, while nitrate peaks during the dry season primarily influenced by municipal inputs. This study established a Bayesian Maximum Entropy - Random Forest (BME-RF) model based on Land Use/Land Cover data to infer the spatio-temporal performance of DIN, achieving an interpretation rate above 90 %. It also highlighted the role of hydrogeological conditions and aquifer types in the evolution of DIN. By employing a DIN environmental interaction model, it further analyzed the eco-hydrological drivers and seasonal trends affecting DIN variability, enhancing the understanding of groundwater nitrogen dynamics and their link to environmental factors with low consumption. SYNOPSIS: This study reveals seasonal shifts in groundwater DIN, links them to human activity, and uses the BME model to guide targeted nitrogen fluctuation.

Research methods for seawater intrusion in China and recommendations for novel radium-radon technologies

Seawater intrusion has been a globally significant environmental issue. This paper comprehensively reviews and highlights the research methods of seawater intrusion in China, recommending the potential application of novel radioactive radium-radon isotopes. Geochemical and geophysical techniques have been extensively utilized in studying seawater intrusion in China, including methods such as hydrochemical analysis, groundwater level observations, geophysical survey techniques, and isotope tracing. The former three methodologies boast a lengthier historical application in seawater intrusion field, while the radium-radon tools in isotope tracing, as newcomers, can specifically indicate crucial scientific questions such as seawater intrusion rates, salt groundwater age, water-rock reactions, and preferential flow dynamics. However, it is imperative to acknowledge the limitations inherent in the utilization of radium-radon tools within the realm of seawater intrusion research, as with any other methodologies. Strategic integration of radium-radon tools with other methodologies will propel advancements in the investigation of seawater intrusion in China. While the primary focus is on research methods in China, insights gained from novel radium-radon tools could have broader value for seawater intrusion research and coastal management globally.

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.

Geochemistry of groundwater and metal(loid) behavior in the costal aquifers of the Maharlu Lake, Iran

Groundwater in coastal aquifers of the Maharlu Lake, southern Iran, has suffered from quality degradation and salinity increases in recent decades. These aquifers are important sources for drinking and agricultural uses in area around the lake. Hydrogeochemical analyses were carried out to identify the geochemical processes controlling groundwater chemistry and heavy metal concentrations in the coastal aquifer of the Maharlu Salt Lake. A total number of 54 water samples (45 samples from three coastal aquifers and 9 water samples from lake water) were collected for laboratory analysis of major ions and heavy metals three times from November-2014 to July-2015. In addition, physiochemical parameters of temperature, electrical conductivity, pH, and redox potential were measured in the field. The findings indicate three major controls of groundwater chemistry in the coastal aquifers of the Maharlu Lake including (1) lake water intrusions, (2) evaporites and carbonate dissolution-precipitation, and (3) input of organic matter probably linked to the seepage of domestic sewage with resulting sulfate reduction. In contrast, dissolution of minerals in surface sediments and direct evaporation of groundwater in the coastal aquifers seem to be insignificant based on geochemical ratios and water table depth. Concentrations of B, Li, Co, Cr, Cu, Ni, and U increase, but Zn concentrations decrease in groundwater due to the lake water intrusions into the costal aquifers. Gypsum dissolution and consequent carbonate reactions cause B, Co, Cr, Cu, Ni, Zn, and U enrichment in the groundwater samples. These findings can provide water managers and local authorities with a comprehensive framework of the coastal groundwater geochemistry, allowing a better understanding of the effects of current management practices and the implementation of mitigation approaches such as reduction of groundwater extraction to limit further lake saltwater intrusion and water resources deterioration.

Evaluation of non-carcinogenic causing health risks (NCHR) associated with exposure of fluoride and nitrate contaminated groundwater from a semi-arid region of south India

Groundwater is the foremost resource for drinking water supply in arid and semi-arid regions of the world, and also intake of contaminated drinking water is the major source for creating a several health risk for humans. To estimate the groundwater suitability for drinking and also to measure the non-carcinogenic health risk for infants, children, and adults, a total of 35 groundwater samples were collected from the semi-arid region of India and analyzed major ions including fluoride and nitrate. The results revealed that the concentration of fluoride ranges from 0.6 to 3.6 mg/L and is about 2.4 times higher than the maximum allowable limit of 1.5 mg/L for drinking water purposes. And nitrate contents varied from 17 to 120 mg/L in which 54.29% of the groundwater samples exceeded the recommended limit of 50 mg/L. The estimated individual non-carcinogenic health risk (INCHR) frequency is evidently displayed that intake of higher concentration of nitrate creates the greater detrimental health effects than fluoride. The contribution of individual non-carcinogenic health risk (INCHR) of nitrate is greater detrimental health effects than the fluoride. The results of total non-carcinogenic health risk (TNCHR) reflect the infants and also children were found to be more susceptible towards fluoride and nitrate-associated health risks in the investigated region. Fluoride-bearing minerals and different anthropogenic sources such as septic tank leakages, nitrogen fertilizers, domestic, agricultural, and animal wastes played a vital role in groundwater pollution and thereby non-carcinogenic human health risks. Therefore, a proper sustainable future plan is most important to mitigate the fluoride and nitrate contamination in the groundwater of the study region.

Direct Electron Transfer Coordinated by Oxygen Vacancies Boosts Selective Nitrate Reduction to N2 on a Co-CuOx Electroactive Filter

Atomic hydrogen (H*) is used as an important mediator for electrochemical nitrate reduction; however, the Faradaic efficiency (FE) and selective reduction to N₂ are likely compromised due to the side reactions (e.g., ammonia generation and hydrogen evolution reactions). This work reports a Co-CuO_x electrochemical filter with CoO_x nanoclusters rooted on vertically aligned CuO_x nanowalls for selective nitrate reduction to N₂, utilizing the direct electron transfer between oxygen vacancies and nitrate to suppress the contribution by H*. At a cathodic potential of -1.1 V (vs Ag/AgCl), the Co-CuO_x filter showed 95.2% nitrate removal and 96.0% N₂ selectivity at an influent nitrate concentration of 20 N-mg L^-1. Meanwhile, the energy consumption and FE were 0.60 kW h m^-3 and 53.5%, respectively, at a permeate flux of 60 L m^-2 h^-1. The presence of abundant oxygen vacancies on Co-CuO_x was due to the change in the electron density of the Cu atom and a decrease of the coordination numbers of Cu-O via cobalt doping. Theoretical calculations and electrochemical tests showed that the oxygen vacancies coordinated nitrate adsorption and subsequent reduction reactions, thus suppressing the contribution of H* to nitrate reduction and leading to a thermodynamically favorable process to N₂ via direct electron transfer.

Response of groundwater chemical characteristics to land use types and health risk assessment of nitrate in semi-arid areas: A case study of Shuangliao City, Northeast China

Groundwater is an important source of water, especially in semi-arid areas. The assessment of the chemical characteristics of groundwater under different land use types the associated risk to human health is of important significance for water resources utilization and protecting the ecological environment. The present study analyzed the hydrochemical characteristics and ion sources of groundwater, taking Shuangliao City as an example. The analysis was based on the field investigation (82 water samples), descriptive statistics, correlation analysis, ion proportionality coefficient method, and principal component analysis (PCA). The results indicated that the concentrations of most ions in the aquifer had wide spatiotemporal variation and were susceptible to environmental influences. NO₃^- showed the highest spatial variability, with concentrations ranging from 0.0 to 529.48 mg·L^-1. The processes contributing the most to the chemical composition of groundwater were leaching/dissolution and cation exchange. The spatial distribution of groundwater chemistry types was visually obtained through the combined use of Piper trilinear charts and a Digital Terrain Model (DTM). The HCO₃-Ca type dominated. Groundwater Cl^-, SO₄^2-, and Ca²⁺ were negatively correlated with the Normalized Difference Vegetation Index (NDVI) due to the absorption of inorganic salt by vegetation roots, indicating that land use types affect groundwater hydrochemistry in the area. The hazard quotient (HQ) used in the human health risk assessment (HHRA) model indicated children (0.0010-6.4162) to be at the highest risk, followed by adult females (0.0007-4.0396), with adult males (0.0005-3.0863) under the lowest risk. The spatial distribution of groundwater nitrate was shown to pose risks to children, adult females, and adult males across 62.97%, 50.01%, and 39.34% of the study area, respectively. This study can improve the understanding of groundwater evolution and the relationship between water chemistry and land use types. This study can also guide the development and utilization of groundwater resources and conservation of water quality in semi-arid areas.

A global meta-analysis of animal manure application and soil microbial ecology based on random control treatments

The processes involved in soil domestication have altered the soil microbial ecology. We examined the question of whether animal manure application affects the soil microbial ecology of farmlands. The effects of global animal manure application on soil microorganisms were subjected to a meta-analysis based on randomized controlled treatments. A total of 2303 studies conducted in the last 30 years were incorporated into the analysis, and an additional 45 soil samples were collected and sequenced to obtain 16S rRNA and 18S rRNA data. The results revealed that manure application increased soil microbial biomass. Manure application alone increased bacterial diversity (M-Z: 7.546 and M-I: 8.68) and inhibited and reduced fungal diversity (M-Z: -1.15 and M-I: -1.03). Inorganic fertilizer replaced cattle and swine manure and provided nutrients to soil microorganisms. The soil samples of the experimental base were analyzed, and the relative abundances of bacteria and fungi were altered compared with no manure application. Manure increased bacterial diversity and reduced fungal diversity. Mrakia frigida and Betaproteobacteriales, which inhibit other microorganisms, increased significantly in the domesticated soil. Moreover, farm sewage treatments resulted in a bottleneck in the manure recovery rate that should be the focus of future research. Our results suggest that the potential risks of restructuring the microbial ecology of cultivated land must be considered.

Regulation of the Tpo, Tg, Duox2, Pds, and Mct8 genes involved in the synthesis of thyroid hormones after subchronic exposure to sodium nitrate in female Wistar rats

Nitrates are natural compounds present in soil and water; however, the intense use of fertilizers has increased their presence in groundwater with deleterious effects on human health. There is evidence of nitrates acting as endocrine disruptors; however, the underlying molecular mechanisms have not been fully described. Here, we investigated the effect of subchronic exposure to different concentrations of sodium nitrate in female Wistar rats, evaluating thyroid hormonal parameters, such as Nis transporter (Na⁺ /I^- symporter, Slc5a5) and Tsh-R receptor protein expression, as well as transcription of the Tpo (thyroperoxidase), Tg (tiroglobulin), Duox2 (dual oxidase 2), Pds (pendrin), and Mct8 (Mct8 transporter, Slc16a2) genes. Hematological and histochemical changes in the liver and thyroid were also explored. Significant differences were found in platelet and leukocyte counts; although a significant increase in the weight of the thyroid gland was observed, no differences were found in the levels of the hormones Tsh, T3, and T4, but a modulation of the mRNA expression of the Tg, Tpo, Duox2, Mct8, and Pds genes was observed. Morphological changes were also found in liver and thyroid tissue according to the exposure doses. In conclusion, subchronic exposure to sodium nitrate induces leukocytosis consistent with an inflammatory response and upregulation of Sod2 in the liver and increases the expression of genes involved in the synthesis of thyroid hormones, keeping thyroid hormone levels stable. Histological changes in the thyroid gland suggest a goitrogenic effect.

Water Quality Assessment and Evaluation of Human Health Risk in Mutangwi River, Limpopo Province, South Africa

Freshwater supply is essential to life on Earth; however, land use activities such as mining and agriculture pose a significant danger to freshwater resources and the wellbeing of aquatic environments. This study temporarily assesses the water quality characteristics of Mutangwi River. Physicochemical parameters (pH, temperature, total dissolved solids (TDS), salinity, electrical conductivity (EC), and turbidity) were determined in situ using an Extech multimeter and turbidity meter. The concentration of the selected metals (Mg, Cr, Fe, Cd, Mn, Pb, Ca, and Na) were analysed using an Atomic Absorption Spectrophotometer. Membrane filtration method was used to analyse microbiological parameters (Escherichia coli and Enterococci). The physicochemical water quality parameters as well as basic anions (fluoride, phosphate, sulfate, nitrate, and chloride) determined complied with the regulatory guideline of the World Health Organization (WHO) and the South Africa National Standards (SANS). Some of the trace metals (Mn, Ca, Fe, and Mg) were found below the guideline values, while others (Pb and Cd) exceeded the threshold limit. The counts for E. coli (814.5-2169 cfu/100 mL) and Enterococci (333-9396 cfu/100 mL) in the study did not comply with the regulatory guidelines. The water quality status using the water quality index (WQI) indicated that on the average, the water quality from Mutangwi River is poor (WQI > 100). The hazard quotient through ingestion exposure did not exceed the threshold limit of 1, for adults and children. This implies that there is no potential non-carcinogenic health risk from trace elements via ingestion of drinking water for children and adults. However, cancer risk for adults and children was computed in relation to Cd and Pb levels and exceeded the threshold limit 10^-4, indicating a possible carcinogenic risk. Water from the river should be adequately treated prior to domestic and agricultural use.

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 chemistry, distribution and potential health risk appraisal of nitrate enriched groundwater: A case study from the semi-urban region of South India

In recent years, an elevated concentration of nitrate in groundwater has been a growing problem on a global scale. It directly shows the adverse effects on human health via various intake pathways. Herein, the aim of the present study was to evaluate the nitrate concentration in groundwater and its associated human health risk in various age groups (females, males and children) in the investigated region. For this purposes, thirty groundwater samples were collected and analyzed physico-chemical parameters including nitrate concentration. The results showed that, the concentration of nitrate ranges from 14 to 82 mg/L and about 43.3% of these groundwater samples beyond the safe level of 45 mg/L according to Indian guidelines. The higher nitrate contamination is observed in the vicinity of Sarvepalli and Timmapur villages where groundwater chemistry is majorly influenced by anthropogenic sources. Health risks were assessed through oral/ingestion and dermal contact exposure routes for females, males and children population in the study region. Oral exposure was much higher than dermal contacts. For the non-carcinogenic risk, the HI_Total values of groundwater in the investigated region varied from 0.313 to 1.976 (mean of 0.941) for males, 0.370 to 2.336 (mean of 1.112) for females and 0.443 to 2.694 (mean of 1.314) for children. The health risk assessment for nitrate divulged that 60%, 57% and 50% of groundwater samples pose a non-carcinogenic health risk for children, females and males, respectively.

Spatial Assessment of Groundwater Quality and Health Risk of Nitrogen Pollution for Shallow Groundwater Aquifer around Fuyang City, China

Prolonged exposure to intensive and extensive agricultural and industrial activities is leading to an increased deterioration of groundwater quality, especially nitrogen pollution in shallow groundwater aquifers. This study was carried out using the fuzzy comprehensive method to assess the overall groundwater quality, and the noncarcinogenic risks were estimated using the human health risk assessment method recommended by the United States Environmental Protection Agency (USEPA) via drinking water intake pathways around Fuyang City, China. A total of 34 samples were collected from shallow groundwater private wells, and 16 parameters were analyzed for each groundwater sample. The evaluation results of groundwater quality show 14.7% of groundwater samples classified as poor and very poor quality, and NO3-N, TH, TDS, Fe3+, and Mn are of high potential to affect the quality of potable drinking water. These are mainly derived from anthropogenic pollutants, predominantly due to uncontrolled agricultural and industrial activities, as well as some natural processes. The noncarcinogenic risk of nitrate indicates that 8.82% of groundwater samples surpass the permissible limit recommended by the USEPA for both adults and children. This study may provide the local authority with insights into making scientific decisions for exploiting groundwater in a sustainable manner so as to protect public health.

Possible effect of submarine groundwater discharge on the pollution of coastal water: Occurrence, source, and risks of endocrine disrupting chemicals in coastal groundwater and adjacent seawater influenced by reclaimed water irrigation

This study investigated occurrence, source, and risks of endocrine disrupting chemicals (EDCs) in coastal groundwater and adjacent seawater influenced by reclaimed water irrigation in a typical coastal region of China. All target EDCs were detected in coastal groundwater and reclaimed water while only estrone, bisphenol A (BPA), and nonylphenol were detected in seawater. Concentrations of BPA that was the predominant EDC in coastal groundwater ranged from 35.9 to 52.9 ng/L and estradiol was easy to accumulate in groundwater under reclaimed water irrigation. Concentrations of all target EDCs in seawater ranged from 18.9 to 30.9 ng/L, much lower than those in groundwater. Ecological risks posed by EDCs in groundwater and seawater were very high. Estrone contributed to 51.3%-62.9% of total acute risk quotients for seawater while detected 17-α-ethynylestradiol contributed to 41.1%-56.2% of total acute risk quotients for groundwater. Estradiol equivalent concentrations of target EDCs in groundwater/seawater were in the range of (3.5-7.6)/(1.4-2.3) ng/L while non-cancer risks posed by EDCs in groundwater/seawater were acceptable. Dual-isotope analysis illustrated that reclaimed water was the main source of EDCs in coastal groundwater. About 82% of EDCs was discharged into the Laizhou Bay through the submarine groundwater discharge based on the flux analysis. The pollution of the coastal groundwater through reclaimed water irrigation subsequently led to EDCs pollution of the adjacent seawater through the submarine groundwater discharge. Therefore, effective control of EDCs in reclaimed water for irrigation will be beneficial to control EDCs in groundwater and seawater of the coastal regions.

Seasonal distribution, risks, and sources of endocrine disrupting chemicals in coastal waters: Will these emerging contaminants pose potential risks in marine environment at continental-scale?

Coastal waters are the critical ecologically fragile regions under the influence of the fastest economic developing pace and the extensive anthropogenic activities in coastal zone. Little information on the seasonal distribution, risks, and sources of endocrine disrupting chemicals (EDCs) which are emerging contaminants to pose potential risks at very low concentrations in coastal waters at continental-scale is available. This study investigated the coastline-based distribution, risks, and sources of target EDCs in coastal water of China. EDCs in coastal waters of China showed significant spatio-temporal variation with phenolic compounds serving as predominant EDCs. Bisphenol A (BPA) was detected in all water samples with average concentration of 449.2/186.3 ng/L in winter/summer while estrone was the main steroidal estrogen with the average concentration of 87.2/2.7 ng/L in winter/summer. EDCs in coastal waters of South China Sea Area showed higher concentrations. EDCs in coastal waters exerted high ecological risks and estrone/BPA averagely accounted for over 61%/71% of total risk quotient in winter/summer. Average estradiol equivalent concentration of all target EDCs reached 68.87/1.76 ng/L in winter/summer. EDCs in coastal waters did not pose potential non-cancer health risks for humans. The positive matrix factorization (PMF) model was firstly used to identify and quantify possible sources of EDCs. The PMF analysis showed that wastewater and sewage might be the main source for EDCs in coastal waters. EDCs in coastal waters showed high estradiol equivalent concentration and ecological risks at continental-scale, highlighting that EDCs contamination has become a crucial stress affecting the sustainable development of coastal regions.

Assessment of Groundwater Quality and Human Health Risk (HHR) Evaluation of Nitrate in the Central-Western Guanzhong Basin, China

To investigate the quality of domestic groundwater and assess its risk to inhabitants of the Guanzhong Basin, China, 191 groundwater samples were collected to analyze major ions, nitrate, pH, total dissolved solids (TDS), total hardness (TH), and electrical conductivity (EC). The physiochemical parameters, hydrochemical facies, and sources of major ions were analyzed using Durov diagrams, bivariate diagrams, and chloro-alkaline indices (CAI-I and CAI-II). The suitability of groundwater for drinking, the nitrate distribution, and human health risk (HHR) for different age groups were evaluated. The results showed that the relative abundance of cations in the groundwater samples was K⁺+Na⁺ > Ca²⁺ > Mg²⁺, while that of anions was HCO₃⁻ > SO₄²⁻ > Cl⁻ > NO₃⁻. Groundwater samples mainly contained HCO₃-Na and HCO₃-Ca, which were introduced mainly by rock weathering and ion exchange. The groundwater in the Guanzhong Basin contained mainly good and medium water, and the groundwater in the southern part of the Wei River was better than that north of the Wei River. Areas containing high nitrate concentrations were mainly located in the central and western parts of the Guanzhong Basin. The percentages of low risk (<45 mg/L), high risk (45–100 mg/L), and very high risk (>100 mg/L) of nitrate pollution in the study area were 90.58%, 8.9%, and 0.52%, respectively. The HHR assessment results indicated that people in the 6–12 month age group were more likely to suffer from health complications due to a higher nitrate concentration, followed by 6–11 years, 21–65 years, 18–21 years, ≥65 years, 11–16 years, and 16–18 years age groups, which was mainly due to the different exposure parameters. The results of this study will be useful in regional groundwater management and protection.