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Due to adverse impact of the global warming on hydrological resources, we intended to document the hydrogeochemical evolutions of surface and groundwater at tropical central-south Mexico in terms of seasonality of rock-water interaction, precipitation/evaporation variation and moisture source by evaluating the major ion chemistry in Piper and Gibbs plots, Durov diagram and through estimation of the chloro-alkaline indices as well as assessing the stable isotope compositions (δ 18 O and δ 2 H) in samples from different seasons of a year. Surface water of the Lake Coatetelco shifted from mostly Ca-Mg-HCO 3 facies in wet summer-autumn to Na-HCO 3 -Cl facies in the dry spring due to elevated Na, Cl and HCO 3 . Greater evaporation in spring led to a maximum δ 18 O enrichment of ca.7‰ compared to the other seasons, and much depleted deuterium excess (-40.92‰ to -39.20‰). Interaction of the lake water with subsurface carbonate lithologies, and comparable isotopic compositions reflected the enhanced interaction between the surface water body and aquifers in the wet autumn. Effect of seasonality, however, was unclear on the groundwater facies, and its heterogenous composition (Ca-Mg-HCO 3 , Na-HCO 3 -Cl and Na-HCO 3 ) reflected the interactions with different lithologies. Fractionations in isotope compositions of the groundwater were caused from recharge at different elevations, seasonality of moisture sources and moisture recycling. The water-mineral saturation index was an efficient proxy of seasonality as the lake water and groundwater (avg SI calcite  > 0.5) of the dry autumn were saturated with calcite. This vital information about carbonate precipitation, pCO 2 and chemical facies would be useful for the better interpretation of paleoclimate archives in this region., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Oscar Agesandro Garcia-Arriola reports financial support was provided by Conahcyt, Mexico. Priyadarsi D. Roy reports financial support was provided by DGAPA-UNAM. Oscar Agesandro Garcia-Arriola reports a relationship with Conahcyt that includes: funding grants. Priyadarsi D. Roy reports a relationship with DGAPA-UNAM that includes: funding grants. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

This study aims to investigate and understand the temporal and spatial movement of seawater intrusion into the coastal aquifers. Groundwater salinity increase has affected the entire eastern part of the study area and is primarily influenced by direct and reverse ion exchange reactions associated with intrusion and freshwater influx phases, which alternate over monsoons. To gain insights into the spatiotemporal dynamics of the seawater intrusion process, hydrochemical facies analysis utilizing the HFE-Diagram was employed. Additionally, the study considered the major ionic changes during both the monsoons. The HFE-Diagram analysis of hydrochemical facies revealed distinctions in the behaviour of each coastal aquifer concerning seawater intrusion-induced salinization. In PRM 2020, the data shows that approximately 65% of the samples fall under the freshening phase, while the remaining 35% were categorized as intrusion phase. Within the freshening phase, seven different hydrochemical facies were identified, including Na-Cl, Na-MixCl, MixNa-MixCl, Na-MixHCO 3 /MixSO 4 , MixNa-MixSO 4 , Na-HCO 3 , and MixCa-HCO 3 . In contrast, the intrusion phase had four facies: MixCaMixHCO 3 , MixNa-Cl, Ca-Cl, and Na-Cl. Especially, the Na-Cl facies (f 1 ) within the freshening phase attributed for the largest percentage, contributing 30% of the samples. In POM 2021, the distribution of samples shifted slightly, with approximately 72.5% belonging to the freshening phase and 27.5% to the intrusion phase. Within the freshening phase of POM 2021, five hydrochemical facies were identified: Na-Cl, Na-MixCl, Na-MixHCO 3 /MixSO 4 , MixNa-MixSO 4 , and Na-HCO 3 . The intrusion phase of POM 2021 had three facies: MixNa-Cl, Na-Cl, and MixCa-Cl. Similar to PRM 2020, the Na-Cl facies (f 1 ) remained the most predominant in the freshening phase, comprising 30% of the samples. The relation between total dissolved solids (TDS) and various ionic ratios, such as HCO 3 - /Cl - , Na + /Cl - , Ca 2+ /Cl - , Mg 2+ /Cl - , K + /Cl - , and SO 4 2- /Cl - , clearly demonstrates the presence of seawater influence within the coastal aquifers of the study area., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Due to an increasing reduction of hydrological resources across Mexico and their growing contamination from global warming and anthropogenic activities, this study evaluated water from the perennial Lake Coatetelco (Ca-Mg-HCO 3 ) in tropical central-southern Mexico and groundwater (Ca-Mg-HCO 3 and Na-HCO 3 -Cl) from the surrounding wells for drinking as well as irrigation qualities. Comparison with the WHO guidelines and the estimated water quality indices (DWQI and IWQI) grouped almost all the samples collected after the warm season rainfall in excellent and good categories (DWQI < 100) for drinking, even though fluoride remained > 1.5 mg/L in 50% samples. Except for one groundwater sample, all showed > 25% permeability (classes I and II) in Donnen classification indicating their suitability for irrigation. USSL and Wilcox classifications, however, catalogued some in the high-salinity hazard group and some as doubtful for irrigating regular plants. Samples from about 53% wells were also in high and severe restriction categories of IWQI for the irrigation. Total Hazard Quotient Index (THQI) for estimating the non-carcinogenic risk (HQ fluoride  > 1) showed that at least one lake water sample and 53% of groundwater might expose the adult and child population to dental and skeletal fluorosis. This water quality assessment data posterior to the rainfall season could be useful as a baseline for both the short- and long-term monitoring in attention to the United Nation's Sustainable Development Goal 6., (© 2023. The Author(s).)

The influx of fresh groundwater and re-circulated sea water into coastal ecosystem occurs through the submarine groundwater discharge (SGD). Measurement of salinity, radium tracers ( 224 Ra, and 226 Ra isotopes) and nutrients in estuarine water, coastal surface water and groundwater during December 2019 estimated the SGD and associated nutrient fluxes near the Karameniyar estuary (Gulf of Mannar) and surroundings of the Manapad region at southern part of Tamil Nadu state in India. The presence of excessive radium tracers revealed that the SGD was contributing to Ra desorption from the sediments and enrichment in the coastal waters. We estimated SGD of approximately 0.03-0.59 m 3  m -2  d -1 for the Manapad region and relatively more homogeneous but comparatively less values in the Karameniyar estuary (0.03-0.34 m 3  m -2  d -1 ). Higher average values of dissolved inorganic nitrogen (DIN; 43.62 μmol L -1 ) and soluble reactive phosphate (SRP; 1.848 μmol L -1 ) suggested greater influence of SGD on the overall coastal water nutrient budget. This study also indicated simultaneous occurrence of fresh and saline SGD in this region., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Climate models for the 21st century project further reduction in the warm season precipitation and more frequent droughts across Mexico. In the possible scenario of enhanced aridity from global warming, the δ 18 O (-10.6 to -6.3 ‰) and δ 2 H (-71.1 to -57.1 ‰) compositions and deuterium-excess (0.2-14.6‰) of shallow groundwater from two different basins (Sandia and El Potosi) with similar geological and geomorphological settings were considered to evaluate the influences of early summer rainfall and later summer tropical storms on aquifers at water-scarce southeast margin of the Chihuahuan Desert. Groundwater of the Sandia Basin was recharged mainly from tropical storms. Higher CO 2 partial pressure (log pCO 2 : -2.70 to -1.61) caused more gypsum dissolution (Ca-Mg-SO 4 facies) and the effect of irrigation return flow (Ca-Mg-Cl facies) was minor. Even though the El Potosi Basin is in proximity, its groundwater was recharged from both the early and late summer precipitations. The multivariate factor analysis helped to separate the process of rock-water interactions from the recharge seasonality. Gypsum dissolution was less as the partial pressure of CO 2 was comparatively lower (log pCO 2 : -3.01 to -2.15), and the ion exchange along with carbonate mineral dissolutions led to Ca-Mg-HCO 3 facies. Over-exploitation under the condition of reduced warm season rainfall would continue to enhance the salinity of groundwater in this region. Hence, the drought mitigation policies should prioritize sustainability of the depleted aquifers and cultivation of salinity resistant crops., (Copyright © 2021 Elsevier Inc. All rights reserved.)

The accurate evaluation of groundwater contamination vulnerability is essential for the management and prevention of groundwater contamination in the watershed. In this study, advanced multiple machine learning (ML) models of Radial Basis Neural Networks (RBNN), Support Vector Regression (SVR), and ensemble Random Forest Regression (RFR) were applied to determine the most accurate performance for the evaluation of groundwater contamination vulnerability. Eight vulnerability factors of DRASTIC-L were rated based on the modified DRASTIC model (MDM) and were used as input data. The adjusted vulnerability index (AVI) with nitrate values was used as output data for the modeling process. The performance of three models was verified using the statistical performance criteria of MAE, RMSE, r 2 , and ROC/AUC values. The ensemble RFR model showed the highest performance in comparison with standalone SVR and RBNN models. Specifically, ensemble RFR kept all promising solutions during the model performance due to its flexibility and robustness, and the vulnerability map obtained by the RFR model was more accurate for predicting the most vulnerable areas to contamination. It was concluded that ensemble RFR was a robust tool to enhance the evaluation of groundwater contamination vulnerability, and that it could contribute to environmental safety against groundwater contamination., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

Application of natural tracers such as radon isotope mass balance has been useful in estimating the submarine groundwater discharge (SGD). This study used 222 Rn and evaluated the magnitude of SGD at Tiruchendur coast of southeast India in the Gulf of Mannar (Indian Ocean). Higher magnitudes of 222 Rn in the porewater and seawater in comparison with the groundwater suggest simultaneous SGD with fluxes of 0.1-0.25 m 3  m -2  d -1 at offshore and 0.4-0.20 m 3  m -2  d -1 at the near shore. These baseline data would contribute to the management and protection of the Gulf of Mannar region in near future., (Copyright © 2021. Published by Elsevier Ltd.)

We assessed the groundwater quality in an industrial area (Tiruchendur Taluk) of Tamil Nadu state in coastal south India for human health risk from drinking as well as irrigation suitability by using the drinking water quality index (DWQI), irrigation factors (sodium adsorption ratio, sodium percentage, residual sodium carbonate and permeability index) and health hazard valuation (THQI- by consuming NO 3 - and F - ). About 57% of the samples represented Ca 2+ -Mg 2+ -Cl - -SO 4 2- ) suggested the order of health risk as children > women > men with about 64%, 70% and 79% of the samples posing non-carcinogenic risks for men, women and children, respectively. Different mitigation measures and sustainable development should be enforced to minimize the health issues from contamination caused by industries, fertilizers in agro-fields and natural processes and reduce the sodium dominance in groundwater. The spatial distribution maps of this study could also be helpful in organization of proper treatment plans to provide safe and hygienic groundwater to the community.nitrate and HQ fluoride ) suggested the order of health risk as children > women > men with about 64%, 70% and 79% of the samples posing non-carcinogenic risks for men, women and children, respectively. Different mitigation measures and sustainable development should be enforced to minimize the health issues from contamination caused by industries, fertilizers in agro-fields and natural processes and reduce the sodium dominance in groundwater. The spatial distribution maps of this study could also be helpful in organization of proper treatment plans to provide safe and hygienic groundwater to the community., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Beach sediments of Kanyakumari at the southernmost India were evaluated for metals and trace elements and to assess their possible impact on coastal ecosystems. Positive correlations (except for Cd and Sr) between them indicated metamorphic lithologies and heavy mineral deposits as possible sources. Significant-extremely high enrichment and very high contamination of Th, Zr, Mo, Ti and U reflected the presence of different heavy minerals. The geo-accumulation index, however, mirrored their variable abundances at different sites. Association of Cd with P suggested the influence of anthropogenic solid waste from fishing industry. It might have caused >41-fold enrichment of Cd and the Fe- Mn-oxides possibly acted as scavengers for 13-fold enrichment of As compared to UCC. Concentrations of Zn and Cr between ERL and ERM in 13% and 93% of the samples, and Ni > ERM in 87% of sediments suggest their bioavailability to seawater with a potential risk for coastal aquifers., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

We assessed groundwater pollution index (GPI) and groundwater quality of coastal aquifers from Tiruchendur in South India for drinking and irrigation by evaluating the physico-chemical parameters of 35 samples of mainly Na-Cl type in an area of 470 km 2 with respect to the World Health Organization (WHO) standard as well as by estimating different indices such as total hardness (TH), sodium percentage (Na%), magnesium ratio (MR), Kelley's ratio index (KR), potential salinity (PS), Langelier saturation index (LSI), residual sodium carbonate (RSC), sodium adsorption rate (SAR), permeability index (PI), and the irrigation water quality index (IWQI). Minimal influence of aquifer lithology and the dominant influence of evaporation on groundwater chemistry reflected the semi-arid climate of the study area. Electrical conductivity (EC) of about 89% of the samples across 418 km 2 exceeded the permissible limit and Ca values of 74% of samples, however, remained within the allowable limit for drinking. More chloride was caused by influx of seawater and salt leaching and higher K was due to excessive fertilizer usage for agriculture. The spatial distribution map created using inverse distance weighting (IDW) method shows that the suitable groundwater is present close to the river basin. GPI values between 0.40 and 4.7, with an average of 1.5, classify insignificant pollution in 43% of the study region and the groundwater suitable for drinking purposes. In addition, 17% of the groundwater samples are also marginally suitable for drinking. The irrigation water quality indices provided contradictory assessments. Indices of TH, Na%, MR, PS, and LSI suggested 32-95% of the samples as unsuitable for irrigation, whereas the indices of RSC, SAR, and PI grouped 72-100% samples as permissible for irrigation. The IWQI map, however, indicated that the groundwater from more than half of the study area are not apt for irrigation and the groundwater of about one-third of the area could only be applied to salt-resistant plants.

A study was conducted to evaluate the suitability of groundwater in the drought-prone Shanmuganadhi River basin of south India for best agricultural practices since the surface water that exists in this basin is not sufficient to meet out the demand. As the quality of groundwater is not uniform in the hard rock aquifers of this basin, the work was carried out to demarcate the suitable groundwater quality zones for the agricultural activities. Sixty-one groundwater samples were collected and analyzed for various parameters such as electrical conductivity (EC), pH, TDS, major cations (Ca 2+ , Mg 2+ , Na + , and K + ) and anions (Cl - , SO 4 2- , HCO 3 - , PO 4 ). To demarcate the feasible zones for agricultural practices, irrigation water quality parameters like EC, sodium adsorption ratio (SAR), percent sodium (Na %), residual sodium carbonate (RSC), magnesium hazard ratio (MHR), Kelly's ratio (KR), and permeability index (PI) were computed. Furthermore, the irrigation water quality representation diagrams like USSL, Wilcox, and Doneen were prepared, and their outputs were spatially plotted using the Geographical Information System (GIS) to identify the suitability domains of groundwater for irrigational practices. Interpretation of irrigation water quality parameters and diagrams indicate that 2% of groundwater samples represented "low" salinity, 26% of samples represented "medium" salinity, 66% of samples represented "high" salinity, and 6% of samples represented "very high" salinity. Similarly, about 59% of samples represented the low alkaline/sodium category and 41% of them represented the medium alkaline category. The USSL output shows that about 2% of samples of the basin signified "low salinity with low alkalinity" category (C1S1), 28% of samples signified the "medium salinity with low alkalinity" category (C2S1), 33% of samples signified "high salinity with low alkalinity" category (C3S1), 28% of samples signified the "high salinity with medium alkalinity" category (C3S2), and 10% of samples signified the "very high salinity with medium alkalinity" category (C4S2). Groundwater is suitable for irrigation in 277.52 km 3- , NO 3 - . This study recommends that groundwater with moderate suitability could only be used for irrigating permeable soils and for cultivating salt-tolerant crops. The addition of gypsum to soil might be helpful to increase the infiltration capacity and osmotic activity. However, poorly suitable area should be avoided for agricultural practices.- ). To demarcate the feasible zones for agricultural practices, irrigation water quality parameters like EC, sodium adsorption ratio (SAR), percent sodium (Na %), residual sodium carbonate (RSC), magnesium hazard ratio (MHR), Kelly's ratio (KR), and permeability index (PI) were computed. Furthermore, the irrigation water quality representation diagrams like USSL, Wilcox, and Doneen were prepared, and their outputs were spatially plotted using the Geographical Information System (GIS) to identify the suitability domains of groundwater for irrigational practices. Interpretation of irrigation water quality parameters and diagrams indicate that 2% of groundwater samples represented "low" salinity, 26% of samples represented "medium" salinity, 66% of samples represented "high" salinity, and 6% of samples represented "very high" salinity. Similarly, about 59% of samples represented the low alkaline/sodium category and 41% of them represented the medium alkaline category. The USSL output shows that about 2% of samples of the basin signified "low salinity with low alkalinity" category (C1S1), 28% of samples signified the "medium salinity with low alkalinity" category (C2S1), 33% of samples signified "high salinity with low alkalinity" category (C3S1), 28% of samples signified the "high salinity with medium alkalinity" category (C3S2), and 10% of samples signified the "very high salinity with medium alkalinity" category (C4S2). Groundwater is suitable for irrigation in 277.52 km 2 area of the basin. It is moderately suitable in an area of 318.46 km 2 and poorly suitable over 38.64 km 2 . This study recommends that groundwater with moderate suitability could only be used for irrigating permeable soils and for cultivating salt-tolerant crops. The addition of gypsum to soil might be helpful to increase the infiltration capacity and osmotic activity. However, poorly suitable area should be avoided for agricultural practices.

Sub-surface water samples from the delta of Thamirabarani River of south India were evaluated for human health risks and seawater intrusion using the geochemical signatures. Electrical conductivity (EC), total dissolved solids (TDS), pH and the concentrations of major cations and anions in 40 samples collected during the winter (January) and summer (July) of 2018 show comparable values. Subsequently, the results were verified with respect to the international drinking water quality standards. The piper trilinear diagram shows mixed Ca-Mg-Cl, Na-Cl, Ca-HCO 3 and mixed Ca-Na-HCO 3 facies in the samples. Similarly, the plenteous of cations are sequenced as Na +  > Ca 2+  > Mg 2+  > K + and the plenteous of anions are sequenced as Cl -  > SO 4 2-  > HCO 3 - >Br -  > NO 3 -  > PO 4 - . Gibbs plots illustrate that rock-water interaction and evaporation control the geochemistry of sub-surface water. More than 40% of the samples are unsuitable for drinking, and their higher EC and TDS values reflected the seawater intrusion, in addition to the anthropogenic activities (salt panning). Interrelationship between ions of sub-surface water was used to get a better insight into the saline water intrusion in the study area. To mitigate the river water salinization and seawater incursion in the aquifers, engineering solution such as weir construction across the Thamirabarani River near Mukkani village has been proposed. After construction of the weir, freshwater in the river can be diverted to the salt-affected and seawater-intruded areas to improve the scenario.

Groundwater quality investigations were carried out in one of the urban parts of south India for fluoride and nitrate contaminations, with special focus on human health risk assessment for the rapidly growing and increasingly industrialized Coimbatore City. Twenty-five groundwater samples were collected and analyzed for physico-chemical parameters (EC, pH, TDS, Ca 2+ , Mg 2+ , Na + , K + , Cl - , SO 4 2- , HCO 3 - , PO 4 ) and the piper diagram characterized 60% of them as Ca-Mg-Cl type. Analysis of fluoride (0.1 to 2.4 mg/l) shows that 32% of the groundwater samples contain F 3- , NO 3 . Nitrate (0.1 to 148 mg/l) is over the permissible limit in 44% of the groundwater samples spread over an area of 429.43 km - , and F - ) and the piper diagram characterized 60% of them as Ca-Mg-Cl type. Analysis of fluoride (0.1 to 2.4 mg/l) shows that 32% of the groundwater samples contain F - over the permissible limit, affecting a region of 122.10 km 2 . Nitrate (0.1 to 148 mg/l) is over the permissible limit in 44% of the groundwater samples spread over an area of 429.43 km 2 . The total hazard indices (THI) of non-carcinogenic risk for children (0.21 to 4.83), women (0.14 to 3.35), and men (0.12 to 2.90) shows some of the THI values are above the permissible limit of the US Environmental Protection Agency. The THI-based non-carcinogenic risks are 60%, 52%, and 48% for children, women, and men. This investigation suggests higher health risk for children and also recommends that proper management plan should be adopted to improve the drinking water quality in this region in order to avoid major health issues in the near future.

The possible zones of submarine groundwater discharge (SGD) and seawater intrusion (SWI) along the west coast of Kanyakumari in the southernmost Indian Peninsula were identified by integrating the surface temperature anomaly, water table fluctuation, and water quality analysis. Temperature map of the sea surface from Landsat 8 satellite data, which helped to demarcate SGD in areas with significant thermal contrast, exists between the seawater and discharging groundwater. Monitoring data of 2019–2021 illustrated patchy, diffuse, and temporally variable groundwater seepage. The spatial distribution map created from groundwater level, and water quality parameters depicted high SGD in areas of high groundwater level and high chances of SWI in regions with low groundwater level. This study identified that the areas with low groundwater level, high EC, and high chloride contents are prone to SWI. Similarly, the regions with high thermal contrast, high groundwater level, and low EC have more SGD. These methods have the potential to be used as preliminary screening tools before implementing detailed studies about the mixing process. [ABSTRACT FROM AUTHOR]

Identification of groundwater vulnerability is important in the utilization and protection of groundwater resources. The present study assessed vulnerability of the Tiruppur taluk of Tamil Nadu state in south India where the groundwater is increasingly polluted from industrialization (textile) and over population. Mitigation of this threat demanded a careful water resource management and thorough groundwater susceptibility assessment with the help of vulnerability map in DRASTIC index model and weighted overlay analysis method in GIS from the evaluation of depth to water table, net recharge, aquifer media, soil media, topography, impact of the vadose zone, and hydraulic conductivity. The drastic index map of this study classified the area into very low, low, medium, high and very high vulnerability and demarcated the areas of Mangalam, Mudalipalaiyam, Veerapandi, Peruntoluvu, Kettanur and Avanashipalaiyam as high and very highly vulnerable. Sensitivity analysis showed very low index for depth to water table (68 %), net recharge (79 %) and impact of vadose zone (75 %), indicating their higher influence on vulnerability. This vulnerability map might serve as a starting point for improving the management and planning of groundwater in this area. [ABSTRACT FROM AUTHOR]

The main objective of the present research was to examine the risk of fluoride-rich groundwater in the Shanmuganadhi River basin, south India on human health. The non-carcinogenic risks were estimated into two classes: (1) risks associated with oral intake of water and (2) risks associated with dermal contact. Hazard Quotient for oral intake and dermal contact was separately calculated for adult men, adult women and children from the geochemical results of 61 representative samples collected from the wells constructed in hard rock aquifers during the post- (January-2018) and pre-monsoon (May-2018) seasons. The collected samples were analyzed immediately after the field work for all the major ions and fluoride. Finally, total hazard index was calculated for adults (men and women) and children to evaluate the risk. It directed that 41%, 49% and 74% of post-monsoon samples and 30%, 43% and 62% of pre-monsoon samples possessed a non-carcinogenic risk for men, women and children, respectively. Because the basin falls in the drought-prone region, the water supply for drinking and cultivation are commonly based on groundwater resources. The study revealed that the minerals such as apatite, fluorite, biotite and pyroxene in the hornblende–biotite gneiss formation contribute fluoride ions to the groundwater system due to water–rock interaction mechanism. The Durov diagram depicted that dissolution of silicate minerals and cation exchange are the foremost hydrogeochemical activities, which decide the overall chemical composition of groundwater in this region. The ionic concentrations including fluoride increased with respect to depth of occurrence of groundwater. Escalation of the water table due to monsoon recharge and artificial recharge through a check dam decreased the total dissolved solids and fluoride ion concentration. The investigation conducted around the existing check dam at Kaldurai village highlighted that the fluoride concentration is below the allowable limit of 1.5 mg/l (WHO in World health statistics 2017: monitoring health for the SDGs, Sustainable Development Goals. World Health Organization, Geneva, 2017) in the wells closer to the check dam toward the downstream side. The concentration increased with distance, which lead the groundwater unsuitable for consumption. Therefore, it is recommended to implement the managed aquifer recharge using check dams in the other parts of the basin to enrich the quantity and applicability of groundwater. [ABSTRACT FROM AUTHOR]

Application of natural tracers such as radon isotope mass balance has been useful in estimating the submarine groundwater discharge (SGD). This study used 222Rn and evaluated the magnitude of SGD at Tiruchendur coast of southeast India in the Gulf of Mannar (Indian Ocean). Higher magnitudes of 222Rn in the porewater and seawater in comparison with the groundwater suggest simultaneous SGD with fluxes of 0.1–0.25 m3 m−2 d−1 at offshore and 0.4–0.20 m3 m−2 d−1 at the near shore. These baseline data would contribute to the management and protection of the Gulf of Mannar region in near future. [Display omitted] • Quantification of groundwater discharge (SGD) at southeast coast of India using 222Rn mass balance. • SGD fluxes of 0.1–0.25 m3 m−2 d−1 at offshore and 0.4–0.20 m3 m−2 d−1 at nearshore. • Simultaneous SGD through comparison of magnitudes of 222Rn in porewater and seawater with the groundwater. • Necessity of public awareness for better coastal management and environmental protection at Gulf of Mannar (Indian Ocean). [ABSTRACT FROM AUTHOR]

The correct name of the 1st Author is presented in this paper. [ABSTRACT FROM AUTHOR]

The Sustainable Development Goal (SDG) 6 declares that water and hygiene are available for everyone. In the Arjunanadi River basin of southern India, 94 geo-labelled water samples are gathered from open and bore wells. Quality variables such TDS, pH, EC, Ca2+, Mg2+, Na+, K +, HCO 3 −, Cl−, NO 3 − , SO 4 2- and F−are tested. The pH ranges from 7.12 to 8.28 with an average of 7.59. None of the samples exceed the acceptable limits. The fluoride concentration ranges from 0.1 mg/L to 2.5 mg/L with the mean value of 1.13 mg/L. The Piper diagram shows that the predominant (58%) water samples have secondary salinity followed by 21% (n=20) of samples have primary salinity, and 11% (n=10) of samples have secondary alkalinity. In Gibbs diagram, almost all the samples fall in the rock-water interaction facies. Fluoride shows a negative correlation with pH, bicarbonate, calcium, nitrate, and sulphate and a positive correlation with EC, TDS, sodium, potassium and magnesium. Improved Water Quality Index (IWQI) shows that 60 samples (ca.599 km2) have good quality, and 34 samples (ca.537 km2) posses poor quality water for drinking throughout the study area. The fluoride distribution shows, 27 samples (ca.173 km2) exceed the values of 1.5 mg/L for drinking and 73 samples (ca.963 km2) are suitable for drinking. The fluoride-enriched water from 66% of samples are risk to infants, teens, and women, and 53% of samples are risk to men through the oral (drinking) and dermal (showering) pathways. This study suggests eco-friendly measures to enhance groundwater quality and assist the local community in sustainable groundwater management techniques to achieve sustainable development for betterment of the society with the help of government authorities. • An area of 173.19 km2 has high fluoride level than WHO standard. • About 599.8 km2 and 536.8 km2 area possess good and poor groundwater quality, respectively. • Leaching of ions through rock-water interaction is the main source for groundwater fluoride. • Younger age people are vulnerable to fluoride health risk compared to elder people. [ABSTRACT FROM AUTHOR]

Pollution risk assessment is an important task for sustainable management of groundwater resources. In this pilot study, we demarcated areas of different pollution vulnerabilities within the Vattamalaikarai River Basin (ca.435 km2) of south India using the DRASTIC index and involving the combined geospatial techniques of remote sensing, geographical information system and global positioning system. Seven major hydrogeological factors such as depth to water level, net recharge, aquifer media, soil characteristics, topography, impact of vadose zone and hydraulic conductivity, gathered from well inventory, were considered as variables in this model. Additionally, we took into account the rainfall, geology, digital elevation model (DEM) and borehole lithology data to understand the above variables. Our vulnerability map divided the study area into zones of 'high', 'moderate' and 'low' groundwater pollution risks. Most of the basin is under the moderate pollution risk, and the regions of "high" vulnerabilities are associated with the shallow and permeable aquifer formations. The partial validation of this modelling with respect to the spatial distribution of nitrate in groundwater suggests that studies similar to ours in other regions can provide quick information to decision makers for better groundwater resource management and protection. [ABSTRACT FROM AUTHOR]

Effluents from leather tanneries and other small-scale industries have caused groundwater contamination in one of the biggest industrial centers (i.e. Vellore) of south India. This study evaluated quality of 70 different open and tube wells for consumption and health risks by collecting groundwater samples in four different seasons between 2017−2018. We compared physicochemical parameters of the groundwater samples with international drinking water standards (World Health Organization) to know their suitability for human consumption. Piper's trilinear diagram classified most of them as Ca-Cl and mixed Ca-Mg-Cl types. Inverse Distance Weighted (IDW) spatial interpolation showed the spatial distributions of different groundwater quality parameters. These parameters, including the Water Quality Index (WQI), indicated that most of the samples collected during the non-rainfall seasons (post-NE monsoon: 82.8 %; pre-SW monsoon: 78.6 %) were 'poor' for consumption. However, the qualities of 40–44.3 % of samples collected during both the rainfall seasons (NE and SW monsoon) were "good". We evaluated non-carcinogenic health risks for children and adults from consumption of the nitrate-rich groundwater by estimating the Hazard Quotient (HQ). Our results did not suggest any health risk for children and adults during both the rainfall seasons. In the non-rainfall seasons, about 59–63 % of samples posed health risk to children and 37–39 % caused possible health risk to the adult population. [ABSTRACT FROM AUTHOR]

Contamination of fluoride in drinking water affects human health, and its reduction is essential for the safe utilization of groundwater for domestic and agricultural uses. Groundwater in the ephemeral (monsoonal) Shanmuganadhi River basin, situated at rain shadow of the Western Ghats (south India), is indiscriminately utilized for rural water supply and agricultural activities. Fluoride contamination in groundwater of the river basin was evaluated using geochemical characteristics of sixty-one groundwater samples collected from the observation wells. Groundwater quality evaluation was attempted by estimating pH, Total Dissolved Solids (TDS), Electrical Conductivity (EC), and concentrations of Ca2+ Mg2+, Na+, K+, HCO3-, Cl-, SO 4 2-, NO3-, PO 4 3- and F-. Multivariate statistical techniques helped to identify the factors responsible for fluoride enrichment. The fluoride ion ranges from 0.01 to 2.5 mg/l with 77 % of the samples having less than 1.5 mg/l. Groundwater samples (23 %) with more than 1.5 mg/l of F- are unsuitable for consumption. Fluoride vulnerable zones were mapped using the Geographical Information System (GIS) in which fourteen villages of the basin are with risk category for dental fluorosis among children. The multivariate statistical techniques (including correlation matrix) highlight the relationship among various geochemical parameters, and the cluster analysis apprehends the sources/processes contributing the chemical variables. Based on this study, it is recommended to adopt natural remediation technique like Managed Aquifer Recharge (MAR) for the enhancement of groundwater quality in this basin. [ABSTRACT FROM AUTHOR]

The main objective of the present investigation is appraisal of human health hazard based on the intake and dermal contact of fluoride enriched potable groundwater used for rural water supply in a semi-arid region (Shanmuganadhi River basin) of south India. A variance decomposition based Sobol sensitivity method was used to assess the relative contribution as well as interaction of input variables for both oral and dermal models. Three different scores were evaluated: FOE (first order effect), SOE (second order effect) and TE (total effect) for different age groups of population including gender (kids, women and men). The spatio-temporal mapping indicates that about 26% of water supply wells exceeded the recommended limit (WHO) of fluoride (>1.5 mg l−1) for safe intake. These wells spread over 104.03 km2 area consisting 16 villages in the basin. To assess the human health risk related to fluoride enrichment in potable water, hazard index (HI) was calculated as per USEPA guidelines. The non-carcinogenic risk based on oral intake ranges from 0 to 1.81, from 0 to 1.59 and from 0 to 1.29 for kids, women and men respectively. Nearly 30%, 21% and 12% of well samples exceeded the upper permissible limit (HI > 1) for kids, women and men respectively. The Sobol sensitivity analysis reveals that, C w (concentration of F− in water) and IR (intake rate) combination plays a vital role in the HQ oral model for the appraisal of health hazard in kids. However, these two parameters have negligible effect on health hazard for adult population (men and women). Therefore, lower age group people especially kids have significant ill effect due to the consumption of fluoride enriched potable water. The model output suggests that body weight (BW) has least effect on health hazard in the lower age group of population. Interestingly 'exposure frequency (EF)' and 'body weight (BW)' have not much effect on health hazards related to dermal contact, and 'skin surface area (SA)' has minimal effect for men (TE = 0.92) and women (TE = 1.26). However, 'SA' has vital effect for kids (TE = 17.39). Because of this, older age group people have more dermal risk than the younger people. Therefore, the HQ dermal results indicate that 49%, 64% and 67% of samples possess non-carcinogenic risk to the kids, women and men respectively. • More than 1/4th of the sampled well waters in Shanmuganadhi Basin have > 1.5 mg l−1 of fluoride. • Appraisal of health hazard is based on Sobol sensitivity approach on oral intake and dermal contact of fluoride enriched groundwater. • Hazard Quotient (HQ) on oral intake indicates higher non-carcinogenic risk for kids compared to women and men. • HQ on dermal contact indicates higher non-carcinogenic risks for men and women compared to kids. [ABSTRACT FROM AUTHOR]

Groundwater in coastal areas, with surging population and growing settlements, is constantly at risk of pollution. Alappuzha is one of the most well-developed coastal districts in the southwestern Indian state of Kerala and employing various physico-chemical parameters (pH, EC, TDS, alkalinity, hardness, and contents of sodium, potassium, calcium, magnesium, carbonate, bicarbonate, chloride, sulphate, nitrate, and fluoride), this study aims to evaluate the drinking and irrigation water qualities of its groundwater resources and present their spatial distributions using the GIS platform. In the moderately hard to very hard groundwater of Ca-Mg-SO4 type, the ions dominate with order Ca > Na > Mg > K and HCO 3 > Cl > SO 4 > CO 3 > F. The water quality index (WQI) values (0.85–144, avg., 26.77) established the suitability of drinking water, revealing 53 % and 45 % of samples are lies under the categories of excellent and good, respectively. Only 2 % of the sample are in extremely poor water category. SAR, RSC, Na%, PI, KR and MH indices established that almost all of the groundwater can be used for agriculture, and the samples from northern coast showed vulnerability to contamination. • Groundwater in Alappuzha district (India) contains Ca-Mg-SO4 type. • One-fifth of samples in moderately hard to very hard groundwater categories. • WQI revealing 53 % and 45 % samples under the excellent and good. • The study area groundwater more suitable for dinking and agriculture purposes. [ABSTRACT FROM AUTHOR]

Nitrate and fluoride are two of the most prevalent pollutants in drinking water and exposure to their high concentrations could cause methemoglobinemia and fluorosis. This study attempted to evaluate the groundwater quality (pH: 4.4–9) from a relatively understudied part of the southwestern coast in India (i.e., Alappuzha, Kerala state) and assessed the associated health risks from exposures to nitrate (0.2–5.8 mg/l) and fluoride (0.2–1.9 mg/l) present in the groundwater. Pollution index (PIG: 0.35–5.43) grouped about 21% samples in high pollution and very high pollution categories because of fluoride content above the WHO guidelines. The total hazard index (THI) for adult male (0.17–1.70; average: 0.75), adult female (0.19–1.85; average: 0.81) and children (0.35–3.40; average: 1.50) suggested more non-carcinogenic risks for children from 41.6% samples compared to adult male and female from 33.3% samples in the absence of any mitigation measure. These results provide additional data from the country with highest population and the largest groundwater use in the context of sustainability in availability and supply of groundwater under the increasing risks of population growth, climate change and industrial development. • Groundwater in Alappuzha district (India) contains up to 1.9 mg/l of fluoride. • One-fifth of samples in high and very high pollution categories. • Health risk for adults from 33.3% groundwater samples. • Non-carcinogenic risk for children from 41.6% of groundwater samples. • Demarcation of areas with elevated fluoride posing health risk. [ABSTRACT FROM AUTHOR]