Environmental chemistry, toxicity and health risk assessment of groundwater: Environmental persistence and management strategies.

Groundwater is a significant supply of freshwater for the world's population, being used for residence, agricultural, and industrial purposes. One-third of the world's population relies on groundwater for drinking applications. Groundwater pollution is a global issue with serious consequences for human health and the environment. It needs a thorough understanding because access to safe drinking water is a basic human right. However, groundwater quality is being threatened by urbanisation, agricultural activities, industrial activities, and climate change, among others. Pollutants like hydrocarbons, toxic metals, pesticides, microplastics, nanoparticles and other emerging contaminants mean a risk to human health and sustainable socioeconomic development. To ensure sustained groundwater usage to assess, monitor, and regulate groundwater quality issues is essential. Excess withdrawal alters groundwater flow together with contaminants like uranium, radon, radium, salinity, arsenic and fluoride, resulting in mediocre water quality. Consequently, chemical and biological contaminants owing to domestic, industrial, and agricultural practices alter water quality and threaten human health. Controlling and management of groundwater pollution and related health risks require developing vulnerability, hazard, and risk maps.

Hydrogeochemical characteristics and risk evaluation of potential toxic elements in groundwater from Shanmughanadhi, Tamilnadu, India.

Hydrogeochemical and Health Risk Assessments of trace elements are integral to groundwater resource assessment, utilization, and human health. Investigation of groundwater chemistry and trace elemental impact on local inhabitants were attempted in Shanmuganadhi basin, Tamilnadu, India. About 60 groundwater samples were collected during the pre-monsoon period and analyzed for hydrochemical composition, including major and trace elements (Fe, Cr, Ni, Cu Pb, Mn, and As) to isolate chemical characteristics and human health risk assessment. Groundwater geochemistry is prejudiced by geochemical reactions uniting cation exchange, dissolution and precipitation, adsorption, and anthropogenic contributions. About thirty-two percent of groundwater samples recorded higher F-(>1.5 mg/L) than the prescribed limit suggests sources from rock weathering and silicate dissolution. Nitrates (>45.0 mg/L) suggest sources from agricultural influences. Water types indicate alkalis (Na+ + K+) dominating alkali earth (Ca2+ - Mg2+) and strong acids (Cl- and SO42-) looming weak acid (CO32- and HCO3-) irrespective of water samples. The geochemical stability diagram suggests precipitation of silica, carbonate, and magnesium and dissolution of sulphate minerals along the groundwater flow path. Significant correlation between major ions and trace elements (Pb, Mn, Ni, and Cu) suggests origin from rock weathering, human impacts, and cultivation practices. Non-carcinogenic human risk for trace elements was higher in children compared with adults via ingestion and dermal exposure. The carcinogenic result suggests that Cr in CHK (7.1 × 10-2) and HBG (4.3 × 10-2) have the most excellent chance of cancer risk. The environmental risk category attempted using Comprehensive risk factor (CRI) suggests Pb (3.2-CHK, 2.6-HBG) with potential cancer risk. The comprehensive evaluation index recommends environmental damage between mild to moderate, indicating continuous exposure of traceable elements might result in cancer cause to the inhabitants. The study suggests water quality seems to be prejudiced by various geological and anthropogenic causes and endorses counteractive measures and proper execution of existing laws to protect groundwater resources in the study area.

Sources and Consequences of Groundwater Contamination.

Groundwater contamination is a global problem that has a significant impact on human health and ecological services. Studies reported in this special issue focus on contaminants in groundwater of geogenic and anthropogenic origin distributed over a wide geographic range, with contributions from researchers studying groundwater contamination in India, China, Pakistan, Turkey, Ethiopia, and Nigeria. Thus, this special issue reports on the latest research conducted in the eastern hemisphere on the sources and scale of groundwater contamination and the consequences for human health and the environment, as well as technologies for removing selected contaminants from groundwater. In this article, the state of the science on groundwater contamination is reviewed, and the papers published in this special issue are summarized in terms of their contributions to the literature. Finally, some key issues for advancing research on groundwater contamination are proposed.

Chemical weathering and atmospheric carbon dioxide (CO2) consumption in Shanmuganadhi, South India: evidences from groundwater geochemistry.

Chemical weathering in a groundwater basin is a key to understanding global climate change for a long-term scale due to its association with carbon sequestration. The present study aims to characterize and to quantify silicate weathering rate (SWR), carbon dioxide consumption rate and carbonate weathering rate (CWR) in hard rock terrain aided by major ion chemistry. The proposed study area Shanmuganadhi is marked with superior rainfall, oscillating temperature and runoff with litho-units encompassing charnockite and hornblende-biotite gneiss. Groundwater samples (n = 60) were collected from diverse locations and analysed for major chemical constituents. Groundwater geochemistry seems to be influenced by geochemical reactions combining dissolution and precipitation of solids, cation exchange and adsorption along with minor contribution from anthropogenic activities. The SWR calculated for charnockite and hornblende-biotite gneiss was 3.07 tons km-2 year-1 and 5.12 tons km-2 year-1, respectively. The calculated CWR of charnockite and hornblende-biotite gneiss was 0.079 tons km-2 year-1 and 0.74 tons km-2 year-1, respectively. The calculated CO2 consumption rates via silicate weathering were 1.4 × 103 mol km-2 year-1 for charnockite and 5.8 × 103 mol km-2 year-1 for hornblende-biotite gneiss. Lithology, climate and relief were the key factors isolated to control weathering and CO2 consumption rates.

Submarine Groundwater Discharge from an Urban Estuary to Southeastern Bay of Bengal, India: Revealed by Trace Element Fluxes.

Submarine groundwater discharge and associated trace element fluxes from the Coleroon River estuary to south bay, India, has been attempted, because increasing trace elements could result in harmful algal blooms and eutrophication. Trace elements (Al, Cr, Mn, Fe, Ni, Cu, Zn, Sr, Mo, Ba, Pb, Th, and U) in surface water, pore, and groundwater samples were monitored for 10 days in three locations (A, B, and C) by considering tidal fluctuations. The trace elements Al, Cr, Fe, Ni, Zn, Sr, Mo, Pb, Th, and U were greater and found to be influenced by processes, such as fresh groundwater discharge and seawater intrusion. Lower Mn, Cu, and Ba signifies impact due to sediment adsorption, mixing, and elemental exchange during fresh groundwater and seawater mixing. Salinity versus trace element plot infers greater trace element mobility with cumulative salinity influenced by the conformist behavior of freshwater, seawater, and mixing. The calculated submarine groundwater discharge supported dissolved trace elements fluxes were 107,047.8 n mol d-1 m-1 for location A, 183,520.2 n mol d-1 m-1 for location B, and 181,474.4 n mol d-1 m-1 for location C, respectively. Variations in dissolved trace elements fluxes are attributed to variations in pH, free redox environment in the aquifer, adsorption or desorption by sediments, and the environmental cycle of marine organisms.

Hydrochemical and statistical techniques to decode groundwater geochemical interactions and saline water intrusion along the coastal regions of Tamil Nadu and Puducherry, India.

The study attempts to decipher saline water invasion and aided geochemical influences activated along the coastal zones of Tamil Nadu and Puducherry. Total 76 groundwater samples representing pre- and post-monsoon seasons were collected and examined for various parameters like Ca2+, K+, Na+, Mg2+, Cl-, HCO3-, NO3- and SO42-. Multiple techniques such as hydrochemical ionic changes, hydrochemical facies evolution model and seawater mixing index were incorporated to decipher the salinization process in the study area. Hydrochemical facies suggests 38.00% of groundwater samples representing CaHCO3 facies indicating fresh groundwater, mixed Ca-Cl groundwater by 26.00% of samples and about 36.00% samples suggest Na-Cl indicating saline water. Hydrochemical facies evolution diagram differentiated groundwater facies into freshening and intrusion phase irrespective of seasons. About 23.60% and 21.00% of samples during pre- and post-monsoon suggest samples influenced by seawater intrusion. Hydrochemical ionic changes of samples signify the positive fraction of seawater in both seasons, which shows the mixing of fresh groundwater with saline water. The seawater mixing index confirms a greater percentage of samples during post-monsoon (42.00%) have been influenced by seawater with values greater than one. Principle component analysis extracted three factors with a total variance of 67.31% and 62.03% during pre- and post-monsoon seasons, respectively. Factor 1 replicates the natural processes such as saline water intrusion and ion exchange, whereas factors 2 and 3 signify anthropogenic actions such as improper sewage disposal, use of fertilizers, domestic and industrial waste discharge influencing groundwater chemistry.

Submarine groundwater discharge as sources for dissolved nutrient fluxes in Coleroon river estuary, Bay of Bengal, India.

Groundwater contributed nutrients aided with increasing population threaten the global coastal ecosystems. In this study, attempt has been made using major ions and nutrients to evaluate the significance of submarine groundwater discharge (SGD) in a semi-arid estuary of south India. Surface, seepage and groundwater chemistry altered from fresh (NaK-CaMg-NO3Cl) to mixed (NaK-NO3Cl) to saline water (NaCl) type from upstream to outlet that connects Bay of Bengal. We predicted abundant nitrate (NO3-) along upstream and towards the bay due to application of fertilizers and aquaculture activities, respectively. Elevated ammonium (NH4+) observed in the recirculated groundwater/sea water suggests contribution from sea water intrusion and higher phosphate (PO43-) noted at the outer bay suggests sources from phosphatic nodules. Decreasing Redfield ratio towards the bay suggests anoxic aquifer condition due to salinization. The SGD driven nutrient fluxes were 40.0-47.0% for NO3-, 43.0-51.0% for NH4+ and 9.0-32.0% for PO43- from the total input fluxes. The estimated nutrient fluxes showed that NO3- and PO43- discharges to the sea due to SGD and NH4+ removed from the coast due to consumption by microorganisms that creates toxic algal blooms in the study area.

Evaluation of non-carcinogenic risks due to fluoride and nitrate contaminations in a groundwater of an urban part (Coimbatore region) of south India.

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, Ca2+, Mg2+, Na+, K+, Cl-, SO42-, HCO3-, PO43-, NO3-, 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 km2. 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 km2. 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.

Geochemical evaluation of fluoride contamination in groundwater from Shanmuganadhi River basin, South India: implication on human health.

In order to assess the geochemical mechanism liable for fluoride contamination in groundwater and its health effects on the people of the Shanmuganadhi River basin, Tamil Nadu, India, 61 groundwater samples were collected during post- and pre-monsoon seasons from the wells used for drinking purposes. Collected samples were analysed for various physico-chemical parameters. The parameters estimated in the present study are hydrogen ion concentration (pH), total dissolved solids, electrical conductivity, calcium (Ca2+), magnesium (Mg2+), sodium (Na+), potassium (K+), bicarbonate (HCO3-), chloride (Cl-), sulphate (SO42-), nitrate (NO3-), phosphate (PO43-) and fluoride (F-). The fluoride ion concentration in the groundwater samples of this region varied from 0.01 to 2.50 mg/l and 0.01 to 3.30 mg/l during post- and pre-monsoon seasons, respectively. Out of 61 groundwater samples, 14 samples of post-monsoon season and 16 samples of pre-monsoon season represented high, very high and extremely high classes of fluoride, which cause dental fluorosis in this region. The fluoride-bearing minerals in the granitic and gneissic rocks such as apatite, hornblende, muscovite, biotite and amphiboles are the major sources for fluoride contamination in this area. In addition to the geogenic sources, applications of synthetic fertilizers in the agricultural fields also contribute significant amount of fluoride ions to groundwater. The spatial distribution of fluoride in different geological formations clearly indicate that the wells located in charnockite terrain were possessing very low fluoride concentration when compare with the wells located in the hornblende-biotite gneiss formation. Therefore, dental fluorosis risks are mostly associated with rock types in this region. People living over the basement rock comprising of hornblende-biotite gneiss are prone for fluorosis. Fluoride exhibited good positive correlation with bicarbonate in groundwater. As fluoridated endemic regions normally acquire lot of bicarbonate in groundwater samples, Shanmuganadhi basin falls under fluoride endemic category. The present study identified 26 villages in Shanmuganadhi basin as probable fluorosis risk areas where attention should be given to treat the fluoride-rich groundwater before drinking water supply. The groundwater level fluctuation study also designates that rise in water level reduces the concentration of fluoride due to dilution mechanism. Therefore, recharge of groundwater by artificial methods will definitely improve the present scenario.

Tracing groundwater salinization using geochemical and isotopic signature in Southeastern coastal Tamilnadu, India.

Attempt has been made to discriminate groundwater salinity causes along the east coast of India. A total of 122 groundwater samples (61/season) were collected for two diverse seasons (Pre Monsoon and Post Monsoon) and analyzed for physical and chemical components along with stable isotopes. The Piper diagram proposes samples along the coast predisposed by saltwater incursion. Ionic ratio plots recommend groundwater discriminatory by changing geochemical signatures. The statistical correlation suggests impact of saltwater incursion, anthropogenic and rock water interaction as sources for dissolved constituents in groundwater. The thermodynamic stability plot suggests higher silicate dissolution, weathering and ion exchange prompting water chemistry nevertheless of seasons. The δ18O and δ2H increases towards the sea suggesting enrichment attributed to the sea water influence and rainfall influences along the southwestern parts of the study area.

Evaluation of groundwater suitability for domestic, irrigational, and industrial purposes: a case study from Thirumanimuttar river basin, Tamilnadu, India.

The Thirumanimuttar sub-basin forms an important groundwater province in south India, facing serious deficiency in both quality and quantity of groundwater due to increased demand associated with rapid population explosion, agricultural growth and industrial activities. A total of 194 groundwater samples were collected and 15 water quality parameters were analyzed using standard procedures. Na( + ), Cl( - ), Ca(2 + ), HCO(-)(3), Mg(2 + ) and SO(2-)(4) concentration ions are more dominant in both seasons. The total dissolved solids and electrical conductivity was observed good correlation with Na( + ), Cl( - ), HCO(-)(3), Ca(2 + ), Mg(2 + ), Cl( - ), PO(3-)(4) and NO(-)(3) ions indicating dominance of plagioclase feldspar weathering, anthropogenic input and over drafting of groundwater irrespective of seasons. The Hill-Piper diagram indicates alkaline earths exceed the alkalis, an increase of weak acids was noted during both the seasons. For assessing the groundwater for irrigation suitability parameters like total hardness, sodium adsorption ratio, residual sodium carbonate (RSC), permeability index, and sodium percentage are also calculated. Permanent hardness was noted in higher during both the seasons due to discharge of untreated effluents and ion exchange process. The RSC indicates 56% of the samples are not suitable for irrigation purposes in both seasons, if continuously used will affect the crop yield. From the results, nearly 72% of the samples are not suitable for irrigation.

Application of water quality index for groundwater quality assessment: Thirumanimuttar sub-basin, Tamilnadu, India.

An attempt has been made to understand the hydrogeochemical parameters to develop water quality index in Thirumanimuttar sub-basin. A total of 148 groundwater samples were collected and analyzed for major cations and anions. The domination of cations and anions was in the order of Na>Mg>Ca>K for cations and Cl>HCO(3) >SO(4) in anions. The hydrogeochemical facies indicate alkalis (Na and K) exceed alkaline earths (Ca and Mg) and strong acids (Cl and SO(4)) exceed weak acid (HCO(3)). Water quality index rating was calculated to quantify overall water quality for human consumption. The PRM samples exhibit poor quality in greater percentage when compared with POM due to effective leaching of ions, over exploitation of groundwater, direct discharge of effluents and agricultural impact. The overlay of WQI with chloride and EC correspond to the same locations indicating the poor quality of groundwater in the study area. SAR, Na%, and TH were noted higher during both the seasons indicating most of the groundwater locations not suitable for irrigation purposes.

Study of evaluation of groundwater in Gadilam basin using hydrogeochemical and isotope data.

Gadilam river basin has gained its importance due to the presence of Neyveli Lignite open cast mines and other industrial complexes. It is also due to extensive depressurization of Cuddalore aquifer, and bore wells for New Veeranam Scheme are constructed downstream of the basin. Geochemical indicators of groundwater were used to identify the chemical processes that control hydrogeochemistry. Chemical parameters of groundwater such as pH, electrical conductivity, total dissolved solids, sodium (Na(+)), potassium (K(+)), calcium (Ca(+)), magnesium (Mg(+)), bicarbonate (HCO(-)(3)), sulfate (SO(-)(4)), phosphate (PO(-)(4)), and silica (H(4)SiO(4)) were determined. Interpretation of hydrogeochemical data suggests that leaching of ions followed by weathering and anthropogenic impact controls the chemistry of the groundwater. Isotopic study reveals that recharge from meteoric source in sedimentary terrain and rock-water interaction with significant evaporation prevails in hard rock region.