Assessment of hydrochemical backgrounds and threshold values of groundwater in a part of desert area, Rajasthan, India

Water Quality and Associated Human Health Risk Assessment Related to Some Ions and Trace Elements in a Series of Rural Roma Communities in Transylvania, Romania

This research aims to assess the content of some ions and trace elements in water sources in 24 rural Roma communities in Transylvania in order to assess the human health risk associated with exposure to such elements and ions. To this end, eight ions (F-, Cl-, Br-, NO2-, NO3-, SO42-, PO43-, NH4+) and ten trace elements (Cr, Ni, As, Pb, Cd, Mn, Cu, Zn, Fe, and Hg) were determined in 71 water samples by ion chromatography coupled with a conductivity detector for ions and atomic absorption spectrophotometry for all trace elements. General parameters were also determined. Non-conformity (as number of samples), according to the EU Drinking Water Directive, was observed as follows: pH (7), EC (7), hardness (1), oxidizability (15), Cl- (4), NO3- (30), SO42- (6), Fe (16), Mn (14), As (3), and Ni (1 sample). The incidence of ions was Cl- (71), SO42- (70), F- (67), NO3- (65), NH4+ (21), Br- (10), PO43-, and NO2- (1 sample) and for trace elements, Mn (59), Fe (50), As (38), Ni (32), Cu (29), Zn (28), Cd (12), Cr (11), and Pb (3 samples). Hg was not detected. Non-carcinogenic (HI) values exceeded one for As in 13 Roma communities, with higher values for children than for adults. For NO3-, the HI values were >1 in 12 for adults and 14 communities for children. The carcinogenic risk (CR) for As through ingestion ranged from 0.795 to 3.50 × 10-4 for adults and from 1.215 to 5.30 × 10-4 for children. CR by dermal contact was in the range of ×10-6 both for adults and children.

Analyzing post-2000 groundwater level and rainfall changes in Rajasthan, India, using well observations and GRACE data

Research on groundwater and water resources is essential for preserving viable environments. Although the arid area has been identified as a significant hotspot for groundwater depletion, the Indian desert region was not included in the initial analysis. This study intends to evaluate Rajasthan's groundwater level (GWL) and rainfall trends from 2000 to 2021 and how variations in GWLs are related to long-term rainfall. Annual GWL and rainfall data time series were collected from 921 monitoring stations for 33 districts of Rajasthan. The GWL trends and rainfall were identified using non-parametric modified Mann-Kendall test and Spearman rho techniques. Pearson's, Kendall's (tau b), and Spearman's analyses were used to determine the correlation between GWL and rainfall. The results from the modified Mann-Kendall and Spearman rho methods reveal that GWL has a significant declining trend in 38 % of districts, where 13 % have no trend, and the rest of 49 % have a rising trend. The yearly rainfall trend at 70 % and 30 % of the districts are rising and stable, respectively. A negative correlation between GWL depth and rainfall was discovered in each district, where 15 % are firm, 58 % are moderate, and 27 % are weak negative correlations. Also, the regression analysis estimates the effect of rainfall on GWL, which was observed: rainfall negatively influenced the depth of GWL at 58 % of the districts, had a positive impact at 33 %, and others had no effect. GRACE TWS anomaly shows a decreasing trend of -1.22 cm/yr, and GRACE and GWL anomalies have a positive relationship (r = 0.471). Results conclude that rainfall is the primary influencer on GWL in this semi-arid region vulnerable to drought.

Evaluating natural background levels of heavy metals in shallow groundwater of the Pearl River Delta via removal of contaminated groundwaters: Comparison of three preselection related methods

Assessing natural background levels (NBLs) in groundwater is a global concern. Knowledge on groundwater NBLs in urbanized areas is challenging due to the impact of complex human activities. Preselection related methods are common ones for assessing groundwater NBLs. The present study used three preselection related methods to assess groundwater heavy metals (lead, zinc, barium) NBLs in four groundwater units of the Pearl River Delta (PRD) where urbanization continues, and to identify the best one for assessing groundwater NBLs in urbanized areas. Here, methods include a preselection method (method-P), a preselection dominated method (method-PD), and a statistic dominated method (method-SD). Results showed that the method-PD was better than other two methods for assessing groundwater NBLs of heavy metals in the PRD. This is supported by the evidence that differences among heavy metals concentrations in various land-use types in residual datasets formed by the method-PD were insignificant. NBLs of lead in groundwater units I to IV assessed by the method-PD were 2.8 μg/L, 5.9 μg/L, 5.8 μg/L, and 2.6 μg/L, respectively. NBLs of zinc in groundwater units I to IV assessed by the method-PD were 30 μg/L, 180 μg/L, 160 μg/L, and 100 μg/L, respectively. NBLs of barium in groundwater units I to IV assessed by the method-PD were 120 μg/L, 120 μg/L, 90 μg/L, and 50 μg/L, respectively. Compared to the method-PD, the method-SD often underestimates groundwater NBLs of heavy metals because of using the experiential evaluation for residual datasets. The method-P also has an inaccurate evaluation of groundwater NBLs of heavy metals in comparison with the method-PD, owing to both of using the experiential evaluation and the absence of a function for outliers test. The method-P combining with an outliers test would be better than itself for assessing groundwater NBLs. Therefore, the method-PD is the first choice to be recommended for assessing groundwater NBLs in urbanized areas such the PRD. However, this method should not be taken into account for assessing groundwater NBLs in areas where groundwater Cl/Br mass ratios are invalid. Instead, the method-SD and the method-P combining with one outliers test may be choices, because no constraint for these two methods.

Hydrochemical characteristics and potential health risks of nitrate, fluoride, and uranium in Kota district, Rajasthan, India

This study examines the uranium, fluoride, and nitrate dispositions in groundwater as well as potential health risks in Kota district, Rajasthan, India. Total 198 groundwater samples were collected in both dry and wet periods and analyzed for physicochemical parameters along with U, F^-, and NO₃^- using standard methods. Results indicate that the electrical conductivity, total dissolved solids, total hardness, alkalinity, Ca²⁺, Mg²⁺, HCO₃^-, Cl^-, NO₃^-, and F^- exceed the WHO standard limits of drinking water in both periods. Uranium concentration is at the broader of drinking water permissible limit (30 μg/L) and found about 1.05 times more. Nitrate and fluoride concentrations ranged from 9.8 to 412.0 mg/L and 0.1 to 4.0 mg/L for the dry season, while in the wet period, they varied from 10.0 to 954.0 mg/L and 0.1 to 3.5 mg/L, respectively. Correlation studies show a significantly strong positive correlation between uranium and total alkalinity and carbonate. Natural background levels (NBLs) were explored to assess the source of groundwater pollution. It shows that the second inflection points of NBLs estimated for NO₃^-, F^-, and U are about 168 mg/L, 1.2 mg/L, and 7.3 μg/L, respectively, during the experimental period. The USEPA technique was used to evaluate the non-carcinogenic health risks associated with consuming the NO₃^- and F^--contaminated groundwater. The health risks in Kota district show that children are more at risk than adults. The risk assessment of uranium reveals that the excess cancer risk (ECR) and hazard quotient (HQ) are found to be below the standard limits, but a high concentration of uranium (31.6 μg/L) is observed at Amarpura village of Digod block. This study will provide a baseline of uranium, fluoride, and nitrate dispositions in groundwater for simulating mass transport model and safe use of drinking water.

Risk Control Values and Remediation Goals for Benzo[a]pyrene in Contaminated Sites: Sectoral Characteristics, Temporal Trends, and Empirical Implications

Benzo[a]pyrene (BaP) is a highly carcinogenic pollutant of global concern. There is a need for a comprehensive assessment of regulation decisions for BaP-contaminated site management. Herein, we present a quantitative evaluation of remediation decisions from 206 contaminated sites throughout China between 2011 and 2021 using the cumulative distribution function (CDF) and related statistical methodologies. Generally, remediation decisions seek to establish remediation goals (RGs) based on the risk control values (RCVs). Cumulative frequency distributions, followed non-normal S-curve, emerged multiple nonrandom clusters. These clusters are consistent with regulatory guidance values (RGVs), of national and local soil levels in China. Additionally, priority interventions for contaminated sites were determined by prioritizing RCVs and identifying differences across industrial sectors. Notably, we found that RCVs and RGs became more relaxed over time, effectively reducing conservation and unsustainable social and economic impacts. The joint probability curve was applied to model decision values, which afforded a generic empirically important RG of 0.57 mg/kg. Overall, these findings will help decision-makers and governments develop appropriate remediation strategies for BaP as a ubiquitous priority pollutant.

A double pre-selection method for natural background levels assessment in coastal groundwater bodies

To evaluate the chemical status of groundwater bodies (GWB) according to the European Groundwater Directive, EU Member States are required to take into account natural background levels (NBLs) where needed. Assessing the NBLs in coastal GWBs is complicated by seawater intrusion which can be amplified by groundwater withdrawals increasing the salinization of such groundwater systems. This paper proposes a new method for the NBLs assessment in coastal areas based on a double pre-selection (PS) with fixed/dynamic limits. A case study in the Apulia region, located in southeastern Italy, is proposed, where we investigated four adjacent GWBs which form the complex karst, fractured Murgia aquifer, hosted in the Jurassic-Cretaceous carbonate platform, bounded by two seas and sustained by saltwater of marine intrusion in the coastal areas. Data related to 139 monitoring stations (MSs) of the regional groundwater monitoring network were used. The first PS, "static", based on a fixed limit of anthropogenic contamination markers (NO₃ and NH₄), allows for the elimination of MSs impacted by human activities. On these, the second PS, "dynamic", based on the identification of Cl anomalous values, allows for the identification of additional MSs affected by saline contamination. The residual dataset of MSs was used for the definition of NBLs of Cl, SO₄, F and B. A statistical comparison with historical Cl observations finally allowed us to verify if the salinity of current groundwater is representative of pristine conditions. The calculated NBLs of salinity parameters are higher for the two coastal GWBs, with chloride values between 0.8 and 2 mg/L. Conversely, fluorides always show very low NBLs. The double PS approach seems more effective for NBLs calculation in coastal aquifers affected by saline contamination, where the use of a fixed Cl limit fails. It may respond to the international needs for a standardized procedure for NBL assessment.

Coupling of multi-hydrochemical and statistical methods for identifying apparent background levels of major components and anthropogenic anomalous activities in shallow groundwater of the Liujiang Basin, China

Natural background levels (NBLs) is a prerequisite for distinguishing anthropogenic groundwater pollution and judging the evolution of groundwater quality. However, due to regional differences of hydrogeochemitry and water-rock interaction, coupled with long-term anthropogenic activities, it is no longer accurate to assess NBLs with only statistical methods or without considering human impact. Herein, multi-hydrochemical and statistical methods were examined to identify apparent background levels and anthropogenic anomalous activities of shallow groundwater by selecting Liujiang Basin as a study area. The results showed that the differences in hydrochemical characteristics among each hydrogeological unit (HU) fully illustrated the necessity of rationally dividing HU for background value identification. The application of the concept of apparent background levels (ABLs), that is, incorporating normal human activities into the background levels, efficiently solved the problem of being unable to obtain pristine NBLs due to long-term human activities. The coupling of Hydrochemistry and Grubbs' test (Hydro-Grubbs) was confirmed as the optimal method in identifying and eliminating anthropogenic groundwater anomalies, performing sufficiently superiority when compared with purely statistical methods. It is mainly because the Hydro-Grubbs method not only considers the discreteness of the data itself, but also considers the internal connection and evolution process of the hydrochemical compositions. For the eliminated abnormal points, 91.0-93.6% of which have been effectively explained by pollution percentage index and the impact of coal mining, industrial activities, residents, agricultural activities, and septic tanks leakage, proving the rationality and reliability of Hydro-Grubbs method and ABLs evaluation result. This finding will assist in accurately identifying anthropogenic pollution on a regional scale and guiding future efforts to protect groundwater resources.

Health risk assessment of fluoride exposure due to groundwater consumption in Romania

Fluoride has both beneficial and detrimental effects on human health. Concentrations of fluoride less than 1.0 mg/L in ingested water are beneficial for the rate of tooth decay, especially in children. The aims of the paper are as follows: (i) to monitor fluoride concentrations in drinking water samples (well water and tap water from the rural district of Valea Râmnicului, Romania); (ii) to study and select the optimal buffer solution and the optimal volume used in the analyses and (iii) to validate the potentiometric method for determining fluoride ions with a selective ion electrode. The values of fluoride ion concentrations in the groundwater samples and in tap water varied from 0.01 to 0.138 mg^/L. The values for the hazard quotient for the studied samples varied from 0.01 to 0.13.

Impact of Flooding on Shallow Groundwater Chemistry in the Taklamakan Desert Hinterland: Remote Sensing Inversion and Geochemical Methods

Understanding the effect of flooding on groundwater quality is imperative for oasis vegetation protection and local ecological environment development. We used geochemical and remote sensing inversion methods to evaluate the effects of flood recharge on the groundwater hydrochemical and geochemical processes in the Daliyaboy Oasis. Groundwater samples were collected from 30 ecological observation wells in the study area before (PRF) and after (POF) the flood. Except for small changes in HCO3− and K+ and a decrease in pH, ion levels were higher POF than PRF, and the water chemistry was essentially unchanged. In the POF groundwater, HCO3− was correlated with Cl−, Na+, Mg2+, total soluble solids (TDS), and electrical conductivity (EC), but not with SO42−, Ca2+, K+, or pH, and was positively correlated with all other variables, while the remaining variables, except for pH, were strongly positively correlated with each other. PRF water chemistry was controlled by silicate and evaporite mineral weathering and evaporation processes, resulting in high groundwater TDS, EC, and a major ion content, while POF major groundwater ions were regulated by mineral weathering and flood recharge. We demonstrated the high accuracy of remote sensing inversion, confirming this as a reliable method for evaluating groundwater chemistry. The results of the study help to reshape and predict the history of the regional hydrogeological environment and hydrogeochemical development, and provide a theoretical basis for assessing the rational use of local water resources and protecting the ecological environment.

Source apportionment and natural background levels of major ions in shallow groundwater using multivariate statistical method: A case study in Huaibei Plain, China

Understanding the sources, natural background levels (NBLs), and threshold values (TVs) of the major ions in groundwater is essential for the effective protection of water resources. In this study, a total of 70 shallow groundwater samples were collected in Suzhou, Huaibei Plain, China. A variety of statistical methods and cumulative probability distribution techniques were performed to identify the sources, NBLs, and TVs of the major ions. The major ion concentrations found in decreasing order as follows: HCO₃^- > SO₄^2- > NO₃^- > Cl^- and Na⁺ > Ca²⁺ > Mg²⁺. Piper diagram for hydrochemical types shows that groundwater types were Mg-HCO₃ (36%), Ca-HCO₃ (34%), and Na-HCO₃ (30%). According to the factor and the Unmix model analysis, anthropogenic (agriculture-related) and geogenic source (water-rock interactions-related) were identified to be responsible for the chemical composition of the groundwater in the study area, and their mean contributions for the major ion concentrations are 47.9% and 52.1%, respectively. The NBLs for Na⁺, Ca²⁺, Mg²⁺, Cl^-, SO₄^2-, and NO₃^- were determined to be 29.5-44.2, 26.2-38.9, 18.9-39.5, 1.0-9.9, 12.9-19.4, and 2.1-16.5 mg/L, respectively, and the TVs were calculated as 122.1, 169.5, 39.5, 129.6, 134.7, and 18.3 mg/L, respectively. Moreover, this study shows the feasibility and reliability of using these multivariate statistical methods and natural background levels to evaluate the status of groundwater quality.

Distributed groundwater recharge potentials assessment based on GIS model and its dynamics in the crystalline rocks of South India

Extensive change in land use, climate, and over-exploitation of groundwater has increased pressure on aquifers, especially in the case of crystalline rocks throughout the world. To support sustainability in groundwater management require proper understating of groundwater dynamics and recharge potential. GIS based studies have gained immense popularity in groundwater exploration in recent years because they are fast and provide recent information on the resource for future growth. Thus, the present study utilized a GIS-based Weighted Overlay Index (WOI) model to identify the potential recharge zones and to gain deep knowledge of groundwater dynamics. The in situ infiltration tests have been carried out, which is the key process in groundwater recharge and is neglected in many cases for WOI. In the WOI, ten thematic layers from the parameters influencing and involved in the recharge process are considered to identify potential recharge zones. The results suggested a significant underestimation of recharge potential without considering site-specific infiltration rates that one needs to be considered. The present WOI model considered in situ infiltration information and classified the entire area into four recharge zones, good, moderate, poor, and very poor. The final integrated map compared with the real-time field data like water level fluctuation and infiltration to analyse occurrence and quantification of recharge. The estimated average groundwater draft is 21.9 mcm, while annual renewable recharge is only 5.7 mcm that causing a continuous fall of the groundwater table. The study is useful in selecting regions with more focussed recharge studies and suggested the need of reducing groundwater demand by changing cropping patterns through a predictive decision support tool.

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.

Arsenic enrichment and its natural background in groundwater at the proximity of active floodplains of Ganga River, northern India

Arsenic contaminated groundwater is seen as one of the most critical routes of human exposure to geogenic pollutants. Recently around 40 million inhabitants of the world are living in the hazardous zone having groundwater As level >50 μg/L. As problem of groundwater in Bhagirathi-Ganga deltaic plain is well-known for over the last three decades. Hydrogeochemical analytical data related to the As concentration had been analysed to identify the As sources in groundwater of the active floodplains of the Ganga basin in Northern India. The natural background level of As was also estimated using Grubb's test and cumulative probability plots. The natural background level is a crucial parameter for identifying and quantifying groundwater pollution and assessing measures to control pollution. The anthropogenic addition of As in groundwater was separated by the estimated inflection point. The results show that the highest As concentration, which is 8-times more than the permissible limit, is observed at Gyantoli village in Begusarai district in Bihar state. Groundwater is alkaline with a high concentration of HCO₃^- as compared to other chemical parameters. Further, it indicates the dominance of carbonate weathering and relatively high pH values (range: 8.00-9.00) helps to release As in groundwater. The reducing environment of the aquifer system becomes oxic at the shallow depth due to comparatively shallow groundwater level, and impressive water level fluctuation resulting in vertical mixing of anthropogenic As contaminants.