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High concentrations of metal(loid)s in phosphate rocks and wastewater associated with phosphate mining and fertilizer production operations pose potential contamination risks to water resources. Here, we propose using Sr isotopes as a tracer to determine possible water quality impacts induced from phosphate mining and fertilizers production. We utilized a regional case study in the northeastern Negev in Israel, where salinization of groundwater and a spring have been attributed to historic leaking and contamination from an upstream phosphate mining wastewater. This study presents a comprehensive dataset of major and trace elements, combined with Sr isotope analyses of the Rotem phosphate rocks, local aquifer carbonate rocks, wastewater from phosphate operation in Mishor Rotem Industries, saline groundwater suspected to be impacted by Rotem mining activities, and two types of background groundwater from the local Judea Group aquifer. The results of this study indicate that trace elements that are enriched in phosphate wastewater were ubiquitously present in the regional and non-contaminated groundwater at the same levels as detected in the impacted waters, and thus cannot be explicitly linked to the phosphate wastewater. The

Northwest India suffers from severe water scarcity issues due to a combination of over-exploitation and climate effects. Along with concerns over water availability, endemic water quality issues are critical and affect the usability of available water and potential human health risks. Here we present data from 243 groundwater wells, representing nine aquifer lithologies in 4 climate regions that were collected from the Northwestern Indian state of Rajasthan. Rajasthan is India's largest state by area, and has a significant groundwater reliant population due to a general lack of surface water accessibility. We show that the groundwater, including water that is used for drinking without any treatment, contains multiple inorganic contaminants in levels that exceed both Indian and World Health Organization (WHO) drinking water guidelines. The most egregious of these violations were for fluoride, nitrate, and uranium; 76% of all water samples in this study had contaminants levels that exceed the WHO guidelines for at least one of these species. In addition, we show that much of the groundwater contains high concentrations of dissolved organic carbon (DOC) and halides, both of which are risk factors for the formation of disinfectant byproducts in waters that are treated with chemical disinfectants such as chlorine. By using geochemical and isotopic (oxygen, hydrogen, carbon, strontium, and boron isotopes) data, we show that the water quality issues derive from both geogenic (evapotranspiration, water-rock interactions) and anthropogenic (agriculture, domestic sewage) sources, though in some cases anthropogenic activities, such as infiltration of organic- and nitrate-rich water, may contribute to the persistence and enhanced mobilization of geogenic contaminants. The processes affecting Rajasthan's groundwater quality are common in many other worldwide arid areas, and the lessons learned from evaluation of the mechanisms that affect the groundwater quality are universal and should be applied for other parts of the world.

Extensive development of horizontal drilling and hydraulic fracturing enhanced energy production but raised concerns about drinking-water quality in areas of shale-gas development. One particularly controversial case that has received significant public and scientific attention involves possible contamination of groundwater in the Trinity Aquifer in Parker County, Texas. Despite extensive work, the origin of natural gas in the Trinity Aquifer within this study area is an ongoing debate. Here, we present a comprehensive geochemical dataset collected across three sampling campaigns along with integration of previously published data. Data include major and trace ions, molecular gas compositions, compound-specific stable isotopes of hydrocarbons (δ13C-CH4, δ13C-C2H6, δ2H-CH4), dissolved inorganic carbon (δ13C-DIC), nitrogen (δ15N-N2), water (δ18O, δ2H, 3H), and noble gases (He, Ne, Ar), boron (δ11B) and strontium (87Sr/86Sr) isotopic compositions of water samples from 20 drinking-water wells from the Trinity Aquifer. The compendium of data confirms mixing between a deep, naturally occurring salt- (Cl >250 mg/L) and hydrocarbon-rich groundwater with a low-salinity, shallower, and younger groundwater. Hydrocarbon gases display strong evidence for sulfate reduction-paired oxidation, in some cases followed by secondary methanogenesis. A subset of drinking-water wells contains elevated levels of hydrocarbons and depleted atmospherically-derived gas tracers, which is consistent with the introduction of fugitive thermogenic gas. We suggest that gas originating from the intermediate-depth Strawn Group (“Strawn”) is flowing along the annulus of a Barnett Shale gas well, and is subsequently entering the shallow aquifer system. This interpretation is supported by the expansion in the number of affected drinking-water wells during our study period and the persistence of hydrocarbon levels over time. Our data suggest post-genetic secondary water quality changes occur following fugitive gas contamination, including sulfate reduction paired with hydrocarbon oxidation and secondary methanogenesis. Importantly, no evidence for upward migration of brine or natural gas associated with the Barnett Shale was identified.

The management and disposal of flowback and produced waters (FP water) is one of the greatest challenges associated with unconventional oil and gas development. The development and production of unconventional natural gas and oil is projected to increase in the coming years, and a better understanding of the volume and quality of FP water is crucial for the safe management of the associated wastewater. We analyzed production data using multiple statistical methods to estimate the total FP water generated per well from six of the major unconventional oil and gas formations in the United States. The estimated median volume ranges from 1.7 to 14.3millionL (0.5 to 3.8milliongal) of FP per well over the first 5-10years of production. Using temporal volume production and water quality data, we show a rapid increase of the salinity associated with a decrease of FP production rates during the first months of unconventional oil and gas production. Based on mass-balance calculations, we estimate that only 4-8% of FP water is composed of returned hydraulic fracturing fluids, while the remaining 92-96% of FP water is derived from naturally occurring formation brines that is extracted together with oil and gas. The salinity and chemical composition of the formation brines are therefore the main limiting factors for beneficial reuse of unconventional oil and gas wastewater.

Hexavalent chromium (Cr(VI)) is a groundwater contaminant that is potentially harmful to human health. Understanding the occurrence of Cr(VI) in groundwater resources is critical for evaluating its risks to human health. Here we report a large dataset (n = 1362) of Cr(VI) and total chromium (CrT) concentrations in public, private, and monitoring wells from different aquifers across North Carolina. These water quality data come from new and previous measurements conducted at Duke University, as well as data reported by the U.S. Environmental Protection Agency, the N.C. Department of Environmental Quality, and the U.S. Geological Survey. The data confirm that Cr(VI) is the predominant species of dissolved Cr and that groundwater from aquifers in the Piedmont region contain significantly higher concentrations than groundwater from the coastal plain. Though there is only one exceedance of the U.S. EPA Maximum Contaminant Level (100 µg/L for CrT) in the dataset, over half of all wells measured for Cr(VI) (470 out of 865) in the dataset exceeded the N.C. Health Advisory Level of 0.07 µg/L. Using information from this dataset, we explore three different approaches to predicting Cr(VI) in groundwater: (1) CrT concentrations as a proxy for Cr(VI); (2) Exceedance probabilities of health goals for groundwater from aquifers located in specific geologic areas; and (3) Censored linear regression using commonly measured field parameters (pH, electrical conductivity, dissolved oxygen) with relationships to Cr(VI) as regressors. Combining these approaches, we have identified several areas in the Piedmont region where Cr(VI) in drinking water wells is expected to be higher than the advisory level, which coincide with large population groundwater reliant populations. While this study focuses on N.C., the wide-spread occurrence of Cr(VI) in groundwater at concentrations above health guidelines in aquifers of the Piedmont region could pose high human health risks to large populations in the eastern U.S.

The worldwide expansion of shale gas production and increased use of hydraulic fracturing have raised public concerns about safety and risks of groundwater resources in shale gas extraction areas. China has the largest shale gas resources in the world, most of which are located in the Sichuan Basin. Shale gas extraction in the Sichuan Basin has been increasing rapidly in recent years. However, the potential impact on shallow groundwater quality has not yet been systematically investigated. In order to evaluate the possible impact of shale gas extraction on groundwater quality, we present, for the first time, the hydrochemistry and Sr isotopic data of shallow groundwater, as well as flowback and produced water (FP water) in the Changning shale gas field in Sichuan Basin, one of the major shale gas fields in China. The Changning FP water is characterized by high salinity (TDS of 13,100–53,500 mg/L), Br/Cl (2.76 × 10−3) and 87Sr/86Sr (0.71849), which are distinguished from the produced waters from nearby conventional gas fields with higher Br/Cl (4.5 × 10−3) and lower 87Sr/86Sr (0.70830–0.71235). The shallow groundwater samples were collected from a Triassic karst aquifer in both active and nonactive shale gas extraction areas. They are dominated by low salinity (TDS of 145–1100 mg/L), Ca-HCO3 and Ca-Mg-HCO3 types water, which are common in carbonate karst aquifers. No statistical difference of the groundwater quality was observed between samples collected in active versus nonactive shale gas extraction areas. Out of 66 analyzed groundwater, three groundwater samples showed relatively higher salinity above the background level, with low 87Sr/86Sr (0.70824–0.7110) and Br/Cl (0.5–1.8 × 10−3) ratios relatively to FP water, excluding the possibility of contamination from FP water. None of the groundwater samples had detected volatile organic compounds (VOCs). The integration of geochemical and statistical analysis shows no direct evidence of groundwater contamination caused by shale gas development.

This cross-sectional study explores the relationships between children's F(-) exposure from drinking groundwater and urinary F(-) concentrations, combined with dental fluorosis (DF) in the Main Ethiopian Rift (MER) Valley. We examined the DF prevalence and severity among 491 children (10 to 15 years old) who are life-long residents of 33 rural communities in which groundwater concentrations of F(-) cover a wide range. A subset of 156 children was selected for urinary F(-) measurements. Our results showed that the mean F(-) concentrations in groundwater were 8.5 ± 4.1 mg/L (range: 1.1-18 mg/L), while those in urine were 12.1±7.3 mg/L (range: 1.1-39.8 mg/L). The prevalence of mild, moderate, and severe DF in children's teeth was 17%, 29%, and 45%, respectively, and the majority (90%; n=140) of the children had urinary F(-) concentrations above 3 mg/L. Below this level most of the teeth showed mild forms of DF. The exposure-response relationship between F(-) and DF was positive and non-linear, with DF severity tending to level off above a F(-) threshold of ~6 mg/L, most likely due to the fact that at ~6 mg/L the enamel is damaged as much as it can be clinically observed in most children. We also observed differential prevalence (and severity) of DF and urinary concentration, across children exposed to similar F(-) concentrations in water, which highlights the importance of individual-specific factors in addition to the F(-) levels in drinking water. Finally, we investigated urinary F(-) in children from communities where defluoridation remediation was taking place. The lower F(-) concentration measured in urine of this population demonstrates the capacity of the urinary F(-) method as an effective monitoring and evaluation tool for assessing the outcome of successful F(-) mitigation strategy in relatively short time (months) in areas affected with severe fluorosis.

Elevated level of fluoride (F(-)) in drinking water is a well-recognized risk factor of dental fluorosis (DF). While considering optimization of region-specific standards for F(-), it is reasonable, however, to consider how local diet, water sourcing practices, and non-F(-) elements in water may be related to health outcomes. In this study, we hypothesized that non-F(-) elements in groundwater and lifestyle and demographic characteristics may be independent predictors or modifiers of the effects of F(-) on teeth. Dental examinations were conducted among 1094 inhabitants from 399 randomly-selected households of 20 rural communities of the Ziway-Shala lake basin of the Main Ethiopian Rift. DF severity was evaluated using the Thylstrup-Fejerskov Index (TFI). Household surveys were performed and water samples were collected from community water sources. To consider interrelations between the teeth within individual (in terms of DF severity) and between F(-) and non-F(-) elements in groundwater, the statistical methods of regression analysis, mixed models, and principal component analysis were used. About 90% of study participants consumed water from wells with F(-) levels above the WHO recommended standard of 1.5mg/l. More than 62% of the study population had DF. F(-) levels were a major factor associated with DF. Age, sex, and milk consumption (both cow's and breastfed) were also statistically significantly (p0.05) associated with DF severity; these associations appear both independently and as modifiers of those identified between F(-) concentration and DF severity. Among 35 examined elements in groundwater, Ca, Al, Cu, and Rb were found to be significantly correlated with dental health outcomes among the residents exposed to water with excessive F(-) concentrations. Quantitative estimates obtained in our study can be used to explore new water treatment strategies, water safety and quality regulations, and lifestyle recommendations which may be more appropriate for this highly populated region.