Hydrogeochemistry and isotope hydrology were carried out to investigate the spatial distribution of fluoride (F−) and the mechanisms responsible for its enrichment in the western region of the Ordos basin, northwestern China. Sixty-two groundwater samples from the unconfined aquifer and fifty-six from confined aquifer were collected during the pre-monsoon (June 2016). Over 77% of groundwater samples from the unconfined aquifer (F− concentration up to 13.30 mg/L) and approximately 66% from confined aquifer (with a maximum F− concentration of 3.90 mg/L) exhibit F− concentrations higher than the Chinese safe drinking limit (1.0 mg/L). High-F− groundwater presents a distinctive hydrochemical characteristic: a high pH value and HCO3− concentration with Ca-poor and Na-rich. Mineral dissolution (e.g., feldspar, calcite, dolomite, fluorite), cation exchange and evaporation in the aquifers predominate the formation of groundwater chemistry, which are also important for F− enrichment in groundwater. Mixing with unconfined groundwater is a significant mechanism resulting in the occurrence of high-F− groundwater in confined aquifer. These findings indicate that physicochemical processes play crucial roles in driving F− enrichment and that may be useful for studying F− occurrence in groundwater in arid and semi-arid areas.

Natural subsurface environment is a complex heterogeneous system. To investigate the effect of ionic strength (IS) and heterogeneity on the transport and remobilization of graphene oxide (GO)-facilitated uranium (U(VI)) in saturated porous media, column experiments were performed by the injection of U(VI) alone and U(VI)+GO mixtures into homogeneous and heterogeneous porous media under low and high ionic strength (1 and 50 mM) conditions, and then the columns were successively flushed with background solution and DI water. Results showed that when U(VI) only was introduced into the columns, IS had little effect on the migration of U(VI) alone in both media and the presence of preferential flow in heterogeneous media slightly enhanced the mobility of U(VI). As U(VI)+GO mixtures were injected into the columns, GO showed strong mobility at low IS and high released peak at high IS. The appearance of GO significantly enhanced U(VI) transport in both media. Under low IS condition, the mobility of U(VI) was significantly enhanced at the injection phase, and the medium heterogeneity further promoted the amount of GO-sorbed U(VI) transport. At high IS, less GO-sorbed U(VI) was observed during injection phase, and a large amount of retained GO-sorbed U(VI) were released with GO remobilization during water flushing phase, and the release showed the longer-tailing phenomenon and the release amount was more pronounced in heterogeneous media. The findings in this study showed that the coupled effect of solution chemistry and media heterogeneity played important roles on GO-facilitated U(VI) transport and release in soil and groundwater system.

Groundwater pollution is a critical concern in karst areas. This study used the PLEIK (P: protective cover; L: land use; E: epikarst development; I: infiltration conditions; K: karst development) method to assess the vulnerability of groundwater pollution in Guangxi Province, which is the largest karst area in China. The pollution sources and attenuation consist of groundwater pollution hazards. The attributions for the vulnerability and hazard were measured using the geodetector method from geographical information system in Luzhai County in Guangxi. The results confirmed that the vulnerability of groundwater pollution was higher in karst areas than in non-karst areas. In Guangxi, 36.35% of the groundwater samples were polluted. A total of 49.73% of the areas in Luzhai County contained hazardous levels of pollution. The risk assessment map, which interacted with the vulnerability and hazards, was 58.2% similar to the groundwater pollution distribution. The influence of the hazard on groundwater pollution was 2.6 times that of the vulnerability. It is crucial to control pollution sources to prevent groundwater pollution.

To investigate the removal characteristics of ammonium-nitrogen (NH₄⁺-N), nitrite-nitrogen (NO₂⁻-N), nitrate-nitrogen (NO₃⁻-N), and total nitrogen from groundwater by a degradable composite active medium, kinetics, thermodynamics, and equilibrium adsorption, experiments were performed using scoria and degrading bacteria immobilized on scoria. Removal of NH₄⁺-N, NO₂⁻-N, and NO₃⁻-N was conducted in adsorption experiments using different times, initial concentrations, pH values, and groundwater chemical compositions (Ca²⁺, Mg²⁺, HCO₃⁻, CO₃²⁻, Fe²⁺, Mn²⁺, and SO₄²⁻). The results showed that the removal of nitrogen by the composite active medium was obviously better than that of scoria alone. The removal rates of NH₄⁺-N (C₀ = 5 mg/L), NO₂⁻-N (C₀ = 5 mg/L), and NO₃⁻-N (C₀ = 100 mg/L) by the composite active medium within 1 h were 96.05%, 82.40%, and 83.16%, respectively. The adsorption kinetics were well fitted to a pseudo-second order model, whereas the equilibrium adsorption agreed with the Freundlich model. With changes in the pH, variation in the removal could be attributed to the combined effect of hydrolysis and competitive ion adsorption, and the optimum pH was 7. Different concentration conditions, hardness, alkalinity, anions, and cations showed different promoting and inhibiting effects on the removal of nitrogen. A careful examination of ionic concentrations in adsorption batch experiments suggested that the sorption behavior of nitrogen onto the immobilized medium was mainly controlled by ion exchange. The degrading bacteria on the scoria surface were eluted and analyzed by metagenomic sequencing. There were significant differences in the number of operational taxons, relative abundances, and community diversity among degrading bacteria after adsorption of the three forms of nitrogen. The relative abundance of degrading bacteria was highest after NO₃⁻-N removal, and the diversity was highest after NO₂⁻-N removal. Pseudomonas and Serratia were the dominant genera that could efficiently remove NH₄⁺-N and NO₂⁻-N.

Groundwater with elevated As concentrations is a global concern, and low-cost, high-efficiency removal technologies are necessary. Therefore, we have prepared three adsorbent FeMnLa-impregnated biochar composites (FMLBCs) for the efficient removal of As(III) from aqueous solutions and characterized them using a variety of techniques. We found that the efficiency of As(III) removal increased with increasing La content and that the removal mainly occurred via adsorption and oxidation. Moreover, the removal of As(III) by FMLBCs was rapid and was best fitted to a pseudo-second-order kinetic model. The adsorption isotherms were well described by the Langmuir equation, and the maximum As(III) adsorption capacity was 15.34 mg g⁻¹. These results highlight the significant potential of FMLBCs as adsorbents for As(III) removal from aqueous solutions.

Elevated inorganic arsenic concentrations in groundwater has become a major public and environmental health concern in different parts of the world. Currently, As-contaminated groundwater issue in many countries and regions is a major topic for publications at global level. However, there are many regions worldwide where the problem has still not been resolved or fully understood due to inadequate hydrogeochemical investigations. Hence, this study evaluates for the first time the hydrogeochemical behavior of the arid and previously unexplored inland basin of Sirjan Plain, south east (SE) Iran, in order to assess the controlling factors which influence arsenic (As) mobility and its distribution through groundwater resources. Total inorganic arsenic concentration was measured using inductive-coupled plasma optical emission spectrometry (ICP-OES). Arsenic content in groundwater of this region ranged between 2.4 and 545.8 μg/L (mean value: 86.6 μg/L) and 50% of the samples exceeded the World Health Organization (WHO) guideline value of 10 μg/L in drinking water. Groundwater was mainly of Na-Cl type and alkaline due to silicate weathering, ion exchange and evaporation in arid conditions. Elevated As concentrations were generally observed under weakly alkaline to alkaline conditions (pH > 7.4). Multivariate statistical analysis including cluster analysis and bi-plot grouped As with pH and HCO3 and demonstrated that the secondary minerals including oxyhydroxides of Fe are the main source of As in groundwater in this region. The desorption of As from these mineral phases occurs under alkaline conditions in oxidizing arid environments thereby leading to high levels of As in groundwater. Moreover, evaporation, ion exchange and saltwater intrusion were the secondary processes accelerating As release and its mobility in groundwater. Based on the results of this study, desorption of As from metal oxy-hydroxides surfaces under alkaline conditions, evaporation and intrusion of As-rich saline water are considered to be the major factors causing As enrichment in arid inland basins such as those in southeast Iran. This study proposes the regular monitoring and proper groundwater management practices to mitigate high levels of arsenic in groundwater and related drinking water wells of Sirjan Plain.

Waste water of the Kettara village, as well as the abandoned tailings, constitute a potential environmental issue with direct consequences on air, soil, water resources qualities and, on human health. In this paper, experimental investigations examine the environmental impact which is induced by the wastewater, mine tailings and the lithological factors of rocks. This multidisciplinary research allows to i) understand the transfer of the Metallic Trace Elements (selenium, arsenic, nickel and zinc) and sulfate ions in the fractured shales media, ii) to assess the water potability by using the microbiological analysis. The microbiological results reveal the domestic impact by the presence of several kinds of bacteria in the groundwater resources: E. coli, Fecal coliforms, Total coliforms, Enterococci, Mesophilic Aerobic Flora, Sulphite-reducing bacteria and Salmonella.Selenium, arsenic and the bacteriological contamination of the groundwater could be explained by five kinds of factors: i) the geological formations and the nature of the hydrogeological system (unconfined layer), ii) the groundwater flow, the hydraulic relation between the hydrogeological wells and, the fractures network in the shale aquifer. The piezometric map allows to highlight the groundwater flow from the North-East to North-West and to the South-West, the drainage axis towards the P21 well and the presence of the dividing axis in the contaminated zone by the arsenic, iii) the absence of the unhealthy habitats with permeable traditional septic tanks in the village; iv) the transfer of the spreading animal excrements from the soil to groundwater and, v) the migration of the wastewater towards downstream of the groundwater flow. The presence of the reed beds could explain the reduction of bacteria in the hydrogeological wells of the study area.

Remediation of hexavalent chromium [Cr(VI)] has been widely studied for its high mobility and toxicity. As Cr(VI) migrates in natural environment, both soils and groundwater are contaminated simultaneously. In the present study, a novel reactor combining adsorption and microbial fuel cell (A-MFC) using Platanus acerifolia leaves was developed for removing Cr(VI) from groundwater and soils. When initial Cr(VI) concentration was 50 mg/L, the adsorption efficiency of A-MFC achieved 98% after 16 h. Afterwards, the leaves were used for fabricating an MFC-integrated leaching reactor. The A-MFC significantly improved the overall Cr(VI) removal efficiency through leaching and 40% of Cr(VI) in the soil column was removed. The electrical voltage and current of A-MFC reactor achieved averagely 343 mV and 141 μA to maintain the system operation without extra energy supply. This novel A-MFC reactor is an environmentally friendly technology which achieved efficient Cr(VI) removal from groundwater and soils using natural materials, proving the concept that integrated self-remediation of Cr(VI) in contaminated soil and groundwater with natural material and energy.

In the Kebili region of southern Tunisia, there is increasing demand of water from the Lower Cretaceous Continental Intercalaire (CI) aquifer and the Upper Cretaceous-Miocene Complex Terminal (CT) aquifer. The CI aquifer, given limited low recharge of water and increasing amounts of water extraction, has suffered intense overexploitation since the year 2000. Currently, the sustainability of CI resources is threatened by oil and brine contamination detected at a number of water wells in the Kebili region.Hydrocarbon pollution of the aquifers seems to be ubiquitous because the groundwaters sampled in El Fedjej and Nefzaoua basins exhibit bad water quality according to a number of toxicity indices. Geochemical data indicate that, on a regional scale, groundwater quality, salinity, and dissolved element concentrations are best correlated to petroleum contamination-extraction and to aquifer vulnerability to human perturbations rather than to multiple interactions within the hydrogeological system of the region.The analyses of petroleum compounds in sampled waters indicate that these waters are most consistent with increasing concentrations of organic pollutants; the organic matter is crude and unaltered, testifying to continuous flows of contaminants. The brine contamination, however, is limited to the Djemna water well where the water exhibits a salinity of 20 g L⁻¹. Combined, these findings suggest that groundwater composition in CI water wells in Kebili field is influenced by the migration of hydrocarbons and brine-enriched waters through fractures, and (or) by aquifer decompression.

In early nineteen century, a gas field was operational in southern part of Sindh, Pakistan for power production. The plant was completely un-operational for last three decades, whereas all wastage and raw materials are still dumped there, which might be the source to contaminate the ground water. The most of the workers population still living in different villages nearby the gas field. In present study, evaluated the undesirable effects of the toxic metals (lead and cadmium) via consuming groundwater for drinking and other domestic purpose especially in children of ≤5.0 years. For comparative purpose groundwater of nonindustrial area (nonexposed) was also analysed and their impact on age matched children was carried out. Biological samples (scalp hair and blood) were collected from children of exposed and nonexposed areas. The Cd and Pb in scalp hair and blood samples were carried out by graphite furnace atomic absorption spectrometry. Whereas, Cd and Pb in groundwater obtained from both areas were determined prior to applied preconcentration method as reported in our previous works. The Cd and Pb contents in the groundwater of villages of exposed area were found in the range of 5.18–10.9 and 19.9–69.5 μg/L, respectively. Whereas, the groundwater of nonexposed area contains Cd and Pb in the range of 1.79–3.78 and 5.07–24.3 μg/L, respectively. It was observed that the concentrations of Cd and Pb in scalp hair and blood samples of children belongs to exposed area have ≥2.0 fold higher than the resulted data attained for age matched control children, indicating as the exposure biomarkers of toxic metals. The children belong to exposed area have poor health, anemic and low body mass index (<13 kg/m2). A significant positive correlations among Cd and Pb concentrations in biological samples of exposed subjects and groundwater was observed (p < 0.01).