China’s socioeconomic transitions have dramatically accelerated its economic growth in last three decades, but also companioned with continuous environmental degradation. This study will advance the knowledge of heavy metal water pollution in China from a spatial–temporal perspective. Specifically, this study addressed the following: (1) spatial patterns of heavy metal water pollution levels were analyzed using data of prefecture-level cities from 2004 to 2011; and (2) spatial statistical methods were used to examine the underlying socioeconomic and physical factors behind water pollution including socioeconomic transitions (industrialization, urbanization, globalization and economic development), and environmental characteristic (natural resources, hydrology and vegetation coverage). The results show that only Cr pollution levels increased over the years. The individual pollution levels of the other four heavy metals, As, Cd, Hg, and Pb, declined. High heavy metal water pollution levels are closely associated with both anthropogenic activities and physical environments, in particular abundant mineral resources and industrialization prosperity. On the other hand, economic development and urbanization play important roles in controlling water pollution problems. The analytical findings will provide valuable information for policy-makers to initiate and adjust protocols and strategies for protecting water sources and controlling water pollution; thus improving the quality of living environments.

Groundwater is a vital source of fresh water for drinking and agricultural purposes in the region of Hatiya Island, Bangladesh, yet it is subject to contamination by natural and anthropogenic activities. Over time, the contamination has resulted in a variety of negative effects on human health. This research aims to examine groundwater hydrogeochemical characterization and suitability for irrigation and drinking purposes on different indices utilizing a combined geochemical method, multivariate statistical approaches, and geospatial analysis. Results of hydrogeochemical analyses of 15 groundwater samples from the intermediate aquifer (60–90 m depth) represent the order of cations, anions, and metal concentrations as Na⁺ > Mg²⁺ > Ca²⁺ > K⁺, Cl⁻ > SO₄²⁻ > HCO₃⁻ > NO₃⁻, and Fe > I > Br > Mn > As, respectively. Saltwater intrusion has been determined to be the most important hydrogeochemical process influencing the chemistry of groundwater. Principal component analysis, Pearson’s correlation matrix, and hierarchical cluster analysis indicate that groundwater quality is highly governed by geogenic influences. This information has been evaluated using a drinking water quality index map, which found that six (40%) of the groundwater samples are suitable for human consumption, whereas the other nine (60%) are unfit for drinking. The analysis of irrigation quality parameters revealed that eight (54%) of the groundwater samples are in excellent or good condition for agricultural uses; however, the other seven (46%) samples are unsuitable.

This research demonstrates that biogenic pyrite formed by stimulation of indigenous sulfate-reducing bacteria (SRB) in a natural aquifer can remove dissolved arsenic from contaminated groundwater under strongly reducing conditions. SRB metabolism led to the precipitation of biogenic pyrite nanoparticles capable of sorbing and co-precipitating arsenic. The field site is an industrial site where shallow groundwater in an unconfined sandy aquifer is contaminated by arsenic. Therefore, biodegradable organic carbon, ferrous iron, sulfate, and fertilizer were injected into groundwater and SRB metabolism began about 1 week later. Microscopic, X-ray diffraction, X-ray fluorescence, and electron microprobe analyses confirm the bio-mineralization of pyrite and over time, pyrite nanoparticles grew to form well-formed crystals (1–10 µm in diameter) or spherical aggregates that contain 0.05–0.4 wt. % arsenic, indicative of their capacity to sequester arsenic. Consequently, dissolved arsenic decreased from its initial concentration of 0.3–0.5 mg/L to below the regulatory clean-up standard for the site of 0.05 mg/L in three downgradient wells in a matter of weeks after injection. The main sequestration stage, with total arsenic removal rates greater than 90%, lasted for at least 6 months until the arrival and mixing of untreated groundwater from upgradient. Treated groundwater with most active bacterial sulfate reduction became enriched in heavy ³⁴S (range from 2.02 to 4.00 ‰) compared to unaffected well water (0.40–0.61 ‰). One to three orders of magnitude increases in SRB cells were observed in treated wells for at least 2 months after injection. For a full-scale remediation, the injection of solution should start at positions hydrologically upgradient from the major plume and proceed downgradient. If needed, aquifers may be repeatedly amended with biodegradable organic carbon to reestablish the reducing conditions that favor arsenic sequestration.

We integrate groundwater geochemistry, microbiology, and numerical modeling techniques to study the origin of elevated salinity and chemical evolution of groundwaters in the coastal plain aquifers of Alabama. Our field data indicate that chemical composition of groundwater evolves by various geochemical and microbial processes as it moves deeper into the subsurface. Sequential peaks of Ca²⁺, Mg²⁺, K⁺, and Na⁺ along flow paths indicate that separation of ions may be driven by cation exchange. Microbial‐mediated reactions are important for the formation of several discrete hydrochemical zones containing Fe²⁺, Mn²⁺, Sr²⁺, and SO₄²⁻ rich groundwaters. Elevated Fe²⁺, Mn²⁺, and Sr²⁺ concentrations may be derived from bacterial iron and manganese reduction. High sulfate concentrations observed a short distance from the recharge may be partly explained by microbial sulfur oxidation and nitrate reduction (denitrification). The presence of denitrifying and sulfur‐oxidizing bacteria in water further supports these reactions. Major ion compositions and δD and δ¹⁸O values are used to determine the source of salinity and the nature of mixing of different groundwaters. Three water types were identified; these include carbonate groundwater, brines associated with evaporites, and groundwater of meteoric origin. Groundwater age differences and flow velocities were calculated using the ³⁶Cl/Cl ratios. Calculated groundwater flow velocities within the Eutaw and Tuscaloosa aquifers are about 0.20 m/yr and 0.15 m/yr, respectively. We modeled basin‐scale hydrologic and solute transport processes in a cross section extending from the aquifer outcrops to the Gulf Coast. The modeling result shows that the buried Jurassic Louann Salt can significantly increase groundwater salinity in the overlying coastal plain aquifers by density‐driven advection and hydrodynamic dispersion. The modeling results are consistent with Cl/Br ratios and O/H isotope signatures, which indicate that salinity of the groundwater could be derived from seawater that has been evaporated beyond halite saturation. The predicted groundwater flow pattern reveals the mixing of meteoric water, carbonate groundwater (from the Ordovician Knox Group), and saline brines associated with the Louann Salt. The hydrologic model is consistent with the hydrochemical facies distribution in the Alabama coastal plain.

We integrate groundwater geochemistry, mineralogy, and numerical modeling techniques to study the reactive transport of heavy metals and isotopes in the Eutaw coastal plain aquifer, Alabama. Geochemical data show that the elevated concentrations of Fe, Mn, and Sr can be correlated with high pH and alkalinity. These geochemical correlations suggest that that elevated metal concentrations may be derived from bacterial iron and manganese reduction. Geochemical modeling of bacterial Fe(III) and Mn(IV) reduction shows that the biotransformation of iron and manganese minerals could control mobility and concentrations of Fe and Mn in coastal plain aquifers. Petrographic, SEM, and EDAX studies of sediments show the formation of biogenic siderite, rhodochrosite, and pyrite in sediments associated with Fe‐ and Mn‐rich groundwater. Rhodochrosite and siderite occur together as spheroids (≈1.0 mm) in which rhodochrosite forms the center and siderite forms an outer rind, which is consistent with the redox sequence of mineral precipitation predicted by the geochemical modeling. The low δ¹³C ratios of siderite and rhodochrosite (−14.4 to −15.4‰, PDB) and groundwater DIC (−20.6 to −14.1‰, PDB) imply carbon of biogenic origin. Higher DIC‐δ¹³C levels are found to be correlated with elevated Fe and Mn concentrations and high pH values of groundwater. This unexpected result implies novel carbon isotopic fractionation processes associated with bacterial Fe(III) reduction. We used ³⁶Cl/Cl ratios of groundwater and isotope transport modeling to calculate the residence time of regional groundwater in the Eutaw aquifer. The calculation considering the natural decay only would yield ³⁶Cl levels that are significantly higher than field data, suggesting that a significant mixing with Cl‐rich, older groundwater at depth is an important reason for substantial ³⁶Cl depletion along flow path.