Improper exploitation and massive coal mines closures without proper solutions bring about the extensive occurrence of goaf water in China where over 3500 coal mines have been shut down in the last 30 years. Discharge of goaf water poses severe environmental impact, especially in fragile karst areas. Based on the extensively literatures reading, field investigation combined with hydrogeochemical and isotopic (delta S-34) analysis, this paper reviewed the distribution, characteristics and formation of coal mine goaf water in karst areas in China. The occurrence of goaf water is reported in over 50% of the coal fields, with more than 30 water discharges. Distinct major ion chemistry in goaf water (low pH, high total dissolved solids, SO42- and negative delta S-34 values) are closely related to a combination of comprehensive physical, chemical and biological interactions. Recharge water, water filling channels and storage space constitute hydrogeological conditions necessarily for the produce of goaf water. Oxidation of sulfides minerals with air and water, acidic dissolution of minerals (e.g., gypsum, calcite and dolomite) and cation exchange, under the action of bacteria, are major processes in the genesis of goaf water. A case study on the environmental impact of goaf water is also done at Jinci, northern China. Our research suggests that goaf water in Jinci (TDS: 3595 mg/L - 9841 mg/L, SO42-: 2463 mg/L - 3256 mg/L; negative delta S-34 values < -5 parts per thousand) may pollute the surface and karst water via fractures or faults evidenced by the high SO42- and low delta S-34 values in these waters. Finally, a conceptual model is established to demonstrate the influences of goaf water on karst water-surface water environment in karst areas. (C) 2020 Elsevier Ltd. All rights reserved.

ConclusionLake reclamation cut off the direct seepage from the lake to groundwater in reclaimed farmland, the aquifer showed a connection with lake water by horizontal groundwater flow. The chemical analysis demonstrated that after reclamation, groundwater hydrodynamic conditions are gradually weakening. The lake-groundwater interaction interface is gradually varied and moves into the lake during this period. This change is easily ignored because the modification may take years to be observed. However, the lake ecology may be threatened seriously during this process. Lake reclamation project exerts anthropogenic pressures on the groundwater environment and lake ecosystem function, would affect the natural resilience of the lake systems and increases their vulnerability.

Substitution of aluminum under natural environmental conditions has been proven to inhibit the transformation of weakly crystalline iron (oxyhydr)-oxides towards well crystalline iron oxides, thereby enhancing their long-term stability. However, exploration on the role of aluminum substitution in bacteria-mediated iron oxides transformation is relatively lacking, especially in the anaerobic underground condition where iron (oxyhydr)-oxides are easy to reduced. In this study, we selected four different levels of substitution aluminum prevalent in iron oxides under natural conditions, which are 0mol%, 10mol%, 20mol%, and 30mol% (mol Al/mol (Al+Fe)) respectively. With the presence of Shewanella oneidensis MR-1, we conducted a 15-day anaerobic microcosm experiment in simulated groundwater conditions. The experiment data suggested that aluminum substitution result in a decrease in bio-reduction rate constants of ferrihydrite from 0.24 in 0mol% Al to 0.17 in 30mol% Al. Besides, when containing substituted aluminum, secondary minerals produced by biological reduction of ferrihydrite changed from magnetite to akaganeite. These results were attributed to the surface coverage of Al during the reduction process, which affects the contact between S. oneidensis MR-1 and the unexposed Fe(III), thus inhibiting the further reduction of ferrihydrite. Since iron (oxyhydr)-oxides exhibit a strong affinity on multiple kinds of pollutants, results in this study may contribute to predicting the migration and preservation of contaminants in groundwater systems. © 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.

Groundwater contamination by heavy metals (HMs) released by weathering and mineral dissolution of granite, gneisses, ultramafic, and basaltic rock composition causes human health concerns worldwide. This paper evaluated the heavy metals (HMs) concentrations and physicochemical variables of groundwater around enriched chromite mines of Malakand, Pakistan, with particular emphasis on water quality, hydro-geochemistry, spatial distribution, geochemical speciation, and human health impacts. To better understand the groundwater hydrogeochemical profile and HMs enrichment, groundwater samples were collected from the mining region (n = 35), non-mining region (n = 20), and chromite mines water (n = 5) and then analyzed using ICPMS (Agilent 7500 ICPMS). The ranges of concentrations in the mining, non-mining, and chromite mines water were 0.02-4.5, 0.02-2.3, and 5.8-6.0 mg/L for CR, 0.4-3.8, 0.05-3.6, and 3.2-5.8 mg/L for Ni, and 0.05-0.8, 0.05-0.8, and 0.6-1.2 mg/L for Mn. Geochemical speciation of groundwater variables such as OH-, H+, Cr+2, Cr+3, Cr+6, Ni+2, Mn+2, and Mn+3 was assessed by atomic fluorescence spectrometry (AFS). Geochemical speciation determined the mobilization, reactivity, and toxicity of HMs in complex groundwater systems. Groundwater facies showed 45% CaHCO3, 30% NaHCO3, 23.4% NaCl, and 1.6% Ca-Mg-Cl water types. The noncarcinogenic and carcinogenic risk of HMs outlined via hazard quotient (HQ) and total hazard indices (THI) showed the following order: Ni > Cr > Mn. Thus, the HHRA model suggested that children are more vulnerable to HMs toxicity than adults. Hierarchical agglomerative cluster analysis (HACA) showed three distinct clusters, namely the least, moderately, and severely polluted clusters, which determined the severity of HMs contamination to be 66.67% overall. The PCAMLR and PMF receptor model suggested geogenic (minerals prospects), anthropogenic (industrial waste and chromite mining practices), and mixed (geogenic and anthropogenic) sources for groundwater contamination. The mineral phases of groundwater suggested saturation and undersaturation. Nemerow's pollution index (NPI) values determined the unsuitability of groundwater for domestic purposes. The EC, turbidity, PO4-3, Na+, Mg+2, Ca+2, Cr, Ni, and Mn exceeded the guidelines suggested by the World Health Organization (WHO). The HMs contamination and carcinogenic and non-carcinogenic health impacts of HMs showed that the groundwater is extremely unfit for drinking, agriculture, and domestic demands. Therefore, groundwater wells around the mining region need remedial measures. Thus, to overcome the enrichment of HMs in groundwater sources, sustainable management plans are needed to reduce health risks and ensure health safety.

Microbially driven Fe(II) oxidation is vital for Fe-cycling processes. In the present study, a novel strain of nitrate-dependent Fe-oxidizing bacteria (FOB) was isolated from the riparian zone sediment of the Hanjiang River, China. It was identified as Comamonas terrigena strain HJ-2. The strain HJ-2 oxidized 2.80 mmol l(-1) Fe(II) within 144 h to form Fe(III)/Fe(II) complex on the cell surface using 1.63 mmol l(-1) nitrate as an electron acceptor. The formed nitrite from nitrate reduction chemically oxidized Fe(II). Surprisingly, this strain also reduced nitrilotriacetic iron to form 0.5 mmol l(-1) Fe(II) in 120 h in anaerobic conditions primarily mediated by the NADH flavin oxidoreductase. Besides, the strain completely reduced 0.18 mmol l(-1) nitrobenzene to aniline in 24 days and 15.6 mu mol l(-1) arsenate to arsenite in 7 days due to the existence of nitro and arsenate reductases. However, the Fe(II) inhibited the reduction of nitrate, nitrobenzene, and arsenate, possibly due to the impeding of transport of the solutes through the membrane or the synthesis of the related enzymes. These results provide new knowledge about the Fe(II)-cycling and the fate of some pollutants in the riparian zone. It also informed that some bacteria have universal functions on elements and contaminants transformation.

Arsenic (As) bioremediation has been an economical and sustainable approach, being practiced widely under several As-contaminated environments. Bioremediation of As involves the use of bacteria, fungi, yeast, plants, and genetically modified organisms for detoxification/removal of As from the contaminated site. The understanding of multi-factorial biological components involved in these approaches is complex and more and more efforts are on their way to make As bioremediation economical and efficient. In this regard, we systematically reviewed the recent literature (n=200) from the last two decades regarding As bioremediation potential of conventional and recent technologies including genetically modified plants for phytoremediation and integrated approaches. Also, the responsible mechanisms behind different approaches have been identified. From the literature, it was found that As bioremediation through biosorption, bioaccumulation, phytoextraction, and volatilization involving As-resistant microbes has proved a very successful technology. However, there are various pathways of As tolerance of which the mechanisms have not been fully understood. Recently, phytosuction separation technology has been introduced and needs further exploration. Also, integrated approaches like phytobial, constructed wetlands using As-resistant bacteria with plant growth-promoting activities have not been extensively studied. It is speculated that the integrated bioremediation approaches with practical applicability and reliability would prove most promising for As remediation. Further technological advancements would help explore the identified research gaps in different approaches and lead us toward sustainability and perfection in As bioremediation.

Arsenic (As) bioremediation has been an economical and sustainable approach, being practiced widely under several As-contaminated environments. Bioremediation of As involves the use of bacteria, fungi, yeast, plants, and genetically modified organisms for detoxification/removal of As from the contaminated site. The understanding of multi-factorial biological components involved in these approaches is complex and more and more efforts are on their way to make As bioremediation economical and efficient. In this regard, we systematically reviewed the recent literature (n=200) from the last two decades regarding As bioremediation potential of conventional and recent technologies including genetically modified plants for phytoremediation and integrated approaches. Also, the responsible mechanisms behind different approaches have been identified. From the literature, it was found that As bioremediation through biosorption, bioaccumulation, phytoextraction, and volatilization involving As-resistant microbes has proved a very successful technology. However, there are various pathways of As tolerance of which the mechanisms have not been fully understood. Recently, phytosuction separation technology has been introduced and needs further exploration. Also, integrated approaches like phytobial, constructed wetlands using As-resistant bacteria with plant growth-promoting activities have not been extensively studied. It is speculated that the integrated bioremediation approaches with practical applicability and reliability would prove most promising for As remediation. Further technological advancements would help explore the identified research gaps in different approaches and lead us toward sustainability and perfection in As bioremediation.

Groundwater with low levels of arsenic (As) in deep aquifers has been overexploited for decades in many regions (such as South Asian and American countries), resulting in the compaction of clayey aquitards and the release of pore water with As into deeper aquifers. However, the release mechanism of arsenic during clayey aquitards compaction is poorly understood. An indoor compaction experiment using muddy sediments was conducted to identify the As-releasing mechanisms during clayey aquitards compaction. The chemical characteristics and As species in pore water and sediment samples collected at different stages during the compaction experiment were analyzed. Initially, the reductive dissolution of iron oxides was a key process controlling As release during compaction. With increased pressure, As desorption from Fe (hydr)oxides became more important than the reductive dissolution as the main driver for As release. At the end of the compaction, the release of As was weak and the dominant process was desorption of As from clay or carbonate minerals. Our estimate result in the Jianghan Plain suggested that As concentration release from aquitard compaction by overexploited into groundwater would be 9.33-118.09 mu g/L.

We found a mistake in the acknowledged funding number. The statement of "This work was supported by the Natural Science Foundation of China (Nos. 41702040, 41830862, 41521001)" should be corrected to "This work was supported by the Natural Science Foundation of China (Nos. 41772374, 41830862, 41521001)". We apologize for this mistake.
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