Xishan mining area in Taiyuan is a typical coal industry cluster with a variety of coal-related industrial sites such as coal mines, power plants and coking plants, which seriously pollute the native ecological environment. Study of the hydrochemical characteristics and pollution sources of groundwater in the area can contribute to the ecological protection and remediation of regional groundwater resources. In this study, we collected surface water and groundwater samples from the Xishan mining area and measured and analyzed hydrochemical and sulfur–oxygen isotopes. Results showed that 64.7% of groundwater in the study area exceeded the sulfate standard due to the influence of the coal industry, with some karst groundwater up to 2000 mg/L. In the runoff and discharge area of karst groundwater, the proportion of anthropogenic input of SO₄²⁻ increased, which led to the hydrochemical type of karst groundwater gradually changing from HCO₃-Ca·Mg (recharge area) to SO₄-Ca·Mg (discharge area). Results of sulfur–oxygen isotope tests indicated that the δ³⁴S_SO4 and δ₁₈O_SO4 values of samples were −10.01~24.42‰ and −4.90~12.40‰, respectively, and the sulfur–oxygen isotope values of some karst groundwater were close to the dissolved end of sulfide minerals, indicating their sulfate mainly came from the oxidation of pyrite. Sulfate sources in groundwater water were parsed using IsoSource model. Calculated results revealed that sulfate in pore groundwater mostly originated from pyrite oxidation, and karst groundwater in the recharge area was mainly influenced by atmosphere precipitation, while groundwater in the runoff and discharge areas were significantly affected by pyrite oxidation, accounting for up to 90% in some karst groundwater. Comparing the sulfur–oxygen isotope values of karst groundwater in 1989, 2016 and 2022, we found that the δ³⁴S_SO4 values in 2022 decreased significantly, which indicated the expansion of karst groundwater pollution in the Xishan mining area. This study highlights the pollution of regional groundwater by coal-related industrial agglomerations, and the groundwater pollution in the Xishan mining area requires urgent remediation and restoration.

To deeply investigate the impact of closed coal mines on groundwater sulfate contamination in the Panlong River basin, Zaozhuang, Shandong Province, China, the hydrochemical characteristics and controlling factors of groundwater were analyzed based on 64 surface water and groundwater samples. The sources of sulfate contamination were identified by sulfur and oxygen isotope analysis. The results indicate that the sulfate content in the pore groundwater exceeds the Standard for Groundwater Quality (China) Category III (250 mg/L), with a maximum content of 666.2 mg/L. Specifically, the exceedance rate of sulfate in pore water near the western boundary of the Taozao coal field is directly related to mine water. The exceedance rate of sulfate in karst groundwater is 28%, peaking at 1131 mg/L, and is mainly distributed outside the western boundary of the Taozao coalfield and near the Dingzhuang water source in the southeast of the coalfield, indicating a significant influence from high-sulfate mine water in the coal-bearing strata. The sulfur and oxygen isotope differences are significant between surface water, mine water, karst water, and pore water. Through Bayesian end-member analysis, it was determined that 40–83% of sulfate in the downstream pore water of the Taozao coal field originated from mine water, while 48–86% of the sulfate in the karst water originated from mine water, which greatly affects the groundwater in the western and southeastern parts of the Taozao coalfield. Therefore, measures should be taken as soon as possible to control the risk of sulfate pollution of neighboring groundwater, especially karst groundwater, by mine water from closed coal mines.

Long-term coal mining has created unique microbial communities in deep coal mines. Revealing the microbial community structure and metabolic functions in the underground environment can contribute to a better understanding of the coal mine ecosystem. In this study, we collected underground sediment samples from producing mines in eastern China at mining depths of −400 to −1100 m and performed high-throughput sequencing. Results showed that most of the genera in the underground sediment can degrade organic matter, such as polycyclic aromatic hydrocarbons (PAHs), benzene, toluene, and xylene, etc. The dominant genera in the underground sediment were Hydrogenophaga, Thauera, Pseudomonas, Rhodobacter, and Dietzia. Samples were divided into coal roadway (CR) and rock roadway (RR) groups according to the sampling location. The microbial community structure differed significantly (p < 0.05) between these two groups of samples, with the distribution of main genera in the CR group samples showing a negative correlation with Cu and a positive correlation with temperature. The samples from the CR and RR groups were significantly different (p < 0.05) in their metabolic functions, including membrane transport, metabolism of other amino acids, folding, sorting, and degradation. Microorganisms in the RR group samples showed high resistance to heavy metals, while microorganisms in the CR group had higher degradation functions of organic pollutants. Bugbase phenotypic predictions indicated a high potential pathogenicity of microorganisms in coal mine sediment, which was mainly contributed by the genera Hydrogenophaga, Pseudomonas, Geothermobacter, and Methylophaga, etc. This study deepens the understanding of microbial communities in deep coal mine environments; however, the organic contamination and biological health risks of underground environments require extensive attention.