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Oxidative potential (OP) is considered to be an efficient indicator of particulate matter (PM) to induce oxidative stress in the lungs and is increasingly considered to be a relevant health metric. In this study, two complementary OP assays were deployed, including dithiothreitol (DTT) and ascorbic acid (AA) assays, to investigate the potential toxicity (as generators of oxidative stress) of respirable fractions (DD4, < 4 μm) of deposited dust (DD500, < 500 μm) in underground low-S and low-pyrite coal mines in Henan Province, Central China. The OPDTT of DD4 is higher than that reported for other types of atmospheric PM, whereas the OPAA of DD4 is similar and/or slightly higher. Cross-correlation and multilinear regression analyses are applied using datasets of major mineral and geochemical patterns in the DD4 samples and the respective OP values to identify the major drivers for OP in respirable coal dust. Thereafter, the patterns of DD4 are compared with those of DD500 and the parent coals to determine the sources of OP-relevant substances. OPDTT is mainly governed by some trace elements (Sb, As, Li, B, Sr, and Pb) and minor minerals (anatase, quartz, siderite), and their synergistic effect may be one of the reasons for the high DTT consumption. For OPAA, quartz, total clay (sum of illite, kaolinite, tobelite, and clinochlore) and Ni, Cr, Co, Si, and S, play an important role in regulating the OPAA of pyrite-free DD4 samples. These OP-relevant substances have three sources: coal dust, which has a similar composition in DD4, DD500, and the parent coal (such as siderite and its associated elements); gangue dust, which does not occur in the parent coal but is widely detected in DD4 and DD500 (such as quartz, kaolinite, and relevant elements); and cement dust (from gunite galleries), which is mainly calcite- and calcite-associated elements. • A study of the mineralogy, geochemistry and OP of deposited dust, respirable dust and coal in underground coal mines. • OPDTT of size-segregated respirable dust (DD4) is mainly governed by anatase, siderite, quartz, and Sb, As, Li, B, Sr, Pb. • OPAA of DD4 is regulated by anatase, tobelite, kaolinite, and total clay, as well as Ni, Cr, Co, Si, and S. • The parent coal dust, gangue dust, and cement dust are the primarily source of these hazardous materials. [ABSTRACT FROM AUTHOR]

This study systematically investigates the mineralogical and geochemical variations in parent coal, coal gangue (roof, parting, and floor), deposited coal mine dust (DD), and respirable fractions of DD (RD) in an underground coal mine using the blasting mining method in China to evaluate the major sources of DD. The emission of dust in this study is affected by coal gangue sources during the mining process, which causes different geochemical patterns in the DD samples. Moreover, weathering of the cement gunite walls plays an important role in the enrichment of specific elements in the DD from air uptake and air out galleries. Furthermore, the spatial variation in RD characteristics, including mineralogy, geochemistry, and oxidative potential (OP), is discussed, with emphasis on the major health-relevant species and elements. Organic species from coal dust seem to be the essential components contributing to OP rather than metals, although some metals (e.g., Cr, Co, Ge, Se, Zn, Ba, Rb, Cs, Sn, and Pb) influence OP to some degree. [Display omitted] • Deposited coal mine dust, parent coal, and gangue in an underground coal mine using blasting mining method were studied. • Gangue and cement dust mixed into coal dust result in the enrichment of abundant elements. • The primary species driving the oxidative potential are site-dependent. • Organic species, quartz, calcite, and Cr, Co, Ge, Zn, Ba, Rb are highly correlated with toxicity. [ABSTRACT FROM AUTHOR]

Shaanxi is among the provinces with abundant coal resources in North China. These enormous coal resources (approx. 4143 Gt) are widely distributed in the Ordos Basin and its marginal fold belts. The main coal-bearing strata consist of the late Carboniferous Taiyuan Formation, the early Permain Shanxi Formation, the late Triassic Wayaobao Formation, and the middle Jurassic Yan'an Formation, which were respectively deposited in coastal plains and a lagoon environment, a continental environment, an inland open lake and a confined lake environment. The Permo-Carboniferous coals are low volatile bituminous and characterized by relatively high vitrinite content, which decreases from south to north, and from the lower coal seams upwards. By contrast, the late Triassic and middle Jurassic coals are highly volatile bituminous, but are respectively characterized by relatively high vitrinite and high inertinite content. Minerals in the Permo-Carboniferous coals, the late Triassic coals, and the middle Jurassic coals, are respectively dominated by kaolinite and calcite, quartz and kaolinite, and quartz and calcite. Furthermore, contemporary coals deposited in different coal fields or even different mines of the same coal field present different mineral characteristics. The Permain Shanxi Formation coals from the Shanbei C-P coalfield in the north of Shaanxi Province are characterized by higher kaolinite and lower carbonate contents compared to those from the Weibei C-P coalfield in the south of Shaanxi Province. The distinctive mineralogical characteristics of coals formed in different coalfields and different geological ages were ascribed to integrated influences of different terrigenous detrital input from sediment provenance, sedimentary settings (e.g., subsidence rate, sea transgression, and regression process), and hydrothermal activities. [ABSTRACT FROM AUTHOR]

Underground coal mining produces large amounts of mine water annually in the Shendong mining area of China. Due to the severe scarcity of water resources, mine water is extensively used for productive, domestic, and ecological demands. However, mine water exhibits high fluoride levels. For water-use security, reduction of fluoride exposure and environmental protection, knowledge of sources and geochemical controls of fluoride enrichment in mine water is required. The results showed that F− concentrations of mine waters vary from 0.05 to 11.65 mg/L, with a mean value of 1.96 mg/L, and 51% of the mine waters contain F− concentrations exceeding the Chinese drinking water standard (1 mg/L). The overall mine water quality is influenced by cation exchange, mineral dissolution, pyrite oxidation, silicate weathering and so on. The high-fluoride mine waters are all associated with Na–type, with a remarkable cation composition feature of higher Na+ and lower Ca2+ and Mg2+ concentrations. Overall, the high-fluoride mine waters are well-matched with the water environment with higher pH, TDS, and EC levels. PCA reveals that the geochemical controls on the enrichment of F− in mine waters include dissolution of fluoride-bearing minerals and F−-OH− ion exchange; the former process is mainly caused by the decrease in Ca2+ concentrations resulting from Na + -Ca2+ cation exchange and mineral precipitation, and the latter process benefits from a highly alkaline water environment, facilitating the substitution of OH− in the mine water for F− within or absorbed on the minerals. Evaporation also controls F− enrichment in local areas. [Display omitted] • 51% of mine water samples exceed the Chinese drinking water limit for fluoride (1 mg/L). • The overall mine water quality is influenced by cation exchange, dissolution of minerals and so on. • NaHCO 3 type mine water possesses the highest average fluoride concentration. • Fluoride concentrations are overall proportional to higher pH, TDS, and EC levels. • Fluoride enrichment is related to ion exchange, mineral precipitation, and evaporation. [ABSTRACT FROM AUTHOR]

This study evaluates geochemical and oxidative potential (OP) properties of the respirable (finer than 4 μm) fractions of 22 powdered coal samples from channel profiles (CP 4 ) in Chinese mined coals. The CP 4 fractions extracted from milled samples of 22 different coals were mineralogically and geochemically analysed and the relationships with the OP evaluated. The evaluation between CP 4 /CP demonstrated that CP 4 increased concentrations of anatase, Cs, W, Zn and Zr, whereas sulphates, Fe, S, Mo, Mn, Hf and Ge decreased their CP 4 concentrations. OP results from ascorbic acid (AA), glutathione (GSH) and dithiothreitol (DTT) tests evidenced a clear link between specific inorganic components of CP 4 with OP AA and the organic fraction of OP GSH and OP DTT . Correlation analyses were performed for OP indicators and the geochemical patterns of CP 4 . These were compared with respirable dust samples from prior studies. They indicate that Fe (r = 0.83), pyrite (r = 0.66) and sulphate minerals (r = 0.42) (tracing acidic species from pyrite oxidation), followed by S (r = 0.50) and ash yield (r = 0.46), and, to a much lesser extent, Ti, anatase, U, Mo, V and Pb, are clearly linked with OP AA . Moreover, OP GSH correlation was identified by organic matter, as moisture (r = 0.73), Na (r = 0.56) and B (r = 0.51), and to a lesser extent by the coarse particle size, Ca and carbonate minerals. In addition, Mg (r = 0.70), B (r = 0.47), Na (r = 0.59), Mn, Ba, quartz, particle size and Sr regulate OP DTT correlations. These became more noticeable when the analysis was done for samples of the same type of coal rank, in this case, bituminous., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Crown Copyright © 2021. Published by Elsevier B.V. All rights reserved.)