Environmental issues of self-heating coal waste dumps in Poland

During coal mining, an enormous amount of economically not used humic or sapropelic coals, coal shales are deposited as wastes nearby the coal mines in urbanised areas, e.g. Upper Silesia, Katowice – Rybnik Industrial Region, in Upper Silesian Coal Basin, Poland. These wastes start to oxidise or lose out weathering immediately; in the worst cases, they will undergo self-heating. During exothermic reactions, the heavy metals contained in these rocks, especially sulfur compounds of  Pb, Cd, Cr, Cu, Zn, Ni, Hg, As are mobilised to the environment due to their high volatility at elevated temperatures and due to low pH levels (2 – 4) occurring on the dumps (Nádudvari et al., 2021, 2022). Amongst them, the Hg mobilisation and enrichment make such coal waste dumps more dangerous. Nádudvari et al. (2021, 2022) reported >1000 mg/kg enrichment of Hg in crusts of expelled bitumen and in gases from thermally affected wastes Hg concentration reached ~100 times higher than in polluted urban air from Upper Silesia. Additionally, the MeHg formation - Methylmercury (10 – 30 μg/kg) was also significant and probably formed via chemical reactions. Furthermore, other toxic gases emitted from the vents like benzene, formaldehyde, NH_3, HCl, H₂S, CO, Cl₂, NH₃, SO₂, and NO were detected, and many of their average annual concentrations exceeded numerous times the permissible Polish norms limits (Nádudvari et al., 2022). The formation of PAHs – Polycyclic Aromatic Hydrocarbons is also very common due to the burning processes, therefore, the lifetime cancer risks due to PAHs and heavy metals accumulations in the dumps are significant. Thus access to these dumps should be prohibited (Nádudvari et al., 2021). Abundant phenols are typical products of self-heating dumps, and their occurrence shows the coking conditions inside the dumps (Nádudvari et al., 2020). The potential ecological and human health risks of these dumps are moderate to very high due to the significant influence of the high Hg concentrations (Nádudvari et al., 2022).