Mercury occurrence and speciation in sediments from hard coal mining in Czechia

This study examines Hg distribution in stream sediments impacted by hard coal mining in the Upper Silesian Coal Basin (USCB), Czechia. By means of a comparative analysis, geological samples and samples from stream sediments were used to carry out a comprehensive assessment of the effects of anthropogenic activities on Hg distribution and speciation. Total Hg (THg), total organic and inorganic carbons (TOC and TIC), and total sulphur (TS) were measured in the samples to reveal a potential relationship. In addition, THg and TS species were discussed in order to elucidate their mobility pattern in the environment. The results have shown that there are no correlations between THg, TS, and TOC indicating overlapping Hg sources attributed to industrial processes. Geological samples, particularly coal and associated sedimentary rocks, contained lower Hg concentrations compared to a variety of stream sediments. The main Hg species identified in the samples was a stable β-HgS, which decreases its mobility in the riverine environment. It follows that Hg enrichment and speciation is linked to industrial processes, which are the main origin/cause for Hg enrichment and transformation. Minor proportions of HgO in some samples show Hg oxidation upon diagenesis, while HgCl₂ is attributed to the chemical loads from the former coking plant.