Risk elements in soils affected by long-term gold and mercury (Hg) mining related to soil microbial activity

Representative soil samples were collected from three areas in the Czech Republic surrounding two former cinnabar mines and a former gold mine, where mercury (Hg) was historically used in the amalgamation process for gold extraction. This study aimed to assess the potential impact of long-term soil contamination by risk elements on microbial activity. The soil risk element content was determined based on location, with Hg identified as the predominant pollutant at all three sites, where the individual pollution index (<i>I_Hg</i>) ranged from 0.7 to 450. To evaluate the impact of Hg pollution on soil biological properties, a suite of soil enzyme activities was analyzed. The results indicated no significant reduction in enzymatic activities, suggesting a negligible harmful effect of long-term Hg pollution on microbial activity. However, significant (<i>p</i> &lt; 0.05) positive correlations between soil Hg content and chitinase and cellobiohydrolase activities at one location suggested that other factors, beyond Hg pollution levels, influenced microbial activity. These findings point to the low bioaccessibility of Hg in the studied areas and/or potential microbial adaptation to elevated Hg levels in soils.