Distribution and pools of mercury in forest soils near recent and historical mercury emission sources in the central Czech Republic

Abstract The fate of atmospherically deposited mercury (Hg) was studied in forest soils situated near various Hg anthropogenic emission sources, including chlor-alkali plants, cement production, and pig iron and steel factories in the Czech Republic. Some of these emission sources were more active in the past, while others continue operation with lowered dust and Hg emissions up to the present day. The impact of Hg emission sources on forest soil was assessed with respect to other soil parameters, including organic carbon, soil nitrogen, soil sulfur, and soil oxalate-extractable aluminum and iron concentrations. The site-specific mean Hg concentrations in organic horizons (174–479 μg kg−1) were greater than mean Hg concentrations in mineral soil (15–88 μg kg−1). Site specific mean Hg/C ratios in organic horizons at four study sites ranged from 0.8 to 2.4 μg g−1, while mean mineral soil Hg/C varied from 2.0 to 3.4 μg g−1. Near cement plants, an 8- to 30-cm thick layer composed of dust particles was identified below or mixed with current O and A horizon material (Hg concentrations 122 to 401 μg kg−1). Mean mineral soil pools of Hg (13–24 mg m−2) dominated over the mean organic horizon Hg pools (2–11 mg m−2). Near cement plants and steel works, Hg concentrations and pools in organic horizons and mineral soils were within the range reported from pristine Czech forest soils. Elevated Hg concentrations in organic horizons were found near a chlor-alkali plant. Thermal decomposition analysis indicated that Hg in A horizons at all sites and dust horizons near cement plants was bound similarly to Hg in foliage.