Potentially wildfire-induced mercury release in the Mediterranean basin: Evidence from a former mining area in Italy

The Mediterranean basin faces growing climate change threats; among them wildfires may impact on the biogeochemical cycle of toxic elements like mercury (Hg). This study quantified the Hg uptake by vegetation and soils in the former Mt. Amiata Mining District (MAMD) and assessed Hg release from hypothetical wildfires. Mercury concentrations were analyzed in different plant species (beech, chestnut and pine trees), as well as in litterfall and soils from five MAMD sites and two background sites. Results showed significant differences in Hg concentrations among tree species, with pine bark showing the highest values (from 98 ± 28–1552 ± 752 μg kg−1), and beech wood the lowest (6 ± 5–13 ± 5 μg kg−1). The highest Hg concentrations for both soil (5685 ± 4010 μg kg−1) and litterfall (4971 ± 703 μg kg−1) were found in beech forest, underlying litter decomposition role in Hg translocation to organic soil. Estimates of plant biomass allowed the calculations of potential Hg release under three hypothetical wildfire scenarios. A severe wildfire consuming plant biomass, litterfall, and soil could release over 2 kg Hg ha−1 in pure beech forests. Specific contributions were estimated (as average) to 8 g Hg ha−1 for litterfall, 28 g Hg ha−1 for aboveground plant biomass, and 1063 g Hg ha−1 for top-soil. The study provides new insights into the Hg cycle and the impact of wildfires in the Mediterranean area, with implications for environmental management and human health.