Sources and fate of mercury pollution in Almadén mining district (Spain): Evidences from mercury isotopic compositions in sediments and lichens

• Hg isotope signatures have enabled tracing aquatic and atmospheric Hg sources.
• Hg isotope composition and contamination displayed a dilution downstream the mines.
• MDF of Hg isotopes allowed to track biogeochemical alterations downstream Hg mines.
• Sediments and lichens can act as complementary Hg reservoirs as revealed by MIF signatures.
• Isotopic data from this emblematic mining district can be used as an isotopic reference.

Variations in mercury (Hg) isotopic compositions have been scarcely investigated until now in the Almadén mining district (Spain), which is one of the most impacted Hg areas worldwide. In this work, we explore and compare Hg isotopic signatures in sediments and lichens from Almadén mining district and its surroundings in order to identify and trace Hg aquatic and atmospheric contamination sources. No statistically significant mass independent fractionation was observed in sediments, while negative Δ201Hg values from −0.12 to −0.21‰ (2SD = 0.06‰) were found in lichens. A large range of δ202Hg values were reported in sediments, from −1.86 ± 0.21‰ in La Serena Reservoir sites far away from the pollution sources to δ202Hg values close to zero in sediments directly influenced by Almadén mining district, whereas lichens presented δ202Hg values from −1.95 to −0.40‰ (2SD = 0.15‰). A dilution or mixing trend in Hg isotope signatures versus the distance to the mine was found in sediments along the Valdeazogues River-La Serena Reservoir system and in lichens. This suggests that Hg isotope fingerprints in these samples are providing a direct assessment of Hg inputs and exposure from the mining district, and potential information on diffuse atmospheric contamination and/or geochemical alteration processes in less contaminated sites over the entire hydrosystem. This study confirms the applicability of Hg isotope signatures in lichens and sediments as an effective and complementary tool for tracing aquatic and atmospheric Hg contamination sources and a better constraint of the spatial and temporal fate of Hg released by recent or ancient mining activities.