The role of hydrological conditions for riverine Hg species transport in the Idrija mining area

• Published in: Environmental pollution (1987) Vol. 247; pp. 716 - 724
• Main Authors: Baptista-Salazar, Carluvy, Biester, Harald
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.04.2019
• Subjects: Cinnabar; Environmental Monitoring; Flux; Hg mining area; Hydrology; Italy; Mercury - analysis; Mercury Compounds; Mining; NOM-Hg; Rivers - chemistry; Slovenia; Soil; Water Pollutants, Chemical - analysis; Italy; Slovenia; Flux; Soil; Hg mining area; Cinnabar; NOM-Hg
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2019.01.109

Estimation of mercury (Hg) species fluxes in Hg contaminated rivers is crucial to predict Hg methylation in connected sediment sinks. Cinnabar (HgS) was mined and roasted for ∼500 years in the Idrija mining area, Slovenia, which is drained by the Idrijca River to the Gulf of Trieste (GT), Italy. Mining residues dumped into the Idrijca River caused high proportions of cinnabar in sediments, whereas soils containing high proportions of natural organic matter bound to Hg (NOM-Hg) are attributed to atmospheric Hg deposition. Previous calculations of Hg fluxes have been based on the erosion of cinnabar only, and neglected transport of NOM-Hg derived from soil. Here, we estimated NOM-Hg and cinnabar fluxes in the Idrijca River and evaluated the extent of variability under changing hydrological conditions. We estimated the discharge of NOM-Hg by Idrijca's tributaries and the importance of NOM-Hg fluxes for Hg methylation in the GT. Mass balance calculations reveal that approximately 11.2 Mg y−1 of NOM-Hg and 38.9 Mg y−1 of cinnabar are transported by the Idrijca River to the GT under median-flow conditions. In the past 520 years, a total of 53,000 tons of Hg have been released from the Idrija mining area, of which ∼32,000 tons were NOM-Hg. Under low-flow conditions, Idrijca's tributaries deliver more than 1280 kg y−1 of NOM-Hg. This study highlights the importance of Hg species analyses and their flux calculations to estimate risks of biological Hg uptake in sedimentary Hg sinks connected to Hg mining areas. [Display omitted] •Hydrology influences transport of Hg species in areas surrounding former Hg mines.•Bioavailable Hg is transported under low to high-flow conditions in the Idrijca river.•Hg fluxes must be based on Hg species proportions and no solely in Hg concentrations.•Soil erosion is important for Hg cycling, in contrast to transport of river sediments in former Hg mining areas.•Tributaries supply substantial amounts of organically-bound Hg forms derived from soils. Hg species analysis and their flux calculations allow evaluating Hg transformations downstream in former Hg mining areas which cannot be solely explained by total Hg concentrations.