Mercury dispersion from the Mt. Amiata mining district to the upper reach of the Paglia River (Central Italy): A geomorphological-geochemical approach defines the interaction between river deposits and mining activity

The Paglia River drains the Mt. Amiata Mercury District (the 3rd most important district worldwide exploited from 1880 to 1980) before becoming a tributary of the Tiber River. A combined geochemical-geomorphological approach was applied to understand Hg distribution in the fluvial morphological units (MUs). The Hg mean values in the terraces (here after indicated as Tn) seem to be linked to the mining activity: T1, formed before the activity, has values within the local background (2÷6 mg/kg); T2, T3 and T5, formed either at the beginning or in the final phases, have values lower than 9 mg/kg; T4, formed during the peak activity, has 26 mg/kg. The current baseflow channel and bar have mean value of 9 mg/kg. The high value of the modern floodplains (19 mg/kg) could be related to intense flood events causing greater erosion of contaminated MUs upstream. The total contained mass of Hg in the studied stretch is estimated at 63 tonnes.