Mercury dispersion through streams draining the Mt. Amiata district, southern Tuscany, Italy

The Mt. Amiata area hosts the 3rd largest Hg district in the world, overlapping with a present-day geothermal system that is exploited for energy production. Mining activity ceased in 1980; remediation of mining areas was only partial, and is still under way. A significant transport of mercury is documented in the streams draining the district. By far the largest output occurs to the southeast in the Paglia River catchment; this river is tributary of Tiber River, the largest river of central Italy. A much smaller transport occurs to the north, in the Orcia-Ombrone catchment. Most transport is in particulate form; mercury is temporarily stored in stream and overbank sediments, and can be significantly mobilized and redistributed by extreme events such as flash floods. Transfer to the biosphere and food chain is not negligible, as some fish in Paglia and Tiber Rivers show Hg contents that may be harmful for human consumption. The overall output from the Monte Amiata district represents a significant contribution to the Mediterranean Sea budget of this metal.