Mercury distribution around the Siele Hg mine (Mt. Amiata district, Italy) twenty years after reclamation: Spatial and temporal variability in soil, stream sediments, and air

The Siele mine and its smelting plant are part of the world class Monte Amiata Hg district (southern Tuscany, Italy). After closure in 1981, the area was subjected to the first reclamation in the district, completed in 2001. However, stream sediments in the Siele creek downstream of the mine still present highly anomalous Hg values (up to 5400 mg/kg). Gaseous elemental mercury (GEM) concentrations in air near the former metallurgical buildings, and immediately downstream of the mining area, are also high (up to 16,233 ng/m3), although lower than before reclamation, when values up to 237,000 ng/m3 had been measured. On the other hand, Hg mobility, determined by leaching tests, is mostly below the limits defined by pending regulations (1 μg/L), and methyl-Hg concentrations are mostly below 1 ng/kg (with a single value of 6 ng/kg). Therefore, the actual risk to environment and health is deemed low. In summary, reclamation reduced, but did not stop, the release of Hg from the Siele mining area. Results show that the Siele system has a low resilience and natural recovery will take many years (probably decades), during which the area will remain an important source of Hg for the Paglia and Tiber River systems, and eventually for the Mediterranean Sea.