Mass loading of Hg in the Monte Amiata mining district, Southern Tuscany (Italy)

Mercury (Hg) transport in natural environments is of concern because Hg bioaccumulates in the food web. Particularly methyl-Hg is the form of Hg of major concern as it is highly toxic to humans and is ingested through food consumption, dominantly fish. Quantification of Hg mass loads in watersheds draining Hg mine districts allows (1) the identification of sources of contamination, (2) the evaluation of the effect of Hg on the environment, and (3) the identification of processes affecting Hg transport. This study focuses on the determination of Hg loads in the Paglia River, which drains the Hg district of Monte Amiata (Italy), world’s 4th largest Hg producing district. Mass loads were determined for total Hg, particulate Hg, and dissolved Hg. Data obtained from two sampling campaigns carried out in 2011 indicated that up to 34 g/d of Hg were transported during the rainy season, of which up to 99% was as particulate Hg. Maximum Hg loads were related to runoff from the Abbadia San Salvatore mine (ASSM), and thus, this mine is the main source of Hg to the Paglia River basin. Data indicate that particulate Hg has been deposited along with river sediment, forming a natural sink where resultant chemical reactions promote conversion of Hg from particulate matter to dissolved Hg. These results suggest that mining of Hg has affected this area. Even today, 30 years after the cessation of mining, considerable amounts of Hg are continuously transported downstream from mined areas by local rivers.