Total mercury mass load from the Paglia-Tiber River system: the contribution to Mediterranean Sea Hg budget

The Mediterranean Sea is characterized by a marked mercury (Hg) geochemical anomaly,arising in part from large Hg deposits. Mercury mass loads discharged from the Monte Amiatamining district (Central Italy) to the Mediterranean Sea through the Paglia-Tiber River system wereestimated. Data from two seasons showed that up to 40 kg year-1 of Hg are drained to Tiber Riverand finally to the Mediterranean Sea. The mercury mass loads varied in different seasons, from3 mg day-1in the upper section of Paglia River in November to 42 g day-1 before the confluencewith Tiber River in June. Along Tiber River, up to 15 ng L-1 of the total Hg found at a site afterRome showed that Hg can be discharged to the sea. The Alviano reservoir along Tiber River actsas a temporary trap for Hg-rich particulate, while dam operations may promote Hg release (up to223 g day-1). The combination of hydrologic factors controlling Hg transport, the torrential regimein the upper catchment of Paglia River, the waterway steepness, together with Hg-contaminatedlegacy sediments in the Paglia River floodplain, make the Paglia-Tiber River system a long-lastingintermittent source of Hg to Tiber River and the Mediterranean Sea.