TOTAL GASEOUS MERCURY VARIATIONS IN THE ATMOSPHERE IN THE AREA OF TRIESTE-GRADO (NE ITALY)

The Gulf of Trieste (NE Italy) and the adjacent Grado-Marano Lagoon have been affected by significant mercury (Hg) contamination during the last 500 years due to the existence of mining tailings in Idrija (Slovenia) and their subsequent transportation along with sediments via the Isonzo River into the north-eastern Adriatic Sea. Although most of the metal is present as cinnabar compound in the coastal sediments and soils of the area, there is great concern on the potential evasion of gaseous Hg from contaminated surface materials into the atmosphere. The coastal area hosts several economic, industrial but also touristic activities, the last one representing the most important resource for local inhabitants during summer season. Sandy beaches show Hg concentrations well above national regulations and they are then thought as potential source of the metal in the gaseous form in the air. Beach sediments are supposed to be a potential risk for humans during the warmest period of the year considering the possible emission, and consequently inhalation, of gaseous Hg from these sands. This communication reports total gaseous mercury (TGM) concentrations measured in this area during surveys carried out during years 2013 and 2104 in the area of Trieste-Grado: one survey was carried out during 2013 in the Grado lagoon, using a boat as vehicle; during 2014 surveys were performed from fixed locations in Grado town, in Trieste town, and in a farm located between these two localities, in the immediate proximity to the mouth of Isonzo River. Results indicate that TGM concentrations in the studied area show differences in the geographic distribution that can be related to the presence of Hg contaminated sediments, such as those at the Isonzo river mouth, which act as emission source of this contaminant. Besides, it has been recognized that diurnal periods TGM concentrations are more stable, and in general lower than during night. This is particularly evident in the proximity of the riverine source areas. Measured concentrations are however away from worrying levels, even in the proximity of the most characteristic potential source areas. This is particularly true during diurnal hours.