Variability of gaseous elemental mercury concentrations in the northern Adriatic coastal area (Gulf of Trieste-Marano and Grado Lagoon)

Gaseous elemental mercury (GEM) concentrations in pristine, urban and mercury (Hg)-contaminated sites, over the period from May 2013 to June 2015, were monitored for their temporal dynamics of variability. Results of GEM measurements along a E-W transect from the city of Trieste (NE Italy) to the Marano and Grado Lagoon were recorded during periods of more than 24 hours. Most of the monitored sites are affected by the presenceof Hg in soils, sediments and waters, since the Isonzo River, carrying Hg-contaminated sediments coming from the Idrija (Slovenia) mining district, is the major fluvial input ofthe Gulf of Trieste. Two LUMEX RA95M devices were used to analyze GEM concentrations at fixed intervals (1 to 5 sec., depending on the availability of continuous electricity power) by meansof atomic absorption spectrometry with Zeeman effect. This is a technique usually employed during GEM monitoring surveys worldwide. Results indicate that GEM concentrations are systematically low (2-5 ng m-3) in the study area. Restricted areas with the highest GEM values were found in the proximity of the Isonzo River mouth and in the alluvial plain between the river and the Lagoon (East sector). Here, soils show high concentrations of Hg (up to 30 mg/kg) since the whole area belonged to the former lagoon environment and it was drained in 1920-30 for agricultural purposes. In these areas, GEM concentrations were higher (up to 30-50 ng m-3) duringnight periods and in particular during wind cessation moments, although they are scarce and short in time in this coastal area.