il mercurio nella colonna d'acqua

Recent contamination of mercury in an estuarine environment (Marano lagoon, Northern Adriatic, Italy)

Covelli S., Acquavita A., Piani R., Predonzani S., De Vittor C. 2009. Recent contamination of mercury in an estuarine environment (Marano lagoon, Northern Adriatic, Italy). Estuarine, Coastal and Shelf Science 82 (2), 273-284.
The role of suspended particulate matter (SPM) as an important carrier of mercury (Hg) dispersed into the Gulf of Trieste and in the adjacent Grado lagoon (northern Adriatic Sea) was studied during a high Isonzo River inflow and the resulting river plume formation. Despite the fact that extreme flood events are rare during the year, they account for most of the PHg influx (37-112 ng L-1) into the Gulf of Trieste. When the river plume is diverted to the SW under the influence of an E-NE wind, the tidal flux acts as a “transport belt” carrying the PHg, mostly inorganic, into the Grado lagoon. A preliminary estimation indicates that the amount of PHg entrapped in the lagoon basin following a tidal semi-cycle accounts for 1.4 kg/12 h, which corresponds to about 49% of the total Hg carried by the tidal flow. These findings should be considered in future remediation strategies in the lagoon environment.

Transport and dispersion of particulate Hg associated to a river plume in coastal Northern Adriatic environments

Covelli S., Piani R., Acquavita A., Predonzani S., Faganeli J. 2007. Transport and dispersion of particulate Hg associated to a river plume in coastal Northern Adriatic environments. Marine Pollution Bulletin, 55 (10-12), 436-450.
The Marano Lagoon, in the northern Adriatic Sea (Italy), has been affected by mercury (Hg) contamination from industrial and mining activities. It has been estimated that 186,000 Kg of Hg were deliberately discharged into the main drainage system (Aussa-Corno River) by a chlor-alkali plant (CAP) from 1940’s to 1984. The lagoon has also experienced a secondary long-term Hg input, originated from mining activity in Idrija (Slovenia), due to the supply of fluvial suspended particles carried by the Isonzo River in the Gulf of Trieste. Since local fishing activities are extensively conducted, there is great concern on the risk posed by potentially harmful effects of Hg to the trophic chain. Present inputs of this metal, both in dissolved (52.4-4.1 ng L-1) and particulate (130.8-3.4 ng L-1) phases, were preliminary investigated in the water column. Although direct discharge of Hg from the CAP no longer exists, the metal is still released from the source area into freshwaters, and its distribution and abundance is controlled by the saltwedge circulation system, which is tide-influenced. Remobilization from bottom sediments can also be a secondary source of Hg into the aquatic environment. A speciation technique, used to investigate the main binding sites and phase associations of Hg in sediments (5.69-0.82 µg g-1), evidenced the presence of mobile (1.8-11%) and potentially available species for methylation processes. The results are particularly important if related to resuspension effects caused by natural events and anthropogenic activities. Preliminary considerations on Hg behaviour in this estuarine environment are reported.

Behaviour of Hg species in a microtidal deltaic system: The Isonzo River mouth (northern Adriatic Sea)

Covelli S., Piani R., Kotnik J., Horvat M., Faganeli J., Brambati A., 2006. Behaviour of Hg species in a microtidal deltaic system: The Isonzo River mouth (northern Adriatic Sea). Science of the Total Environment, 368 (1), 210-223.
Mercury species in the highly stratified water column of the Isonzo river mouth (northern Adriatic Sea) were investigated in February, May and August 2002 (low-normal fluvial discharge). Total, dissolved and particulate mercury (Hg) and methylmercury (MeHg) were measured and their concentrations were related to physico-chemical parameters in terms of temperature, salinity, turbidity, O2 concentrations and total suspended matter (TSM) as well as particulate organic carbon (POC) content. Particulate Hg and MeHg are well correlated to medium-fine silty suspended sediment and organic matter, respectively. Desorption of Hg from particles in the brackish layer was observed. Due to the presence of a saltwedge, the lower river course seems to be a trap for Hg carried by fluvial waters. MeHg normally decreases approaching the sea but the local increase in the inner zone of the saltwedge could be related to methylation processes in the bottom water layer. Hg export is effective only during medium and high riverine flows acting as an important source of Hg into the northern Adriatic and the adjacent lagoon system.

Mercury and methylmercury in the Gulf of Trieste (northern Adriatic sea)

Faganeli J., Horvat M., Covelli S., Fajon V., Logar M., Lipej L., Cermelj B. 2003. Mercury and methylmercury in the Gulf of Trieste (northern Adriatic sea). Science of the Total Environment, 304, 315-326.
The distribution, sources and fate of mercury (Hg) in the water column of the Gulf of Trieste (northern Adriatic Sea), affected by the Hg polluted river Soca-Isonzo for centuries draining the cinnabar-rich deposits of the Idrica mining district (NW Slovenia), were studied in terms of total and dissolved Hg, reactive Hg, total and dissolved methylmercury (MeHg), mesozooplankton Hg and MeHg, and sedimentation rates of particulate Hg. Higher total Hg concentrations in the surface layer were restricted to the area of the Gulf in front of the river plume expanding in a westerly direction. Higher concentrations in bottom water layers were the consequence of sediment resuspension. Dissolved Hg exhibited higher concentrations in the surface layer in the area in front of the river plume. Higher bottom concentrations of dissolved Hg observed at some stations were probably due to remobilization from sediments, including resuspension and benthic recycling. The relationship between dissolved Hg in the surface layer and salinità showed nonconservative mixing in June 1995 during higher riverine inflow and nearly conservative mixing in September 1995 during lower riverine inflow. Both mixing curves confirm the river Soca-Isonzo to be the most important source of total and dissolved Hg, which are significantly correlated, in the Gulf. Reactive Hg is significantly correlated with dissolved Hg, indicating that the majority of dissolved Hg is reactive and potentially involved in biogeochemical transformations. The higher total MeHg in the bottom layer is the result of remobilization of MeHg from sediments including benthic fluxes. Strong seasonal variation of sedimentation rates of particulate Hg was found during a 2-year study in the central part of the Gulf. These variations followed those of total sedimented matter, indicating that sedimented Hg is mostly associated with inorganic matter. About a 2.5-fold higher fluxes of particulate Hg were observed at the depth of 20 m relative to 10 m which is attributed to bottom sediment resuspension. Temporal variability of mesozooplankton Hg and MeHg is the consequence of biomass and species variations, and grazing behaviour. From the preliminary Hg mass balance it appears that the Gulf is an efficient trap for total Hg and a net source of MeHg.