engleski

Speciation of mercury in surface and deep-sea waters in the Mediterranean Sea

A summary of data recently obtained for mercury analysis and speciation (reactive Hg, total Hg and monomethylmercury (MMHg) in filtered and non-filtered seawater samples, dissolved gaseous mercury (DGM) and dimethylmercury (DMHg) in open and coastal waters of the Mediterranean Sea is presented. The majority of the results were obtained during an oceanographic cruise aboard the research vessel Urania from 14 July to 9 August, 2000, as part of the MED-OCEANOR Project funded by the National Research Council of Italy. The results are compared with those obtained in contaminated coastal environments of the Adriatic (The Gulf of Trieste and Kaštela Bay) and non-contaminated coastal waters of the eastern Adriatic coast obtained in 1998. Total mercury concentrations in surface ocean waters are relatively low with an awerage of 0.8 pM (0.49-1.91 pM). Reactive Hg represents a substantial part with an average of 57% of total Hg (15-97%). Most mercuryin open ocean waters was present in the dissolved form (32-95%, av. 70%), which is mainly due to the low abundance of particulate matter, a phenomenon well known for the Mediterranean open ocean waters. On average the percentage of Hg as MMHg was about 20%, of which about 66% was present in the dissolves form. The percentage of DGM in the surface ocean watersrepresents about 9% of total Hg (2.5-24.5%) and may originate from photochemical, biologically mediated mechanisms or diffusion from deeper layer eitherdue to biological and/or to tectonic activity which is typical of the Mediterranean region. The presence of DMHg was confirmed only in waters body below 20 m (up to 12 fM), while in surface waters DMHg was below the limit of detection (<0.1 fM). Surface concentrations of Hg in thee eastern and western part (mean value: 0.22 pM). The distribution of Hg species with depth was only measured at two stations, and indicated variability comparing the eastern and western leg of the Urania cruise. The depth profile pattern confirm the importance of dynamic processes at the surface layers, while deep water continuously supplies DGM to the surface layer. The importance of analytical quality control is also discussed in this paper.

mercury; methyl mercury; dissolved saseous mercury; speciation; Mediterranean Sea

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