Mercury in the Mediterranean: Status, Impacts and Policy Implications

An interesting feature of mercury biogeochemistry in the Mediterranean is that several fish species from the Mediterranean show higher concentrations of Hg than same fish species in the Atlantic ocean, although the concentrations of total-Hg in the open waters of both oceans are similar. Elevated Hg levels have been noted in environmental matrices from the Mediterranean regions adjacent to known mercury anomalies, yet, the data do not clearly indicate that these contaminated sites have contributed to open waters or to lower trophic level species. Recent studies indicated that the main source of MeHg in organisms in the coastal areas is related to methylation in sediments, while net mercury methylation in the open ocean occurs in the water column and is linked to organic matter regeneration promoted by the presence of small-sized nano- and picophytoplankton, that dominate under oligotrophic conditions. Relatively large portion of mercury in waters is present as dissolved gaseous Hg, originating from photochemical, biologically mediated mechanisms and/ or diff usion from deeper layer either due to biological and/or to tectonic activity which is typical of the Mediterranean region. Recent studies on distribution and cycling of Hg and a mass balance were implemented. It was shown that the total-Hg exchanges at the straits are not unbalanced, while mercury entering the western Mediterranean is mainly in inorganic Hg forms and is exported to the Atlantic partially as methylated species. It has been shown that exchange with the atmosphere is the most important source/sink of Hg for the water compartment. Measurements have shown that the evasion of Hg varied between the different seasons with the highest evasion during the autumn and an estimate of yearly evasion from the Mediterranean Sea surface was 77 tons. Based on policy target scenarios and integrated models developed, it is expected that Hg concentration in the Mediterranean will decrease by 2020 for about 3 to 12% as compared to 2005. Based on mercury measured in sea food, it was indicated that a consumption of certain fish species may pose a health risk. A review of health related studies in the Mediterranean, particularly the effects of prenatal Hg exposure through fish consumption on neurodevelopment, will be presented and discussed in the light of inconsistencies found in similar studies around the world. Any fish advisories should carefully be balanced against the benefit of the fish consumption in the region.