Mediterranean Mercury Assessment 2022: An Updated Budget, Health Consequences, and Research Perspectives

An international team of researchers lead by Daniel Cossa (Université Grenoble Alpes, France) and Lars-Eric Heimbürger-Boavida (Mediterranean Institute of Oceanography, France) published a review on all aspects of mercury in the Mediterranean Sea. Mercury (Hg) is classified by the United Nations Environment Programme (UNEP) as a chemical element toxic to living organisms inclduing humans. This paper adresses current knowledge on the marine mercury cycle and relevant Mediterranean-specific features and presents an updated budget of Hg cycles including emissions, the geographical distribution in the waters and in the sediements of the Mediterranean Sea. The authors adress the strategy for building a comprehensive understanding of the Hg cycle in the Mediterranean, in order to allow future assessemnt of global change impacts in conjunction with the Minamata Convention Hg policy.

Abstract: Mercury (Hg) and especially its methylated species (MeHg) are toxic chemicals that contaminate humans via the consumption of seafood. The most recent UNEP Global Mercury Assessment stressed that Mediterranean populations have higher Hg levels than people elsewhere in Europe. The present Critical Review updates current knowledge on the sources, biogeochemical cycling, and mass balance of Hg in the Mediterranean and identifies perspectives for future research especially in the context of global change. Concentrations of Hg in the Western Mediterranean average 0.86 ± 0.27 pmol L–1 in the upper water layer and 1.02 ± 0.12 pmol L–1 in intermediate and deep waters. In the Eastern Mediterranean, Hg measurements are in the same range but are too few to determine any consistent oceanographical pattern. The Mediterranean waters have a high methylation capacity, with MeHg representing up to 86% of the total Hg, and constitute a source of MeHg for the adjacent North Atlantic Ocean. The highest MeHg concentrations are associated with low oxygen water masses, suggesting a microbiological control on Hg methylation, consistent with the identification of hgcA-like genes in Mediterranean waters. MeHg concentrations are twice as high in the waters of the Western Basin compared to the ultra-oligotrophic Eastern Basin waters. This difference appears to be transferred through the food webs and the Hg content in predators to be ultimately controlled by MeHg concentrations of the waters of their foraging zones. Many Mediterranean top-predatory fish still exceed European Union regulatory Hg thresholds. This emphasizes the necessity of monitoring the exposure of Mediterranean populations, to formulate adequate mitigation strategies and recommendations, without advising against seafood consumption. This review also points out other insufficiencies of knowledge of Hg cycling in the Mediterranean Sea, including temporal variations in air–sea exchange, hydrothermal and cold seep inputs, point sources, submarine groundwater discharge, and exchanges between margins and the open sea. Future assessment of global change impacts under the Minamata Convention Hg policy requires long-term observations and dedicated high-resolution Earth System Models for the Mediterranean region.

Full text accessible here.

Daniel Cossa, Joël Knoery, Daniela Bănaru, Mireille Harmelin-Vivien, Jeroen E. Sonke, Ian M. Hedgecock, Andrea G. Bravo, Ginevra Rosati, Donata Canu, Milena Horvat, Francesca Sprovieri, Nicola Pirrone, Lars-Eric Heimbürger-Boavida, Environmental Science & Technology,  2022-03-04, DOI: 10.1021/acs.est.1c03044

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