The Global Mercury Cycle: Oceanic and Anthropogenic Aspects

The global mobilization and biogeochemical cycling of Hg at the Earth’s surface has been studied using a variety of mass balance formulations [e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]. The prominent role of atmospheric and oceanic processes, and anthropogenic Hg emissions in modern Hg cycle are evident. Most research however, has focused on terrestrial systems, with the biogeochemistry of Hg in fresh water systems receiving much attention. Paradoxically, the oceans have been largely ignored, yet the primary exposure of humans to methylmercury (MMHg) is through the consumption of marine fish and fish products. MethylHg compounds are considerably more toxic than elemental Hg and its inorganic salts, and prenatal life is more susceptible to MMHg-induced brain damage than adults [8]. The risk to public health is evident in the fish consumption advisories that have been issued in Canada, Scadanavia, by more than 30 states, the US FDA, the World Health Organization (WHO) and numerous other governments. Moreover, the coupling between atmospherically-borne Hg contamination and high MMHg concentrations in fish has been recognized. For example, a principal theme for the recently formed SCOPE Committee on Hg in the environment is a reevaluation of the influence of atmospheric Hg cycling and sea-air exchange on MMHg levels in oceanic fish [11]. In the U.S.A., the 1990 Clean Air Act Amendments require an assessment of health risk to humans and wildlife caused by Hg emissions. The potential adverse impact of atmospheric Hg deposition to coastal waters is contained in a planned Environmental Protection Agency (EPA) report to Congress [12].