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Recent models of global mercury (Hg) cycling have identified the downward flux of sinking particles in the ocean as a prominent Hg removal process from the ocean. At least one of these models estimates the amount of anthropogenic Hg in the ocean to be about 400 Mmol, with deep water formation and sinking fluxes representing the largest vectors by which pollutant Hg is able to penetrate the ocean interior. Using data from recent cruises to the Atlantic, we examined the dissolved and particulate partitioning of Hg in the oceanic water column as a cross-check on the hypothesis that sinking particle fluxes are important. Interestingly, these new data suggest particle-dissolved partitioning (Kd) that is approximately 20× greater than previous estimates, which thereby challenges certain assumptions about the scavenging and active partitioning of Hg in the ocean used in earlier models. For example, the new particle data suggest that regenerative scavenging is the most likely mechanism by which the association of Hg and particles occurs.This article is part of the themed issue 'Biological and climatic impacts of ocean trace element chemistry'.

Mercury is a toxic, bioaccumulating trace metal whose emissions to the environment have increased significantly as a result of anthropogenic activities such as mining and fossil fuel combustion (1,2). Several recent models have estimated that these emissions have increased the oceanic mercury inventory by 36-1,313 million moles since the 1500s (2-9). Such predictions have remained largely untested owing to a lack of appropriate historical data and natural archives. Here we report oceanographic measurements of total dissolved mercury and related parameters from several recent expeditions to the Atlantic, Pacific, Southern and Arctic oceans. We find that deep North Atlantic waters and most intermediate waters are anomalously enriched in mercury relative to the deep waters of the South Atlantic, Southern and Pacific oceans, probably as a result of the incorporation of anthropogenic mercury. We estimate the total amount of anthropogenic mercury present in the global ocean to be 290 ± 80 million moles, with almost two-thirds residing in water shallower than a thousand metres. Our findings suggest that anthropogenic perturbations to the global mercury cycle have led to an approximately 150 per cent increase in the amount of mercury in thermocline waters and have tripled the mercury content of surface waters compared to pre-anthropogenic conditions. This information may aid our understanding of the processes and the depths at which inorganic mercury species are converted into toxic methyl mercury and subsequently bioaccumulated in marine food webs., Mercury (Hg) is emitted to the atmosphere by natural and human sources primarily as [Hg.sup.0], which is unusually volatile for a metal (1). The elemental form is removed from the [...]

The precision and bias of monomethylmercury (MMHg) determinations in environmental samples can be improved by directly coupling and automating the numerous steps involved with analysis of this toxic Hg species. We developed a simple and robust mercury speciation analyzer (MSA) for measurement of MMHg in environmental matrixes. This on-line hyphenated system couples the main analytical steps, including sample introduction, aqueous-phase ethylation, Tenax preconcentration, and gas chromatographic separation, to cold vapor atomic fluorescence detection and data acquisition. Here we describe the MMHg-MSA, present results of laboratory optimization and performance tests, and compare the reproducibility between dual analytical channels. With alternating sample concentration and analysis, a dual-channel system permits six high-accuracy MMHg determinations per hour. Additional advantages compared to the traditional manual method include ease of operation and high precision (

We examined monomethylmercury (MMHg) in sediment reference material IAEA-405 and sediments from Long Island Sound. MMHg was extracted by both aqueous distillation and leaching with dilute solutions of nitric acid. MMHg was formed from both ambient and added inorganic mercury in extracts of IAEA-405 by either technique. Artifact MMHg in IAEA-405 was related linearly with ambient reactive mercury ([Hg.sub.R]) in leachates having > 1.2 M acid, but little or no artifact was measured in less acidic extracts. Addition of potassium chloride enhanced extraction of [Hg.sub.R] from IAEA-405 but had no effect on artifact MMHg for each leachate molarity tested. Mercury methylation occurred in solution and was a function of both the availability of [Hg.sub.R] and a methylation potential, being limited by [Hg.sub.R] in less acidic solutions (0.5-1.2 M) and by the methylation potential in more acidic ones (> 1.2 M). Formation of artifact MMHg in Long Island Sound sediments was inconclusive, but additions of inorganic mercury demonstrated that a potential exists. A potential for abiotic mercury methylation seems always present in sediment, and the availability of [Hg.sub.R] appears to control MMHg production under environmental conditions. Abiotic methylation of mercury may occur in environs where the reactivity of inorganic mercury is enhanced, such as river-seawater mixing zones.

The research work related to biogeochemistry, speciation, distribution, behavior, and status of mercury in the ocean and global is reviewed. The findings will help to address international problems associated with to monomethylmercury (MMHg) which is highly toxic form of Hg that accumulates in aquatic and terrestrial organisms.