Mercury Behaviour In Estuarine And CoastalEnvironment

Abstract

General facts about the global mercury cycle with particular emphasis on the coastal and ocean environment are summarized. In the coastal environment the largest source of mercury is river-born particulate bound species. This portion of mercury is unreactive and is quickly buried in nearshore sediments. Only a small fraction of reactive mercury (ionic mercury in solution that is immediately available for reaction) originates from river inputs. The most important source of reactive mercury in the coastal and oceanic environment is through atmospheric input and via upwelling. Biologically-mediated processes, mainly connected to primary production, are responsible for active redistribution of reactive mercury. In this process a large part of reactive Hg is reduced to elemental mercury which is returned to the atmosphere by evasion, while the rest is scavenged by particles and transported to deeper oceanic waters. Because of the active atmospheric mercury cycle oceans acts as a source and a sink of atmospheric mercury and the global oceanic evasion is balanced by the deposition. Current studies show that methylated species are primarily formed in the deeper ocean and the mam source of monomethylmercury (MMHg) compounds in coastal areas is through upwelling of oceanic waters and from in-situ methylation in coastal waters. All these environmental processes occur at extremely low concentration levels of mercury species; however MMHg in marine organisms accounts for a high proportion of this toxic compounds owing to its property for bioaccumulation and biomagnification. Coastal areas on the local scale may account for geochemical differences that significantly influence the conversion between various Hg species. In order to assess the impact of mercury in contaminated and noncontaminated coastal areas on man and his environment, it is of the greatest importance to understand these processes. The paper also identifies uncertainties and gaps in current knowledge of mercuy cycling