Mercury Cycling in the Coastal and Open Ocean and Associated Health Risks

This chapter provides a global and up-to-date overview of understanding of Hg sources and cycling in the coastal and open oceans, affecting aquatic organisms and human populations. Mercury in the environment exists in three main forms: elemental Hg as metallic Hg and Hg vapor, inorganic Hg compounds, and organic Hg, which includes Hg bonded to a structure containing carbon atoms. Mercury cycling between the ocean, atmosphere, and terrestrial ecosystems undergoes a series of complex chemical and physical processes. Mercury cycling among various reservoirs results both from anthropogenic and natural Hg emission sources. Among them, the atmosphere, through wet and dry deposition, generally dominates the majority of Hg inputs to open ocean. Vegetation plays an important role in the Hg cycle that ultimately reaches the coastal area through runoff. In coastal environments, biotic methylation of inorganic Hg into MeHg is also done by microorganisms, and Hg methylation occurs in both anaerobic and aerobic conditions.