Overview of major processes and mechanisms affecting the mercury cycle on different spatial and temporal scales

Mercury emissions to the atmosphere and its transport, transformation and deposition to and re-emission from terrestrial and aquatic ecosystems on hemispherical and global scales has received increasing attention from both the scientific and the regulatory communities during the last twenty years. It is well known that the atmosphere is the major transport media through which mercury is redistributed on global scale once it is released from point and diffuse emission sources. A substantial amount of research has been carried out worldwide aiming to assess the relationships between emissions from natural vs. anthropogenic sources, inter-hemispherical atmospheric transport patterns, and atmospheric deposition to and re-emission from oceans, its bioaccumulation in fish, and evaluation of policy strategies to reduce the impact of mercury emissions on human health and ecosystems. This chapter provides a highlight of key aspects related to mercury contamination, including: a) major processes affecting the mercury cycle between the atmosphere and aquatic and terrestrial ecosystems, b) mercury emissions from natural and anthropogenic sources, c) spatial and temporal distributions and trends of mercury species over the northern and southern hemispheres, d) the chemical and physical processes affecting the transport and fate of atmospheric mercury, and e)major policy frameworks aiming to control the impact of mercury on human health and ecosystems.