Mercury in the terrestrial environment: a review

Background Environmental contamination by mercury is and will continue to be a serious risk for human health. Pollution of the terrestrial environment is particularly important as it is a place of human life and food production. This publication presents a review of the literature on issues related to mercury pollution of the terrestrial environment: soil and plants and their transformations. Results Different forms of atmospheric Hg may be deposited on surfaces by way of wet and dry processes. These forms may be sequestered within terrestrial compartments or emitted back into the atmosphere, and the relative importance of these processes is dependent on the form of Hg, the surface chemistry, and the environmental conditions. On the land surface, Hg deposition mainly occurs in the oxidized form (Hg2+), and its transformations are associated primarily with the oxidation-reduction potential of the environment and the biological and chemical processes of methylation. The deposition of Hg pollutants on the ground with low vegetation is as 3-5 times lower than that in forests. The estimation of Hg emissions from soil and plants, which occur mainly in the Hg(0)form, is very difficult. Generally, the largest amounts of Hg are emitted from tropical regions, followed by the temperate zone, and the lowest levels are from the polar regions. Areas with vegetation can be ranked according to the size of the emissions as follows: forests > other areas (tundra, savannas, and chaparral) > agricultural areas > grassland ecosystems; areas of land devoid of vegetation emit more Hg than those with plants. In areas with high pollution, such as areas near Hg mines, the Hg content in soil and plants is much higher than in other areas. Conclusions Mercury is recognized as a toxic, persistent, and mobile contaminant; it does not degrade in the environment and becomes mobile because of the volatility of the element and several of its compounds. Atmospheric contamination by mercury continues to be one of the most important environmental problems in the modern world. The general conclusions were drawn from a review of the literature and presented in this paper.