revised final - Agency for Toxic Substances and Disease Registry ...

MERCURY 379
5.1 OVERVIEW
5. POTENTIAL FOR HUMAN EXPOSURE
Mercury occurs naturally as a mineral and is distributed throughout the environment by both natural and
anthropogenic processes. The natural global bio-geochemical cycling of mercury is characterized by
degassing of the element from soils and surface waters, followed by atmospheric transport, deposition of
mercury back to land and surface water, and sorption of the compound to soil or sediment particulates.
Mercury deposited on land and open water is in part revolatilized back into the atmosphere. This
emission, deposition, and revolatilization creates difficulties in tracing the movement of mercury to its
sources. Major anthropogenic sources of mercury releases to the environment include mining and
smelting; industrial processes involving the use of mercury, including chlor-alkali production facilities;
combustion of fossil fuels, primarily coal; production of cement; and medical and municipal waste
incinerators and industrial/commercial boilers (EPA 1996b).
The element has three valence states and is found in the environment in the metallic form and in the form
of various inorganic and organic complexes. The major features of the bio-geochemical cycle of mercury
include degassing of mineral mercury from the lithosphere and hydrosphere, long-range transport in the
atmosphere, wet and dry deposition to land and surface water, sorption to soil and sediment particulates,
revolatilization from land and surface water, and bioaccumulation in both terrestrial and aquatic food
chains.
Potential sources of general population exposure to mercury include inhalation of mercury vapors in
ambient air, ingestion of drinking water and foodstuffs contaminated with mercury, and exposure to
mercury through dental and medical treatments. Dietary intake is the most important source of
nonoccupational exposure to mercury, with fish and other seafood products being the dominant source of
mercury in the diet. Most of the mercury consumed in fish or other seafood is the highly absorbable
methylmercury form. Intake of elemental mercury from dental amalgams is another major contributing
source to the total mercury body burden in humans in the general population (WHO 1990, 1991).
Because the two major sources of mercury body burden include dietary intake and intake from dental
amalgams, mercury is present at low concentrations in a variety of human tissues. Mercury has been
detected in blood, urine, human milk, and hair in individuals in the general population. Inhalation of