21.4.3 Relative Significance of Different Routes of Environmental Exposure
Human exposure to the three major forms of mercury present in the environment is
summarized in Table 21.1 (based on IPCS, 1991). Although the choice of values given
is associated with some uncertainty, the numbers provide a perspective on the relative
magnitude of the contributions from various media.
Humans may be exposed to additional quantities of mercury occupationally, from living
in heavily polluted areas or through the use of skin-lightening creams. The intake from
drinking water is about 50 ng mercury per day, mainly asHg2þ; of which only a small fraction
is absorbed. The main pathway of exposure is through the intake offish and seafood products,
mainly in the form of methylmercury. Very high exposures occur in arctic populations,
whose diets include marine mammals. Increased levels also occur in Japanese and
Mediterranean populations, who frequently eat fish high in the food chain. Exposures are
lower in countries, such as the United States, where NHANES III data suggest that 85% of