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MERCURY 433
5. POTENTIAL FOR HUMAN EXPOSURE
Dietary Sources of Mercury. Galal-Gorchev (1993) analyzed dietary intakes of mercury from
14 countries, including the United States, between 1980 and 1988. This author reported that the
contribution of fish to the total intake of mercury varied from a low of 20% in Belgium and the Netherlands
to 35% in France, the United Kingdom, and the United States. The highest contribution of fish to mercury
intake (85%) was reported for Finland. The author further pointed out (based on information from the
Netherlands on levels of mercury contamination in a variety of foods) that although mercury was found at
higher concentrations in fish (0.1 mg/kg [ppm]) than in other foods (0.01 mg/kg or less), higher
consumption of cereals and meats render the contributions of these food groups to the total mercury intake
about the same as that from fish. Therefore, the general assumption that fish is the main contributor to the
intake of mercury may, at times, not be justified because of dietary habits of a given population (Galal-
Gorchev 1993).
The FDA's Total Diet Study (April 1982–April 1984) estimated an average daily intake of mercury (total)
based on measured levels and assumed trace amounts in foods to be representative of the "total diet" of the
U.S. population (Gunderson 1988). Estimated daily exposures for mercury were 0.49 µg/day for infants
ages 6–11 months, 1.3 µg/d for 2-year-old children, 2.9 µg/day for females ages 25–30, and 3.9 µg/day for
males 25–30 years of age. Expressed on a per body weight basis, the intake for all age groups, except
2-year-old children, was approximately 50 ng/kg/day (Clarkson 1990; Gunderson 1988). For 2-year-old
children, the intake was estimated to be approximately 100 ng/kg/day (assuming 50% of the fish intake was
due to fish caught locally). More recently, MacIntosh et al. (1996) calculated average daily dietary
exposure to mercury and 10 other contaminants for approximately 120,000 U.S. adults by combining data
on annual diet, as measured by a food frequency questionnaire, with contaminant residue data for tableready
foods that were collected as part of the annual FDA Total Diet Study (1986–1991). The estimated
mean dietary exposure (µg/day) for 78,882 adult females and 38,075 adult males in 1990 was 8.2 µg/day
(range, 0.37–203.5 µg/day) for females and 8.6 µg/day (range, 0.22–165.7 µg/day) for males. Assuming a
body weight of 65 kg for women and 70 kg for men, the daily intakes of mercury would be 126 ng/kg/day
(range, 5.7–3,131 ng/kg/day) for women and 123 ng/kg/day (range, 3.1–2,367 ng/kg/day) for men
respectively. These authors found that the coefficient of variation was 44% for mercury, indicating that the
exposures to this chemical estimated for a given individual may be accurate to within approximately a
factor of 2. Lack of data about the actual amount of food consumed accounted for 95% of the total
uncertainty for mercury. Individual food items contributing most to the uncertainty of mercury
measurements were canned tuna and other fish (MacIntosh et al. 1996).