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

MERCURY 252
2. HEALTH EFFECTS
Cernichiari et al. (1995), and 137–585 in Birke et al. (1972). Therefore, this ratio (250) should not be used
as the sole basis for determining levels of exposure and potential effect for individuals.
Calculation of dietary intake of mercury from blood concentration.
Fraction of mercury in diet that is absorbed (A D). Radiolabeled methyl-mercuric nitrate was administered
in water to three healthy volunteers (Aberg et al. 1969). The uptake was >95%. Miettinen et al. (1971)
incubated fish liver homogenate with radiolabeled MeHgNO 3 to yield a methylmercury proteinate. The
proteinate was then fed to fish that were killed after a week, cooked, and fed to volunteers after
confirmation of the methylmercury in the fish. Mean uptake exceeded 94%. For the derivation of an MRL,
an absorption factor of 0.95 is used.
Fraction of the absorbed dose that is found in the blood (A B). The value 0.05 has been used for this
parameter in the past (Berglund et al. 1971; WHO 1990). Three studies report observations of the fraction
of the absorbed methylmercury dose distributed to blood volume in humans. Kershaw et al. (1980) report
an average fraction of 0.059 of the absorbed dose in the total blood volume, based on a study of 5 adult
male subjects who ingested methylmercury-contaminated tuna. In a group of 9 male and 6 female
volunteers who had received 203Hg-methylmercury in fish, approximately 10% of the total body burden was
present in 1 L of blood in the first few days after exposure, dropping to approximately 5% over the first
100 days (Miettinen et al. 1971). In another study, an average value of 1.14% for the percentage of
absorbed dose in 1 kg of blood was derived from subjects who consumed a known amount of methylmercury
in fish over a period of 3 months (Sherlock et al. 1984). Average daily intake for the 4 groups
observed in the study ranged from 43 to 233 µg/day. The authors report a dose-related effect on the
estimated percentage of the absorbed dose in 1 kg of blood, with 1.26% of the absorbed dose in 1 kg of
blood at an average daily intake of 43 µg/day and 1.03% of the absorbed dose in 1 kg of blood at an
average daily intake of 233 µg/day. The average for all subjects in the study was 1.14%. When individual
values for distribution to one kilogram of blood reported in the study are converted into the percentage of
the absorbed dose in the total blood volume (assuming that blood is 7% of body weight [Best 1961] and
using body weights reported for individuals in the study), the average value for AB for all individuals is
0.056 (0.057 using the values for percentage in 1 kg normalized for body weight as reported in the study).
The average value for AB for 6 women as reported in Sherlock et al. (1984) is 0.048 (0.047 using values
normalized for body weight). The average for 14 men is 0.059 (0.061 using values normalized for body
weight).