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

MERCURY 167
2. HEALTH EFFECTS
(1 mg/kg) of methylmercuric chloride, the level of mercury in the blood of mice declined slowly. At day
14 post-dosing, the blood level was still around 25% of the value at day 1 (Nielsen 1992). Blood levels of
mercury were closely correlated to whole-body retention of mercury during the first 3 days after
administration of methylmercuric chloride (1 mg Hg/kg) (Nielsen and Andersen 1992). However, at later
times after administration, the amount of mercury in the blood declined more rapidly than the whole-body
burden. The gastrointestinal retention of mercury slowly decreased in mice given organic mercury. This
phenomenon is probably the result of biliary excretion and reabsorption of mercury (Nielsen and Andersen
1992).
Bioavailability of methylmercury in food. Measurements of absorption and toxicity have generally been
made using aqueous solutions of methylmercury. The absorption and bioavailability of methylmercury in
food, specifically fish and bread, may be affected by dietary components. Potential confounders that may
affect bioavailability of methylmercury are dietary phytate and other dietary fibrous materials found in
bread and the complexation of methylmercury with selenium in fish.
Dietary fiber and phytate. Dietary fiber and phytate are known as potential inhibitors of the absorption of
divalent cations; however, the literature regarding the effect of dietary fiber and phytate on the
bioavailability of minerals is contradictory. Data by Yannai and Sachs (1993) indicate that phytate does not
affect methylmercury absorption. Yannai and Sachs (1993) compared the absorption by rats of mercury
found intrinsically in experimental fish meal with and without added phytate and found no significant
differences in the absorption of Hg (93±5%) between 2 experimental fish meal diets (containing 1.4 µmol
Hg/kg diet), with or without added sodium phytate. The authors speculated that phytate might be
preferentially bound to zinc, iron, and copper, which were present at much higher concentrations in the diet.
In another experiment by Yannai and Sachs (1993), the absorption of mercury was reduced when rats were
fed a mercury-contaminated corn diet and corn silage meal. Mercury was incorporated intrinsically into the
corn diet using radioactive isotopes ( 203 Hg) infused by capillary action into the stalks of developing corn
plants, which then incorporated trace amounts of isotopes into developing kernels. The corn silage meal
was from a crop grown in the vicinity of an industrial zone and contained elevated amounts of mercury.
Reduced absorptions of 48 and 51% were found for the corn silage and corn diet experiments, respectively.