Dose
Humans are primarily exposed to methyl mercury through consumption
of fish containing high levels of mercury. Commercial fish species
such as canned tuna, salmon, and cod contain a mean mercury level
of approximately 0.1 micro g/g.
According to the U.S Environmental Protection Agency (EPA), a reference
dose (RfD) of methyl mercury is 3E-04 mg/kg/day. This dose is based
on the intake that would be required to produce a blood mercury
level of 200 µg/mL, which is a level associated with minimal
health effects. The EPA estimates that inhalation of this concentration
or less, over a lifetime, is not likely to cause chronic noncancer
effects.
Absorption
Methyl mercury is readily absorbed by ingestion, inhalation, and
through the skin. It is lipid soluble, and 90% to 100% is absorbed
from the gastrointestinal tract. Up to 80% of volatile methyl mercury
compounds such as methyl mercury chloride vapor may be absorbed
upon inhalation. Methyl mercury appears in the lipid fraction of
the blood and brain tissue.
Methyl mercury readily crosses the blood-brain barrier and the
placenta, allowing fetuses to be affected. The blood mercury levels
of a fetus are equal to or higher than maternal those of the mother.
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