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

MERCURY 162
2. HEALTH EFFECTS
metallic mercury. The mercurous ion is unstable in the presence of sulfhydryl groups, and undergoes
disproportionation into one atom of metallic mercury and one ion of mercuric mercury. As with metallic
mercury, organic mercury can also be converted to inorganic divalent mercury; however, the extent of
conversion is less than with metallic mercury.
Following exposure to metallic mercury, the elimination of mercury can occur via the urine, feces, and
expired air. Following exposure to inorganic mercury (mercuric), mercury is eliminated in the urine and
feces. Organic mercury compounds are excreted predominantly via the feces in humans. In animals,
methylmercury is excreted in the feces, and phenylmercury compounds are initially excreted in the feces
and then in the urine. Organic mercury compounds are excreted predominantly in the inorganic form. Both
inorganic mercury and methylmercury are excreted in breast milk.
Absorption of metallic mercury vapor is believed to occur by rapid diffusion through the lungs. Oral
absorption of inorganic mercuric mercury compounds may also involve rapid diffusion through the gastro­
intestinal tract. The mechanism for oral absorption of mercurous mercury compounds is not known. Oral
absorption of organic mercury is believed to depend on the ability of the organic mercury molecule to bind
to molecules such as cysteine. The mechanism of action of inorganic and organic mercury compounds may
involve the affinity of these chemicals for sulfhydryl or thiol groups of proteins and other biological
compounds.
2.3.1 Absorption
Absorption following inhalation of metallic mercury vapors is relatively high. Absorption following acute
oral exposure to metallic mercury is negligible in both humans and animals. Methyl- and phenylmercury
compounds are absorbed much more readily than inorganic mercury. Animal studies suggest oral
absorption of both organic and inorganic mercury may be influenced by age and diet. Limited information
was located regarding dermal absorption of inorganic or organic mercury compounds in humans or animals.