Toxicokinetics - trdoer40201

There is some evidence of genotoxicity of Hg based upon an epidemiological

study (ATSDR 1989) in which there was a statistical relationship between

chromosome breaks and concentrations of methyl mercury in the blood of

Swedish subjects on fish diets.

Toxicokinetics

The pharmacokinetics of Hg depend largely on its chemical form. At low

doses, most of the elemental Hg is oxidized to the divalent cation which does not

cross the blood-brain barrier. Oral absorption of elemental Hg has been

estimated to be between 0.01 and 0.1 percent (ATSDR 1989). Dermal absorption

of metallic Hg is estimated to be approximately 2 percent, while the absorption

efficiency via inhalation is probably closer to 80 percent. Oral absorption

efficiency of inorganic Hg is estimated to be approximately 7.5 percent based

upon animal and human feeding studies. The oral absorption efficiency of

methylmercury is reported to be as high as 95 percent.

Ecological effects

Mercury is recognized as one of the most toxic of the heavy metals.

Numerous physical factors can affect the acute and chronic toxicities and

bioaccumulation of the various forms of Hg. Data are available on the acute

toxicity of Hg to at least 28 genera of freshwater animals. Acute values for

water-borne invertebrate species range from 2.1 ug/L for Daphnia to 2,000 ug/L

for three insects. Acute values for fishes range from 30 ug/L for the guppy to

1,000 ug/L for some tropical marine organisms. Few data are available for

various organomercury compounds, although they appear to be at least five times

more acutely toxic than metallic mercury. Available chronic data indicate that

methylmercury is the most chronically toxic of the mercury compounds. This is

in part because of the ability of methylmercury to bioconcentrate.

References

Agency for Toxic Substances and Disease Registry. (1989). "Toxicological

profile for mercury," U.S. Public Health Service, Washington, DC.

D49

Appendix D Toxicological Profiles