Toxicity Profiles

RAGs A Format for Methyl Mercury - CAS Number 2269926

Mercury may undergo biotic and abiotic methylation to form methyl mercury (organic mercury). Commercially produced methyl mercury has been used as a fungicide, seed disinfectant, alkylating agent in organic synthesis of other organometallic compounds, and as a preservative in paints.

Methyl mercury is highly toxic and is readily absorbed by the body following ingestion or inhalation. The target organ for methyl mercury toxicity is the central nervous system (CNS), especially the brain, and may occur at doses as low as 3 µg/kg in humans. Methyl mercury is neurotoxic to several species of experimental animal and to humans. Manifestation of toxic effects (neurobehavioral alterations and degenerative changes in the central and peripheral nervous system) is probably a function of accumulation of critical levels of mercury. Exposure to methyl mercury in the diet (fish and contaminated grain) has caused epidemic poisonings in Iraq and Japan, characterized by severe developmental effects (impaired motor and cognitive functions) in infants of exposed mothers. Data on the effects of inhalation exposure to methyl mercury are lacking for both humans and animals.

EPA has given methyl mercury Classification C, possible human carcinogen, on the basis of inadequate data in humans and limited evidence of carcinogenicity in animals. Mice exposed to methylmercuric chloride in the diet had an increased incidence of renal adenomas, adenocarcinomas and carcinomas. The renal epithelial cell hyperplasia and tumors were observed only in the presence of profound nephrotoxicity and were suggested to be a consequence of reparative changes in the cells. Several non-positive cancer bioassays were also reported. Although genotoxicity data suggest that methylmercury is capable of producing chromosomal and nuclear damage, there are also non-positive genotoxicity data.

The following is a presentation of the toxicity information associated with Methyl mercury

Noncarcinogenic Health Effects

• The Oral Chronic Reference Dose is 1.00E-04 (mg/kg-day).
• The Oral Chronic Reference Dose has a modifying factor of 1.
• The Oral Chronic Reference Dose has an uncertainty factor of 10.
• The Oral Chronic Reference Dose is based on the Seafood Safety study from 1991.
• The Oral Chronic Reference Dose study critical effects are developmental neurologic abnormalities in infants.
• The overall confidence in the Oral Chronic Reference Dose is medium.
• The Dermal Chronic Reference Dose is 9.00E-05 (mg/kg-day).
• The Dermal Chronic Reference Dose is based on a gastrointestinal absorption factor of 0.9000.