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Methylmercury (MeHg) Quickview (CASRN 22967-92-6)

Health assessment information on a chemical substance is included in IRIS only after a comprehensive review of toxicity data by U.S. EPA health scientists from several Program Offices, Regional Offices, and the Office of Research and Development.

Disclaimer: This QuickView represents a snapshot of key information. We suggest that you read the IRIS Summary to put this information into complete context.

For definitions of terms in the IRIS Web site, refer to the IRIS Glossary.

Status of Data for Methylmercury (MeHg)

File First On-Line: 01/31/1987; Last Significant Revision: 07/27/2001

Category (section)
Last Revised
Oral RfD Assessment Yes 07/27/2001
Inhalation RfC Assessment No
Carcinogenicity Assessment Yes 05/01/1995
  • 22967-92-6
  • MEHG
  • Methylmercury
  • Methylmercury ii
  • Mercury(1+), methyl-
  • Mercury (1+), methyl-, ion
  • Methyl mercury
  • Methylmercury (ii) cation
  • Methylmercury ion
  • Methylmercury (MeHg)
Revision History
Date Section Description
04/01/1997 III., IV., V. Drinking Water Health Advisories, EPA Regulatory Actions, and Supplementary Data were removed from IRIS on or before April 1997. IRIS users were directed to the appropriate EPA Program Offices for this information.
Chronic Health Hazard Assessments for Noncarcinogenic Effects

Reference Dose for Chronic Oral Exposure (RfD)

Critical Effect
Point of Departure*
Developmental neuropsychological impairment BMDL5 : 1.472 x10-3 mg/kg-day 10 1 x10-4 mg/kg-day
(High end of BMDL05 range)

* The Point of Departure listed serves as a basis from which the Oral RfD was derived. See Discussion of Conversion Factors and Assumptions for more details.

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Reference Concentration for Chronic Inhalation Exposure (RfC)

Not Assessed under the IRIS Program.

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Carcinogenicity Assessment for Lifetime Exposure
  • Weight-of-Evidence Characterization
    • C (Possible human carcinogen)
  • Weight-of-Evidence Narrative:
    • Based on inadequate data in humans and limited evidence of carcinogenicity in animals. Male ICR and B6C3F1 mice exposed to methylmercuric chloride in the diet had an increased incidence of renal adenomas, adenocarcinomas and carcinomas. The tumors were observed at a single site and in a single species and single sex. 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 nonpositive cancer bioassays were also reported. Although genotoxicity test data suggest that methylmercury is capable of producing chromosomal and nuclear damage, there are also nonpositive genotoxicity data.
    • This may be a synopsis of the full weight-of-evidence narrative. See IRIS Summary.

Quantitative Estimate of Carcinogenic Risk from Oral Exposure

  • Information reviewed but value not estimated. See IRIS Summary.

Quantitative Estimate of Carcinogenic Risk from Inhalation Exposure

  • Not Assessed under the IRIS Program.

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