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

Status of Data for Methylmercury (MeHg)

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

Category (section)	Status	Last Revised
Oral RfD Assessment	On-line	07/27/2001
Inhalation RfC Assessment	No data	07/27/2001
Carcinogenicity Assessment	On-line	05/01/1995

Synonyms

22967-92-6 MEHG Methylmercury Methylmercury ii Mercury(1+), methyl-

Mercury (1+), methyl-, ion Methyl mercury Methylmercury (ii) cation Methylmercury ion Methylmercury (MeHg)

Chronic Health Hazard Assessments for Noncarcinogenic Effects

Reference Dose for Chronic Oral Exposure (RfD)

Critical Effect	Point of Departure*	UF	MF	RfD
Developmental neuropsychological impairment	BMDL5 : 0.000857 mg/kg-day	10	1	1 x10-4 mg/kg-day (Low end of BMDL05 range) 1
	BMDL5 : 0.001472 mg/kg-day	10	1	1 x10-4 mg/kg-day (High end of BMDL05 range) 1

* 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.

¹ This is one endpoint in a range of RfDs. See Principal and Supporting Studies (Oral RfD).

• Principal and Supporting Studies (Oral RfD)
  • Human epidemiological studies, Grandjean et al., 1997; Budtz-Jorgensen et al., 1999a
• Confidence in the Oral RfD
  • Study -- High
  • Database -- High
  • RfD -- High

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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.

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Quantitative Estimate of Carcinogenic Risk from Oral Exposure

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

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Quantitative Estimate of Carcinogenic Risk from Inhalation Exposure

• Not Assessed under the IRIS Program.