IRIS

Methylmercury (MeHg)

System	RfD (mg/kg-day)	Basis	PoD	Composite UF	Confidence
Nervous, Developmental	1 x 10^-4 (High end of BMDL05 range)	Developmental neuropsychological impairment	BMDL₅ : 1.5 x 10^-3 mg/kg-day	10	High
Nervous, Developmental	1 x 10^-4 (Low end of BMDL05 range)	Developmental neuropsychological impairment	BMDL₅ : 8.6 x 10^-4 mg/kg-day	10	High

Weight of Evidence for Cancer (PDF) (44 pp, 258 K) Last Updated: 05/01/1995

WOE Characterization	Framework for WOE Characterization
C (Possible human carcinogen)	Guidelines for Carcinogen Risk Assessment (U.S. EPA, 1986)

Basis:

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.

Not assessed under the IRIS Program.

Not assessed under the IRIS Program.

Additional EPA toxicity information may be available by visiting the following sites:

Human Health Benchmarks for Pesticides (HHBP). This database provides human health benchmarks for pesticides that may be present in drinking water.
Office of Pesticide Programs Pesticide Chemical Search. This database provides links to health effects information and registration status for pesticides.
Chemistry Dashboard. This database provides information on chemical structures, experimental and predicted physicochemical, and toxicity data.

Methylmercury (MeHg) is being reassessed.

Assessment Manager(s): Deborah Segal (segal.deborah@epa.gov)

Step	Assessment Materials Released to the Public	Release Date	Public Meeting Date
1	Problem Formulation Materials	04/2019	05/2019
1	Preliminary Assessment Materials	05/2020	N/A
4	Public Comment Draft	TBD	TBD
4	Peer Review Draft	TBD	TBD
7	Post Final Assessment	TBD