EPA IRIS — Methylmercury Oral Reference Dose
The EPA Integrated Risk Information System chemical assessment for methylmercury (CASRN 22967-92-6) provides the operative US federal oral reference dose for methylmercury exposure, anchored on developmental neurotoxicity observed in the Faroe Islands and Seychelles cohort studies (EPA IRIS MeHg). The RfD was last revised July 27, 2001 and remains in force; methylmercury is currently in step 1 of EPA’s IRIS reassessment process (EPA IRIS MeHg).
| Parameter | Value |
|---|---|
| Oral RfD | 0.1 µg MeHg/kg b.w./day (1 × 10⁻⁴ mg/kg/day) |
| CASRN | 22967-92-6 |
| Critical endpoint | Developmental neurotoxicity in offspring of mothers consuming methylmercury-contaminated seafood |
| Cohort basis | Faroe Islands (primary); Seychelles considered |
| Last revised | 2001-07-27 |
| Reassessment status | In step 1 (draft scoping) at IRIS |
The EPA RfD of 0.1 µg/kg/day (EPA IRIS MeHg) is approximately equivalent to the JECFA PTWI of 1.6 µg/kg/week (daily-equivalent ~0.23 µg/kg/day) (JECFA 61st) and the EFSA TWI of 1.3 µg/kg/week (daily-equivalent ~0.19 µg/kg/day) (EFSA Hg 2012) — all three are anchored on the same developmental neurotoxicity endpoint and the same cohort literature, and arrive at similar daily-equivalent values despite different averaging windows.
Sources
- EPA IRIS MeHg — EPA IRIS Chemical Assessment Summary, Methylmercury.