Methylmercury (MeHg)

Overview

In May 2020, EPA released the Systematic Review Protocol for the Methylmercury IRIS Assessment (Preliminary Assessment Materials). As part of developing a draft IRIS assessment, EPA presents a methods document, referred to as the protocol, for conducting a chemical-specific systematic review of the available scientific literature. Protocols communicate the rationale for conducting the assessment of methylmercury, describe screening criteria to identify relevant literature, outline the approach for evaluating study quality, and describe the dose-response methods.

Background

Gaseous elemental mercury is released into the atmosphere from natural (e.g., volcanoes) and manmade (e.g., fossil-fuel combustion) sources. Elemental mercury can be converted to inorganic mercury, which then can be transported and deposited to land or water. Methylmercury is formed from methylation of inorganic mercury by biota in water and soil. Once converted, methylmercury bioaccumulates in fish tissue and increases in concentration at successively higher levels of the food chain.

The general population is predominantly exposed to methylmercury through consumption of contaminated fish and other seafood. Subsistence fishing communities and other populations with high dietary intakes of predatory fish species could be exposed to higher-than-average levels of methylmercury. Contaminated rice and rice-based food products, such as infant cereals, also can be a source of methylmercury exposure.

Methylmercury readily crosses the placenta and concentrates in cord blood. It is also transferred from mothers to children via breastmilk. The developing nervous system is particularly sensitive to methylmercury, so gestational, lactational, and other postnatal exposures are of concern.

History/Chronology

Date	Description
Dec 1997	EPA released the Mercury Study Report to Congress.
Oct 2000	EPA released a draft document titled, Reference Dose for Methylmercury (NCEA-S-0930)" for a 30-day public review and comment period. Following the review an external peer-review workshop was held to review the document.
Jan 2001	EPA released the IRIS Summary for Methylmercury on the IRIS website and released the water quality criteria guidelines for states and authorized tribes.
Jan 2009	EPA released the Methylmercury Implementation Guidance.
Apr 2010	EPA released an update, referred to as the Methylmercury Implementation Guidance (Updated Apr 2010).
Apr 2019	EPA released the IRIS Assessment Plan (IAP) for Methylmercury for public comment and review. [Federal Register Notice Apr 4, 2019]
May 2019	EPA hosted a public science meeting to discuss preliminary meeting materials for methylmercury.
May 2020	EPA released the Systematic Review Protocol for the Methylmercury IRIS Assessment (Preliminary Assessment Materials) for a 45-day public review and comment period. [Federal Register Notice May 28, 2020]

Status

The IRIS Program will use the methods for conducting the systematic review as described in the protocol to develop the draft assessment.

This download(s) is distributed solely for the purpose of pre-dissemination peer review under applicable information quality guidelines. It has not been formally disseminated by EPA. It does not represent and should not be construed to represent any Agency determination or policy.

• Systematic Review Protocol for the Methylmercury IRIS Assessment (Preliminary Assessment Materials) (PDF)  (83  pp, 1.2 MB, about PDF)

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Document Related Link(s)

• Mercury Study Report to Congress (Final, 1997)
• Reference Dose for Methylmercury (External Review Draft, 2000)
• IRIS Summary Update (2001) and EPA Guidelines for Methylmercury (2009 & 2010)
• IRIS Assessment Plan for Methylmercury (Scoping and Problem Formulation Materials)

HERO Project

• Literature Search References Sorted by Author (Methylmercury)

Federal Register Notices

• FR Notice: May 28, 2020

Docket

Comments on the assessment may be submitted and reviewed using the Docket ID EPA-HQ-ORD-2018-0655