Clinic Submits Comments on EPA’s Proposed IRIS Assessment Plan for Methylmercury

May 6, 2019 – The Clinic submitted comments today on behalf of a group of leading scientists on the Environmental Protection Agency’s (EPA) proposed Integrated Risk Information System (IRIS) Assessment Plan for methylmercury.

The Clinic submitted the comments on behalf of Philippe Grandjean, Elsie M. Sunderland, David C. Bellinger, Joel D. Blum, Esben Budtz-Jørgensen, Laurie H.M. Chan, Celia Y. Chen, Charles T. Driscoll. Jr., David C. Evers, Kathy Fallon Lambert, Irva Hertz-Picciotto, Margaret Karagas, Sally Ann Lederman, Gina Muckle, Frederica Perera, and Ellen K. Silbergeld.  Students Nanding Chen and Veronica Wang wrote the comments in collaboration with Emmett Clinic Deputy Director Shaun Goho as well as Professors Grandjean and Sunderland.

The IRIS Program allows staff in EPA’s Office of Research and Development to assess the toxicity of chemicals independently of any specific regulatory program.  The results of IRIS Assessments then serve as a key source of toxicity information for EPA as well as state and local health agencies and other federal agencies.  At the conclusion of an assessment, EPA may establish a Reference Dose (RfD)—an estimate of the “daily oral exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime.”

Methylmercury is a highly toxic and bioaccumulative contaminant.  People are exposed to methylmercury primarily through consuming seafood and freshwater fish.  EPA last completed an IRIS Assessment for methylmercury in 2001.

Our comments:

  • Commend EPA for deciding to reassess the methylmercury RfD. We agree with EPA that a reassessment of the developmental neurotoxicity reference dose is “justified by recent epidemiological studies that analyzed effects at lower methylmercury exposure levels than those in studies used to derive the existing RfD.”
  • Urge EPA to acknowledge the imprecisions in exposure measurements that have deflated the RfD level, and account for such biomarker imprecisions in the reassessment.
  • Recommend that EPA account for genetic differences in susceptibility to methylmercury toxicity both in setting the RfD and in deriving the dose response relationship for developmental neurotoxicity outcomes.
  • Support EPA’s proposal to study a variety of DNT outcomes, including cognitive function and behavioral, structural, and electrophysiological effects, when setting the RfD. Specifically, IQ is not the optimal neurobehavioral outcome measurement for DNT effects of methylmercury.
  • Argue that EPA should include cardiovascular impacts in the IRIS assessment.
  • Advise EPA to be mindful of the possible complexities created by the confounding effects when interpreting studies of methylmercury exposure from fish consumption.

The Clinic’s comments are available here.