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Q&A: A Fishy Formula for Measuring Mercury

Fish are loaded with protein, fatty acids, vitamins and minerals that are important for brain development and overall health. Unfortunately, some fish are also high in methylmercury, a toxicant that impairs brain development in young children, infants and developing fetuses. The US Food and Drug Administration and Environmental Protection Agency issue fish consumption advisories to prevent mercury poisoning, but Matthew D. Rand, Ph.D., associate professor of Environmental Medicine at the University of Rochester Medical Center, believes those advisories could be more accurate.

Rand sat down with me to talk about mercury toxicity and how his new method of measuring methylmercury could improve fish consumption guidelines.

Q: What is the current EPA Fish Consumption Advisory?

A: The EPA fish consumption advisory acknowledges the health benefits of nutrients in fish, but their recommendations for amounts of fish to eat are formulated solely on the concerns for methylmercury exposure. The EPA advisory recommends that women and children should eat two to three servings (8-12 ounces for those over 10 years of age, smaller amounts for younger children) each week of a variety of fish and shellfish that are low in methylmercury. A guide from the EPA and US Food and Drug Administration shows which fish are fine to eat and which to avoid.

Q: How does the EPA create these advisories?

A: The advisories are based on a "reference dose for chronic oral exposure", which refers to the amount of methylmercury that can be safely consumed. The EPA estimates the amounts of fish that can be eaten per week, by combining this reference number with knowledge of how much mercury is present in certain fish species.

There is great concern, however, about how the reference dose is derived. People vary broadly in how they metabolize methylmercury, meaning some people clear the toxicant faster than others. Since this variation is not well studied, the EPA errs on the safe side, building a safety factor of 10 into the reference dose. This could mean the fish advisories are stricter than necessary.

Q: You just published a study showing a new way to measure mercury in people. How could this improve the EPA guidelines?

A: Our study showcases our new method to determine how fast an individual metabolizes and eliminates methylmercury from their body after eating just three fish meals. We directly measured methylmercury elimination using a single hair from each study participant. This gave us personalized methylmercury elimination rate results, which could help create a more scientifically sound reference dose formulation and more tailored fish consumption recommendations.

Q: How are you carrying this research forward?

A: There is currently almost no data for methylmercury metabolism rates for the most vulnerable populations: pregnant women and young children. Our method will enable us to make these measurements using the current EPA fish consumption guidelines and could help refine the EPA advisory using a reference dose specific to pregnant women and children.

We will also explore the role of the gut microbiome in methylmercury metabolism in people. We expect that changes in the gut microbiome, for example using probiotics, could speed up methylmercury elimination rates. We hope to begin this study in the coming year.

Matthew D. Rand, Ph.D., has studied the methylmercury and its effects on the developing nervous system for over a decade. Some of his current projects involve understanding the molecular, cellular and genetic mechanisms of neural development responsible for variation in tolerance or susceptibility to methylmercury toxicity.

Susanne Pritchard Pallo | 12/6/2017