This resource has been factchecked by policy experts, using the latest scientific research. Find all our sources linked below.
Ever wonder why pregnant people are advised to minimize eating tuna?
Large fish are contaminated with mercury, a potent neurotoxin. An estimated 75,000 newborns in the United States yearly may have increased risk of learning disabilities associated with in-utero exposure to mercury. But how did mercury get into fish in the first place?
The answer is coal-fired power plants, the largest source of toxic mercury pollution in the United States. When a coal smokestack is not adequately filtered, mercury and other poisons—arsenic, lead, nickel, chromium, and acid gases, like sulfur dioxide (SO2) and nitrogen oxides (NOx)—are released into the air. That mercury drifts across the globe and rains into our waterways, affecting communities located near coal plants the most.
Microorganisms and bacteria in lakes and rivers convert this mercury from power plants into a highly toxic form called methylmercury. It’s absorbed by fish through their gills and dispersed through their bodies. Methylmercury accumulates in fatty tissue.
When humans eat contaminated fish, they ingest mercury. Mercury-polluted fish is eaten by other fish, birds, and mammals too. Typically, the longer a fish lives, and the larger it is, the more mercury accumulates in its flesh. Bluefish, grouper, king mackerel, marlin, shark, swordfish, and tuna all contain high levels of mercury.
Once we eat contaminated fish, methylmercury accumulates in the organs that have the most fats, like the brain. This is a unique concern for pregnant people and developing babies. It’s also an environmental justice concern as historically marginalized communities of color bear the heaviest burden of air pollution.
Breasts: mercury is found in breast milk.
Brains: methylmercury is able to cross the blood-brain barrier.
Placenta: methylmercury crosses the placenta. Fetuses and young children are especially vulnerable to mercury, which can impact nervous system and brain development and impair growth as well as learning after birth.
What can we do?
Mercury poisoning from coal plants can be prevented by installing scrubbers to reduce emissions. The Mercury and Air Toxics Standards (MATS), first implemented by EPA in 2012 and updated in 2024 with new protections against mercury and other air toxics, have been largely successful. Still, there’s more work to do.
Join Moms Clean Air Force to urge EPA to consistently update MATS with the strongest new standards possible. Babies should not be exposed to pollution before they take their first breath.
Learn more about Moms’ work on mercury pollution.
Full list of sources.
Updated: April 2024