What should the public know?
The U.S. Food and Drug Administration measures mercury in seafood, but its advisories are informational rather than actionable, according to Reinfelder. In other words, the agency doesn’t prohibit food from going to market — that means it’s up to the public to research and understand the guidelines.
The Environmental Protection Agency and the World Health Organization have guidelines about mercury, as does each U.S. state. Advisories in New Jersey and Pennsylvania are lengthy, and detail how often residents can safely consume specific fish species from each waterway in the state — whether that’s once a week, once a month, or never.
“It’s a bit of a patchwork,” Reinfelder said.
The situation is more opaque when it comes to the world market, he argues, because fish caught in one area are transferred to another part of the world. More than 90 percent of the bluefin tuna that he and his colleagues sampled between 2017 and 2019 exceeded the FDA and WHO limit for mercury in a top predatory fish. Those were fish that went to market, he said.
“Individual fish don’t carry a mercury content marker,” he said. “If information about the age and location of capture was linked in some way to each fish in the market, regulatory agencies, commercial buyers, and the public could assess the level of mercury in individual fish and make better informed decisions about human consumption.”
Pregnant people and parents of young children should be careful about what’s on their dinner plate, the experts say, since mercury is a developmental neurotoxin that inhibits the central nervous system’s development.
Consuming above the recommended amount of fish per week, month, or year is not healthy for anyone, however.
Levels can vary — salmon is a low mercury choice, while bluefin tuna contains some of the highest levels of mercury. Canned tuna falls somewhere in the middle.
Changes must be made globally to reduce mercury pollution, Reinfelder and Li said. Fossil fuel combustion makes up a significant amount of global mercury emissions.
“The majority of the mercury in the environment right now is anthropogenic [human-caused]. So if climate change is the culprit to making that increase in the future, that means we should mitigate or reduce the CO2 emission and other greenhouse gasses to combat the CO2 level,” Li said. “If we can’t achieve that, and we want to maintain the safety of the seafood, then we have to have a more stringent mercury emissions policy.”
Scientists hope that the 2017 Minamata Convention, which aims to control the supply and trade of mercury and reduce mercury emission, will result in positive environmental trends by the next decade.