Environmental success stories are seemingly in short supply, but the fall of mercury is one of them. Released by coal-burning power plants and other industries, mercury—a toxic metal—circulates in the atmosphere, enters the ocean, worms up the food web and, via the seafood we eat, ends up in our bodies. For decades mercury in seafood has been a health scourge, because it inflicts long-term harm on the brain and increases the risk of heart disease. It’s especially risky for developing fetuses, and mothers-to-be have long been warned away from mercury-rich tuna and swordfish.
But from 1995 to 2010, mercury concentrations in the Northern Hemisphere fell by 30 percent, thanks to aggressive regulations, falling coal use, and phaseouts of mercury in commercial goods. And in 2017, the first global treaty on reducing mercury emissions came into force.
You’d expect, then, that mercury levels in fish would have also fallen, and would continue to fall. But Amina Schartup and Elsie Sunderland of Harvard University have found that in some cases, tomorrow’s seafood will contain more mercury, not less.
That’s thanks to two unlikely culprits—overfishing and climate change, both of which could nudge fish toward pursuing more heavily contaminated prey. Although there’s less mercury in the environment, our actions mean that fish like tuna are more likely to concentrate what’s already in their bodies. The carbon we pump into the atmosphere ends up affecting the amount of neurotoxin on our dinner plate.