Positive news about the environment is as common as a well-fed polar bear.
Thanks to a decrease in coal use in North America and better technology to make the fossil fuel less harmful, the amount of mercury in the atmosphere is on the decline—and our air, our oceans, and even our food appear to be getting safer.
Mercury levels in Atlantic bluefin tuna plunged by 19 percent from 2004 to 2012, according to a study published in Environmental Science & Technology that examined more than 1,000 specimens. That correlates with a 20 percent decrease in mercury in North Atlantic air from 2001 to 2009, the study notes, meaning that human efforts to decrease the amount of mercury in the atmosphere appear to be paying off.
Coal is one of the top culprits for atmospheric mercury, which eventually finds its way into the ocean, where it is transformed into methylmercury, a toxic form of the element. It can accumulate in fish at the top of the food web, such as tuna and swordfish, leading many consumers to avoid them, especially children and pregnant women. 1
“We have not conclusively proven that these declines in the tuna are attributable to declines in emissions,” said Nicholas S. Fisher, who is a distinguished professor in the School of Marine & Atmospheric Sciences at Stony Brook University and an author of the study. But, he adds, it’s “a striking parallel.”
Elsie Sunderland, an associate professor of environmental science and engineering in the Department of Environmental Health at the Harvard T.H. Chan School of Public Health, said she wouldn’t discount the importance of reducing the amount of coal burned for electricity, the implications for an individual’s diet, and the other research that has been done to show the connection, including her own.
“There is a direct association between reducing the environmental burden of mercury and the declines in tuna,” she said. “The paper just didn’t necessarily show it.”
But the environmental benefits could be undone or diminished if the U.S. starts to burn more coal and the regulations limiting its mercury emissions get rolled back. One of President-elect Donald Trump’s clarion calls at campaign rallies in coal country was to bring the industry back.
“The reduction in mercury levels in the bluefin tuna over the last decade or so could be reversed if the mercury loadings increased,” Fisher said, noting that he can’t say for sure because that’s not what the study tested.
Then there’s the rest of the world. While in China, for example, improved technology has mitigated mercury emissions to an extent, coal combustion is poised to accelerate.
The study didn’t deal with causation, just correlation, so “it’s not a smoking gun,” Sunderland cautioned. “There are a lot of steps and many climate-driven factors that influence what you see in fish,” she said. “If you’re a fish, it really depends on where you’re swimming and what you’re eating.”
Americans don’t eat much bluefin tuna, and when they do, it’s both expensive and controversial. This particular type of tuna is notoriously overfished, putting the chefs who serve it in the crosshairs of environmentalists. Plus, the mercury levels are still very high, Fisher said.
“Americans, per capita, eat about the weight of a paperclip in bluefin tuna annually,” said Gavin Gibbons, a representative of the National Fisheries Institute, a seafood trade group. Although a similar decline was recorded in bluefish last summer, scientists are reluctant to translate a reduction in one species of tuna to another.
“That would be my guess,” Fisher said. “But we don’t have the data to support that.”
As for bringing back coal, any expectations that emission rules will immediately be lifted under the new administration should be tempered, said Cary Coglianese, a professor at the University of Pennsylvania Law School and the director of the Penn Program on Regulation. These rules, which affected both new and existing coal-burning facilities, went through the full rule-making process, rather than being implemented by presidential executive order, and have survived court challenges so far.
“It could be plausible that the administration would want to target this rule,” he said. “But it’s a rule that’s less vulnerable than others.”