The mystery of how mercury gets into fish has been solved, according to researchers from the University of Michigan and the University of Hawai’i.
But next time you take a bite out of a salmon filet or make a tuna fish sandwich, here’s something else to chew on: The researchers’ findings suggest that mercury levels in the Pacific Ocean are expected to rise in coming decades.
The new study, published online in Nature Geoscience, found that much of the methylmercury, in the Pacific Ocean—this is the most toxic form of mercury—is likely to have traveled thousands of miles from industrializing nations before being deposited in the ocean through rainfall. Developing nations, such as China and India, are heavily reliant on coal-burning power plants, which remain the largest source of mercury emissions.
Lead author of the paper and University of Michigan environmental specialist Joel Blum said, “The study reinforces the links between mercury emitted from Asian countries and the fish that we catch off Hawai’i and consume in this country.”
The implication is that until global emissions of mercury are reduced, the levels of mercury found in fish are not going to decrease. On the contrary, evidence shows that levels of mercury in fish are expected to rise as a result of increasing mercury emissions.
In 2011, the U.S. Environmental Protection Agency (EPA) set forth clean air safeguards to reduce pollution, including that caused by mercury. The EPA predicted that its regulations would reduce mercury emissions by 80 percent by 2016 compared to 1990 levels.
However, the new study suggests that this prediction might not come to fruition because it found that not only does methylmercury become deposited from mercury-emitting sources, but it also continues to be produced by bacteria at depths of about 2,000 feet below the ocean surface. This process, which currently accounts for about 80 percent of the methylmercury found in the tissues of deep-feeding North Pacific fish, is expected to cause mercury levels at intermediate-to-deep depths (660-3,300 feet) to increase in coming decades.
Researchers said that predictions of increased production of methylmercury, combined with the long-range transport of mercury from surrounding countries, will increase the threat to North Pacific fisheries, which supplies the majority of the world’s seafood. Researchers said it is possible that North Pacific mercury levels could double by 2050.
Jeff Drazen, a professor at the University of Hawai’i at Manoa’s Department of Oceanography, said mercury deposition from mercury emissions being mixed in the atmosphere can be expected to become a global problem, not just an issue for the Pacific Ocean.
“Given that mercury enters the marine food web in the deep sea, if we would like to monitor for increasing mercury in seafood, we should focus our attention on deep living and foraging species,” Drazen said.