Mercury levels in fish have always been a question, but researchers have solved the mystery and suggest that levels of the toxin will likely rise. The research about the mercury was conducted by the University of Michigan.
Using isotopic measurement techniques developed at U-M, the researchers determined that up to 80 percent of the toxin, called methylmercury, found in the tissues of deep-feeding North Pacific Ocean fish is produced deep in the ocean, most likely by bacteria clinging to sinking bits of organic matter.
The study also confirmed that the mercury found in Pacific fish near Hawaii likely traveled through the air for thousands of miles before being deposited on the ocean surface in rainfall, said U-M environmental scientist Joel Blum. The North Pacific fisheries are downwind from rapidly industrializing nations such as China and India that are increasingly reliant on coal-burning power plants, a major source of mercury pollution.
“This study reinforces the links between mercury emitted from Asian countries and the fish that we catch off Hawaii and consume in this country,” said Blum, the lead author of a paper scheduled for online publication Aug. 25 in Nature Geoscience.
“The implications are that if we’re going to effectively reduce the mercury concentrations in open-ocean fish, we’re going to have to reduce global emissions of mercury, including emissions from places like China and India,” Blum said. “Cleaning up our own shorelines is not going to be enough. This is a global atmospheric problem.”
The main pathway for human exposure to methylmercury is the consumption of large predatory marine fish such as swordfish and tuna. Effects of methylmercury on humans can include damage to the central nervous system, the heart and the immune system. The developing brains of fetuses and young children are especially vulnerable.
In December 2011, the Environmental Protection Agency released new standards sharply limiting future emissions of mercury and other toxic pollutants from coal- and oil-burning power plants in the United States. Earlier this year, the United Nations Environment Programme negotiated the Minamata Convention on Mercury, an international treaty aimed at curbing future mercury emissions; it is still unclear what level of mercury-emission reductions will result.
It has been known for some time that large predatory marine fish contain high levels of methylmercury in part because they eat lots of smaller, mercury-containing fish. The toxin builds up in the tissues of the top-of-the-food-chain predators through a process called bioaccumulation.
Lantern fish are small, deep-dwelling fish named for the fact that they glow through a process called bioluminescence. Lantern fish were one of nine fish species analyzed in a new study of mercury levels in open-ocean fish. Credit: C. Anela Choy.