Mercury Levels to Rise in Fish Populations Due to Toxin's Saturation in Oceans

New research is pointing to increasing levels of the toxin Mercury found in the world's fish populations, with the problem expected only to get worse in the coming decades.

Researchers at the University of Michigan and University of Hawaii used isotopic measurement techniques and found that nearly 80 percent of the toxin, called methylmercury, found in deep-feeding North Pacific fish stems from the fish consuming bacteria found deep underwater that consumes organic material in the oceans depths.

The study also showed that mercury is being carried by the wind from emerging industrialized nations such as China and India that are increasingly reliant on coal-burning power plants. As the coal emissions are released they get picked up in global weather patterns and then deposited in the ocean's surface in the form of rain, environmental scientist Joel Blum, explained.

"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 the research which will appear in Nature Geoscience.

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.

"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."

It has been known for some time that large predatory marine fish contain high levels of methylmercury, through a process called bioaccumulation, when predatory fish eat smaller mercury-containing fish and the toxin builds up in the tissue.