Researchers of a new study found that most fish get contaminated with mercury in deep ocean and predict that the contamination levels of Pacific Ocean fish are likely to rise in the coming years.
Researchers from Michigan University found that more than 80 percent of methylmercury, the most toxic form of mercury, is produced deep within the ocean by bacteria that cling to sinking organic material. They also found that the mercury found in Pacific fish in Hawaii travelled through air for thousands of miles before settling into the oceans due to rainfall.
The researchers said that the level of mercury contamination in fish in North Pacific continued to rise because of industrialization of India and China. These countries rely heavily 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 Joel Blum, the lead author the study in a press release. "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. Cleaning up our own shorelines is not going to be enough. This is a global atmospheric problem."
The findings led researchers to predict a rise in mercury levels at intermediate depths (660 to 3,300 feet) in the North Pacific in coming decades. They predict that it could double by 2050. Moreover, researchers worry that oxygen depleted regions caused by climatic changes may further accelerate the process of this rise in mercury level.
A 2009 study conducted by researchers at the University of Hawaii found that the depth at which fish feed plays an important role in determining how much mercury it consumes.
"We found that predatory fish that feed at deeper depths in the open ocean, like opah and swordfish, have higher mercury concentrations than those that feed in waters near the surface, like mahi-mahi and yellowfin tuna," said Brian Popp, a professor of geology and geophysics at the University of Hawaii at Manoa and co-author of both the 2009 paper and the new Nature Geoscience paper. "We knew this was true, but we didn't know why."
Humans' basic exposure to mercury comes from consuming mercury contaminated fish. The consumption of methylmercury leads to damage in the central nervous system, the heart and the immune system. It also hampers the cognitive development of young children and can even affect brain development of fetuses.
The United States Environmental Protection Agency released a report informing people and expecting mothers about what they need to know about mercury content in fish.