Mercury In Pacific Fish On The Rise
August 26, 2013

Researchers Expect Mercury Levels In Pacific Fish To Increase

redOrbit Staff & Wire Reports - Your Universe Online

The amount of toxic mercury found in Pacific Ocean fish is expected to increase over the next several decades, claims new research appearing in the August 25 edition of the journal Nature Geoscience.

Using recently-developed isotopic measurement techniques, researchers from the University of Michigan and the University of Hawaii reported that they have discovered how methylmercury gets into open-ocean fish, thus infecting the human seafood supply with the potentially harmful substance.

Up to 80 percent of this highly toxic form of the element discovered in the tissues of deep-feeding North Pacific Ocean fish originates from deep within the ocean, most likely by bacteria clinging to sinking bits of organic matter. According to the study authors, the bacteria changes atmospheric mercury into organic monomethylmercury, which is capable of accumulating in animal tissues.

Furthermore, their research confirmed that the mercury found in Pacific fish near Hawaii probably travels through the air for thousands of miles before it enters the ocean as a result of precipitation, said Michigan environmental scientist Joel Blum.

Fisheries in the North Pacific are located downwind from countries such as China and India, two industrializing nations that are becoming increasingly reliant on coal-burning power plants - a primary source of mercury pollution. Blum said that their research “reinforces the links between mercury emitted from Asian countries and the fish that we catch off Hawaii and consume in this country.”

“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,” he added.

The researchers also discovered that mercury accumulation in seafood typically occurs in deeper waters due in part because of photochemical reactions that break down organic mercury in surface waters. The bulk of this accessible organic mercury is also being generated in the deeper parts of the ocean, they said.

“The results of our research allow us to determine which marine fish are likely to have lower mercury concentrations, and why mercury concentrations are higher in some fish compared to others,” explained Jeffrey Drazen, associate professor of oceanography at the University of Hawaii Manoa. “This research is exciting because it allows us to gather new insight about both the biogeochemistry of mercury and the ecology of animals living in Earth's largest habitat – the open ocean.”

Their findings could also have important implications when it comes to estimating how mercury levels in marine fish could respond to future changes in the deposition of the substance in the ocean – especially in light of proposed treaties governing the global release of industrial mercury emissions, the authors said.

“In the next few decades there will be changes in mercury concentrations in the Pacific Ocean, and those changes are likely to be different for surface waters than for deep waters,” said co-author Brian Popp, professor of geology and geophysics at UH Manoa. “Understanding the competing processes that produce and destroy monomethlylmercury at different depths in the ocean is critical to tracing its bioaccumulation in fishes and the potential consequences for human food supply.”