Why deep sea fish contain more toxic mercury than shallow water fish

Date: August 26, 2013

Source: The Christian Science Monitor

Author: Elizabeth Barber

Ocean fish plucked from great depths are packed with more mercury than are their counterparts fished from shallower waters, according to new research from the University of Michigan and the University of Hawaii at Manoa.

A new paper, published in Nature Geoscience, pinpoints the difference in mercury levels in shallow and deep-water fish as in the amount of sunlight to which the animals are exposed and proposes that most of the mercury that humans consume is produced in the deep ocean. The researchers propose that the findings will be critical in assessing which fish are safe to eat as the mercury content of the Pacific Ocean changes over the next few decades.

“How atmospheric mercury deposited in the surface ocean will impact fish mercury levels (and how it will change over time) requires understanding the mechanisms controlling the depths at which elemental mercury is transformed to organic mercury,” says Brian Popp, professor of geology and geophysics at UH Manoa and a co-author on the paper.

The process through which mercury ends up in fish bedding on supermarket ice shavings begins with oceanic bacteria in the deep, dark ocean. These microbes convert mercury from the atmosphere into monomethylmercury, a form of the compound especially toxic to humans that can accumulate in animal tissue. Little fish snack on those bacteria, taking in that organic compound. Big fish then feast on those little fish, building up mercury in their own bodies – and build up, and build up, since these large fish live long lives packed with mercury-laden meals. Some studies have indicated that high levels of mercury in pregnant or breastfeeding women have been linked to cognitive problems in their children.

For more, go to: www.csmonitor.com/Environment/2013/0826/Why-deep-sea-fish-contain-more-toxic-mercury-than-shallow-water-fish

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