An alarming new study has found that human activities mostly associated with burning fossil fuels has resulted in a massive increase in the levels of toxic mercury in the world’s oceans.

Published last week in the prestigious international journal Nature, the study, A global ocean inventory of anthropogenic mercury based on water column measurements, revealed that levels of the environmental poison in marine waters less than 100 metres deep have more than tripled since the Industrial Revolution.

Using water samples collected during research trips in the Pacific, Atlantic, Southern and Arctic oceans from 2006 until 2011, scientists analyzed mineral mercury levels attributed to fossil fuels, mining and sewage in both shallow and deep seawater.

While they found that mercury levels in ocean waters less than 100 metres deep had increased by a factor of 3.4 since the dawn of the Industrial Revolution, concentrations of mercury throughout the entire ocean had only jumped about 10 percent.

The scientists were affiliated with the Woods Hole Oceanographic Institution, Wright State University, Observatoire Midi-Pyréneés in France, and the Royal Netherlands Institute for Sea Research.

“With the increases we’ve seen in the recent past, the next 50 years could very well add the same amount we’ve seen in the past 150,” said Woods Hole marine chemist Carl Lamborg, who led the study.

“The trouble is, we don’t know what it all means for fish and marine mammals. It likely means some fish also contain at least three times more mercury than 150 years ago, but it could be more. The key is now we have some solid numbers on which to base continued work.”

Medical experts have long been warning people — especially pregnant women and small children — to limit or avoid eating some fish like albacore tuna and swordfish because toxic levels of mercury have been found to accumulate in certain species. Numerous studies have shown that mercury can cause reproductive and neurological problems.

According to an accompanying Nature article, the scientists said ocean circulation patterns have helped to blunt the effects of some of the rise in marine mercury.

“Circulation patterns that drive very cold, salty and dense water to sink into the deep ocean carry large amounts of mercury from shallower depths where life abounds,” the article said.

“That provides some protection to marine life, as mercury’s toxic effects magnify with every step up the food chain. For example, the mercury levels in a top predator such as tuna are 10 million times higher than those in the surrounding seawater.”

But Lamborg added that the deep water’s ability to sequester mercury may soon be exhausted.

“You’re starting to overwhelm the ability of deep water formation to hide some of that mercury from us, with the net result that more and more of our emissions will be found in progressively shallower water,” Lamborg was quoted as saying, an event that would increase the odds that mercury levels in key food species will rise, furthering humans’ exposure.

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