A new study provides the first direct calculations of mercury in the global ocean based on data from 12 sampling cruises that took place over the past eight years.
Mercury is a naturally occurring element, but can also be a by-product of human activities such as burning coal and making cement; this element imposes significant health risks on humans, Woods Hole Oceanographic Institution reported. Estimates of "bioavailable" mercury could have an impact on an international treaty that would help protect humans and the environment from mercury emissions.
Surprisingly little is known about the bioavailability of mercury, but a new paper hopes to change that. The study, published in the journal Nature, offers a look at global mercury distribution.
"It would seem that, if we want to regulate the mercury emissions into the environment and in the food we eat, then we should first know how much is there and how much human activity is adding every year," WHOI marine chemist Carl Lamborg said. "At the moment, however, there is no way to look at a water sample and tell the difference between mercury that came from pollution and mercury that came from natural sources. Now we have a way to at least separate the bulk contributions of natural and human sources over time."
The research team started off by looking at oceanic levels of phosphate, which behaves similarly to mercury. Bycomparing the levels of mercury and phosphate in water deeper than 1,000 meters (which has not been exposed to the environment since the Industrial Revolution) researchers determined which mercury came from natural sources. The North Atlantic proved to be the most polluted from man-made sources while The Tropical and Northeast Pacific remain "relatively unaffected."
To obtain readings in shallower waters the team looked at carbon dioxide; mercury and carbon dioxide tend to come from the same source, so researchers were able to create and index of the two and calculate global distribution. The analysis results agreed with past models suggesting the ocean contains between 60,000 and 80,000 tons of pollution mercury. Shallow waters have tripled in mercury concentration since the industrial revolution.
"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," Lamborg said. "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."
