Monday, May 05, 2008

Mercury in Marshes

The Baltimore Sun shows the key role that wetlands play in cycling mercury from air pollution into water and then into fish.

Mercury isn't created by marshes. The element occurs naturally in rocks, dirt and coal, and it floats into the air when coal is burned in power plants and factories. This airborne form of the metal, called inorganic mercury, doesn't usually get into people, Mitchell said.

The metal becomes a health hazard when it's changed by microorganisms that multiply in the oxygen-deprived muck at the bottoms of rivers, lakes and wetlands. In this mud, bacteria transform inorganic mercury into methylmercury, which is at least 10 times more toxic and collects in the bodies of animals.

Tainted worms are gobbled by small fish, and these are eaten by big fish - such as tuna and shark - that are eventually eaten by humans. The methylmercury accumulates as it moves up the food chain, with the toxicity multiplying 10-fold at each step.
The Smithsonian researchers at the center of the article see the production of methylmercury as something that artificial wetland designs need to alleviate if possible. In particular, how the planners handle mercury will influence the outcome of a 12,000-acre wetland construction project at Blackwater NWR. The wetlands are planned to remove some of the carbon dioxide being emitted by those same power plants that are causing the problem.
Mitchell said natural wetlands - such as Kirkpatrick Marsh, owned by the Smithsonian research center - should be left alone so the wildlife is not disturbed.

But to the east, on the other side of the Bay Bridge, the federal and state governments are studying a vast wetlands-building proposal at the Blackwater refuge. Funding for this effort could come in part from power companies that face new state greenhouse gas limits and want to build wetlands as a way of "offsetting" their pollution.

The Maryland Department of Natural Resources will look carefully at the mercury-producing potential of the proposed Blackwater wetlands as they are designed, said John Sherwell, manager of DNR's power plant research program.
The article mentions a few methods of remediation, such as adding charcoal to wetland beds to reduce mercury and building new wetlands on gravel to increase the flow of oxygen and discourage bacteria. Ultimately, reducing mercury at the source would help more.