Mercury studied in swamp

Published 9:16 pm Thursday, July 19, 2012

Survey shows birds affected by heavy metal

Learned local fishermen have long known about mercury dangers in the waters of the Great Dismal Swamp.

Since 2003, the swamp canal from Deep Creek Lock south to the Virginia-North Carolina line, including Lake Drummond’s feeder ditch, has been under a state fish-consumption advisory.

Lake Drummond was included in 2005.


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No matter how good the fishing, there’s not much point in casting a line when the authorities warn against eating more than two eight-ounce meals per month of bowfin or chain pickerel.

And humans, it turns out, aren’t the only creatures partial to a meal of fish.

A researcher at the College of William & Mary, after initially studying the public health risk of contaminated swamp fish, found they are also hurting our feathered friends.

After the human study, “The point then came up … the fish-eating birds out there, what’s going to happen to those creatures?” said Mike Newman, of the college’s Virginia Institute of Marine Science.

Newman and another researcher subsequently became involved with the U.S. Fish and Wildlife Service in just such a study, focusing on three avian species.

The findings: Great blue heron were unlikely to be ingesting enough mercury to exceed dangerous levels, but 98 percent of belted kingfisher, and 32 percent of the bald eagle, exceeded ingestion levels — which biologists call toxicity reference values — that would trigger an negative response.

“We’re not talking about birds falling dead from the sky. It’s more of a chronic, long-term exposure in which you have less fledglings, or you might have a behavioral thing which make them less fit as an organism,” Newman said.

The way mercury builds up in birds, called biomagnification, works like compound interest, Newman explained.

Little fish feeding on organisms living in what is known as the mercury danger zone, where the water meets the bog, are eaten by bigger fish, which in turn are devoured by even bigger fish, which then become dinner for a bald eagle swooping down to Lake Drummond’s shimmering surface.

“The concentration gets higher and higher and higher,” Newman said. “Every time something eats something else, it will retain more and more and more mercury.”

Mercury has various sources, but most commonly comes from coal-fired power plants, some factories, and car exhausts, experts say.

Inorganic mercury moves from the atmosphere into the swamp, whose environment converts it to so-called methylmercury, a form that more readily enters the food chain.

Between 2004 and 2006, prompted by public health advisories in North Carolina, the fish and wildlife service studied mercury levels in both fillets and whole bodies of fish from four national wildlife refuges.

The environments were similar to the Great Dismal Swamp, which was not included, said service ecologist and wildlife toxicology expert Sara Ward.

Mercury concentrations that have been shown in mallards to reduce egg-laying and to cause young birds to be over-sensitive to fright stimulus, were detected in 67 percent of fillets tested, and in all of the whole bodies except for one species, gizzard shad.

While Ward says the impact of mercury on birds needs further study, Newman, meanwhile, is proposing a return to the swamp.

He wants to develop a tool for predicting mercury concentrations in aquatic species, which would be used for things like allocating money for mercury reduction efforts and assessing power plant proposals.

His study needs funding and fish and wildlife support to get off the ground.

“This is the first I’m hearing about it … but we would be happy to take a look and give it a review,” Ward said.

She said mercury in the swamp is “a problem, but one without a tangible and immediate fix.”