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Mercury Advisory Committee Information

Electro Fishing

DEQ routinely monitors fish in Virginia's water bodies for contaminants. The fish contaminant data from 2002 showed elevated levels of mercury in some fish samples of largemouth bass, chain pickerel, bowfin, and redear sunfish collected from portions of the Blackwater River (Southampton and Isle of Wight Counties), Dragon Run Swamp/Piankatank River and the Great Dismal Swamp Canal.

Based on this information, in October 2003, the Virginia Department of Health issued three fish consumption advisories for the affected portions of these water bodies. Additional fish tissue sampling conducted in 2003 by DEQ found elevated levels of mercury in some fish from other water bodies. This prompted the Virginia Department of Health in September 2004 to issue six additional new fish consumption advisories affecting portions of the Mattaponi River and its tributary Herring Creek, the Pamunkey River and three small lakes. Most of these affected rivers have significant wetlands or swamps associated with them. These advisories and other previously issued fish consumption advisories can be found on the VDH website.

There are no known significant industrial sources of mercury in the three watersheds affected by the recent advisories, and potential sources of the mercury in these watersheds are unknown. This is the first time Virginia has had to deal with fish consumption advisories for mercury where the source of the mercury is not readily attributable to a point source. However, this situation is not unique to Virginia. In recent years, there has been a growing realization that some water bodies can have fish with elevated concentrations of mercury, even though there are no significant sources of direct mercury pollution to the water. This phenomenon has been seen in Scandinavia, Canada, New England, the Great Lakes States, Florida, North Carolina, Maryland and areas in the country.

One of the key factors that can influence the bioaccumulation of mercury into fish tissue is the presence of mercury in the form of methylmercury. Methylmercury is the chemical form of mercury that readily bioaccumulates in fish tissue. Mercury can be converted into methylmercury by certain species of bacteria that are naturally found in sediment or soil. Once converted into methylmercury, it is quickly assimilated into the bodies of aquatic insects and fish. Concentrations of mercury can increase or magnify as it passes up the food chain, with top predator fish such as bass, pickerel or bowfin often having the highest concentrations of mercury. Certain environmental conditions appear to favor the specific bacteria that produce methylmercury and can result in the increased bioaccumulation of mercury in fish. These environmental conditions include low pH (acidic conditions), high levels of organic matter and lower dissolved oxygen levels; conditions which are often associated with swamps and wetlands as well as ponds and lakes.

Elevated levels of mercury have been found in fish in these types of water bodies in many areas in the U.S. and Canada and many of these water bodies are not directly affected by significant discharges of pollutants into the water body. In many of these cases the suspected source is mercury originally released into the air as a result of burning, especially of coal. The airborne mercury can be transported many miles and is eventually deposited onto the land and into the water and ends up in soil or sediments where it is converted into methylmercury which then enters the food chain. It is thought that water bodies with low pH, low oxygen levels and high organic matter are more “sensitive” to small amounts of mercury. That is, mercury can be more quickly converted into methylmercury in these types of environments and these waters can be more likely to have fish with elevated levels of mercury.

As this understanding of the link between environmental conditions, methylmercury and accumulation of mercury into fish have become better known in recent years, DEQ has begun monitoring more ponds and rivers that are associated swamps, even if there are few or no significant discharges of pollutants into those water bodies. In the past, DEQ concentrated our fish monitoring in rivers where there were significant industrial or municipal discharges, assuming these were the most likely areas where fish might be most contaminated. Unfortunately, we have discovered some of these relatively unpolluted rivers can have fish with elevated levels of mercury. The discovery of mercury contaminated fish in waters without readily identifiable significant sources of pollution will require DEQ to look at the issues involved with mercury in new ways.

More information on mercury contamination issues can be found at the U.S. Environmental Protection Agency website at and a fact sheet on mercury contamination in the aquatic environment can be found on the U.S. Geological Survey website at

DEQ has formed a Mercury Advisory Committee to help advise DEQ on how to address waters where mercury contamination is found. The committee is composed of DEQ staff and representatives of the Virginia Department of Health, Virginia Department of Game and Inland Fisheries, North Carolina Department of Environmental and Natural Resources, U.S. Environmental Protection Agency, U.S. Geological Survey, U.S. Fish and Wildlife Service, James Madison University, Mary Washington University, University of Virginia, Virginia Commonwealth University, Virginia Institute of Marine Science, Blackwater/Nottoway Riverkeepers, Friends of Dragon Run, DuPont Co. and Dominion Virginia Power.

DEQ has asked the Mercury Advisory Committee for advice on three issues:

  1. Investigation of potential land-based sources of mercury within the affected watersheds.

  2. Investigation of the potential for airborne mercury to be a source of mercury in these watersheds.

  3. Assist in developing a plan to address the related source assessment and cleanup issues.

The first meeting of the Mercury Advisory Committee took place on April 16, 2004. Presentations were made by DEQ, the Virginia Department of Health and the North Carolina Department of Environmental and Natural Resources.
During the summer of 2004, DEQ collected additional fish tissue and sediment samples at nine sites in the Blackwater River, seven sites in the Dragon Run Swamp/Piankatank River and eight sites in the Great Dismal Swamp. DEQ's 2004 monitoring targeted an expanded area within each of the three water bodies affected by the 2003 fish consumption advisories and we collected additional samples of fish, focusing on the affected species as well as other popular game fish species in the watersheds. The information collected from these samples was reviewed by the Virginia Department of Health in the summer of 2005 and used to modify the three fish consumption advisories to include additional species and better describe the geographic boundaries of the fish consumption advisories areas. Also, an investigation for the source of mercury has begun for the Dragon Run Swamp watershed.

A second meeting of the Mercury Advisory Committee was held on September 30, 2005. At this meeting, the results of the 2003 and 2004 sampling and the new fish consumption advisories were discussed with the Committee. Other DEQ mercury projects were also discussed with the Committee, including the source identification investigation in the Dragon Run Swamp/Piankatank River, potential mercury air emission sources and work in the Great Dismal Swamp with U.S. Fish and Wildlife Service. Information on the Mercury Advisory Committee meetings can be found at the bottom of this page.

During the summer of 2005, as part of DEQ’s Fish Tissue Monitoring Program, fish and sediment samples were collected at about 100 sites across Virginia, including several water bodies that could be influenced by environmental conditions that would make the water bodies more sensitive to the production of methylmercury. These water bodies include several lakes and ponds across Virginia and the Chickahominy River which is a river flowing primarily through the coastal plain north and east of Richmond. The Chickahominy River has not been as extensively sampled for fish in the past because there are few industrial discharges into this river and previous fish sampling had not indicated elevated levels of mercury or other pollutants in fish. The Chickahominy River is the last remaining large, swamp or wetland dominated river in the coastal plain that had not been extensively sampled for fish in the past few years. In 2005, DEQ collected fish from several sites along an 80 mile section of the Chickahominy River. The fish and sediment samples collected in 2005 will be analyzed over the winter and the results should be back from the analytical lab by early summer 2006.

Environmental mercury issues are very complex, involving air, land and water issues. DEQ is addressing the identification of sources of mercury and efforts to reduce mercury in the environment in several different ways in different programs. DEQ is developing a statewide mercury strategy to help coordinate all of DEQ’s efforts in addressing mercury contamination issues in Virginia.

Copies of the agendas and presentations for the Mercury Advisory Committee meetings can be found here:

For more information on the Mercury Advisory Committee or the fish tissue monitoring work, contact Gabriel Darkwah at (804) 698-4127 or at

Other Virginia DEQ Mercury-Related Pages

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Virginia Department of
Environmental Quality
P.O. Box 1105
Richmond, VA 23218
(804) 698-4000

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