Mercury-Tainted Fish Found in U.S. Streams

The next time you go to your favorite restaurant and decide to order the new fish entrée, you might want to think twice. Researchers have detected mercury contamination in every one of hundreds of fish they have sampled from 291 freshwater streams in the United States.

The U.S. Geological Survey report stated that more than a quarter of the fish that were tested contained concentrations of mercury that exceeded the levels that are set by the Environmental Protection Agency for the protection of the people who eat average amounts of fish. More than two-thirds of the fish exceeded the EPA-set level of concern for mammals that consume fish.

The Interior Secretary, Ken Salazar, said, “This study shows just how widespread mercury pollution has become in our air, watersheds, and many of our fish in freshwater streams.” The USGS is a part of the Interior Department.

The neurotoxin enters our environment mainly as an air pollutant that is spewed into the atmosphere by industrial emissions, and then falls back down to the surface in precipitation and particulate matter that is carried over long distances. The main source of mercury in the atmosphere, according to the EPA, is power plants that are powered by coal.

The USGS study was conducted from 1998 through 2005 and is the first comprehensive survey of mercury contamination in the sediments, water, and the fish of creeks and rivers that run throughout the United States. Most of the previous studies conducted have focused mainly on reservoirs, wetlands and lakes. Mercury contaminations in species in the ocean, such as tuna, have also received widespread attention.

In the most recent study, some of the highest levels of mercury were found in the costal “blackwater” streams which are in South and North Carolina, Florida, Louisiana and Georgia, which are relatively undeveloped areas that are marked by abundant wooded wetlands and pine forests.

Barbara Scudder, who is a USGS hydrologist, stated that those characteristics somehow enhance the conversion of mercury from its inorganic form in our atmosphere to a much more toxic organic form called methyl mercury, which accounts for approximately 95 percent of the mercury that is found in fish. She stated, “Just as there are members of the human population, such as children and developing babies, that are sensitive to the mercury that they get, there are some ecosystems that are also more susceptible to producing methylmercury.” Scudder also stated that high concentrations of mercury were also found in some streams that were in the West fed by areas where mining had taken place.

As with many pollutants on our planet, mercury concentrates as it moves up our food chain, from algae, to insects to small fish and then larger predators. The main source of mercury poisoning that occurs in humans comes from eating shellfish and fish.

Scudder stated that the researchers typically sampled about five fish for each of the 291 streams that were surveyed. They focused on the bigger species in the streams such as largemouth bass because they are at the top of the in-stream food chain.

She suggested that the people who are concerned about the mercury contamination in fish caught in streams should eat more of the smaller pan species, such as crappie, perch, or bluegill. The EPA stated that this year it intends to issue new rules under the Clean Air Act to help control air emissions of mercury for plants powered by coal.