Current Issues in the Minnesota Water Science Center

Mercury in Stream Ecosystems

The U.S. Geological Survey recently released a study that assesses mercury contamination in fish, bed sediment, and water from 291 streams across the nation, sampled from 1998 to 2005.

Scientists detected mercury contamination in every fish sampled in every stream. About a quarter of these fish were found to contain mercury at levels exceeding the criterion for the protection of people who consume average amounts of fish, established by the U.S. Environmental Protection Agency (EPA). More than two-thirds of the fish exceeded the EPA level of concern for fish-eating mammals.

Atmospheric mercury is the main source to most of these streams coal-fired power plants are the largest source of mercury emissions in the United States — but 59 of the streams also were potentially affected by gold and mercury mining. Since USGS studies targeted specific sites and fish species, the findings may not be representative of mercury levels in all types of freshwater environments across the United States. The report, along with a press release, podcast, and summary of major findings can be accessed at http://water.usgs.gov/nawqa/mercury/.