A report by the United States Geological Survey has taken an in-depth look at the level of mercury contamination in America’s streams. The national assessment, Mercury in the Nation’s Streams—Levels, Trends, and Implications, has found unhealthy mercury levels in 25 percent of streams with the highest concentrations in the southeast and the west. The contamination in these regions is attributed in part to the degradation caused by historic mining activities.
The report called mercury, “a potent neurotoxin that accumulates in fish to levels of concern for human health and the health of fish-eating wildlife. Mercury contamination is the primary reason for issuing fish consumption advisories,” which are currently in place in all 50 states of the nation. The USGS also indicates “Much of the mercury originates from combustion from coal and can travel long distances in the atmosphere before being deposited.”
The report identified three key factors that determine the level of mercury contamination in fish:
- Amount of inorganic mercury available to an ecosystem,
- Conversion of inorganic mercury to methylmercury, and
- Bioaccumulation of methylmercury through the food web.
While mercury originates from a number of natural sources, “humans have more than doubled the amount of inorganic mercury in the global atmosphere since pre-industrial times, with substantially greater increases occurring at locations closer to major urban areas.”
The report provides four key findings about mercury in America’s streams:
- Methylmercury concentrations in fish exceeded the U.S. Environmental Protection Agency criterion for the protection of human health at about one in four streams across the United States.
- Wetlands increase the amount of inorganic mercury that is converted to methylmercury, the form that accumulates to harmful levels in fish.
- In contrast to other environmental contaminants, mercury emission reduction strategies need to consider global mercury sources in addition to domestic sources.
- Existing mercury monitoring programs focus mostly on methylmercury concentrations in fish, and lack design elements and data to link these levels to mercury sources.
The good news is that “many of the most acute sources of direct mercury discharges” have been controlled since the late 1960s. That leaves atmospheric emissions as the primary source of contamination of the U.S. lakes and streams. From 1990 to 2005, mercury emissions decreased by 60 percent in large part because mercury was removed from products and waste streams. Unfortunately, in order for mercury levels in fish to reach desired levels, mercury must be decreased by 93 percent.
To read the full USGS report, visit http://pubs.usgs.gov/circ/1395/.
Teledyne Leeman Labs Mercury analyzers are used to test soil and water for mercury contamination. For more information on these analyzers, visit http://www.teledyneleemanlabs.com/products/mercury/index.asp