Mercury has been discovered in fish in some of the most remote national park lakes and streams in the western United States and Alaska. Mercury levels in some fish exceeded U.S. Environmental Protection Agency health thresholds for potential impacts to fish, birds, and humans.
This study of mercury in fish is the first of its kind to incorporate information from remote places at 21 national parks in 10 western states, including Alaska. Western parks were selected for this study because of the significant role that atmospheric mercury deposition plays in remote places, and the lack of broad-scale assessments on mercury in fish in remote areas of the west.
Mercury concentrations in fish sampled from these parks were generally low, but were elevated in some instances. The study examines total mercury in fish, of which 95 percent is in the form of methylmercury, the most dangerous form to human and wildlife health.
Mercury is harmful to human and wildlife health, and is among the most widespread contaminants in the world. It is distributed at a global scale from natural sources, such as volcanic eruptions (responsible for approximately half of atmospheric mercury emissions), emissions from the ocean, and forest fires, and from human sources such as burning fossil fuels in power plants, gold mining, and incineration of municipal and medical waste. Mercury is also distributed at local or regional scales as a result of current and historic mining activities. These human activities have increased levels of atmospheric mercury at least three fold during the past 150 years.
Between 2008 and 2012, NPS resource managers collected more than 1,400 fish from 86 lakes and rivers, and USGS scientists measured mercury concentrations in fish muscle tissue. The authors found that mercury levels varied greatly, both between parks and among sites within each park. In most parks, mercury concentrations in fish were moderate to low. In fact, mercury concentrations were below EPA’s fish tissue criterion for safe human consumption in 96 percent of the sport fish sampled.
However, the average concentration of mercury in sport fish from two sites in Wrangell-St. Elias and Lake Clark (Alaska) national parks exceeded EPA’s human health criterion. Additionally, mercury levels in individual sport fish at some sites from Lassen Volcanic (California), Mount Rainer (Washington), Rocky Mountain (Colorado), Yellowstone (Wyoming), and Yosemite (California) national parks also exceeded the human health criterion.
The National Park Service is currently coordinating with state officials regarding potential fish consumption advisories. Exposure to high levels of mercury in humans may cause damage to the brain, kidneys, and the developing fetus. Pregnant women and young children are particularly sensitive to the effects of mercury.
Mercury at elevated levels can also impact wildlife resulting in reduced foraging efficiency, survival, and reproductive success. Mercury concentrations exceeded the most conservative fish toxicity benchmark at 15 percent of all sites, and the most sensitive health benchmark for fish-eating birds at 52 percent of all sites.
For more information and to view the report, please click here.
Hiking in Glacier National Park