A new USGS report, Mercury in the Nation's Streams—Levels, Trends, and Implications, presents a comprehensive assessment of mercury contamination in streams across the United States. It highlights the importance of environmental processes, monitoring, and control strategies for understanding and reducing stream mercury levels. This report summarizes selected stream studies conducted by the U.S. Geological Survey (USGS) since the late 1990s, while also drawing on scientific literature and datasets from other sources.
Worldwide, mercury inputs to aquatic ecosystems are primarily from atmospheric sources such as coal combustion. Mercury can travel long distances in the atmosphere and be deposited in watersheds in areas with no obvious source of mercury pollution.
Methylmercury (inorganic mercury that is converted to organic mercury within the ecosystem) poses a significant threat to wildlife because of its high bioavailability, its substantial bioaccumulation in food webs, and its extreme toxicity.
Methylmercury concentrations in predator fish exceeded the U.S. Environmental Protection Agency criterion for human health in about one in four of the nearly 300 U.S. streams sampled. Some of the highest fish mercury levels were found in coastal plain streams in the southeastern United States. Coastal plain streams typically drain forested watersheds that contain abundant wetlands.
Wetlands can increase the amount of inorganic mercury that is converted to methylmercury, the form that accumulates to harmful levels in fish. Elevated mercury levels also were noted in fish in areas of the western United States affected by historical gold and mercury mining. Fish mercury levels were lowest in urban streams, despite an abundance of sources of inorganic mercury. This occurs because urban streams lack conditions, such as wetlands, that are conducive to the production and bioaccumulation of methylmercury.
Most mercury exposure in the U.S. population is from fish consumption. Fish consumption advisories exist in every State in the Nation. Methylmercury exposure from fish consumption has been associated with various adverse effects on human health, ranging from central nervous system toxicity (at extremely high levels of exposure) to diminished cardiovascular health and endocrine disruption (at lower exposure levels of exposure).
In contrast to other environmental contaminants, mercury emission reduction strategies need to consider global mercury sources in addition to domestic sources. In response to the widespread contamination of fish, mercury has been effectively removed from many products and product waste streams. Since 1990, mercury emissions in the United States have decreased by about 60 percent. However, to reduce mercury levels in fish to fully meet human health criteria, further reductions in mercury emissions are necessary. The development of a national monitoring approach will be critical to track the effectiveness of future management actions.
This research was funded by the USGS Ecosystems Mission Area’s Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology) and the USGS National Water Quality Assessment Program.
Below are other science projects and information associated with this featured science activity.
Ecologically-Driven Exposure Pathways Science Team
Ecologically-Driven Exposure Pathways Science Team
Body Symmetry in Forster's Terns Related to Mercury Exposure
Efficacy of Eggshell Analyses as a Nonlethal Method to Estimate Mercury Exposure in Bird Embryos
Synthesis of Mercury Distribution and Bioaccumulation Across Western North America
Mercury in Aquatic Ecosystems
North American and European Atmospheric Mercury Declines Explained by Local and Regional Emission Reductions
New Tool to Track Sources and Exposure Pathways of Mercury in the Environment — Application for Predatory Fish in the Great Lakes
Complex Response to Decline in Atmospheric Deposition of Mercury
Environmental Mercury Cycling and Global Change
Some Ecosystems will Respond to Reductions in Mercury Emissions
- Overview
A new USGS report, Mercury in the Nation's Streams—Levels, Trends, and Implications, presents a comprehensive assessment of mercury contamination in streams across the United States. It highlights the importance of environmental processes, monitoring, and control strategies for understanding and reducing stream mercury levels. This report summarizes selected stream studies conducted by the U.S. Geological Survey (USGS) since the late 1990s, while also drawing on scientific literature and datasets from other sources.
Sources/Usage: Public Domain.Burning coal for energy production contributes large amounts of mercury to the atmosphere. Photo Credit: Phillip J. Redman, USGS. Worldwide, mercury inputs to aquatic ecosystems are primarily from atmospheric sources such as coal combustion. Mercury can travel long distances in the atmosphere and be deposited in watersheds in areas with no obvious source of mercury pollution.
Methylmercury (inorganic mercury that is converted to organic mercury within the ecosystem) poses a significant threat to wildlife because of its high bioavailability, its substantial bioaccumulation in food webs, and its extreme toxicity.
Methylmercury concentrations in predator fish exceeded the U.S. Environmental Protection Agency criterion for human health in about one in four of the nearly 300 U.S. streams sampled. Some of the highest fish mercury levels were found in coastal plain streams in the southeastern United States. Coastal plain streams typically drain forested watersheds that contain abundant wetlands.
Wetlands can increase the amount of inorganic mercury that is converted to methylmercury, the form that accumulates to harmful levels in fish. Elevated mercury levels also were noted in fish in areas of the western United States affected by historical gold and mercury mining. Fish mercury levels were lowest in urban streams, despite an abundance of sources of inorganic mercury. This occurs because urban streams lack conditions, such as wetlands, that are conducive to the production and bioaccumulation of methylmercury.
Sources/Usage: Public Domain.Eating fish is a source of mercury exposure for many people in the United States. Photo Credit: Dennis A. Wentz, USGS. Most mercury exposure in the U.S. population is from fish consumption. Fish consumption advisories exist in every State in the Nation. Methylmercury exposure from fish consumption has been associated with various adverse effects on human health, ranging from central nervous system toxicity (at extremely high levels of exposure) to diminished cardiovascular health and endocrine disruption (at lower exposure levels of exposure).
In contrast to other environmental contaminants, mercury emission reduction strategies need to consider global mercury sources in addition to domestic sources. In response to the widespread contamination of fish, mercury has been effectively removed from many products and product waste streams. Since 1990, mercury emissions in the United States have decreased by about 60 percent. However, to reduce mercury levels in fish to fully meet human health criteria, further reductions in mercury emissions are necessary. The development of a national monitoring approach will be critical to track the effectiveness of future management actions.
This research was funded by the USGS Ecosystems Mission Area’s Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology) and the USGS National Water Quality Assessment Program.
- Science
Below are other science projects and information associated with this featured science activity.
Ecologically-Driven Exposure Pathways Science Team
The Ecologically-Driven Exposure Pathways Integrated Science Team identifies how ecological pathways and physiological processes within a single organism can alter exposure and toxicity of contaminants and pathogens and seek to understand outcomes at different scales from individuals to populations and ecosystems.Ecologically-Driven Exposure Pathways Science Team
The Ecologically-Driven Exposure Pathways Integrated Science Team identifies how ecological pathways and physiological processes within a single organism can alter exposure and toxicity of contaminants and pathogens and seek to understand outcomes at different scales from individuals to populations and ecosystems.Body Symmetry in Forster's Terns Related to Mercury Exposure
Body symmetry of Forster's terns (Sterna forsteri) in San Francisco Bay was related to blood and feather mercury concentrations. Body asymmetry can affect a bird's fitness by reducing flight efficiency, thus increasing energetic costs (especially during migration) and interrupting normal feeding and breeding behaviors.Efficacy of Eggshell Analyses as a Nonlethal Method to Estimate Mercury Exposure in Bird Embryos
U.S. Geological Survey (USGS) scientists evaluated a nonlethal method to estimate mercury in the embryos of 23 bird species using mercury content in eggshells. This method was effective for a wide range of ages and species.Synthesis of Mercury Distribution and Bioaccumulation Across Western North America
The unique combination of natural processes and human activities present in western North America can strongly affect the exposure of fish and birds to methylmercury, the most toxic form of mercury (Hg).Mercury in Aquatic Ecosystems
This investigation focuses on understanding mercury sources, pathways and key processes in the environment, with particular emphasis on mercury methylation and accumulation in aquatic ecosystems.North American and European Atmospheric Mercury Declines Explained by Local and Regional Emission Reductions
Recent findings from a consortium of university, State, and U.S. Geological Survey (USGS) scientists indicate that declining atmospheric concentrations of mercury (Hg) can be explained by the phaseout of mercury in many commercial products and by reduced emissions from utilities over the past two decades.New Tool to Track Sources and Exposure Pathways of Mercury in the Environment — Application for Predatory Fish in the Great Lakes
The US Geological Survey (USGS) and collaborators at the University of Wisconsin-Madison have developed a new tool for attributing (fingerprinting) mercury sources to the Great Lakes. This new fingerprinting tool helps resource managers understand which mitigation strategies will be most effective for reducing mercury loading and exposure to fish and wildlife.Complex Response to Decline in Atmospheric Deposition of Mercury
U.S. Geological Survey (USGS) scientists found that mercury concentrations in shallow waters and methylmercury (MeHg) concentrations in fish in four lakes in Voyageurs National Park, Minnesota, were not consistent with decreases in the wet atmospheric deposition of mercury recorded at nearby monitoring stations for over a decade. Methylmercury is a toxic form of mercury (Hg) that accumulates and...Environmental Mercury Cycling and Global Change
Rising global temperatures and changing human actions will significantly affect the environmental distribution of mercury worldwide, according to a recent article in Science by U.S. Geological Survey (USGS) and Harvard University scientists. Higher temperatures and weaker air circulation patterns from climate change will likely have significant impacts on the atmospheric lifetime and patterns of...Some Ecosystems will Respond to Reductions in Mercury Emissions
An international team of scientists investigating mercury cycling in an experimental watershed in Ontario, Canada, conclusively demonstrated at the ecosystem scale that changes in mercury loadings are expected to result in proportional or near proportional changes in mercury bioaccumulation in fish. Policies to reduce atmospheric emissions of mercury are intended to reduce mercury bioaccumulation... - Publications