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.
The fingerprinting tool includes novel analyses of stable mercury isotopic signatures in lake sediments to infer relative contributions of mercury from key end-member sources. The tool works by identifying the different types of mercury atoms present in the Great Lakes. Each mercury atom has a certain mass, which can range from 196-204. The relative abundance of each of these masses is different in each of the mercury sources, and these differences provide the ability to "fingerprint" the mercury source contributions.
Surface sediment samples collected from 58 locations throughout the Great Lakes during 2012-2014 were analyzed for stable isotopes of mercury and used to determine sources. The tool was applied to the entire Great Lakes ecosystem to distinguish among mercury derived from atmospheric deposition, watershed runoff, and industrial point-source inputs. The results show novel insights into mercury sources across the Great Lakes, with Lakes Superior and Huron dominated by atmospheric inputs. Lakes Erie and Ontario dominated by industrial and watershed sources, and Lake Michigan showing about equal contributions from all three source categories.
Mercury is a persistent pollutant that is distributed globally. Previous USGS and other research has shown that human-induced sources of mercury (atmospheric deposition, watershed inputs, or direct inputs through point source discharges) are the dominant sources of mercury to the environment when compared to natural emission sources such as volcanoes and oceans. Understanding the sources contributing to mercury has been an active area of research at USGS for the past 25 years. This study advances this research by providing a new tool to more accurately define mercury sources.
Environmental Health Implications
With this new fingerprinting tool, resource managers can now better understand what mitigation strategies will be most effective for reducing mercury loading and exposure to fish and wildlife. The results from the source model were extended to recent results from mercury isotope work in measurements in predatory fish (Lake trout and Burbot) to ascertain the relative importance of the end-member sources to the food web. Comparison of the mercury signatures in predatory fish from the three lakes (Michigan, Superior, and Ontario) reveals that bioaccumulated mercury in these predator fish is more similar to atmospherically derived mercury than to mercury in a lake's sediment. The study findings suggest that atmospherically derived mercury many be a more important source of methylmercury to higher trophic levels (predator fish) than mercury stored in legacy sediments in the Great Lakes. In aquatic systems microbially mediated processes can transform mercury to methylmercury, a more toxic form that is biomagnified in aquatic food webs. Bioaccumulated methylmercury is a potential threat to aquatic ecosystems and humans health through fish consumption. Providing a better understanding of sources is a key component of managing environmental health risk.
This research was funded by the USGS Ecosystems Mission Area’s Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology), and the U.S. Environmental Protection Agency (EPA) Great Lakes Restoration Initiative, EPA Great Lakes Fish Monitoring and Surveillance Program.
Below are other science projects associated with this project.
Ecologically-Driven Exposure Pathways Science Team
Mercury in Aquatic Ecosystems
North American and European Atmospheric Mercury Declines Explained by Local and Regional Emission Reductions
Comprehensive Assessment of Mercury in Streams Explains Major Sources, Cycling, and Effects
Complex Response to Decline in Atmospheric Deposition of Mercury
Environmental Mercury Cycling and Global Change
Some Ecosystems will Respond to Reductions in Mercury Emissions
Below are publications associated with this project.
Use of stable isotope signatures to determine mercury sources in the Great Lakes
Below are news stories associated with this project.
- Overview
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.
Source attribution (fingerprinting) in the Great Lakes shows how sources vary from east to west across the Great Lakes from atmospheric dominated to industrially dominated. From Lepak and others, 2015. The fingerprinting tool includes novel analyses of stable mercury isotopic signatures in lake sediments to infer relative contributions of mercury from key end-member sources. The tool works by identifying the different types of mercury atoms present in the Great Lakes. Each mercury atom has a certain mass, which can range from 196-204. The relative abundance of each of these masses is different in each of the mercury sources, and these differences provide the ability to "fingerprint" the mercury source contributions.
Surface sediment samples collected from 58 locations throughout the Great Lakes during 2012-2014 were analyzed for stable isotopes of mercury and used to determine sources. The tool was applied to the entire Great Lakes ecosystem to distinguish among mercury derived from atmospheric deposition, watershed runoff, and industrial point-source inputs. The results show novel insights into mercury sources across the Great Lakes, with Lakes Superior and Huron dominated by atmospheric inputs. Lakes Erie and Ontario dominated by industrial and watershed sources, and Lake Michigan showing about equal contributions from all three source categories.
Mercury is a persistent pollutant that is distributed globally. Previous USGS and other research has shown that human-induced sources of mercury (atmospheric deposition, watershed inputs, or direct inputs through point source discharges) are the dominant sources of mercury to the environment when compared to natural emission sources such as volcanoes and oceans. Understanding the sources contributing to mercury has been an active area of research at USGS for the past 25 years. This study advances this research by providing a new tool to more accurately define mercury sources.
Environmental Health Implications
With this new fingerprinting tool, resource managers can now better understand what mitigation strategies will be most effective for reducing mercury loading and exposure to fish and wildlife. The results from the source model were extended to recent results from mercury isotope work in measurements in predatory fish (Lake trout and Burbot) to ascertain the relative importance of the end-member sources to the food web. Comparison of the mercury signatures in predatory fish from the three lakes (Michigan, Superior, and Ontario) reveals that bioaccumulated mercury in these predator fish is more similar to atmospherically derived mercury than to mercury in a lake's sediment. The study findings suggest that atmospherically derived mercury many be a more important source of methylmercury to higher trophic levels (predator fish) than mercury stored in legacy sediments in the Great Lakes. In aquatic systems microbially mediated processes can transform mercury to methylmercury, a more toxic form that is biomagnified in aquatic food webs. Bioaccumulated methylmercury is a potential threat to aquatic ecosystems and humans health through fish consumption. Providing a better understanding of sources is a key component of managing environmental health risk.
This research was funded by the USGS Ecosystems Mission Area’s Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology), and the U.S. Environmental Protection Agency (EPA) Great Lakes Restoration Initiative, EPA Great Lakes Fish Monitoring and Surveillance Program.
- Science
Below are other science projects associated with this project.
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.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.Comprehensive Assessment of Mercury in Streams Explains Major Sources, Cycling, and Effects
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...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
Below are publications associated with this project.
Use of stable isotope signatures to determine mercury sources in the Great Lakes
Sources of mercury (Hg) in Great Lakes sediments were assessed with stable Hg isotope ratios using multicollector inductively coupled plasma mass spectrometry. An isotopic mixing model based on mass-dependent (MDF) and mass-independent fractionation (MIF) (δ202Hg and Δ199Hg) identified three primary Hg sources for sediments: atmospheric, industrial, and watershed-derived. Results indicate atmospheAuthorsRyan F. Lepak, Runsheng Yin, David P. Krabbenhoft, Jacob M. Ogorek, John F. DeWild, Thomas M. Holsen, James P. Hurley - News
Below are news stories associated with this project.