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Sarah E Janssen

Sarah Janssen is an isotope geochemist working in the Mercury Research Lab (MRL) located within the Upper Midwest Water Science Center.

She has a PhD in environmental chemistry from Rutgers University and a bachelor’s in chemistry from
University of the Sciences in Philadelphia. Her work focuses on the application of stable isotope techniques for understanding sources and transformations of mercury (Hg) in the environment. Her research interests include Hg cycling in contaminated ecosystems, the investigation of microbial Hg transformations using stable isotopes, and development of analytical methods to improve Hg isotope measurements.

 

Current Projects

  • Mercury Cycling and Source Identification in the St Louis River Estuary MN/WI (collaboration with US EPA and Minnesota Pollution Control Agency)
  • Mercury Isotope Fractionation during Microbial Uptake and Transformations of Hg (collaboration with Rutgers University and University of Ottawa)
  • Method Development for the Pre-concentration of Waters and Low Concentration Environmental Samples for Mercury Isotopic Analysis

Education and Certifications

  • Ph.D. 2016, Environmental Chemistry, Rutgers University, New Brunswick, NJ

  • B.S. 2011, Chemistry, University of the Sciences, Philadelphia, PA

Science and Products

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Largemouth bass at the USFWS Mountain-Prairie Aquarium

Mercury Isotope Ratios used to Determine Sources of Mercury to Fish in Northeast U.S. Streams

Mercury isotope analyses were used to distinguish different sources of mercury to fish in 23 streams along a forested-rural to urban-industrial land-use gradient in the Northeastern United States. The use of mercury isotope measurements in fish tissue allow for distinguishing different sources of mercury that are bioaccumulating into the food web. Mercury isotope signatures in fish in forested...
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Ecosystems, Contaminant Biology, Environmental Health Program, Toxic Substances Hydrology
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Mercury Isotope Ratios used to Determine Sources of Mercury to Fish in Northeast U.S. Streams

Mercury isotope analyses were used to distinguish different sources of mercury to fish in 23 streams along a forested-rural to urban-industrial land-use gradient in the Northeastern United States. The use of mercury isotope measurements in fish tissue allow for distinguishing different sources of mercury that are bioaccumulating into the food web. Mercury isotope signatures in fish in forested...
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Mercury studies

The USGS Mercury Research Lab is a national leader in advancing mercury research and science, specializing in low-level mercury speciation and isotope analysis and mercury-source fingerprinting. The MRL leads national cutting-edge collaborative studies, including state-of-the-art sample analysis, methods development for field and lab procedures, and data interpretation and dissemination.
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Upper Midwest Water Science Center, Mercury Research Laboratory
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Mercury studies

The USGS Mercury Research Lab is a national leader in advancing mercury research and science, specializing in low-level mercury speciation and isotope analysis and mercury-source fingerprinting. The MRL leads national cutting-edge collaborative studies, including state-of-the-art sample analysis, methods development for field and lab procedures, and data interpretation and dissemination.
Learn More
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Mercury studies

The USGS Mercury Research Lab is a national leader in advancing mercury research and science, specializing in low-level mercury speciation and isotope analysis and mercury-source fingerprinting. The MRL leads national cutting-edge collaborative studies, including state-of-the-art sample analysis, methods development for field and lab procedures, and data interpretation and dissemination.
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Upper Midwest Water Science Center, Mercury Research Laboratory
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Mercury studies

The USGS Mercury Research Lab is a national leader in advancing mercury research and science, specializing in low-level mercury speciation and isotope analysis and mercury-source fingerprinting. The MRL leads national cutting-edge collaborative studies, including state-of-the-art sample analysis, methods development for field and lab procedures, and data interpretation and dissemination.
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Mercury source identification in the Mobile and Tombigbee Rivers

This dataset details mercury concentrations and mercury stable isotope values collected as part of an environmental mercury assessment encompassing the Mobile and Tombigbee Rivers as well as two U.S. Environmental Protection Agency Superfund sites. The Tensaw River was also sampled as part of this study as a reference site, absent of mercury contamination. As a part of this survey, sediments, wate
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Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center

Mercury and Methylmercury Stable Isotope Measurements in Giant Petrels

Methylmercury (MeHg) and total mercury (HgT) stable isotope measurements were made by the USGS Mercury Research Lab (MRL) in different organs on the Giant Petrels (Macronectes spp.) to examine internal mercury cycling in these seabirds. These data were collected as a compliment to x-ray spectroscopy measurements made by the University of Grenoble, France. The tissues and feathers of the southern g
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Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center

Chemical characterization of water and suspended sediment of the Snake River and Hells Canyon Complex (Idaho, Oregon)

This dataset includes laboratory analyses of surface water samples and sediment trap material collected from (1) locations upstream, downstream, and within the Hells Canyon Complex (Idaho, Oregon) of the Snake River, (2) tributaries of the Snake River, and (3) two reservoirs near Boise, Idaho, from 2014 to 2019. The study area spans approximately 232 river miles of the Snake River and includes: si
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Idaho Water Science Center

Mercury Concentrations and Mercury Isotopes in Salmonid fishes from the Snake River and tributaries in Idaho and Oregon, 2015 and 2019 (ver. 2.0, February 2021)

Comma-separated values (.csv) file containing data related to mercury in Salmonid fishes collected from the Snake River and tributaries, Idaho and Oregon.
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Forest and Rangeland Ecosystem Science Center

Mercury concentrations and isotopic compositions in biota and sediments from the Hannibal Pool of the Ohio River

The Hannibal Pool of the Ohio River is heavily industrialized and receives direct effluent discharges from coal power plants, chlor-alkali plants, and sewage treatment facilities. Mercury (Hg) is a contaminant of concern due to the risk of bioaccumulation at wildlife refuges also located within this region. Mercury concentrations and isotopes compositions were measured to assess the levels and sou
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Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center

Mercury Concentrations and Isotopic Compositions in Sediment Cores from North American Lakes (Alaska, Minnesota, and Newfoundland)

Mercury isotope measurements were made across nine sediments cores from remote North American lakes to examine changes in the Hg isotope profiles. The lakes spanned regions of Alaska, Minnesota, and Newfoundland as well as a range of temperate to arctic climates. This data describes the natural record of mass dependent (MDF) and mass independent (MIF) Hg isotope fractionation related to deposition
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Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center

Gruber's Grove Bay Mercury Site Assessment

Mercury (Hg) concentrations and isotopic compositions were collected in sediments, soils, and suspended particulate matter from Gruber's Grove Bay (GGB) and upstream reference sites to inform future remedial efforts. The highest concentrations and isotopic signatures were observed in soils collected from historic water settling ponds from the Badger Army Ammunition Plant (BAAP). Sediments from the
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Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center

Stable Mercury Isotopic Analyses in Natural Matrices via Rapid Pre-Concentration Method

This data relates to the development of a modified pre-concentration method for mercury (Hg) stable isotope measurements that uses chemical Hg reduction and gold trap amalgamation followed by semi-rapid thermal desorption (less than 1 hour) and chemical trapping in a novel oxidizing solution. The thermal desorption method was demonstrated to perform adequately on multiple trapping matrices previou
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Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center

Fox River walleye mercury isotope data

Adult walleye were caught in Fox River (Wisconsin) during April 2014. Age-0 walleye were caught in Fox River during October 2014. Total length, weight, age, and proportion of weight represented by water were determined for each of the walleye. Whole-fish homogenates were prepared during 2014-2015 and during 2017. Total mercury (HgT) concentration, methylmercury (MeHg) concentration, and mercury (H
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Great Lakes Science Center

Data for Biogeochemical and Physical Processes Controlling Mercury and Selenium Bioaccumulation in Bighorn Lake, Bighorn Canyon National Recreation Area, Montana and Wyoming, 2015-2016

This dataset includes the field measurements and laboratory analyses of surface water, seston, fish tissue, and sediment samples collected from Bighorn Lake, within Bighorn Canyon National Recreation area (BICA), during high flow (July 2015) and low flow (August 2016) conditions. The study area includes 7-9 sampling sites that follow a transect spanning the entire length of the reservoir from the
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Wyoming-Montana Water Science Center
Filter Total Items: 13

Mercury isotope fractionation by internal demethylation and biomineralization reactions in seabirds: Implications for environmental mercury science

A prerequisite for environmental and toxicological applications of mercury (Hg) stable isotopes in wildlife and humans is quantifying the isotopic fractionation of biological reactions. Here, we measured stable Hg isotope values of relevant tissues of giant petrels (Macronectes spp.). Isotopic data were interpreted with published HR-XANES spectroscopic data that document a stepwise transformation
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Upper Midwest Water Science Center

Examining historical mercury sources in the Saint Louis River estuary: How legacy contamination influences biological mercury levels in Great Lakes coastal regions

Industrial chemical contamination within coastal regions of the Great Lakes can pose serious risks to wetland habitat and offshore fisheries, often resulting in fish consumption advisories that directly affect human and wildlife health. Mercury (Hg) is a contaminant of concern in many of these highly urbanized and industrialized coastal regions, one of which is the Saint Louis River estuary (SLRE)
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Ecosystems, Water Resources, Forest and Rangeland Ecosystem Science Center, Fort Collins Science Center, Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center

The influence of legacy contamination on the transport and bioaccumulation of mercury within the Mobile River Basin

Past industrial use and subsequent release of mercury (Hg) into the environment have resulted in severe cases of legacy contamination that still influence contemporary Hg levels in biota. While the bioaccumulation of legacy Hg is commonly assessed via concentration measurements within fish tissue, this practice becomes difficult in regions of high productivity and methylmercury (MeHg) production,
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Upper Midwest Water Science Center

Insights into mercury source identification and bioaccumulation using stable isotope approaches in the Hannibal Pool of the Ohio River

Mercury contamination in river systems due to historic and current Hg releases is a persistent concern for both wildlife and human health. In larger rivers, like the Ohio River, USA, it is difficult to directly link Hg discharges to bioaccumulation due to the existence of multiple industrial Hg sources as well as the varied dietary and migratory habits of biota. To better understand how industrial
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Upper Midwest Water Science Center

Tracing the uptake of Hg(II) in an iron-reducing bacterium using mercury stable isotopes

Anaerobic microorganisms play a key role in the biological mercury (Hg) cycle due to their ability to produce bioaccumulative neurotoxic methylmercury (MeHg). However, despite recent advances, how bacteria accumulate inorganic Hg [Hg(II)] prior to methylation is largely unknown. In this study, we applied Hg stable isotopes to measure changes in cellular compartments of Geobacter sulfurreducens and
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Upper Midwest Water Science Center

Isolation of methylmercury using distillation and anion-exchange chromatography for isotopic analyses in natural matrices

The development of mercury (Hg) stable isotope measurements has enhanced the study of Hg sources and transformations in the environment. As a result of the mixing of inorganic Hg (iHg) and methylmercury (MeHg) species within organisms of the aquatic food web, understanding species-specific Hg stable isotopic compositions is of significant importance. The lack of MeHg isotope measurements is due to
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Upper Midwest Water Science Center

The assessment and remediation of mercury contaminated sites: A review of current approaches

Remediation of mercury (Hg) contaminated sites has long relied on traditional approaches, such as removal and containment/capping. Here we review contemporary practices in the assessment and remediation of industrial-scale Hg contaminated sites and discuss recent advances. Significant improvements have been made in site assessment, including the use of XRF to rapidly identify the spatial extent of
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Upper Midwest Water Science Center

Mercury source changes and food web shifts alter contamination signatures of predatory fish from Lake Michigan

To understand the impact reduced mercury (Hg) loading and invasive species have had on methylmercury bioaccumulation in predator fish of Lake Michigan, we reconstructed bioaccumulation trends from a fish archive (1978 to 2012). By measuring fish Hg stable isotope ratios, we related temporal changes in Hg concentrations to varying Hg sources. Additionally, dietary tracers were necessary to identify
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Contaminant Biology, Toxic Substances Hydrology, Upper Midwest Water Science Center

Chemical and physical controls on mercury source signatures in stream fish from the northeastern United States

Streams in the northeastern U.S. receive mercury (Hg) in varying proportions from atmospheric deposition and legacy point sources, making it difficult to attribute shifts in fish concentrations directly back to changes in Hg source management. Mercury stable isotope tracers were utilized to relate sources of Hg to co-located fish and bed sediments from 23 streams across a forested to urban-industr
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Water Resources, Toxic Substances Hydrology, New England Water Science Center, New York Water Science Center, Oklahoma-Texas Water Science Center, Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center

Tracking legacy mercury in the Hackensack River Estuary using mercury stable isotopes

Spatial redistribution of legacy mercury (Hg) contamination in the Hackensack River estuary (New Jersey, USA) was evaluated using mercury stable isotopes. Total Hg varied from 0.06 to 3.8 µg g-1 in sediment from the tidal Hackensack River and from 15 to 154 µg g-1 near historically contaminated sites in upper Berry's Creek, a tributary of the Hackensack River. delta202Hg values for total Hg from
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Toxic Substances Hydrology, Upper Midwest Water Science Center

Rapid pre-concentration of mercury in solids and water for isotopic analysis

The precise quantification of mercury (Hg) stable isotope compositions in low concentration or dilute samples poses analytical challenges due to Hg mass limitations. Common Hg pre-concentration procedures require extended processing times, making rapid Hg stable isotope measurements challenging. Here we present a modified pre-concentration method that combines commonly used Hg reduction and gold t
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Toxic Substances Hydrology, Upper Midwest Water Science Center

Mercury isotopes reveal an ontogenetic shift in habitat use by walleye in lower Green Bay of Lake Michigan

In general, fish residing in rivers differ from fish residing in lakes in their mercury (Hg) isotope ratios. Specifically, fish residing in lakes typically show enriched values for the isotope ratios of δ202Hg (mass-dependent fractionation of isotope 202Hg) and Δ199Hg (mass-independent fractionation of isotope 199Hg) compared with fish residing in rivers, because photochemical effects acting on Hg
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Ecosystems, Contaminant Biology, Great Lakes Science Center, Upper Midwest Water Science Center

Pre-USGS Publications

Janssen, S.E.; Johnson, M.W.; Blum, J.D.; Barkay, T.; Reinfelder, J.R., Separation of monomethylmercury from estuarine sediments for mercury isotope analysis. Chemical Geology 2015
Janssen, S.E.; Schaefer, J.K.; Barkay, T.; Reinfelder, J.R. Fractionation of mercury stable isotopes during microbial methylmercury production in pure culture. Environ. Sci. Technol. 2016
Lloyd, N.; Janssen, S.E.; Reinfelder J.R.; Barkay, T., Exposure to mercury selects for antibiotic resistance in Fundulus heteroclitus gut microbiome, Current Microbiology, 2016
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Isotopic tracers in fish in Northeast provide clue to mercury sources

Isotopes of mercury in fish can indicate the source of that mercury, reports a new study from the USGS Regional Stream Quality Assessment. 

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