Skip to main content
U.S. flag

An official website of the United States government

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

link
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...
By
Ecosystems, Contaminant Biology, Environmental Health Program, Toxic Substances Hydrology
link

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...
Learn More
link

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.
By
Upper Midwest Water Science Center, Mercury Research Laboratory
link

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
link

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.
By
Upper Midwest Water Science Center, Mercury Research Laboratory
link

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
Filter Total Items: 18

African fish mercury burden and isotopic composition from archived museum specimens

Fish collected for taxonomic and systematic purposes are often preserved and then archived in museum collections. Preserved fish are commonly first fixed in a formalin solution and then transferred to ethanol for long-term storage. The wet preservation method can potentially introduce mercury (Hg) contamination or unintentionally extract Hg from tissue. An experiment was designed to test the utili
By
Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center

Mercury Concentrations and Loads in United States and Canadian Tributaries of Lake Superior

In 2021, the U.S. Geological Survey (USGS) Mercury Research Laboratory (MRL) conducted a large-scale assessment of mercury (Hg) concentrations and Hg stable isotope values in tributaries of Lake Superior in order to define the sources and amounts of Hg entering the lake. Water samples were collected monthly from 18 tributaries in the United States from April through October in 2021 and during 2022
By
Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center, Mercury Research Laboratory

Source Identification of Mercury and Methylmercury using Stable Isotope Analysis in the Fox River, WI

The lower Fox River in Wisconsin is a heavily industrialized system and the major tributary to Green Bay within Lake Michigan. The region has been a listed as Area of Concern by the United States Environmental Protection Agency (USEPA), indicating severe impairment of the ecological health of the system. Remedial action has taken place along the river to remove extensive polychlorinated biphenyl (
By
Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center, Mercury Research Laboratory

Assessment of mercury sources in Alaskan lake food webs

This data release includes results of raw water, soil, seston, and fish tissue samples collected from lakes in southwestern Alaska between 2011 and 2016. Specifically, these data include total mercury and methylmercury concentrations in water, size-sieved seston, and particulate matter of 13 remote lakes. Additionally, these data include soil and volcanic ash measurements from the surrounding wate
By
Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center, Mercury Research Laboratory

Total and Methyl Mercury Water and Fish Concentrations within Everglades National Park

The data in this data release includes results from the analysis of water and fish from 76 sites in the Everglades National Park (ENP). Water and particulate matter samples were collected from 2008 to 2018 and analyzed for total mercury (THg) and methylmercury (MeHg). Filtered water samples were also analyzed for dissolved organic carbon (DOC), specific ultraviolet absorbance (SUVA), and major ani
By
Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center, Mercury Research Laboratory

Isotopic Examination of Mercury Methylation and Demethylation Rates in Yellowstone National Park Thermal Features

Data in this data release were obtained for water samples collected under Yellowstone National Park Research Permit YELL-05194 in 2017 through the Integrated Yellowstone Studies Project funded by the Mineral Resources Program. Isotope-spiked incubations were carried out to determine methylation and demethylation potential for Frying Pan spring, Crystal Sister East, Crystal Sister West, and Turbule
By
Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center, Mercury Research Laboratory

Yellowstone Thermal Feature Mercury and Methylmercury Characterization

Data in this data release were obtained from water samples collected under Yellowstone National Park (YNP) Research Permit YELL-05194 in 2017, 2019, and 2020 through the Integrated Yellowstone Studies Project funded by the Mineral Resources Program. These samples were used to assess mercury cycling within YNP. Water samples were analyzed for total mercury and methylmercury, the bioaccumulated form
By
Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center, Mercury Research Laboratory

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
By
Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center, Mercury Research Laboratory

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
By
Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center, Mercury Research Laboratory

Chemical characterization of water and suspended sediment of the Snake River and Hells Canyon Complex (Idaho, Oregon) (ver. 2.0, November 2022)

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 2021. The study area spans approximately 232 river miles of the Snake River and includes: tw
By
Idaho Water Science Center, Upper Midwest Water Science Center, Mercury Research Laboratory

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.
By
Forest and Rangeland Ecosystem Science Center, Upper Midwest Water Science Center, Mercury Research Laboratory

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
By
Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center, Mercury Research Laboratory
Nippon mercury analyzer for sediments and fish
link
MC-ICP-MS used for mercury stable isotope analyses
link
Female scientist working in laboratory
link
Three USGS employees in boat on Lake Wisconsin
link
Internal look at the MC-ICP-MS flight tube when magnet is removed
link
Scientist in field assessing soil sampling locations at the Badger Army Ammunition Plant site
link
Scientist collecting water for isotope analysis on the shore of river with forest surrounding
link
Filter Total Items: 22

Tracing the sources and depositional history of mercury to coastal northeastern U.S. lakes

Mercury (Hg) deposition was reconstructed in sediment cores from lakes in two coastal U.S. National Parks: Acadia National Park (ANP) and Cape Cod National Seashore (CCNS), to fill an important spatial gap in Hg deposition records and to explore changing sources of Hg and processes affecting Hg accumulation in these coastal sites. Recent Hg deposition chronology was assessed using (1) a newly deve
By
Upper Midwest Water Science Center

Elevated mercury concentrations and isotope signatures (N, C, Hg) in yellowfin tuna (Thunnus albacares) from the Galápagos Marine Reserve and waters off Ecuador

We examined how dietary factors recorded by C and N influence Hg uptake in 347 individuals of yellowfin tuna (Thunnus albacares), an important subsistence resource from the Galápagos Marine Reserve (GMR) and the Ecuadorian mainland coast (EMC) in 2015-2016. We found no differences in total Hg (THg) measured in red muscle between the two regions and no seasonal differences, likely due to the age of
By
Upper Midwest Water Science Center

Assessment of mercury in sediments and waters of Grubers Grove Bay, Wisconsin

Mercury is a global contaminant that can be detrimental to wildlife and human health. Anthropogenic emissions and point sources are primarily responsible for elevated mercury concentrations in sediments and waters. Mercury can physically move and chemically transform in the environment, resulting in biomagnification of mercury, in the form of methylmercury, in the food web and causing elevated mer
By
Water Resources, Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center, Mercury Research Laboratory

Decadal trends of mercury cycling and bioaccumulation within Everglades National Park

Mercury (Hg) contamination has been a persistent concern in the Florida Everglades for over three decades due to elevated atmospheric deposition and the system's propensity for methylation and rapid bioaccumulation. Given declines in atmospheric Hg concentrations in the conterminous United States and efforts to mitigate nutrient release to the greater Everglades ecosystem, it was vital to assess h
By
Upper Midwest Water Science Center, Mercury Research Laboratory

Methylmercury stable isotopes: New insights on assessing aquatic food web bioaccumulation in legacy impacted regions

Through stable isotope measurements of total mercury (HgT), identification of crucial processes and transformations affecting different sources of mercury (Hg) has become possible. However, attempting to use HgT stable isotopes to track bioaccumulation of Hg sources among different food web compartments can be challenging, if not impossible, when tissues have varying methylmercury (MeHg) contents.
By
Upper Midwest Water Science Center, Mercury Research Laboratory

Using carbon, nitrogen, and mercury isotope values to distinguish mercury sources to Alaskan lake trout

Lake trout (Salvelinus namaycush), collected from 13 remote lakes located in southwestern Alaska, were analyzed for carbon, nitrogen, and mercury (Hg) stable isotope values to assess the importance of migrating oceanic salmon, volcanic activity, and atmospheric deposition to fish Hg burden. Methylmercury (MeHg) bioaccumulation in phytoplankton (5.0–6.9 kg L–1) was also measured to quantify the bas
By
Upper Midwest Water Science Center, Mercury Research Laboratory

Response to comment on “Mercury isotope fractionation by internal demethylation and biomineralization reactions in seabirds: Implications for environmental mercury science”: Principles and limitations of source tracing and process tracing with stable isot

No abstract available. 
By
Water Resources, Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center

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
By
Upper Midwest Water Science Center, Mercury Research Laboratory

Isotope fractionation from In Vivo methylmercury detoxification in waterbirds

The robust application of stable mercury (Hg) isotopes for mercury source apportionment and risk assessment necessitates the understanding of mass-dependent fractionation (MDF) due to internal transformations within organisms. Here, we used high energy-resolution XANES spectroscopy and isotope ratios of total mercury (δ202THg) and methylmercury (δ202MeHg) to elucidate the chemical speciation of Hg
By
Ecosystems, Forest and Rangeland Ecosystem Science Center, Upper Midwest Water Science Center, Mercury Research Laboratory

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)
By
Ecosystems, Water Resources, Forest and Rangeland Ecosystem Science Center, Fort Collins Science Center, Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center, Mercury Research Laboratory

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,
By
Upper Midwest Water Science Center, Mercury Research Laboratory

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
By
Upper Midwest Water Science Center, Mercury Research Laboratory

Non-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

**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.

link

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. 

Read Article

Science and Products