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
Mercury Isotope Ratios used to Determine Sources of Mercury to Fish in Northeast U.S. Streams
Mercury studies
Mercury studies
Mercury stable isotopes in biota, sediment, groundwater, and waste piles, Clear Lake area, Lake County, California, 2019-2022
Mercury Stable Isotope Assessment of Global Food Webs
Assessment of Mercury and Mercury Stable Isotopes in Sediments and Biota from Reservoirs and Remedial Zones within the Saint Louis River, Minnesota
Particulate mercury isotope results, fiber optic thermal survey data, and nearshore surface sediment results at the Bremerton Naval Complex, Washington, USA, 2020-21
Chemical characterization of water, sediments, and fish from Water Conservation Areas and Canals of the Florida Everglades (USA), 2012 to 2019
African fish mercury burden and isotopic composition from archived museum specimens
Mercury Concentrations and Loads in United States and Canadian Tributaries of Lake Superior
Source Identification of Mercury and Methylmercury using Stable Isotope Analysis in the Fox River, WI
Assessment of mercury sources in Alaskan lake food webs (version 1.1, September 2023)
Total and Methyl Mercury Water and Fish Concentrations within Everglades National Park
Isotopic Examination of Mercury Methylation and Demethylation Rates in Yellowstone National Park Thermal Features
Yellowstone Thermal Feature Mercury and Methylmercury Characterization
Mercury isotope values in shoreline spiders reveal transfer of aquatic mercury sources to terrestrial food webs
Contrasting mercury contamination scenarios and site susceptibilities confound fish mercury burdens in Suriname, South America
National-scale assessment of total gaseous mercury isotopes across the United States
Using mercury stable isotope fractionation to identify the contribution of historical mercury mining sources present in downstream water, sediment and fish
Tracing the sources and depositional history of mercury to coastal northeastern U.S. lakes
Elevated mercury concentrations and isotope signatures (N, C, Hg) in yellowfin tuna (Thunnus albacares) from the Galápagos Marine Reserve and waters off Ecuador
Assessment of mercury in sediments and waters of Grubers Grove Bay, Wisconsin
Decadal trends of mercury cycling and bioaccumulation within Everglades National Park
Methylmercury stable isotopes: New insights on assessing aquatic food web bioaccumulation in legacy impacted regions
Using carbon, nitrogen, and mercury isotope values to distinguish mercury sources to Alaskan lake trout
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
Mercury isotope fractionation by internal demethylation and biomineralization reactions in seabirds: Implications for environmental mercury science
Non-USGS Publications**
**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.
Great Lakes Mercury Sources Revealed
A new "fingerprinting" tool, developed by USGS and collaborators at University of Wisconsin-Madison, can now indicate sources of mercury in the environment.
Science and Products
- Science
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...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.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. - Data
Filter Total Items: 24
Mercury stable isotopes in biota, sediment, groundwater, and waste piles, Clear Lake area, Lake County, California, 2019-2022
Samples were collected from Clear Lake, California from 2019-2022 by the U.S. Geological Survey (USGS) California Water Science Center, the USGS Forest and Rangeland Ecosystem Science Center (FRESC), the US Environmental Protection Agency, and EA Engineering Science and Technology Inc. to assess the extent and cycling of legacy mercury (Hg) contamination from Sulphur Bank Mine. Samples of waste roMercury Stable Isotope Assessment of Global Food Webs
This dataset describes mercury (Hg) stable isotope values in fish dorsal muscle from different freshwater environments across the globe. Fish were collected at numerous field sites in North America, South and Central America, Africa, and Asia from 2006-2020. Sub-samples were provided by cooperators to the U.S. Geological Survey Mercury Research Laboratory and the University of Wisconsin for mercurAssessment of Mercury and Mercury Stable Isotopes in Sediments and Biota from Reservoirs and Remedial Zones within the Saint Louis River, Minnesota
This data release includes mercury concentrations and mercury stable isotope measurements measured in sediments and biological tissues collected from the Saint Louis River located in Minnesota. Sediments and biota were collected by the U.S. Geological Survey, U.S. Environmental Protection Agency, U.S. Army Corps of Engineers, and federal contractors (Battelle) from 2017-2021. Collection regions inParticulate mercury isotope results, fiber optic thermal survey data, and nearshore surface sediment results at the Bremerton Naval Complex, Washington, USA, 2020-21
This data release contains four data sets that support ongoing U.S. Geological Survey investigations, in cooperation with the U.S. Navy, at the Bremerton Naval Complex (BNC), Sinclair Inlet, Washington. Child item #1 includes reported concentrations of mercury isotopes in 28 samples of new (2018-19) or archived (2008-09) particulate samples from the BNC, surface sediment from Sinclair Inlet, or suChemical characterization of water, sediments, and fish from Water Conservation Areas and Canals of the Florida Everglades (USA), 2012 to 2019
This dataset includes field and laboratory measurements of surface waters, pore waters, sediment, and fish from Water Conservation Areas and adjacent canals of the Florida Everglades (USA). Water, sediment, and fish samples were collected from Water Conservation Areas 1 (Arthur R. Marshall Loxahatchee National Wildlife Refuge), 2, and 3 and neighboring canals between 2012 and 2019. The sites samplAfrican 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 utiliMercury 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 2022Source 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 (Assessment of mercury sources in Alaskan lake food webs (version 1.1, September 2023)
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 wateTotal 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 aniIsotopic 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 TurbuleYellowstone 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 - Multimedia
- Publications
Filter Total Items: 26
Mercury isotope values in shoreline spiders reveal transfer of aquatic mercury sources to terrestrial food webs
The transfer of aquatic contaminants, including mercury (Hg), to terrestrial food webs is an often-overlooked exposure pathway to terrestrial animals. While research has implemented the use of shoreline spiders to assess aquatic to terrestrial Hg transfer, it is unclear whether Hg sources, estimated from isotope ratios, can be successfully resolved to inform site assessments and remedy effectiveneAuthorsSarah E. Janssen, Christopher James Kotalik, Collin Eagles-Smith, Gale B. Beaubien, Joel C. Hoffman, Greg Peterson, Marc A. Mills, David WaltersContrasting mercury contamination scenarios and site susceptibilities confound fish mercury burdens in Suriname, South America
In Suriname, mercury (Hg) use has recently increased because of gold mining, which has put fish-reliant communities (e.g., Indigenous and Tribal) at risk of enhanced Hg exposure through the riverine fish these communities consume. To quantify how the magnitude of these risks change according to location and time, we measured total mercury (HgT) in fish at sites downstream and upstream of an artisaAuthorsArioené Vreedzaam, Paul Ouboter, Ashna D. Hindori-Mohangoo, Ryan F. Lepak, Samantha L. Rumschlag, Sarah E. Janssen, Gwen Landburg, Arti Shankar, Wilco Zijlmans, Maureen Y. Lichtveld, Jeffrey K. WickliffeNational-scale assessment of total gaseous mercury isotopes across the United States
With the 2011 promulgation of the Mercury and Air Toxics Standards by the U.S. Environmental Protection Agency, and the successful negotiation by the United Nations Environment Program of the Minamata Convention, emissions of mercury (Hg) have declined in the United States. While the declines in atmospheric Hg concentrations in North America are encouraging, linking the declines to changing domestAuthorsMichael T. Tate, Sarah E. Janssen, Ryan F. Lepak, Laura Elizabeth Flucke, David P. KrabbenhoftUsing mercury stable isotope fractionation to identify the contribution of historical mercury mining sources present in downstream water, sediment and fish
Ecosystems downstream of mercury (Hg) contaminated sites can be impacted by both localized releases as well as Hg deposited to the watershed from atmospheric transport. Identifying the source of Hg in water, sediment, and fish downstream of contaminated sites is important for determining the effectiveness of source-control remediation actions. This study uses measurements of Hg stable isotopes inAuthorsChris S. Eckley, Collin Eagles-Smith, Todd P Luxton, Joel C. Hoffman, Sarah E. JanssenTracing 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 deveAuthorsVivien F. Taylor, Joshua D. Landis, Sarah E. JanssenElevated 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 ofAuthorsLaia Munoz-Abril, Carlos A Valle, Juan Jose Alava, Sarah E. Janssen, Elsie M. Sunderland, Francisco Rubianes-Landazuri, Steven D EmslieAssessment 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 merAuthorsEvan J. Routhier, Sarah E. Janssen, Michael T. Tate, Jacob M. Ogorek, John F. DeWild, David P. KrabbenhoftDecadal 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 hAuthorsSarah E. Janssen, Michael T. Tate, Brett Poulin, David P. Krabbenhoft, John F DeWild, Jacob M. Ogorek, Matthew S. Varonka, William H. Orem, Jeffrey D KlineMethylmercury 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.AuthorsTylor Rosera, Sarah E. Janssen, Michael T. Tate, Ryan F. Lepak, Jacob M. Ogorek, John F. DeWild, David P. Krabbenhoft, James P. HurleyUsing 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 basAuthorsRyan F. Lepak, Jacob M. Ogorek, Krista K. Bartz, Sarah E. Janssen, Michael T. Tate, Yin Runsheng, James P. Hurley, Daniel B. Young, Collin Eagles-Smith, David P. KrabbenhoftResponse 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.AuthorsAlain Manceau, Romain Brossier, Sarah E. Janssen, Brett PoulinMercury 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 transformationAuthorsAlain Manceau, Romain Brossier, Sarah E. Janssen, Tylor Rosera, David P. Krabbenhoft, Yves Cherel, Paco Bustamante, Brett PoulinNon-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 2015Janssen, 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. 2016Lloyd, 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.
- Web Tools
Great Lakes Mercury Sources Revealed
A new "fingerprinting" tool, developed by USGS and collaborators at University of Wisconsin-Madison, can now indicate sources of mercury in the environment.
- News