Lab Members

We are a fun group of chemists dedicated to environmental health.
Please scroll to read who is working on what research in our lab!

Dr. Heather Stapleton, Ph.D | Principal Investigator

Heather received her PhD from the University of Maryland, College Park where she trained in environmental chemistry. After completing her PhD, she accepted an NRC Postdoctoral Fellowship at the National Institute of Standards & Technology in Gaithersburg, MD where she worked for two years in their Analytical Chemistry Division.  In 2005 Heather accepted a faculty position at the Nicholas School of the Environment at Duke University, and became active in the Integrated Environmental Health and Toxicology Program.  Her research interests focus on identifying and understanding the uses of flame retardant chemicals in consumer products, and evaluating human exposure, particularly in pregnant women and children. She seeks to understand how exposure to chemical mixtures impacts health, with a focus on metabolic outcomes (e.g. triglyceride formation). In addition, she is interested in understanding how persistent halogenated contaminants impact thyroid hormone regulation, and specifically during pregnancy.
She was an NIEHS ONES (Outstanding New Environmental Scientist) awardee (2008) and currently serves as the Deputy Director for the Duke Superfund Research Center, and Director of the Duke Environmental Analysis Laboratory. Furthermore, she collaborates with a number of investigators within and outside of Duke to investigate health effects related to flame retardant exposures, and other common contaminants in the indoor environment (e.g. phthalates, pesticides, and per-fluorinated chemicals).  

Dr. Kate Hoffman, Ph.D | Assistant Research Professor

Dr. Kate Hoffman, an environmental epidemiologist, joined the faculty of the Nicholas School of the Environment as a research assistant professor in 2017. Her research is focused on understanding the impact of environmental chemical exposures on children’s growth and development. As a doctoral student at Boston University, Kate investigated associations between perfluoroalkyl chemicals and children's cognitive and behavioral development. During her postdoctoral work, she shifted her focus to flame retardant exposures and came to Duke in 2014 to work in the Stapleton Lab. Her current projects include an assessment of children’s exposure to flame retardant chemicals and an investigation of the impacts of exposure on early immune system development and function. Kate enjoys spending time with her husband Ben, two adorable children and an ever increasing number of pets.

Sharon Zhang | Research Project Manager

As a Research Project Manager with an M.S. in Chemical Engineering, Sharon joined the Stapleton Lab in December, 2016. She has work experience in both the pharmaceutical industry as an Analytical Scientist and in academia as a Researcher. Before she joined the Stapleton Lab, she was involved in metabolic and diabetic research in the Department of Nutrition at Case Western Reserve University. She is experienced in using various analytical instruments to perform drug development and metabolic research. In the Stapleton Lab, Sharon is responsible for LCMS system maintenance, method development and sample analysis to support students and lab projects. Her research gear is switched from how to eat healthier (Nutrition) to how to live healthier (Environment). She is involved in exploring the effect of flame retardant chemicals on both the environment and human health. As two boys’ mom, Sharon loves to cooking delicious foods for her family. She enjoys Zumba and hiking with her friends.

Dr. Nicholas J. Herkert, Ph.D |  Research Project Manager

Nick grew up in Petersburg Il, a small town in the central Illinois before making the long trek north to attend the University of Iowa as an undergraduate. Early on as an undergraduate, Nick began working in an analytical chemistry lab under Dr. Keri Hornbuckle. This was what first piqued Nick’s interest in characterizing the chemical mixtures people are exposed to throughout their lives and inspired Nick pursue a degree in Environmental Engineering. During his senior year, Nick enrolled in a joint undergraduate/graduate degree program under Dr. Keri Hornbuckle. Nick graduated from the University of Iowa with a BSE in Civil Engineering and a Certificate of Sustainability in 2015, and immediately returned to continue working on his Ph.D. Nick graduated in 2018 with a Ph.D. in Environmental Engineering, after successfully completing his thesis entitled Development of the Polyurethane Foam Passive Air Sampler for Novel Applications in Ambient Air Across the Globe.

Nick joined the Stapleton Lab in June 2018 as a Postdoctoral Associate, where he has continued to work to better understand the exposures people experience in their everyday lives, the potential health effects form these exposures, and the subsequent sources for these exposures. Nick first started by putting is analytical chemistry background and modeling background to work on developing a high throughput methods for both target and untargeted analysis of silicone wristbands. This work is largely done on a high-resolution accurate mass (HRAM) Q Exactive GC hybrid quadrupole-Orbitrap GC-MS/MS system, of which Nick is the gatekeeper. The ultimate goal of the work is to provide a quantitative analysis of a suite of target SVOCs, as well and semi-quantitative analysis of suspect chemicals, which will provide a much broader picture of what people are exposure to in their day-to-day lives. Nick has also worked to study the levels of PFAS compounds in local utilities and characterize the effectiveness of various in-home filters at removing such compounds. When not in the lab, Nick is often out running to train for a half or full marathon, out hiking to take pictures, or laying on the couch watching movies with his wife, two dogs, hedgehog, and gecko.

Dr. Ellen Cooper, Ph.D | Research Scientist

Ellen Cooper is originally from Oxford, Pennsylvania. She received her BS (1994) in Plant Science from the University of Delaware, and her MS (1996, Thesis: “Chelate-assisted remediation of lead contaminated soils”) in Plant and Soil Sciences also from the University of Delaware, where she worked as an associate in research until 1998.

In 1999, she came to Duke University Nicholas School of the Environment to work for Dr. Dharni Vasudevan, and later Dr. Andrew Schuler (formerly of Dept. Civil and Environmental Engineering), and eventually matriculated and received her Ph.D. in Environmental Sciences (2009, Dissertation “Biodegradation of a Sulfur Containing PAH, Dibenzothiopene, by a Mixed Bacterial Community.”) under the advisement of Dr. Heather Stapleton, for which she worked as a post-doctoral associate until 2011. Her current research interests include analyzing environmentally important organic compounds in a variety of matrices including sediments, water, biological samples and polyurethane foam and using high resolution mass spectrometry to characterize chemical composition of a variety of samples types.

Apart from scientific research, Ellen actively pursues music, plays a variety of instruments, and studies early music notation and theory from the Medieval and Renaissance periods. She is an avid runner and hiker, a part-time freelance landscape gardener, and is kept firmly in line by three feisty black kitties.

Rachel Smith | Program Coordinator 

Rachel joined the Stapleton Lab in 2019 to assist with a project funded by the National Institute of Environmental Health Sciences. This grant established the Duke Environmental Analysis Lab (DEAL), which will serve as a hub to support national environmental health research, and help develop new methods to measure inorganic and and organic chemical contaminants in human and environmental matrices. Rachel has a B.S. in Environmental Science from the University of Missouri (2009), where she grew a keen interest in water conservation. She worked as a wildlife biologist and program coordinator for six years on various estuary and terrestrial habitat restoration projects in Kauai, Hawaii. Post-island life, Rachel pursued her passion in environmental health and policy, and earned a Masters Certificate in Environmental & Water Conflict Management at Oregon State University (2017).

Rachel oversees the administrative needs for the lab, assists with findings reports, and manages the outreach and communications needs for DEAL and the PFAS projects. Outside of work she enjoys woodturning, bird watching, gardening, and listening to jazz.

Stephanie Hammel Ph.D | Postdoctoral Research Associate

Stephanie is a postdoctoral research associate working with Dr. Kate Hoffman. She is currently working on characterizing environmental exposures in young children and determining how these may impact children’s health outcomes, particularly immune function. Originally from Southern California, Stephanie moved to Durham to join the Stapleton Lab as a PhD student in 2014. She successfully defended her dissertation in 2019, which focused on validating the use of silicone wristbands as exposure metrics for various semi-volatile organic compounds (SVOCs). Her research interests also include identifying sources and routes of exposure for SVOCs commonly used in consumer products. Prior to her time at Duke, Stephanie was a graduate student intern with the California Department of Toxic Substance Control (DTSC) where she assisted with the implementation of their Safer Consumer Products Regulations. Stephanie received B.S. degrees in Chemistry and Biological Sciences from the University of California, Irvine in 2012 and a Master’s in Public Health (MPH) degree in Epidemiology also at UC Irvine in 2014. When she’s not in lab or analyzing data, Stephanie is likely on Google flights looking for her next travel destination, learning to cook something new, training for long race or mountain trek, or hanging out with her dog, Iris.

George Tait | Research Technician II

George, who is half British, moved to Durham from Vermont in 2018 for a Bull City girlfriend. Having completed both his undergrad and Masters in Manchester England he worked for Cascade, a company whose mobile laboratories ran investigations for the EPA, local governments and private clients. There he learnt the intricacies of GCMS instrumentation and environmental analysis. George likes tea, clouds and a well sharpened pencil and has, having joined Duke, discovered that basketball is actually quite a good sport worth his time!
George works on our PFAS projects, mainly collecting and testing water samples from around the Triangle area.


Emina Hodzic | Research Technician II

Emina comes from the small, yet very beautiful, country of Bosnia and Herzegovina. She received her Bachelor of Science degree in Chemistry from Methodist University in Fayetteville in 2014. Shortly after her graduation, Emina joined Shealy Environmental Services where she worked as an Analyst in their analytical lab. Her main responsibility was testing for volatile organic compounds found in water and soil samples. Emina joined the Stapleton lab in August 2015 and is currently working as a research technician for the Analytical Chemistry Core within Duke’s Superfund Research Center. Her main responsibility is analysis of environmental samples (sediments/soils, tissue samples, aqueous solutions, etc.) for organic contaminants and their degradation products; however, her “favorite” responsibility is cleaning the GC/MS source. Outside the lab, Emina enjoys sleeping, reading, yoga, learning new languages and trying food from different cultures.

Duncan Hay | Research Technician II 

Duncan grew up in western NC, near Asheville and moved to Durham after graduating from Elon University in 2017 with a BS in Chemistry and a minor in Spanish.  Upon graduation from Elon, he has worked for the State of North Carolina in pharmaceuticals, quality testing diesel and kerosene.  Duncan joined the Stapleton Lab in November 2019 to help support sample analysis for the Duke Environmental Analysis Lab (DEAL) and the Human Health Exposure Analysis Resource (HHEAR) program.  When not in the lab, Duncan enjoys camping, hiking, golfing, and woodworking.


Sam Hall | PhD Student

Sam is a native North Carolinian originally from Winston-Salem, NC. She graduated from Duke University in 2015 with BS degrees in Biology and in Environmental Sciences. She came back to Duke University in 2017 through the Integrated Toxicology and Environmental Health Program (ITEHP). Prior to starting grad school, Sam worked in labs and groups at Duke, NIEHS, and the Environmental Working Group on various environmental toxicology projects, including studying flame retardants, mitochondria, chromium, and Parkinson’s disease.

In the Stapleton Lab, Sam is researching per- and polyfluoroalkyl substances (PFAS) and contaminants in the placenta for her thesis. When not in the lab, Sam is likely taking care of her plants or painting her nails.

Jessica Levasseur | PhD Student

Jessica grew up in Eastern Connecticut, though has spent the past 10 years moving around the US. She received her bachelor’s degree in Chemistry: Biochemistry from Colby College in 2010, where she graduated with honors and ACS certification. After some time working at a women's health center in Central America, she spent two years working in the development laboratories of a pharmaceutical company. Jessica graduated in 2015 from the University of Washington’s Department of Environmental and Occupational Health Sciences with an MS in Environmental Health (Risk Emphasis). Completing this degree led her to Durham, NC, where she spent three years consulting for the federal government. Her work included developing and maintaining exposure models for both residential chemical exposures and outdoor air pollution as well as evaluating the human health effects and risk associated with particular chemicals and microbial toxins. Jessica joined the Stapleton Lab in 2018, where she has since been investigating the association between particular household products and human exposure. Her research interests include quantifying non-occupational exposures, particularly those associated with the dermal pathway. Outside of the laboratory Jess enjoys travelling with her husband, cooking, being outside, and reading. 

Matt Ruis | PhD Student

Matthew grew up in the Hudson Valley of NY and attended Marist College where he studied environmental science and biology. In 2015, he came to Duke through the Integrated Toxicology and Environmental Health Program. After completing his rotations, he joined the Stapleton lab in 2016. Matthew’s dissertation work focuses on how prenatal exposure to a class of flame-retardant chemicals, known as polybrominated diphenyl ethers (PBDEs), accumulate in the placenta and how they cross the placenta barrier. He also investigates the mechanisms by which they can disrupt thyroid hormone system during pregnancy. His first project was in collaboration with investigators at North Carolina State University where pregnant Wistar rats were orally dosed with a mixture of PBDEs to understand their toxicokinetics. He found that PBDES were accumulating at higher levels in the fetal portion of the placenta relative to the maternal portion. He also observed effects on thyroid hormone regulation in the dam and tissue-specific differences in thyroid hormone levels in the placenta. These findings led him to his next project where he used an in vitro placental cell line to investigate more mechanistically why and how PBDEs were accumulating at higher levels in the fetal portion of the placenta. He is also currently looking at flame retardant accumulation in placentas from fraternal twins and if the sex of the fetus influences the degree of accumulation. When not asking pregnant women for their placenta, Matt spends his free time tending to his 20+ chickens, 2 rescue pigs and fostering dogs.

Kirsten Overdahl | PhD Student

Kirsten is originally from Fort Wayne, IN and came to Duke after five years in Northfield, MN. She attended St. Olaf College, where she received a BA in Chemistry (2015) and a BM in Vocal Performance (2016). Kirsten is in the Toxicology and Environmental Health program at Duke and, after an engaging rotation in the Stapleton lab, is excited to be an official lab member; she is also a member of the Ferguson Lab (Duke CEE). Trained primarily as an analytical chemist, Kirsten’s work in the Stapleton and Ferguson labs has inspired her to consider how best to create comprehensive, iterative workflows for predicting what might happen when humans are exposed to chemicals in the environment. Kirsten plans to explore best practices to move between chemical structure identification, chemical behavior assessment, and hormone and immune response studies. Currently in the Stapleton lab, she is examining azobenzene-based disperse dyes and investigating different analysis techniques to pinpoint the types of hormone or immune activity these dyes might elicit in the body. Outside of the lab, Kirsten can be found singing in Duke Chapel with the Vespers ensemble, running or training for a race, and exploring North Carolina’s beautiful state parks and delicious foods.

Taylor Hoxie | PhD Student

Taylor earned a B.S. in Chemistry with a concentration in biochemistry at Wake Forest University in 2017. As an undergraduate she conducted research in organic chemistry synthesizing novel PI3K inhibitors for prostate cancer treatments. Prior to starting grad school at Duke, she spent two years working at the Duke Human Vaccine Institute (DHVI). At DHVI, she genotyped human and non-human primate samples to characterize Fc gamma receptors and their role in HIV pathogenesis. During her time at Duke, she hopes to pursue research on per- and polyfluoroalkyl substances (PFAS), explore exposure science and complex mixtures, and implement analytical chemistry techniques. Taylor is working on the PFAS UNITEDD project on Aim 2 (evaluate uptake of PFAS into local foods through contaminated soil and water) and Aim 3 (assessing the relative role of the indoor environment in determining exposure for communities impacted by differing sources of PFASs - characterizing PFAS chemicals in dust, air and wristbands). Outside of school and the lab she likes to play with her dog Cocoa, enjoys outdoor activities, reading and traveling.

Shaza Gaballah | PhD Student

Shaza is a second year PhD student in the Stapleton lab. Growing up, Shaza lived all over the triangle, and received her B.S. in Biology with minors in Chemistry and Medical Anthropology from UNC Chapel Hill in 2017.  After graduating, she completed a two-year fellowship at the US EPA, where she investigated how exposure to GenX and other per- and polyfluoroalkyl substances (PFAS) impacts developmental toxicity and developmental neurotoxicity in zebrafish. Her work identified shared toxicity phenotypes in zebrafish based on varying PFAS chemical structures. Shaza’s work at the EPA was her first time delving into toxicology, and she loved it so much that she applied to Duke’s environmental toxicology program.  Shaza is currently using BeWo cells to study how brominated flame retardants cross the placenta and impact fetal growth and development; she hopes to expand this work to study how PFAS may be crossing the placental barrier and to understand their potential involvement in endocrine disruption. When she’s not in the lab, Shaza loves cheating at crosswords, hiking in Durham, and hanging out with her cat, Olive.



Former Lab Members

Undergraduate StudentsMaster's StudentsPhD StudentsResearch TechniciansPostdoctoral Research Associates
Cara Peters (2020)Qianyi Xia (May 2019)Stephanie Hammel (July 2019)Amelia Lorenzo (2014-2017)Dr. Chris Kassotis
Deanna Badger (2016)Allison Killilus (May 2017)Allison Phillips
(May 2019)
Yu-Ping Huang
Dr. Erin Kollitz
Spencer Pecha (2015)Bridget Flaherty
(May 2017)
Chris Leonetti
(July 2016)
Spencer Pecha
Dr. Tara Rafferty
Tom Neufeld (2015)Meredith Frenchmeyer (May 2017)Mingliang Fang
(May 2015)
Albert Chen
Dr. Craig Butt
Amy Trey (2015)Rochelle Cameron
(May 2016)
Laura Macaulay
(July 2015)
Kylie Rock
Dr. Wu Dong
Nikalesh Raju (2013)Rebecca Siebenaler
(May 2016)
Laura Dishaw
(May 2015)
Alex Keller
Dr. Dongli Wang
Katharine Gifford (2014)Peyton Ward (May 2015)Simon Roberts
(August 2014)
Katie Douglas
Matthew Mrozek(2012)Genna Gomes (May 2015)Pam Noyes (May 2013) Sarah Eagle
Alex Keller (2012)Brit’Ny Hawkins
(May 2014)
Elizabeth Davis
(May 2013)
Shannon Kelly
Olay Ayinksku (2011)Zhuoyuan Chen
(May 2014)
Jenifer Fuh (2011)John Misenheimer
(May 2013)
Stephen Lubin (2008)Lauren Gloeckler
(May 2013)
Aminah Cherry (2007) YuChun Kuo
(December 2011)
John Blades (2007) Josie Bamford (May 2007)



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