Research Overview & Impact

Dr. Linda Lee has garnered a distinguished reputation nationally and internationally for her persistent efforts to unravel the complex dynamics of a broad spectrum of environmental contaminants. She is a leader in environmental chemistry, fate, exposure effects, and remediation of contaminants that remain in the environment long after their use, such as industrial solvents, pesticides, and metals. For two decades, she has pioneered research on emerging “compounds of concern,” including hormones and pharmaceuticals, as well as a large infamous family of compounds called per- and polyfluoroalkyl substances (PFAS). PFAS are now widely recognized for their potentially harmful human health or ecological health effects and their virtually infinite persistence in the natural world, thus garnering the name “forever chemicals.” In addition to her distinguished research record, Dr. Lee is a highly regarded environmental professional for her three decades of notable work in teaching, mentoring, and service.

PFAS are a unique and versatile family of synthetic chemicals with a huge commercial market worldwide. They are used in manufacturing processes, heat-stable lubricants, fire-fighting foams, and a myriad of consumer products to impart stain, water or heat resistance, such as textiles, carpets, cookware, and even cosmetics and haircare products, among countless other home goods.
Despite the advancements PFAS have brought to modern lifestyles, they have also brought highly complex environmental and human health challenges. They persist in the environment permanently, and they bioaccumulate and biomagnify in biota, leading to high levels in foods consumed by humans. They are also quite mobile, leading to contamination of drinking water sources and a globally ubiquitous presence. They have been associated with numerous health issues, such as cancer, birth defects, compromised immune systems, and more, in both humans and animals.

Human health effects initially focused on perfluorooctane carboxylic acid (PFOA), prompted by cancer and baby deformities observed in people working at DuPont, where PFOA was produced and used to make TeflonTM. In the early 2000s, perfluorooctane sulfonate (PFOS) was discovered unexpectedly in mammals in the Arctic - a region that is thousands of miles from human population centers - and many global PFAS monitoring studies were begun. These studies revealed PFAS in human blood serum, biota, soil, water, municipal effluent, landfill leachate, and land-applied biosolids (treated sludge from wastewater treatment plants). In the years that followed, scientific, regulatory, and community concerns have risen dramatically.

Dr. Lee’s research group was among a handful of groups in academia in the US that began focusing on developing the science for studying PFAS behavior, beginning in the mid-2000s. At that time, Dr. Lee pivoted much of her research to focus on PFAS environmental occurrence and sorption and degradation (fate) in soils. A few years later, she began the challenge of examining options to treat PFAS-contaminated soils and water, which has now been expanded to biosolids. The early stages of PFAS research required Dr. Lee’s group and others to develop and evaluate approaches for extraction and quantification of PFAS as well as mole balance assessments. Over time this included optimizing identification and quantitation of increasingly-lower concentrations (parts-per-trillion in water and parts-per-billion in solids) of multiple PFAS (parent and byproducts) found in water, soils, sediments, and biota. The environmental dynamics of these complex mixtures required a deep understanding of solubility, sorption, and abiotic/biotic biotransformation of PFAS. Dr. Lee’s earlier fundamental research program, which studied the behavior of a different class of compounds of concern in complex waste mixtures, provided the expertise to develop new methods and approaches for complex mixtures of PFAS in a variety of environmental matrices.

Dr. Lee’s group began evaluating the solubility, sorption, and biotransformation by general soil microbes of fluorotelomer alcohols (FTOHs), which were suspected (now confirmed) precursors to the more mobile perfluoroalkyl carboxylates, including PFOA. The group also confirmed the biotransformation to PFOS of a common 3M-developed PFAS-based stain-repellent. These early findings from Dr. Lee’s group contributed to US EPA’s efforts to reduce FTOH and its residuals in commercial products and to launch a phase-out of long-chain PFAS (greater than 6 carbons), which are prone to accumulate in the environment. Additionally, engineering firms and the military, which use biotransformation strategies to degrade chlorinated solvents and nonpolar organic chemicals such is in jet fuels and gasoline present in our groundwater from anthropogenic activity inadvertently, realized they were likely exacerbating the PFAS problem by hastening the transformation of larger PFAS to smaller, more mobile, biologically recalcitrant, and toxic perfluoroalkyl acids (PFAAs).
Subsequently, Dr. Lee began to investigate remediation technologies for on-site cleanup of groundwater required at over 500 military sites where PFAS-containing foams had been used for decades. She has received a patent for one of her PFAS remediation technologies and recently received funding to do a site-demonstration with an environmental consulting firm at an Air Force base in 2022 using this technology as part of a treatment train.

She has also collaborated with Purdue faculty in Forestry and Natural Resources to evaluate PFAS impact on amphibian development. She formed a similar collaboration with Purdue faculty in Health Science to examine the neurological and immunological impacts on humans. Dr. Lee also frequently works with toxicologists to provide her expertise on exposure contaminant pathways, effects, bioavailability, and biomagnification.

Recently, Dr. Lee has placed her attention on three research directions: (1) evaluating the fate of PFAS and other unregulated organic compounds (UOCs) in biosolids after being land- applied as a soil amendment; (2) changes in PFAS and UOC fate after-treatment by municipal water resource recovery facilities (WRRF; previously called wastewater treatment plants); and (3) remediation and mitigation strategies. Dr. Lee’s existing interdisciplinary collaborations are well-positioned to uncover meaningful findings in these areas. Most of her current research direction is focused on addressing pressing concerns on if and how much re-use of our wastes as soil amendments are contributing significantly to PFAS and UOC contamination of drinking water sources, which is imperative towards appropriate management and regulatory decisions that have to balance human and ecological health, soil health and climate change risks.

Dr. Lee’s research on understanding and predicting contaminant behavior, particularly in regards to her PFAS research, and her national reputation as a thought leader in this area have led to frequent requests to share her research, plan research initiatives, lead workshops, provide input on management guidelines, and serve as an expert witness. She is contacted weekly by government agencies, environmental management units, municipalities, industry, legal companies, the public, and news media in regards to chemical use and persistence, site assessments, remediation strategies, analytical knowledge, biosolids applications, wastewater irrigation, and well water and groundwater pollution concerns.

Dr. Lee has given 37 invited talks since 2019, notably the keynote address at the Emerging Contaminant Conference, as well as for the California Water & Environment Association, the Michigan Water and Environment Association, and a group of Indiana state legislators. Dr. Lee also participates in planning future research initiatives. She was part of the first National Academy of Sciences Environmental Health Matters Initiative and the first Society of Environmental Toxicology & Chemistry PFAS Focus Topic Meeting. She now serves as a National Biosolids Project Advisor and on the EPA Science Advisory Board’s Biosolids Panel, in addition to serving as an expert on chemicals in our products. Dr. Lee co-led two Water Resilience workshops in Indiana to empower local emergency planning committees as they prepare response plans to potential contamination of water supplies. She also co-facilitated an event with the Metropolitan Water Reclamation District of Greater Chicago on innovative ways to mitigate the risks from pollutants and to improve urban soil quality.

As Dr. Lee’s research recognition continues to grow, she has been asked to serve as an expert reviewer, with PFAS being the focus of most of the requests she has accepted recently. For example, Dr. Lee served as an expert for the State of California Department of Toxic Substance Control in prioritizing three types of products for improved standards under the Safer Consumer Products program: PFAS-containing carpets, PFAS use in converted textiles and leathers, and PFAS in food plant fiber-based food packaging. She also served as an Eastern Research Group expert reviewer for EPA’s draft Emerging Issues in Food Waste Management: Persistent Chemicals Report. In earlier years, she served as an EPA peer consultant for two different site evaluations involving industrial discharges of PFOA and ascertaining the extent of drinking water contamination.

Dr. Lee’s international impact has come in the form of international invited talks (approximately 20), mentoring, and academic program reviews. She was invited to speak on the topic of environmental hormones and their impact on fish populations at the International Symposium on Chemicals Risk Prediction and Management in Xiamen, China, and most recently by University of Tübingen for their PFAS Workshop. She was sought by the University of Copenhagen to evaluate their Department of Plant and Environmental Science academic program and she hosted visiting faculty and PhD scholars from China, India, Pakistan, and Nigeria. Dr. Lee also led a USAID-funded effort to improve infrastructure at the University of Peshawar, a public research university in Pakistan, as well as to provide recommendations on improving water quality in the Swat and Kabul river systems. As part of this effort, Dr. Lee mentored 2 MS and 3 PhD Pakistani students.

Dr. Lee has demonstrated a sustained and diverse funding portfolio during her 28 years at Purdue, with over $18.5M to date from federal/national agencies (e.g., USEPA, NSF, USDA-HEC, USDA-AFRI, USDA-NNF, USDA-BARD, USAID, NAS, AFCEC, DOD-SERDP, WRF), state agencies (e.g., INDOT, IDEM, MI DEQ), and industry. Currently she has grants totaling $2.85M for which she serves as PI, and another $2.61M as co-PI. The PFAS-related interdisciplinary partnerships Dr. Lee frequently initiates have generated external funds coming to Purdue of $6.5M in the last 5 years, with 5 additional proposals in the amount of ~$3.21M currently in review. Examples of these interdisciplinary partnerships include: NIH (Cannon, PI, $409K), SERDP-2626 (Sepulveda, PI, $2.46M), SERDP-1537 (Hoverman, PI, $1.3M), and MI-DNR (Hoverman, PI, $115K), among others. Dr. Lee has received Purdue Seed for Success awards for the past four years (2017, 2018, 2019, 2020), which recognizes investigators who obtained external sponsored awards of $1 million or more annually.

In addition, she recently received awards for her research: 2019 Water Environment Research Paper of the Year, 2020 Journal of Hazardous Material Paper of the Year, and the 2021 American Society of Agronomy (ASA) Environmental Quality Research Award, which recognizes contributions that may improve the quality of soil, water, and air resources. For nearly two decades, she has been a Fellow of the ASA and the Soil Science Society of America.

Many of Dr. Lee’s recent accomplishments related to PFAS were made possible by her early discoveries on environmental fate and transport of ionogenic contaminants, as well as environmental dynamics of legacy contaminants such as coal tar.

Environmental Fate & Transport of Ionogenic Contaminants

Dr. Lee’s early research program at Purdue concentrated on broad chemical classes of contaminants, namely ionogenic organic compounds (i.e., organic acids and bases). Ionogenic compounds are common environmental contaminants because of their heavy use in industrial manufacturing and also as herbicides, fungicides, pesticides, pharmaceuticals, and personal care products. They have a high potential to be toxic to ecological receptors, either by design—as in the case of pesticides for a specified pest—or inadvertently, to nontarget plants and animals.
Dr. Lee’s insightful examination of the chemistry impacting solution and sorbent phase interactions of ionizable organic chemicals is fundamental to predicting their transport and bioavailability. Her research within each chemical class of contaminants required increasingly sophisticated analytical techniques to carefully document complex biogeochemical pathways, whose byproducts themselves are also of significant environmental/ecological concern. Her work in this area led to successful algorithms for predicting sorption of organic acids and bases. This work also positioned her well to facilitate bringing together a team that was recently awarded a 2.26M EPA National Priority grant on fate of UOCs, of which most are ionogenic, after land-application of biosolids. This award parallels an award she received as PI in 2020 focused on PFAS fate after land-application of biosolids and wastewater irrigation.
Dr. Lee also demonstrated that bound residue assessments based on organic solvent extractability may be in error for many ionogenic compounds, including some pesticides. Her findings, including those involving soil-water distribution coefficients, desorption rates, irreversibly bound fractions, and abiotic and microbial transformation, have aided the EPA in improving their assessments of contaminated sites and in refining regulations for new chemicals.

Likewise, hormones, as well as some pharmaceuticals and personal care products that can contribute to endocrine disruption, also continue to be an EPA priority research area. Dr. Lee was funded through an EPA STAR grant and a USDA Water & Watersheds grant to evaluate hormone release and fate from land-applied manure and animal waste-derived lagoon effluent, particularly from confined animal feeding operations, and their subsequent effects on aquatic communities. She presented her research results in a wholistic context, providing an appropriate perspective on these land-application practices. As a result, no additional regulations were placed on farmers, which had been a major concern in Indiana and across the US. Her work on hormone sorption, release, and transport also included demonstrating a “chemostatic” behavior for hormones, nitrate, and phosphorus in the ditch/stream network around agricultural fields and that 80% of the chemical discharges to tile-drained fields occurs during the 20% highest intensity rain events, thus limiting many of the traditional best managements practices used to protect surface water quality. In addition, Dr. Lee’s group demonstrated hormone accumulation and reverse transformation processes in sediments, that could lead to serving as a long-term chronic source of impairing water quality.

Environmental Dynamics of Legacy Contaminants

Dr. Lee simplified the predictive tools for identifying major processes controlling environmental chemodynamics; this was demonstrated in her research on complex waste matrices. She proved that a simple approach - a partitioning model, derived from mole-fraction solubility and assuming ideal behavior - could predict chemical release from complex organic waste, including diesel fuel and coal tar.
The partition model she developed provided reliable estimates of polyaromatic hydrocarbon (PAH) source concentrations in groundwater, with only information on waste composition. She extended this work to soils and sediments contaminated by coal tar, a waste product from coal gasification at manufactured gas plants. Her research showed that organic contaminant release from tar soils/sediments exhibits slow desorption rates, large contaminant soil-water distribution coefficients, and small bioavailable PAH fractions, indicating that PAH concentrations released to the groundwater would be smaller than initially expected. These findings directly impacted whether or not active remediation was needed and predicted whether a particular remediation technology would likely be successful. The utility industry incorporated Dr. Lee’s findings to estimate the source term (concentrations being released) needed to make site specific assessments regarding the likelihood of groundwater contamination from coal tar disposed in the subsurface at old manufactured gas plant sites, of which at least 2,000 have been identified in the United States.

From this work and the respect garnered from the utility industry, she involved her Purdue colleagues from Civil Engineering to address coal tar issues from historic sites along the Calumet River, a heavily industrialized waterway near Chicago. Her successful collaborations with her utility industry partners led to additional work to understand and predict the behavior of arsenic, selenium, and boron in ash ponds and landfills. The latter research aided in utility management decisions regarding fly ash management and use as well as landfill site selection.