Last fall, Dr. Tracie Baker, an associate professor in the department of environmental and global health at the University of Florida College of Public Health and Health Professions, embarked on a historic scientific expedition of the Florida Everglades to better understand humans’ impact on the world’s largest subtropical wilderness. Baker and three teammates fought mosquitoes, thick sawgrass and exhaustion to retrace a 130-mile canoe journey first completed by explorer and scientist Hugh de Laussat Willoughby in 1897.
The water samples Willoughby collected on his coast-to-coast trek became the baseline for the Everglades’ water chemistry and his charts led to the first accurate maps of the region.
As the lead scientist for the 21st century Willoughby Expedition, Baker collected more than 100 water samples to evaluate some of the same compounds Willoughby did, as well as substances that didn’t exist then, including microplastics, perfluoroalkyl and polyfluoroalkyl substances (also known as PFAS), pesticides and pharmaceuticals, as well as antibiotic-resistant genes and environmental markers of endangered and invasive species.
The samples are currently being analyzed in UF laboratories, but even without lab tests, Baker observed evidence that the detritus of humans’ daily life has made its way into even the most difficult to reach areas of the Everglades. Case in point: three balloons floating through the waters many miles and worlds away from the nearest birthday party, retirement celebration or New Year’s bash.
Baker is one of several faculty members in the PHHP department of environmental and global health who are working to evaluate contaminants circulating in Florida’s fresh and coastal waters and the threats they may pose to human, animal and environmental health.
Protecting Florida's precious natural resource
With more than 30,000 lakes, 700 springs, 12,000 miles of rivers and streams and 1,350 miles of coastline, there are few states that match Florida for its relationship and dependence on water.
For this core group of PHHP researchers, who are also members of UF’s Center for Environmental and Human Toxicology, Water Institute and Emerging Pathogens Institute, there is an urgent need to identify emerging contaminants in Florida’s waters, assess their impact and use that data to inform local, state and federal agencies. To accomplish this, they collaborate frequently with colleagues at the UF College of Veterinary Medicine and the UF Institute of Food and Agricultural Sciences.
“As environmental toxicologists, we seek to understand how environmental contaminants may impact aquatic ecosystems, and how these impacts may influence the health of both aquatic organisms and humans,” said Dr. Tara Sabo-Attwood, professor and chair of the department of environmental and global health. “So if we observe health effects on aquatic critters, then it is likely that people are being exposed as well and could be at risk for health effects. Or, if aquatic organisms, such as fish, are contaminated and we eat those fish, then people are exposed that way. The aquatic environment serves a vital role in ecosystem and human health.”
Sabo-Attwood’s own research has focused on several chemical pollutants and nanomaterials in aquatic settings. Nanomaterials are teeny bits of matter used in hundreds of household and industrial products and they can contaminate soil, air and water. Experts do not yet have a good handle on how these bits of matter behave in aquatic systems and their potential to cause toxicity to wildlife.
Work by Sabo-Attwood and her department of environmental and global health colleagues provides important contributions to the field of environmental risk that, in turn, help to guide public policy. As a member of the Environmental Protection Agency’s Federal Insecticide, Fungicide and Rodenticide Act Scientific Advisory Panel, Sabo-Attwood knows just how valuable these data are for decision making.
“Regulatory agencies use risk assessments to establish safe levels of exposure to contaminants in our drinking water, food or air,” she said. “However, risk assessments require adequate data to characterize contaminant exposure and potential toxicity. Our faculty are leading the way in providing useable data for these types of assessment frameworks and other decision-making tools.”
Generating new data for stakeholder decision making
In several projects, Dr. Joseph Bisesi, an assistant professor of environmental and global health, is examining the effects and toxic mechanisms of contaminants such as nanomaterials, plasticizers and pharmaceuticals, as well as legacy contaminants of concern, including pesticides and heavy metals, on aquatic species.
“In general, there’s a dearth of data on a lot of the chemical contaminants in our waters,” Bisesi said. “Much of the work I do is focused on what are called emerging contaminants, which are pollutants that we know little about. We know they’re in our water, but there’s not necessarily enough information to make informed decisions about risk to public health and aquatic organisms. Even legacy contaminants that we know more about still present challenges to stakeholders due to missing or incomplete data. The goal of my research program is to provide that kind of data.”
Bisesi has two projects focused on generating new data that can be used by both government and private stakeholders to make more informed decisions about chemicals in aquatic systems. Working with the Florida Fish and Wildlife Conservation Commission, he is examining whether herbicides used to treat aquatic invasive plants that clog Florida waterways may have any effects on largemouth bass, a recreationally and economically important species for the state.
In a second project, Bisesi is collaborating with industry partners to generate data to improve the biotic ligand model, a model used by both government and private sector to predict site-specific heavy metal toxicity in waterways. Bisesi is integrating multiple variables of episodic exposure to ensure the model provides accurate estimates that can be used to mitigate risk to aquatic systems.
“These projects are two examples of how we can work with both government and industry to increase our understanding of aquatic contaminants and potential associated toxicity, with the goal of making the best informed decisions possible,” Bisesi said.
Using AI to understand emerging contaminants
Perfluoroalkyl and polyfluoroalkyl substances (PFAS), are the “DDT story all over again,” Sabo-Attwood says, because these chemicals can persist for years and years in the environment.
This class of more than 5,000 “forever chemicals” are commonly used in coatings and products that resist heat, oil, stains, grease and water. They’re found in everything from waterproof fabric, to nonstick pans to eye makeup. According to the Centers for Disease Control and Prevention, PFAS are considered a health concern because many PFAS do not break down in the environment, can contaminate drinking water and have been known to buildup in fish and other wildlife.
Dr. Zhoumeng Lin, an associate professor in the PHHP department of environmental and global health, is an expert in the use of computational technologies, such as machine learning and artificial intelligence approaches to support human health risk assessments of environmental chemicals. Lin and his team build physiologically-based pharmacokinetic, or PBPK, models in order to describe the absorption, distribution, metabolism and excretion of a chemical in the body using mathematical equations. PBPK models offer several advantages over traditional methods, including the ability to analyze different types of toxicity datasets simultaneously along with the power to extrapolate across many species and exposure scenarios. The result is a more accurate dose-response analysis without the need to conduct toxicokinetic experiments in animals.
Lin is currently applying PBPK models to perfluorooctane sulfonate, or PFOS, one of the substances among the PFAS class of chemicals. Multiple studies on this particular chemical offer a large amount of toxicokinetic and toxicity data sufficient to build reliable PBPK models.
Using this approach, findings published in 2019 by Lin and Dr. Wei-Chun Chou, a research assistant professor in the department of environmental and global health, suggested that the then-U.S. Environmental Protection Agency standards for safe exposure to PFOS in drinking water were too high.
“Together, our research and recommendations from the European Food Safety Authority suggested that the EPA-recommended reference dose may need to be re-visited, based on the latest research findings,” Lin said. “Consistent with our findings, on March 14, 2023, the U.S. EPA announced new drinking water regulations for six PFAS, including PFOS.”
Lin is gratified to know that his models are drawing attention from regulatory agencies and are discussed in the latest European Food Safety Authority risk assessment report, but there is much more work to be done, he said. PFOS is just a single chemical out of thousands of PFAS.
“We need to extrapolate our models from PFOS to other PFAS chemicals. We also plan to incorporate machine learning and artificial intelligence approaches into our PBPK models to build more robust models,” Lin said. “We are actively applying for external funds to support this line of research. We hope to develop better tools to support public health decision-making on this important group of environmental contaminants.”
Fish models as sentinels for human health
In Tracie Baker’s lab, tiny, colorful zebrafish may hold the key to understanding how exposure to PFAS, lead, endocrine disrupting chemicals and other pollutants may affect human health across multiple generations.
Baker is a leader in the use of the zebrafish model for trans-generational toxicity studies. Surprisingly, these little fish share a lot in common with humans, including more than 80% of genes associated with human diseases. And because of the species’ ability to develop quickly, it may only take months for researchers to learn how an environmental exposure to a breeding fish pair affects their progeny several generations down the line.
In a current National Institute of Environmental Health Sciences-funded study, Baker is using zebrafish to better understand the mechanisms of environmentally-induced infertility caused by endocrine disrupting chemicals. These substances, which are found in products such as detergents, flame retardants, food, toys, cosmetics and pesticides, can interfere with the body’s hormones. A single exposure to an environmental contaminant during development may be all it takes to affect fertility in adulthood and later generations.
“We knew these chemicals could cause an effect as an exposure happens. And then it was a big deal to realize that 20 years later, even if you didn’t see an effect during the exposure the effect could show up at that time,” Baker said. “Now we are finding that two, three generations later you’re still seeing effects. Trying to figure out the mechanism by which that could be happening and if there are differences across chemicals is really important.”
Baker’s previous research has shown that endocrine disrupting chemicals can produce changes in the testicular cell genome and epigenome. The new study is expected to shed more light on biomarkers and pathways of endocrine disrupting chemicals so that investigators can develop strategies to prevent and treat reproductive disorders.
Bisesi is also using zebrafish in ongoing research examining how exposure to plasticizers may influence obesity by impacting the gastrointestinal system. Plasticizers are chemicals added to numerous consumer products, including plastic water bottles, food packaging, pipes and more, and they can leach into drinking water and food. Multiple lines of evidence suggest they may be obesogens, or chemicals that contribute to obesity.
“The gastrointestinal system is the first line of defense for food and water borne contaminants,” Bisesi said. “So when we’re drinking water or consuming food that may contain these plasticizers, the gastrointestinal system is the first part of the body to be exposed. We’re interested in how these exposures impact the gastrointestinal system of humans and its microbiome.
“Our hypothesis is that if plasticizers are impacting the gastrointestinal system and its associated microbiome, that may impact our ability to properly metabolize and store lipids, potentially leading to obesity.”
Effects of a changing climate
Florida’s beloved wild oysters have nearly disappeared in many coastal areas. In 2020, the Florida Fish and Wildlife Conservation Commission voted to suspend oyster harvesting for five years in Apalachicola Bay, once the source of 90% of oysters served in Florida and distributed across the nation. The hope is this fishery closure will allow time for wild oyster populations to regenerate.
Habitat sustainability is among the complex factors involved in wild oyster decline, exacerbated by climate change, which affects water flow and salinity in oyster habitats.
“Oysters are great exposure sentinels because they don’t go anywhere,” said Dr. Andy Kane, an associate professor of environmental and global health. “If oysters are exposed to pollutants or parasites or suboptimal water quality, and you want to understand why oysters are in poor health or dying, you don’t need to ask where the exposure occurred. You know exactly where the oysters were exposed.”
Natural threats to oysters and their populations include shell-boring organisms, such as certain sponges, worms and small clams that excavate their way through oyster shells, leaving holes that greatly increase surface area and expose shell material to corrosive seawater. Shell-boring creatures and oyster predators both love salty environments. When extreme conditions exist, such as extended drought associated with climate change, salinity increases and populations of these parasites and other voracious predators like oyster drills explode.
To help with wild oyster restoration, Kane and others use an approach that considers a “shell budget,” that is, the amount of intact shell substrate in an oyster habitat that can be sustained under favorable conditions. It also means working side-by-side with oyster harvesters to support sustainable harvest practices.
Kane has learned that the value of oysters is a lot more than what is on the plate. To people in these coastal fishing communities, harvesting oysters and “working the water” is a way of life handed down for generations. Loss of jobs associated with coastal resources has serious economic and health effects in the community, including a dwindling workforce with scant recruitment of younger workers, and increased incidence of divorce, alcoholism and domestic abuse. The relationships Kane has built with seafood workers has led to additional studies, supported by the CDC’s National Institute for Occupational Safety and Health, focusing on collaborative wellness programs to reduce health and safety risks, and reduce the burden and cost of injuries for commercial seafood workers and their families along the Gulf coast.
As dependent as humans are on our fresh and ocean waters, it is impossible to separate the health of aquatic environments from the health of humans, said Kane, who serves as the deputy director of the Southeastern Coastal Center for Agricultural Health and Safety.
“The epidemiology of everything that could be waterborne is pretty phenomenal and impactful for human health,” he said. “Seventy-five percent of our planet’s surface is water and even though you can drive from east to west in many cities and never see water, that’s just a myopic coincidence. The reality is that the aquatic and marine resources are critical elements that link environmental and human health, and life as we know it.”