Written by Hailey Murphy, interviews conducted by Mary Lide Wallace; S.C. Sea Grant Consortium.
Bottlenose dolphins swimming off Sarasota, FL. Photo courtesy of Brookfield Zoo Chicago’s Sarasota Dolphin Research Program. NMFS Permit No.15543.
Bottlenose dolphins (Tursiops truncatus) are a beloved and familiar sight for coastal South Carolinians and across the Southeast. Dolphins aren’t only iconic for their playful behavior and intelligence; researchers also recognize them as a ‘sentinel species,’ whose health and behavior are key to warning us of environmental hazards. Understanding the health of bottlenose dolphins in other U.S. regions helps us better understand the marine mammal populations found off the coast of S.C.
In Sarasota Bay, Florida, one community of bottlenose dolphins, and the generations before it, has been providing researchers with the data they need to heed those warning signs for more than 55 years. Recently, researchers studying the health of these dolphins have detected prevalent and high concentrations of phthalates, a class of chemicals considered contaminants of emerging concern (CECs).
A Long-Term Study of Dolphin Exposure to Contaminants
This is the focus of the Consortium’s collaborative research project, “Climate factor influences, spatiotemporal variability, and bottlenose dolphin health related to phthalate exposure measured over 30 years in Sarasota Bay, Florida (1993–2023),” led by Principal Investigator Leslie Hart, Ph.D., at the College of Charleston (CofC), with a team of partners and collaborators.
CEC levels are rising in the environment, drawing attention due to their unknown total toxicity to humans and wildlife. In the Southeastern U.S., rapid coastal changes highlight the need for interdisciplinary research on CECs. To address this, the Southeast CEC Program was established through collaboration between the South Carolina Sea Grant Consortium, University of Georgia Marine Extension & Georgia Sea Grant (MAREX), and the National Sea Grant Law Center (NSGLC). This program focuses on the environmental impacts on CECs, such as phthalates and PFAS, in the region.
With support from the Southeast CEC Program, Hart and her team aimed to measure the dolphins’ exposure to phthalates and identify sources of contamination, determine what role weather events or environmental conditions have in the distribution of phthalates, and inform the public about the risks of phthalate exposure caused by plastic pollution.
“We are trying to communicate what our impact is on the ecosystem that we then see in the dolphins,” said Hart, “What can the dolphins also tell us about the risk to people? It’s really a circular, One Health perspective.”
Researchers on the Hypothesizing One-health Pollution Effects (HOPE) Lab team: Savannah Case, Miranda Dziobak, Leslie Hart, Ph.D., and Millie Knowles at the CofC School of Health Sciences Microplastics Laboratory. Photo credit: Catie Cleveland, CofC.
Phthalates: The ‘Everywhere’ Chemical
A class of chemicals commonly added to plastic, household cleaners, and personal care products, phthalates enhance properties such as flexibility, solubility, and durability. Because they are not strongly bonded to these products, they can easily seep into water and enter the natural environment. As water moves across the landscape, it picks up plastics and the contaminants they harbor, such as phthalates, through treated or untreated wastewater, or after draining from landfills, agricultural land, industrial sites, and urban areas.
Research from the Centers for Disease Control and Prevention (CDC) identifies phthalates as endocrine disruptors in humans; chemicals that interfere with the systems by which the body produces, releases, and distributes hormones, impacting metabolism, growth, behavior, fertility, and reproduction. Other health concerns from phthalates include cardiovascular impacts, neurological impacts, obesity, and liver damage.
“Phthalates are in personal care products that we are using multiple times a day, and they are in the packaging we wrap our food in, so they are hard to get away from,” Hart said. “I feel like this is something that can resonate with everybody and maybe bring attention to environmental contamination in general.”
In humans, phthalates are known to metabolize quickly, within 24–48 hours. Despite not being considered bioaccumulative, scientists call phthalates ‘everywhere chemicals’ because they are so widespread that ecosystems, wildlife, and humans are chronically exposed. Scientists suspect that dolphins may be exposed to phthalates through a variety of means, including ingesting plastics either directly while swimming in polluted waters, by consuming fish and other prey that may be contaminated, or by inhaling plastics from the air when they surface to breathe.
Scientists use urine samples to find traces of metabolites—compounds created when phthalates are digested and processed—such as MEHP, a compound created when DEHP, one of the phthalate compounds commonly used in plastic, breaks down. Metabolites like MEHP can be considered a signature of phthalate exposure, allowing researchers to track exposure and environmental contamination over time.
Selected metabolites of two commonly used phthalate compounds, diethyl phthalate (DEP) and di(2-ethylhexyl) phthalate (DEHP). The primary metabolite of DEP is monoethyl phthalate (MEP). Metabolites of DEHP include mono(2-ethylhexyl) phthalate (MEHP), which can further break down into mono(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), mono(2-ethyl-5-oxohexyl) phthalate (MEOHP), and others. Graphic based on original courtesy of Krais et al. 2018.
Generations of Sarasota Bay Dolphins
In 2016, Hart partnered with Brookfield Zoo Chicago’s Sarasota Dolphin Research Program (SDRP), an organization of scientists who have been working with a community of common bottlenose dolphins in Sarasota Bay since 1970. Hart is intimately familiar with SDRP, having worked with them in a variety of roles since her initial start as an SDRP intern in 2000.
As part of their long-term monitoring efforts, SDRP and collaborators from across the globe periodically engage in catch-and-release health assessments, where a single or small group of dolphins is encircled and temporarily restrained by trained animal handlers. The dolphins are brought aboard a specialized vessel and assessed by veterinarians, who record their weight and vitals, collect blood, urine, exhaled breath, and other samples, which are preserved by flash-freezing and cold storage. The researchers also rely on photo-identification surveys in Sarasota Bay to capture the movement of individual dolphins.
“There are about 170 dolphins that live there year-round,” said Hart. “They are able to track generations of these dolphins, so if you go out on a boat with this amazing team of scientists, they will be able to identify that dolphin, and then they can tell you who that dolphin’s mother, grandmother, great-grandmother, and great-great-grandmother were.”
SDRP has been collecting and archiving samples of dolphin urine since 1993, which is the longest-running continuous data source available for a wild dolphin population, and a critical resource for marine mammal, water quality, and environmental research.
“Our samples come from these health assessments, which involve a highly skilled team of veterinarians and animal handlers, the majority of whom work with animals in managed care populations or wild dolphins, so they’ve streamlined the process,” said Hart. “The actual collection of the urine is not challenging because they do this routinely.”
Hart and Dziobak preparing a field blank, or a control sample used to assess contamination from field conditions, for phthalate analyses during a catch-and-release health assessment in Sarasota Bay, Fl. Photo courtesy of Leslie Hart, Ph.D.
Linking Phthalates to Dolphin Hormonal Health
During Hart’s 2010–2019 study on the Sarasota Bay dolphins, University of South Carolina (USC) graduate research assistant Miranda Dziobak screened 51 samples for phthalates and found something unexpected: 75% of these samples had detectable concentrations of at least one metabolite, the most common of which was MEHP. Dziobak also found that MEHP concentrations were correlated with increases in a thyroid hormone (free thyroxine, T4) that helps regulate the body’s metabolism and growth. This research provided some preliminary evidence of hormone changes associated with phthalate exposure.
“In the human literature, we see the most consistent associations as far as endocrine disruption goes with the thyroid hormones, testosterone in males, and some estrogen effects in females,” Hart said. She reflected on the challenges that come with studying wildlife: “For epidemiological studies of phthalate exposure and sex hormones, like testosterone and progesterone, we must consider the sex and age of the animal. Once we divided our data into these demographic groups, our sample sizes were too small.”
These findings sparked Hart, Dziobak, and their team to pursue an expanded study on phthalates, this time utilizing the archive to understand historic trends and look for unexplained differences in exposure across the years. This meant analyzing the impact of major weather events and harmful algal blooms (HABs) on phthalate distribution and conducting spatial analysis of exposure rates around Sarasota Bay. Spatial analysis involves examining data based on geographic location to uncover patterns, relationships, and trends.
Using 201 samples representing 138 individual dolphins who lived in the region during 1993–2024, the team screened for a lineup of eight phthalate metabolites with liquid chromatography and mass spectrometry techniques.
“With the additional samples screened, thanks to the Sea Grant-funded project, we were able to explore linkages with thyroid, sex, and stress hormones, revealing associations that we have not observed in dolphins before,” said Hart, qualifying: “Now, whether or not these correlations lead to negative health outcomes, we’re not there yet, and we have to look at the other factors.”
Dr. Leslie Hart with dolphin during health assessment in Sarasota Bay, FL. Photo courtesy of SDRP. NMFS Permit No. 26622.
Phthalate Exposure ‘Hotspots’ in Sarasota Bay
Dziobak’s early study observed similar phthalate exposure rates in the dolphins between sexes and across age groups, though spatial analysis identified distinct differences in exposure based on their home ranges around Sarasota Bay. These home ranges were identified and confirmed with photo-identification survey data compiled over years of study by SDRP under appropriate marine mammal photography permitting.
“Home ranges in the northern part of the Bay, which is largely residential and has areas of pristine, grassy habitat, were comprised of both exposed and unexposed dolphins,” said Hart, “but in the southern part of the Bay, which is more urbanized and has more varied land uses, home ranges were exclusively among exposed dolphins.”
Bottlenose dolphins in the Sarasota Bay study area (2010–2019) with detectable (dark red) and nondetectable (pink) MEHP concentrations. Courtesy of Leslie Hart, Ph.D., sourced from Dziobak et al. 2022.
Storms, Red Tides, and Rainfall
To better understand the sources, pathways, and distribution of phthalates as they affect the Sarasota Bay dolphins, CofC graduate research assistant Kylie Warden analyzed major storm, rainfall, and HABs—or red tide—events to determine if there was a related shift in MHEP phthalate exposure. They compared the expanded dataset with data from regular intervals prior to the date of the samples’ collection using the National Oceanic and Atmospheric Administration (NOAA)’s storm events database, historical hurricane tracks, the National Weather Service, and NOAA’s Climate Monitoring Database for the Myakka River State Park station. Warden’s preliminary findings suggest that weather events may influence exposure, but no relationships were observed with the red tides.
Hart explained, “Since we suspect that dolphin exposure to MEHP comes from the food they eat, we thought that red tides may influence exposure because dolphins shift their prey consumption during these events. In other words, the fish they prefer to eat, including prey such as pinfish and Gulf toadfish, do not survive these events, so the dolphins must eat other types of fish. As a result of this shift in prey, we suspected a corresponding change in MEHP… that is, if different species are differentially contaminated.” Dr. Hart and her team are currently comparing phthalate metabolite concentrations among species of dolphins’ preferred prey to help address this hypothesis.
Prey, Plastics, and Public Health
Hart’s team has homed in on digestive samples from both the dolphins and their prey—like pinfish, Gulf toadfish, and pigfish—to learn how plastic in these food sources may be linked to phthalate exposure. Additionally, Hart is exploring another common route of exposure for dolphins—inhalation: “We found microplastics in all exhalation samples screened, regardless of whether the dolphin was sampled in an urbanized or rural area, suggesting the pervasiveness of airborne plastic pollution.”
The team is also interested in identifying sources in the southern region of Sarasota Bay that may be leading to higher exposure, such as waterways draining from upland agricultural areas or wastewater treatment facilities in the area.
Warden plans to build on Dziobak’s findings. With guidance from SDRP’s Krystan Wilkinson, Ph.D., and CofC’s Paul Sandifer, Ph.D. and Vijay Vulava, Ph.D., Warden is using the expanded dataset to explore long-term patterns in Sarasota dolphin exposure to MEHP and MEP, a metabolite of DEP—a phthalate compound commonly added to personal care products. Warden aims to identify contamination ‘hotspots’ in Sarasota Bay where local communities may be at risk and offer insight into patterns and changes in the data over time that could be linked to increased development, infrastructure changes such as wastewater treatment practices, or policy implementation like banning the commercial use of plastic bags.
Hart and her team are outspoken about their research, their concern for the health of marine mammals, and the importance of public awareness of the overuse of phthalates and plastics. This has led to coverage by The New York Times and the Smithsonian Magazine. Led by Nadine Slimak, Vetted Communications, they’ve built a web and social media presence, conducted a public survey on awareness of phthalates, disseminated press releases and articles, and have spoken at events in both Sarasota and Charleston, including the Southeastern Wildlife Exhibition and the Consortium’s REconnect Symposium. Ultimately, Hart hopes to see this study inform other work in estuarine-urban areas like Charleston, S.C.
Kylie Warden, Stella Martin, and Hart work with National Marine Mammal Foundation (NMMF) biologist Todd Speakman on a bottlenose dolphin photo-identification survey in Charleston. Similar surveys in Sarasota Bay assisted in identifying dolphin home ranges for spatial analysis of phthalate exposure. Photo credit: Catie Cleveland, CofC. NMFS Permit No. 24359.
How to Help
“I would start with awareness and encouragement of behavior changes, which is never easy,” said Hart. Another way to help is by “letting people know that there are alternatives out there, alternative products, alternative food storage, and alternative ways to reduce phthalates entering the environment.”
For those interested in reducing their own exposure to phthalates—thereby reducing the impact of phthalates on marine life—some of Hart’s tips include looking for personal care products listed as ‘phthalate-free,’ avoiding artificial fragrances, and switching from plastic containers and plastic film for food storage in favor of cardboard, paper, or glass alternatives.
Hart also encouraged changes at a local and regulatory level, suggesting that “as a major contributor to estuarine pollution, a great place to start would be to try to encourage the capability, however possible, to upgrade wastewater treatment plants with technology that we know can filter better.”
Learn more about the Southeast CEC Program by reaching out to Brooke Saari, Coastal Environmental Quality and Extension Services Specialist for the Consortium. You may also reach out to Principal Investigator Leslie Hart, Ph.D., at CofC.
Dziobak, Case, Stella Le Mehaute, and Hart, Ph.D., of the HOPE Lab discuss research on phthalates in personal care products with visitors of the Consortium’s REconnect Symposium at the Boeing Learning Laboratory. Photo credit: Hailey Murphy/S.C. Sea Grant Consortium.
Reference List
Dziobak, Miranda K., Brian C. Balmer, Randall S. Wells, Emily C. Pisarski, Ed F. Wirth, and Leslie B. Hart. 2022. “Temporal and Spatial Evaluation of Mono(2-ethylhexyl) Phthalate (MEHP) Detection in Common Bottlenose Dolphins (Tursiops truncatus) from Sarasota Bay, Florida, USA” Oceans 3, no. 3: 231-249. https://doi.org/10.3390/oceans3030017.
Dziobak, Miranda K., Randall S. Wells, Emily C. Pisarski, Ed F. Wirth, and Leslie B. Hart. “A Correlational Analysis of Phthalate Exposure and Thyroid Hormone Levels in Common Bottlenose Dolphins (Tursiops truncatus) from Sarasota Bay, Florida (2010–2019)” Animals 12, no. 7: 824. https://doi.org/10.3390/ani12070824.
“Emerging Contaminants.” 2025. S.C. Sea Grant Consortium. November 13, 2025. https://www.scseagrant.org/emerging-contaminants/.
“Extramural Papers of the Month.” 2024. National Institute of Environmental Health Sciences. 2024. https://www.niehs.nih.gov/news/factor/2024/3/papers/dert.
Hart, Leslie B., Miranda Dziobak, Randall S. Wells, Elizabeth Berens McCabe, Eric Conger, Tita Curtin, Maggie Knight, and John Weinstein. 2023. “Plastic, It’s What’s for Dinner: A Preliminary Comparison of Ingested Particles in Bottlenose Dolphins and Their Prey.” Oceans 4 (4): 409-22. https://doi.org/10.3390/oceans4040028.
“Hurricanes – Sarasota Bay Estuary Program.” Sarasota Bay Estuary Program. 2024. https://sarasotabay.org/our-estuaries/climate-change/hurricanes/#resilience.
Jingran, Su. 2023. “Phthalates: Friends or Foes?” 2023. EPFL. May 15, 2023. https://www.epfl.ch/labs/hobel/phthalates-friends-or-foes/.
Krais, Annette M, Christina Andersen, Axel Eriksson, Eskil Johnsson, Jörn Nielsen, Joakim Pagels, Anders Gudmundsson, Christian Lindh, and Aneta Wierzbicka. 2018. “Excretion of Urinary Metabolites of the Phthalate Esters DEP and DEHP in 16 Volunteers after Inhalation and Dermal Exposure.” International Journal of Environmental Research and Public Health 15 (11): 2514–14. https://doi.org/10.3390/ijerph15112514.
“Projects – Hart Research Lab.” 2019. Charleston.edu. 2019. https://blogs.charleston.edu/hart-research-lab/projects/.
Slimak, Nadine, and Nadine Slimak. 2025. “Phthalates and Dolphins – Sarasota Dolphin Research Program.” Sarasota Dolphin Research Program. February 17, 2025. https://sarasotadolphin.org/phthalates-and-dolphins/.
Tabuchi, Hiroko. 2024. “Plastics Are Turning up in Dolphin Breath.” The New York Times, October 16, 2024. https://www.nytimes.com/2024/10/16/climate/dolphin-plastic-breath.html.