Abstract
Plastics are concerning to environmental health given their ubiquity and potential for adverse impacts to wildlife.1 Globally, 60% of the 380 million tons produced annually ends up in landfills or the natural environment.2 Coastal ‘hotspots’ of microplastics (particles <5 mm diameter) occur in urbanized areas near industrial and commercial activities, especially in estuarine habitats.3 The public health consequences of this pollution are significant considering the proportion of the world’s population living near the coast.
Sarasota Bay, located on the central west coast of Florida, is an urban watershed with residential, industrial, and commercial centers. Bottlenose dolphins in this area have been studied since 1970, including recent investigations of plastic and plasticizer (i.e., phthalate) exposure. As long-lived apex predators, resident dolphins (i.e., those that remain in the localized Sarasota Bay region for the majority of their lives) are sensitive gauges of environmental disturbances.4 This study used a sentinel species approach to better understand exposure risks for dolphins from plastics and endocrine-disrupting plasticizers in the marine environment.
Plastic exposure in Sarasota dolphins was presumed based on detection of a plasticizer (di2(ethylhexyl) phthalate [DEHP]) metabolite, methyl (2-ethylhexyl) phthalate (MEHP), or ingested particles suspected to be plastic. MEHP concentrations were quantified using liquid chromatography with tandem mass-spectrometry for urine collected during 2010–2019. Using a dissection microscope, ingested particles were quantified and visually characterized from dolphin gastric samples collected in 2019 and prey fish muscle collected in 2022. Plastic particles were confirmed using Fourier-transform Infrared spectroscopy.
MEHP was detected in 55% of dolphins sampled (n=51), with no significant sex- or age-related differences in concentrations (p>0.05).5 While detectable metabolites did not vary demographically, there was evidence of spatial influence. Ranging patterns differed between exposed and unexposed dolphins; dolphins with detectable MEHP were concentrated in the southern portion of the bay where land-use is primarily industrial and residential.6 Concentrations of MEHP were higher in Sarasota dolphins (p<0.05) compared to humans, suggesting the potential for endocrine disruption.7,8 In fact, free thyroxine was positively correlated with MEHP in adult dolphins (females p=0.04; males p=0.02) indicating potential impacts to thyroid homeostasis.9
While the source of DEHP exposure is uncertain, evidence points to a plastic origin. Of the 92 particles observed in gastric samples (n=7), 62% were suspected to be plastic, and at least one suspected plastic particle was observed in every dolphin. All suspected plastics were less than 5 mm in diameter (i.e., microplastics), and several polymers were identified (e.g., PVC zinc, polyethylene, polyamide).10 Additionally, fibers were prevalent in prey fish muscle, supporting trophic transfer, via consumption, as an exposure pathway. Our findings suggest dolphins can serve as a model to study the geographic scope and severity plastic pollution, as well as warn of potential seafood safety risks for human consumption.
Acknowledgements
We are grateful to the staff, collaborators, and volunteers of the Sarasota Dolphin Research Program for ensuring the safe capture, sampling, and release of the dolphins. Additionally, we would like to thank Amanda Moors for assistance with the collection of gastric samples and environmental blanks for this study. Funding for this work was provided by Dolphin Quest Inc., the Department of Health and Human Performance at the College of Charleston, and a grant from the National Institute of Environmental Health Sciences (Award No. R15ES034169). The animal sampling was reviewed and approved by Mote Marine Laboratory’s Institutional Animal Care and Use Committee (IACUC). Samples for this study were collected under Scientific Research Permit No. 20455 from the National Oceanic and Atmospheric Administration’s National Marine Fisheries Service.
*Presenting author
+Student presenter
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