Abstract

Of the 380 million tons of plastic produced annually, approximately 60% ends up in landfills or the natural environment.¹ Macroplastic debris (>5 mm diameter) enters the marine environment directly as waste, while wastewater treatment facilities and fragmentation of larger plastic items create microplastics.¹ In fact, the oceans are suspected to contain over 5.25 trillion plastic particles, of which 92.4% are microplastics.²

Recently, we detected phthalate exposure among long-term resident bottlenose dolphins (Tursiops truncatus) in Sarasota Bay, FL, USA (∼75%; n=51).³ Dolphins had significantly higher concentrations of mono-(2-ethylhexyl) phthalate (MEHP), the metabolite of di-(2-ethylhexyl) phthalate (DEHP), than human populations.⁴ While the exposure source is uncertain, our findings suggest a plastic origin, as DEHP is commonly used in polyvinyl chloride products.⁵ Previous studies demonstrated microplastic ingestion by filter-feeding and lower-trophic level organisms,^6,7 as well as translocation into muscle tissue,⁸ suggesting trophic transfer potential. Microplastic ingestion has been documented in apex pelagic fish and marine mammals through examinations of gastrointestinal tracts from stranded or bycaught animals.⁹

We screened for microplastics in gastric fluid from live dolphins sampled in 2019 (n=7), as well as gastrointestinal tracts and fillets from some of their prey fish (e.g., hardhead catfish, Ariopsis felis; pinfish, Lagodon rhomboides; pigfish, Orthopristis chrysoptera; toadfish, Opsanus beta)¹⁰ sampled in 2022 (n=31). Dolphin gastric samples were collected by a veterinarian passing a small tube into the stomach during health assessments. Fish were collected during seasonal purse-seine operations to monitor fish abundance, and diversity in Sarasota Bay, Florida. Organic material was digested with potassium hydroxide, and samples were subsequently vacuum filtered and dried in glass Petri dishes. Particles were characterized visually according to physical attributes by using a dissection microscope. Particles were tested with a hot needle (250°C), and a subsample of suspected plastic particles was further examined by Fourier transform infrared (FTIR) spectroscopy to determine composition.

Suspected plastic particles were observed in dolphin and fish samples. All suspected plastic particles were <5 mm in diameter, suggesting microplastic ingestion by dolphins and fish. Particle quantity varied across dolphin and fish samples (less than 10 to greater than 100), and particle types included several colors of films, fibers, and foams. Transparent films and white foams were most common in bottlenose dolphin gastric samples. Polymers (e.g., PVC zinc, polyethylene, polyamide) were detected in transparent films, confirming microplastic ingestion in dolphins. Among fish samples, fibers and suspected tire wear particles were observed. Fibers were primarily red, blue, and black.

Although phthalate exposure is prevalent among Sarasota dolphins, sources remain unknown. We hypothesize that dolphins are exposed to these endocrine-disrupting chemicals via microplastic-contaminated fish. If this is true, then seafood may present an additional xenobiotic exposure risk to humans, which is likely to be exacerbated by coastal development and frequent flooding associated with climate change.

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

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