Comparing phthalate exposure between bottlenose dolphins (Tursiops truncatus) residing in urban and rural environments

Abstract

Introduction: Exposure to phthalate esters has previously been documented in bottlenose dolphins (Tursiops truncatus) inhabiting an urban estuary (Sarasota Bay, FL, USA; 2010-2019). Phthalates are chemicals commonly added to plastic products and consumer goods to enhance qualities such as flexibility, fragrance, and stability. Chemical leaching from products into the marine environment leaves wildlife vulnerable to reproductive, developmental, and metabolic impairment. Environmental phthalate exposure has been shown to vary relative to human activity and urbanization.

Methods: To evaluate potential differences in dolphin exposure risk, urine was collected from free-ranging bottlenose dolphins residing in an urban (Sarasota Bay, FL, USA; 2010-2024; n=71) and rural estuary (Barataria Bay, LA, USA; 2011-2023; n=45). Urinary phthalate metabolite concentrations were quantified with high-performance liquid chromatography (HPLC; Agilent 1100; WatersXBridge BEH C18, 2.5 μm, 2.1×50 mm analytical column) coupled to a triple quadrupole mass spectrometer (MS; Applied Biosystems Sciex API 4000) with an electrospray ionization (ESI negative) interface.

Results: The magnitude of MEHP detection did not differ significantly between sampling sites (p=0.97); however, MEHP was detected more frequently in Sarasota Bay dolphins (73.24%; n=52; 95% CI: 61.20-82.73) than Barataria Bay dolphins (33.33%; n=15; 95% CI: 20.00-48.95%). Dolphins from Sarasota Bay may be exposed to a greater diversity of phthalates compared to Barataria Bay dolphins, indicated by differences in the detected phthalate metabolite profile.

Discussion: Notably, dolphins from Barataria Bay were impacted by the Deepwater Horizon oil spill, with evidence suggesting long-term negative health outcomes. The endocrine-disrupting effects of phthalates could exacerbate metabolic, reproductive, or immune dysfunction in dolphins, especially those with compromised health. The higher phthalate detection frequency in Sarasota Bay dolphins suggests increased urban exposure risks; however, detection in dolphins from Barataria Bay raises concerns for dolphins in recovering ecosystems. Further research is needed to assess potential synergistic impacts of chemical mixtures, and targeted mitigation strategies in contaminated environments.

Keywords: Barataria Bay; Sarasota Bay; marine mammal; plastic; pollution.

FIGURE 1

Bottlenose dolphins study sites: (A) Sarasota Bay, Florida and (B) Barataria Bay, Louisiana. Map created using Esri ArcGIS Pro basemap, Esri, TomTom, Garmin, FAO, NOAA, USGS, ^© OpenStreetMap contributors, and the GIS User Community.

FIGURE 2

Percent volume contours (PVCs) determined for bottlenose dolphins sampled (n = 45) from Barataria Bay (2011, 2013–2014, 2017–2018, 2023) using all sighting histories. (Detect and Nondetect maps) Core (50% PVC) and total (95% PVC) spatial usage respectively for dolphins with detectable and undetectable urinary mono(2-ethylhexyl) phthalate MEHP concentrations with black points representing individual sighting records. (50% PVC and 95% PVC maps) Core (50% PVC) and Total (95% PVC) spatial usage respectively for dolphins with detectable urinary MEHP concentrations overlayed with spatial usage for dolphins with nondetectable urinary MEHP concentrations.

FIGURE 3

Percent volume contours (PVCs) determined for bottlenose dolphins sampled (n = 71) from Sarasota Bay (2010–2019, 2022–2024) using photo-identification sighting histories. (Detect and Nondetect maps) Core (50% PVC) and total (95% PVC) spatial usage respectively for dolphins with detectable and undetectable urinary mono(2-ethylhexyl) phthalate MEHP concentrations with black points representing individual sighting records. (50% PVC and 95% PVC maps) Core (50% PVC) and Total (95% PVC) spatial usage respectively for dolphins with detectable urinary MEHP concentrations overlayed with spatial usage for dolphins with nondetectable urinary MEHP concentrations.

FIGURE 4

Comparison of urinary MEHP concentrations (>LOD) between bottlenose dolphins sampled in Barataria Bay, LA (BAR) and Sarasota Bay, FL (SSB). Box plot displays median and quartiles, black points represent concentrations above the limit of detection, and red diamond represents mean among concentrations above the limit of detection.