Abstract

For 84 days following the 20 April 2010 explosion of the Deepwater Horizon MC252 offshore oil drilling rig, an estimated 200 million gallons (4.9 million barrels, 780,000 m³) of crude oil were released into the Gulf of Mexico, with 1.8 million gallons (7,000 m³) of surface and subsurface chemical dispersants applied in an attempt to mitigate shoreline impact.⁶ Of the approximately 456 visibly oiled and 80 not visibly oiled live sea turtles rescued, nearly 90% were successfully rehabilitated and released.⁵ Physiologic and pathologic effects expected from crude oil exposure used to guide treatment of sea turtles came from extrapolation of studies in other species⁷ and from a single loggerhead sea turtle (Caretta caretta) study.⁴ While invaluable starting points, inherent limitations to extrapolation,⁷ and small sample size (5 controls and 5 exposed turtles) with changes in controls that trended with those of exposed turtles⁴ limit utility for clinical guidance and for investigating oil spill impacts. Pending litigation prevents release of clinical data from the MC252 sea turtle response until cases are resolved. Effects of dispersants were not included in the previous sea turtle oil exposure study⁴ and cannot be effectively isolated in the eventual analysis of field data from the MC252 incident.

An ongoing terminal pivotal temperature incubation study utilizing eggs salvaged from doomed loggerhead sea turtle nests provided an opportunity for a separate add-on exposure study to investigate the effects of crude oil, dispersant, and a crude oil/dispersant combination in sea turtle hatchlings. Clinical pathology findings are presented here. Investigations in toxicology assays,³ histopathology, and NMR metabolomics are in progress. Eggs in the pivotal temperature study were incubated at 27.4–31.0°C, and hatchlings were randomly assigned to control, oil, dispersant, and oil/dispersant exposures for 1 d or 4 d. Exposures were begun after a 3 d post-hatching period simulating nest emergence. Turtles were placed in individual glass basins containing aged seawater and exposed to oil (Gulf Coast - Mixed Crude Oil Sweet, CAS #8002-05-9, 0.833 mL/L) and/or dispersant (Corexit 9500A, 0.083 mL/L), replicating concentrations encountered during oil spills and subsequent response. Turtles were weighed and measured before and after exposures. Blood was collected into lithium-heparin tubes immediately following euthanasia. Packed cell volumes were determined by centrifugation and plasma chemistry panels were acquired with an in-house tabletop biochemical analyzer (Abaxis VetScan, Avian/Reptilian Profile Plus rotor) starting within 5 min of blood collection. Statistically significant differences between treatments and their respective nonexposed controls were detected for PCV, AST, uric acid, glucose, calcium, phosphorus, total protein, albumin, globulin, potassium and sodium (all except for calcium were increased where differences were present). The principal dyscrasias reflected osmolar, electrolyte and hydration challenges that were worst in combined oil/dispersant exposures at 4 d. Clinical pathology findings were supported by a failure to gain weight (associated with normal hatchling hydration in seawater)¹ in dispersant and combination exposed hatchlings. These findings indicate potential hazards to consider when deploying dispersants in an oil spill response.

Acknowledgements

The authors recognize the controversial nature of an investigation such as this² and deliberated before proceeding. In the context of eggs from doomed nests being used in an ongoing terminal study, and the paucity of toxicology data for sea turtles exposed to crude oil and dispersants, we opted to maximize use of these turtles destined for euthanasia in order to generate freely accessible data to be available for the next oil spill affecting sea turtles. Support for the pivotal temperature study came from a NOAA Section 6 Research Grant (NA10NMF4720035). Support for the add-on exposure study came from the state of North Carolina. No support for the exposure study was received from the Natural Resource Damage Assessment (NRDA) process, the National Oceanic and Atmospheric Administration (NOAA), British Petroleum (BP) or any of its affiliates, or from any other source constrained by the legal process surrounding the Deepwater Horizon MC252 oil spill. Work was conducted under endangered species permit 13ST50 from the North Carolina Wildlife Resources Commission, with federal authority delegated from the U.S. Fish and Wildlife Service, and with approval of the North Carolina State University Institutional Animal Care and Use Committee (11-078-O, 11-103-O). We thank B. Phillips and E. McCarthy for technical assistance, and J. Griffitt for providing crude oil.

* Presenting author

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