Abstract
Following the explosion of the Deepwater Horizon MC252 oil rig in 2010, 319 live sea turtles exposed to crude oil and oil-dispersant (Corexit) combinations were admitted to rehabilitation centers for decontamination and treatment. Treatment of oiled sea turtles was guided by expected physiological and pathological effects of crude oil exposure extrapolated from studies in other species and from a single loggerhead sea turtle (Caretta caretta) study. While invaluable starting points, inherent limitations to extrapolation, and small sample size of the experimental exposure study, reduce their utility for clinical guidance and for assessing oil spill impacts. Effects of dispersants were not included in the previous experimental exposure study, and cannot be effectively isolated in the analysis of field data from actual spills. A terminal study of pivotal temperature of sex determination using eggs salvaged from doomed loggerhead nests provided an opportunity for an ancillary exposure study to investigate the acute effects of crude oil, dispersant, and a crude oil/dispersant combination in sea turtle hatchlings. Eggs were incubated at 27.2–30.8°C, and hatchlings were randomly assigned to control, oil, dispersant, and combined oil/dispersant exposures for 1 or 4 days. Contaminant exposures were started after a 3 day post-hatching period simulating nest emergence. Turtles were placed in individual glass bowls 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. Statistically significant differences between treatments and non-exposed controls were detected for PCV, AST, uric acid, glucose, calcium, phosphorus, total protein, albumin, globulin, potassium, and sodium. The principal dyscrasias reflected acute osmolar, electrolyte and hydration challenges that were more numerous and greater in combined oil/dispersant exposures at 4 days. Clinicopathological findings were supported by a failure to gain weight (associated with normal hatchling hydration in seawater) in dispersant and combination exposed hatchlings. These findings can help guide clinical response for sea turtles exposed to crude oil and crude oil/dispersant combinations, and indicate potential impacts on wildlife to consider when deploying dispersants in an oil spill response.
Highlights
For 87 days following the explosion of the Deepwater Horizon (DWH) MC252 oil rig in 2010, an estimated 134 million gallons (500,000 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 (Corexit 9500A and Corexit 9527A) applied in an attempt to mitigate impact (1)
The principal alterations found in the present study reflect osmotic, electrolyte, mineral, and hydration challenges that collectively were worst in the 4-day combined oil/dispersant exposure treatment
Albumin determined by the bromocresol green dye binding method is less reliable in non-mammalian plasma (20), and globulin is a calculated value from total protein (TP) and albumin, relative values of these components of TP must be interpreted with caution
Summary
For 87 days following the explosion of the Deepwater Horizon (DWH) MC252 oil rig in 2010, an estimated 134 million gallons (500,000 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 (Corexit 9500A and Corexit 9527A) applied in an attempt to mitigate impact (1). Physiological and pathological effects expected from crude oil exposure used to guide treatment of oiled sea turtles came from extrapolation of studies in other species (4) and from one experimental in vivo loggerhead sea turtle oil exposure study (5). Some expected abnormalities such as hemolytic anemia and extensive skin sloughing previously reported in sea turtles exposed to crude oil were not observed in the case of the DWH spill (3, 6). Subsequent to the DWH oil spill, clinicopathological effects on spill-exposed sea turtles have been published from the Canary Islands (7) and from the DWH spill itself (3, 6) that provide further insights on spill impacts to sea turtles. Dispersants, were not included in the previous sea turtle oil exposure study, were not a component of spill exposures in the Canary Islands, and cannot be effectively isolated in the analysis of field data from the DWH incident. The combined effects of crude oil and dispersant on sea turtles have not previously been documented
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