|Institution:||Louisiana State University|
|Department:||Forestry, Wildlife, & Fisheries|
|Keywords:||crude oil; dispersant COREXIT 9500; toxicity|
|Full text PDF:||http://etd.lsu.edu/docs/available/etd-1113103-122552/|
To address public concern over potential ecological effects on commercially and ecologically important species following use of dispersants during oil spill response efforts, toxicity data was generated for three estuarine species indigenous to the Gulf of Mexico including juvenile Gulf killifish Fundulus grandis, white shrimp Litopenaeus setiferus, and Eastern oyster Crassostrea virginica. The acute toxicity of the dispersant Exxon Corexit 9500, South Louisiana crude oil (SLC), Alaskan north slope crude oil (ANSC) and dispersed oils (SLC+9500 and ANSC+9500) to the species was determined for both nominal concentrations (NC) and hydrocarbon concentrations (HC). Two 24-h field toxicity trials were conducted with the same species in a Louisiana coastal marsh, using ANSC and ANSC+9500, dosed at a NC of 30 ppm. White shrimp were more sensitive to dispersant, crude oils, and dispersed oils than killifish and oysters. The 96-h NC LC50 for crude oil and dispersed oil ranged from 370 to 4,500 ppm for killifish (HC 7.6 to 18.7 ppm) and 60 to 180 ppm for shrimp (HC 5 to 7.5 ppm). Mortality in oysters was not positively correlated with increasing levels of crude oils, or dispersed oils. Dispersed oils were more toxic than crude oils based on nominal concentrations, but no difference in toxicity of crude oils and dispersed oils was observed based on HC concentrations. No synergistic toxicity action was found between SLC or ANSC and dispersant Corexit 9500 based on HC concentrations. Survival was relatively high for all three species during the two 24-h field trials, generally exceeding 83% in crude oil and dispersed oil enclosures. Mortality of white shrimp was slightly higher than observed in killifish and oysters. The HC concentration in ANSC+9500 and ANSC enclosures ranged from 14 to 24 ppm and 10 to 11 ppm, respectively, at 0 h and declined to near 0 ppm in 3 hours. The rapid decrease was attributed to dilution from vertical mixing and tidal action. Both laboratory finding and field studies indicate that short-term exposure to nominal concentrations of ANSC or ANSC+9500 of 30 ppm or less are not likely to have an acute toxic effect on these species.