Ecotoxicological assessment of the effects of crude oil and oil spill dispersants on the sheepshead minnow, Cyprinodon variegatus
Franco, Michelle P.
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The use of chemical dispersants as an oil spill response method has long been a topic of controversy. During the Deepwater Horizon Oil Spill of 2010, millions of gallons of chemical dispersants were applied, and many of the potential toxicological effects on wildlife remain unknown. This project analyzed the effects of two chemical dispersants (Corexit 9500 and Finasol OSR 52), and mixtures of oil and chemical dispersants on a common estuarine teleost fish, the sheepshead minnow, <i>Cyprinodon variegatus</i>. Embryonic and juvenile life stages of <i>C. variegatus</i> were tested in aqueous laboratory exposures. The endpoints assessed include mortality, embryonic development, cellular enzyme activity, and immunological response. Acute median lethal toxicity values were determined for embryonic and adult life stages of <i>C. variegatus</i> for each dispersant individually and in mixture with oil. In the dispersant-alone exposures, Finasol was more toxic than Corexit to adult and embryonic <i>C. variegatus</i>. Finasol exposure also led to decreased embryonic hatching success and increased time-to-hatch. When the dispersants were mixed with oil to create a chemically-enhanced water accommodated fraction (CEWAF), greater concentrations of hydrocarbons were present in the Corexit-CEWAF than in the Finasol-CEWAF. Based on the measured hydrocarbon concentrations in the exposures, acute toxicity was greater in the Finasol-CEWAF than in the Corexit-CEWAF. Induction of p450 enzyme activity, a decrease in lipid peroxidation activity, decreased embryonic hatching success, and delayed hatching occurred with both CEWAFs. No effect on immune response or nervous system enzyme function was measured. Overall, Corexit would be considered the more effective and less toxic dispersant. The results of this study fill a data gap in current understanding of the toxicity of oil and chemical dispersants to important estuarine species and will benefit future environmental management decisions.