Combined effects of chemical dispersant and ultraviolet radiation on the acute toxicity of crude oil to an early life stage marine fish (red drum; <i>Sciaenops ocellatus</i> ) and invertebrate (mysid shrimp; <i>Americamysis bahia</i> )

Crude oil toxicity can be influenced by several physical, chemical, and biological factors, including ultraviolet (UV) radiation from sunlight and chemical dispersant application. Ultraviolet radiation can increase the toxicity of polycyclic aromatic hydrocarbons (PAHs) in oil through photo-induced or photo-enhanced toxicity. Additionally, dispersants can alter the distribution of PAHs in the water column and increase the likelihood of exposure to aquatic organisms. To better understand these modifying factors of toxicity and exposure, the present study investigated the combined effects of oil, UV, and the dispersant Corexit 9500A at three different dispersant-to-oil ratios on larval red drum (Sciaenops ocellatus) and juvenile mysids (Americamysis bahia). Both species were sensitive to the combined effects of these stressors and exhibited pronounced decreases in survival with co-exposure to UV. Furthermore, greater dispersant application increased measured PAH concentrations, leading to greater impacts of photo-induced toxicity. The present study is the first to report the photo-induced toxicity effects of dispersed oil and UV exposure in early life stages of red drum. These results demonstrate the significant effect of dispersant and UV radiation on oil toxicity in two Gulf of Mexico species and can be used to inform future ecological risk assessments and oil spill response planning.