Beginning in April of 2010, the Deepwater Horizon(DWH) spill released millions of barrels of oil into the Gulf of Mexico (GoM) over a period of 87 days. The oil contaminated the water column with droplets and dissolved components, formed slicks on the surface, and visibly oiled over 1500 km of the coast. In order to most realistically estimate the impacts of this disaster on organisms in the GoM, we considered not just the effects of the oil, but the effects of other stressors, including sunlight. Previous studies have suggested that some compounds in oil, polycyclic aromatic hydrocarbons (PAH), can become much more toxic in the presence of ultraviolet (UV) light, especially to small and translucent organisms. Though standard oil toxicity tests are conducted under indoor conditions, realistically modeling damage to life in the GoM required that we characterize the effect of natural levels of sunlight on oil toxicity for various exposure routes.
Our comprehensive toxicity testing program conducted in support of the Deepwater Horizon (DWH) Natural Resource Damage Assessment demonstrated that UV light greatly affected the toxicity of DWH oil to early life stage fish and invertebrates. In bioassays conducted on 10 species of early life stage fish and invertebrates, the toxicity of DWH oil increased by one to two orders of magnitude with co-exposure to natural levels of UV light. The tests also suggested that sensitivity of organisms to UV light is not uniform; some organisms were more sensitive to photo-induced toxicity than others. We incorporated meta-analyses of laboratory test results with data from field sampling, weather stations, satellite imagery, and scientific literature to develop a model of likely effects of oil exposure during the oil spill. In this presentation, we will discuss progress in characterizing photo-induced toxicity of oil and further development of our photo-induced oil toxicity model. Finally, we will also discuss logical future directions and research needs on this topic.