A new study revealed that ultraviolet radiation from the sun could exacerbate the toxicity of the contaminants called polycyclic aromatic hydrocarbons (PAH) from oil spills.

The study, published in the journal Environmental Toxicology and Chemistry, showed that wildlife exposed to both natural sunlight and the oil spill have reduced survival rates, compared to those exposed to the oil spill alone.

"Many marine and estuarine fish eggs and early larva develop at or near the water surface, which is where oil floats and the sun shines. When all three co-occur, the potential for toxicity greatly increases," explained Dr. Matthew Alloy, lead author of the study, in a press release.

For the study, the researchers obtained two species of fish native to Gulf of Mexico from in-house cultures at the Texas Parks and Wildlife Sea Center. The two species used in the study were the red drum and speckled seatrout. Both red drum and speckled seatrout spawn near-shore and produce positively buoyant embryos that hatch into larvae in approximately 24 hours.

To determine whether natural sunlight can increase the toxicity of crude oil, the researchers exposed the larval fish to several dilutions of high-energy water-accommodated fractions (HEWAFs) from 2 different oils collected in the field under chain of custody during the 2010 spill and 3 gradations of natural sunlight in a factorial design.

The researchers observed that larval fishes exposed to both sunlight and oil experience significant reduction in their survival rate, compared to the fishes exposed to the crude oil alone. While both of the larval fish demonstrated sensitivity at PAH concentrations reported during the Deepwater Horizon spill, speckled seatrout appear to be more sensitive to the combined toxicity of sunlight and crude oil compared to the red drum.

With their findings, the researchers hope to demonstrate that even advanced weathering of slicks does not improve the potential for photo-induced toxicity of oil to native species living in the Gulf of Mexico.