New research has revealed that sunlight transforms oil spills on the ocean surface much faster than previously believed, and thereby limits the effectiveness of chemical dispersant solutions.
Dispersants contain detergents known as surfactants, which can break oil into small droplets that can be diluted or eaten by microbes before reaching a vulnerable coastline. To facilitate this breakdown, dispersants must also contain a solvent that allows the oil, surfactants and water to mix.
However, a team of scientists led by the Woods Hole Oceanographic Institution (WHOI) have now demonstrated that sunlight rapidly transforms oil into residues that are not fully soluble. This means that the surfactants are not capable of mixing with or fully breaking down the oil.
“Our findings show that sunlight is a primary factor controlling how well dispersants perform,” says Collin Ward, a scientist at WHOI. “And because photochemical changes happen fast, they limit the window of opportunity to apply dispersants effectively.”
An initial study by WHOI found that sunlight alters the chemical composition of crude oil on the sea surface in a matter of days, or even hours. The researchers then conducted a subsequent study, which confirmed that dispersants could not easily break up these new compounds.
To date, tests to determine dispersants’ effectiveness used only “fresh” oil that hadn’t been altered by sunlight. In the new studies, the researchers conducted extensive lab tests that exposed oil to the sun.
The finding suggests that responders should factor in sunlight when determining the ‘window of opportunity’ to use dispersants effectively. That window will be far shorter than previously thought on sunny days than it would on cloudy days.