Sunlight helps clean up oil spills in the ocean

A team of researchers from the Woods Hole Oceanographic Institution (WHOI) has discovered that almost 17% of the oil that floated in the Gulf after the Deepwater Horizon disaster, which occurred in 2010 and became the largest marine oil spill in United States history , it was dissolved in seawater by sunlight, a process called “photodissolution,” the authors report in the journal Science Advances.

What happened in 2010?

The disaster was caused by an explosion at the Deepwater Horizon oil platform, 70 kilometers southeast of the Mississippi River Delta, which killed 11 people and caused the release of nearly 900 million liters of crude oil into the Gulf of Mexico.

traces of oil

Many hundreds of millions of dollars later, scientists are still working to understand where all this oil ended up. It is known that there is part of the oil that is consumed through biodegradation , that is, microorganisms that consume and break down the oil; also by evaporation, since the liquid oil can be converted into gas and, finally, the oil that is stranded on the coasts.

But, this new work puts on the table that sunlight could have helped remove up to 17% of the oil that was sliding across the surface of the Gulf of Mexico after this catastrophic spill, which means that sunlight plays a role . more important than previously thought, when it comes to cleaning up oil spills in the oceans.

“The amount of oil that was transformed by sunlight into compounds that dissolved in seawater during the 2010 Deepwater Horizon spill rivals commonly accepted fates of oil, such as biodegradation and stranding on shorelines,” said Collin Ward, assistant marine research scientist in WHOI’s Department of Chemistry and Geochemistry.

How does the Sun clean up oil spills?

The researchers explain that when sunlight hits the oil spilled on the sea, it is capable of initiating a chain of chemical reactions that transform the oil into new compounds, increasing the ease with which the oil dissolves in water (photodissolution). But the result, in this case, has been greater than expected.

The researchers used custom-made light-emitting diode (LED) reactors to measure how the rate of this oil’s fate varied for different types of light, such as ultraviolet and visible light. LED measurements also offered the opportunity to determine which conditions were most important to control this process.

So by generating hypothetical spill scenarios with different oil slick thicknesses, times of year, locations around the world, and types of light, they found that some of these changing conditions mattered more than others. The most important factors in photodissolution were the thickness of the spot and the wavelengths of light. Longer wavelengths dissolved less oil than shorter wavelengths, probably because water disperses slicks more easily than at shorter wavelengths. Furthermore, they concluded that the length of time the oil was exposed to sunlight was not relevant to the process.

“The importance of this process changes dramatically if you compare thin versus thick oil slicks,” said Danielle Haas Freeman, a student in the joint Massachusetts Institute of Technology/WHOI program. “We also found, contrary to popular belief, that this process is relevant in Arctic waters , a particularly important finding given the expected increase in cargo ship traffic and the increased risk of spills in that region . modeling is critical when forecasting spills taking into account impacts on marine ecosystems .”

Referencia: Danielle Haas Freeman et al, Sunlight-driven dissolution is a major fate of oil at sea, Science Advances (2022). DOI: 10.1126/sciadv.abl7605