Sunlight can help dissolve oil in seawater

A spot of oil altered by sunlight floats in the Gulf of Mexico after the 2010 Deepwater Horizon disaster. A team of researchers at the Woods Hole Oceanographic Institute has found that nearly 10 percent of the oil that floats in the bay after a spill dissolves in water under sunlight, a process called photo-creation. Credit: Photo by Cabell Davis III © Woods Hole Oceanographic Institute

Dissolving oil in a sunlit sea

The 2010 Deepwater Horizon oil spill became the largest offshore oil spill in United States history. The crash was caused by an explosion at the Deepwater Horizon oil rig, which killed 11 people and dumped nearly 210 million gallons of crude oil into the Gulf of Mexico. Twelve years and hundreds of millions of dollars, scientists are still working to figure out where all this oil ended up, a concept known as the fate of the environment.

The most frequently discussed are the fate of oil spilled at sea – biodegradation (microorganisms that consume and break down oil), evaporation (liquid oil is converted into gas) and the landing of oil on coastlines.

A team of researchers from the Woods Hole Oceanographic Institute (WHOI) found that nearly 10 percent of the oil that floated in the Gulf after the Deepwater Horizon disaster was dissolved in seawater under sunlight – a process called “photo-creation”. The findings were published today in the article “Dissolution caused by sunlight – the main fate of oil in the sea” in Advances in science.

“The amount of oil that has been converted by sunlight into compounds that dissolved in seawater during the Deepwater Horizon spill in 2010 rivals the generally accepted fate of oil such as biodegradation and shore-to-shore,” said co-author Colin Ward. Assistant Scientist WHOI Marine. Department of Chemistry and Geochemistry.

“One of the most exciting aspects of this discovery is that it could affect our understanding of where oil is still going, and whether the outcome will be good or bad,” said lead author Daniel Haas Freeman of the Massachusetts Institute of Technology / WHO Joint Program. . student. “If this significant proportion of oil is converted by sunlight and dissolved in seawater, it could mean that less oil gets to other places, such as sensitive coastal ecosystems. On the other hand, we need to consider the impact of compounds on marine organisms before we can decide whether a result is positive or negative. ”

To come to this important conclusion, Freeman and Ward used special LED (LED) reactors to measure how the speed of this oil changes for different types of light, such as ultraviolet and visible light.

“The process of photo-creating oil has been known for more than fifty years,” Ward said. “But what’s new is our understanding of how this process varies depending on the wavelength of light we’ve determined using LED reactors. This is key information that allowed us to assess the importance of this process during the spill. “

New measurements using LEDs also made it possible to determine which conditions were most important in controlling this process. The team created hypothetical spill scenarios with varying oil slick thicknesses, seasons, locations around the world, and light types. They noticed that some of these changing conditions were more important than others.

“The importance of this process changes dramatically when you look at thin and thick oil slicks,” Freeman said. “We have also found, contrary to popular belief, that this process is relevant in Arctic waters, which is particularly important given the expected increase in cargo ships and the increased risk of spills in the region. This type of modeling is crucial in forecasting spills and accounting for impacts on marine ecosystems. ”

The notion that oil on the surface of the ocean may have a new destiny is monumental to the design of future oil spill research and spill response tactics. It is currently unknown what is the fate and potential toxicity of these compounds produced by sunlight, which poses a problem in assessing the impact of this oil. Freeman and Ward call on the realm to reach out to these gaps in knowledge.

“Although our findings suggest that much of the surface oil may dissolve in the ocean after exposure to sunlight, the logical next step is to assess its sustainability and potential harm to aquatic animals,” Ward said.

Reference: “Dissolution caused by sunlight is the main fate of oil in the sea”, Daniel Haas Freeman and Colin P. Ward, February 16, 2022, Advances in science.
DOI: 10.1126 / sciadv.abl7605 Sunlight can help dissolve oil in seawater

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