Traces of Deepwater Horizon oil still detectable 10 years later

by Gianna Melillo | Aug. 09, 2022

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The Deepwater Horizon oil spill leaked 4 million barrels of oil over nearly 90 days in 2010.

To better understand the long-term transformation of oil compounds released during the spill, researchers collected samples from the surrounding environment.

As late as 2020, residue from crude oil could still be found in surrounding ecosystems.

When it occurred on April 20, 2010, the Deepwater Horizon oil spill became the largest, deepest and longest lasting in the history of marine oil drilling operations in the United States.

Now, a new report published in Frontiers details the persistent nature of the accident, as traces of oil were still detected in surrounding areas as late as 2020.

The small amounts of chemical residues can negatively affect local ecosystems but also offer clues for clean-up efforts and potential future spills, researchers said.

“The better we understand the chemicals and their chemical reactive properties as well as their physical properties, the better we will be able to mitigate oil spills and understand and detect environmental damages from oil spills,” said study co-author Edward Overton of Louisiana State University in a statement.

Researchers assessed both the initial bulk and compound specific composition of the liquid oil spilled and how these substances changed over time. They also focused on those seen at the highest concentrations after the spill and listed as the most toxic according to the EPA.

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Although between 30 and 40 percent of the oil evaporated into the air once released, samples showed weathering changed the oil’s composition over the years, and biodegradation — or the conversion of organic chemicals into simple compounds — was seen in surface and subsurface environments.

In addition, photooxidation, defined as the sun’s action on an oil slick that causes oxygen and carbons to combine and form new products, removed or modified hydrocarbons in oil slicks.

Despite this, 10 years later, some oil residues were still found at multiple locations, including in marshes and deep water sediments.

In total, the spill lasted 84 days and released 4 million barrels of oil.

“The important point about oil spills is that the oil’s compounds are a type of material that can be degraded by sunlight and marine bacteria (biodegradation), in contrast to other types of pollutants such as the chlorinated pesticides like DDT,” remarked Overton, adding most environmental damage from the leaks occur soon after the initial release.

However, the chemically altered oil components can also go on to have their own environmental impacts, but transformations are dependent upon specific local conditions. According to Overton, certain environmental conditions present during spills can affect how much oxygen is taken up in habitats and how quickly compounds can react.

“Therefore, broad generalization about oil spills requires understanding what was spilled and what are the environmental conditions of the spill. Hopefully this paper will help expand our understanding of the types of chemicals that are found in oil and their ability to cause environmental damages,” he said.