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Oil residues from the 2010 Deepwater Horizon disaster in the Gulf of Mexico were still present in the surroundings ten years later, a report has shown.
Once released into the environment, crude oil typically undergoes chemical reactions in the environment that transform it into different chemicals which can impact local ecosystems.
The new study from Louisiana State University (LSU) researchers found that the oil spilled during the accident was largely transformed by the end of that summer, but some small quantities of chemical residues still persisted in the environment even ten years later.
“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 first author Professor Edward Overton from LSU.
“Our paper describes the most abundant chemicals that make up typical crude oil and their potential fates in the environment.”
The study focused on the crude oil components that were present at the highest concentrations in spilled oil and those that are the most toxic. By collecting and analysing environmental samples from the water, seafloor, and surrounding shorelines, the study followed how the oil transformed in the months and years up to 2020.
Once released into the environment, between 30 and 40 per cent of the oil evaporated into the air. Water-soluble chemicals dissolved relatively quickly into the sea and were biodegraded by marine organisms, but this was not true for all of the spilled oil’s components.
Oily layers coated the shoreline’s grasses and some particles even sank to the seafloor, with low quantities still present in 2020. Large portions of the spill also underwent sun-dependent chemical transformations or were degraded by microbes.
“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,” Overton said. “Oil spills release lots of chemicals quickly and most damage from oil spills occurs fairly soon after the spill.”
In addition to the longer persisting oil residues, this research suggests that many environmental impacts are also caused by the chemically altered oil components. These new chemicals can have different toxicities, as well as physical properties that influence the levels of exposure in wildlife to these residues.
However, such transformations are highly dependent on the local conditions and weather, which makes them difficult to predict for future spills.
“Environmental circumstances surrounding specific spills greatly affect how quickly the compounds can react, what they cover or coat and how much oxygen can be taken up in critical habitats,” said Overton.
“Therefore, broad generalisation about oil spills requires understanding what was spilled and what are the environmental conditions of the spill.”
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