Texas A&M Team Examines Role Of Dispersants In 2010 Gulf Oil Spill

(from PublicNow \ Texas A&M University \ Nov. 21, 2016)

Following the 2010 Deepwater Horizon oil spill in the Gulf of Mexico, dispersants were used to keep the oil from coming ashore by dispersing and diluting it. According to a new study led by a Texas A&M University at Galveston researcher, ‘marine oil snow formation’ – a natural process whereby sticky materials excreted by plankton and bacteria can help to enhance dispersing effects by providing a microhabitat for oil degradation – was observed for the first time.

A team of Texas A&M-Galveston researchers have examined how oil and dispersants act together in the ocean to examine the fate of oil spills and have had their work published in the current issue of Limnologyand Oceanography Letters.

The team led by Antonietta Quigg, professor of marine biology, includes Texas A&M-Galveston researchers Laura Bretherton, Manoj Kamalanathan, Alicia Williams, Chen Xu, Saijin Zhang, Kathleen Schwehr, Luni Sun and Peng Lin, and Texas A&M oceanographers Anthony Knap, Peter Santschi, Terry Wade, Shawn Doyle, Jason Sylvan, and colleagues from the University of California-Santa Barbara, University of California-Merced, Old Dominion University and Mount Allison University in New Brunswick (Canada).

In their study which is supported by funds that resulted from the settlement of BP, the team looked especially at the role of EPS (exopolymeric substances) which help determine the fate and transport of oil after a spill, in producing marine oil snow, which is a showering particle aggregates that contain oil, corexit, EPS and other natural organic and inorganic particles into deep waters of the ocean. Marine snow formation is a natural process. After the BP spill, marine oil snow – where the marine snow and oil combined – was visibly seen on the surface of the ocean for the first time. As larger and heavier particle aggregates sink, EPS helps them to stick together, leading in the ocean to what resembles a heavy snowstorm. This storm of marine oil snow takes the oil back down to the sediments.

Conducting large aquaria-type experiments with water samples from the Gulf of Mexico at different locations, and using small amounts of the water-accomodated fraction of oil from the spill and a dispersant called ‘corexit’, the team found that they could produce marine snow and marine oil snow in a laboratory setting. This behavior is attributed to the role that marine snow, which is composed of exopolymeric substances (made up mostly of sugars and proteins) excreted by microbes, play. These microbially derived substances can then act as either soap- or glue-like, depending on conditions, helping not only oil dispersion, but also degradation, and removal from the water column.

‘Exopolymeric substances produced is directly related to the microbes and the environmental conditions,’ says Quigg. ‘The microbes act differently, for example, offshore vs. coastal communities, and so the marine snow also varies.

‘When you combine oil, dispersants and water, you will not get the same reaction every time. Sometimes dispersants help solve the problem by making the oil into smaller droplets. This helps the microbes break it down – those that like the oil at least.’

The Deepwater Horizon explosion and resulting spill started on April 20, 2010 and is considered the largest marine oil spill in history. Before the well was successfully capped on Sept. 19, an estimated 210 million gallons of oil were released, damaging beaches, fishing areas and wildlife throughout the Gulf of Mexico.

An estimated 350,000 gallons of dispersants were used at various locations in the Gulf to help remove the enormous amounts of oil. Dozens of studies are still being conducted to determine the role of dispersants. The Texas A&M-led group’s focus on EPS in alleviating the oil spill, however, is unique.

‘To improve our response to future oil spills, we need a better understanding of the microbes and the exopolymer production under a range of environmental conditions,’ Quigg adds.

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