Chemical Dispersants Used by BP Linger in Deep Sea Plume
FALMOUTH, Massachusetts - Chemical
dispersants that BP injected directly into its damaged wellhead in the
Gulf of Mexico last year, had still not degraded three months after they
were applied, according to the first peer-reviewed research on the fate
of the chemicals, published today.
In the effort to manage the massive Deepwater Horizon oil spill, BP
injected some 771,000 gallons of the chemical dispersant Corexit 9500 a
mile beneath the surface of the Gulf of Mexico. Dispersants function
like detergents to break up oil into small droplets that mix easily with
Today, Woods Hole Oceanographic Institution chemist Elizabeth Kujawinski
and her colleagues reported that a major component of the dispersant
was contained within an oil and gas-laden plume in the deep ocean and
had still not degraded three months after it was applied.
"This study gives our colleagues the first environmental data on the
fate of dispersants in the spill," said Kujawinski, who led a team that
included scientists from UC Santa Barbara. "We don't know if the
dispersant broke up the oil," she said. "We found that it didn't go
away, and that was somewhat surprising."
The study, which appeared online today in the American Chemical Society
journal "Environmental Science & Technology," is the first
peer-reviewed research to be published on the dispersant applied to the
Gulf spill and the first data on deep application of a dispersant,
according to ACS and Kujawinski.
Previous studies had indicated that dispersants applied to surface oil
spills can help prevent surface slicks from endangering marshes and
The study was not aimed at assessing the possible toxicity of the
lingering mixture. Kujawinski said she would "be hard pressed to say it
Still, she said, the results warrant toxicity studies into the effects
of the dispersant on corals and deepwater fish such as tuna. The EPA and
others have already begun or are planning such research, she said.
Researcher David Valentine of UC Santa Barbara said, "The decision to
use chemical dispersants at the sea floor was a classic choice between
bad and worse. And while we have provided needed insight into the fate
and transport of the dispersant we still don't know just how serious the
threat is. The deep ocean is a sensitive ecosystem unaccustomed to
chemical irruptions like this, and there is a lot we don't understand
about this cold, dark world."
"The good news is that the dispersant stayed in the deep ocean after it
was first applied," Kujawinski said. "The bad news is that it stayed in
the deep ocean and did not degrade."
"The results indicate that an important component of the chemical
dispersant injected into the oil in the deep ocean remained there, and
resisted rapid biodegradation," said Valentine, whose team collected the
samples for Kujawinski's laboratory analysis.
Kujawinski and her colleagues found one of the dispersant's key
components, called DOSS (dioctyl sodium sulfosuccinate), was present in
May and June, in parts-per-million concentrations, in the plume from the
spill more than 3,000 feet deep. The plume carried its mixture of oil,
natural gas and dispersant in a southwest direction, and DOSS was
detected there at parts-per-billion concentrations in September.
Using a new, highly sensitive chromatographic technique that she and
WHOI colleague Melissa Kido Soule developed, Kujawinski reports those
concentrations of DOSS indicate that little or no biodegradation of the
dispersant substance had occurred.
The deep-water levels suggested any decrease in the compound could be attributed to normal, predictable dilution.
They found further evidence that the substance did not mix with the 1.4
million gallons of dispersant applied at the ocean surface and appeared
to have become trapped in deepwater plumes of oil and natural gas
reported previously by other WHOI scientists and members of this
The team also found a striking relationship between DOSS levels and
levels of methane, which further supports their assertion that DOSS
became trapped in the subsurface.
The use of dispersants in the aftermath of the Deepwater Horizon
explosion on April 20, 2010 was controversial for three reasons. First,
the total amount of dispersants used was unprecedented - 1.84 million
Second, 771,000 of those gallons were applied at the wellhead, located
5,067 feet below the surface. Little or no prior testing had been done
on the effectiveness and potential adverse environmental consequences of
subsea dispersant use, and never at those volumes.
Third, the existing federal regulatory system pre-authorized dispersant
use in the Gulf of Mexico without limits or guidelines as to amounts or
Kujawinski cautioned that "we can't be alarmist" about the possible
implications of the lingering dispersant. Concentrations considered
"toxic" are at least 1,000 times greater than those her team observed.
In Kujawinski's technique, the target molecule was extracted from water
samples with a cartridge that isolates the DOSS molecule. The scientists
observed the molecule through a mass spectrometer, calculating its
concentration levels in the oil and gas plume.
This method is 1,000 times more sensitive than that used by the EPA and
could be used to monitor this molecule for longer time periods over
longer distances from the wellhead, Kujawinski said.
"With this method, we were able to tell how much was there and where it
went," she said. The scientists detected DOSS up to 200 miles from the
wellhead three months after the dispersant injection took place,
indicating the mixture was not biodegrading rapidly.
Kujawinski and Valentine were joined in the study by Soule and Krista
Longnecker of Woods Hole Oceanographic Institution, Angela Boysen a
summer student at WHOI, and Molly Redmond of UC Santa Barbara.
The work was funded by WHOI and the National Science Foundation. The instrumentation was funded by the National Science Foundation and the Gordon and Betty Moore Foundation.