Oil spill dispersants don't disappear
David L. Valentine, University of California Santa Barbara
A fresh oil slick from the Deepwater Horizon spill, during June 2010. Note that one drop of detergent was added to the oil slick, forming the cleared
circle. A chemical of such dispersants lingers in the deep ocean, a new study found.
By John Roach
When nearly 800,000 gallons of a chemical dispersant were injected into the oil gushing from the busted wellhead on the bottom of the Gulf of Mexico
during last year's Deepwater Horizon disaster, nobody knew for sure what would happen. Now, scientists are getting their first answers, and the
results are mixed.
Tests for a key component of the chemical concoction reveal that the dispersant worked its way into the oil-laden plume in the deep ocean, and stayed
in the deep ocean. But the chemical did not degrade as much as scientists thought it would.
"It is hard for me at this point to say whether or not it is bad or good that it stuck around," study lead author Elizabeth Kujawinski, a chemist at
the Woods Hole Oceanographic Institution in Massachusetts, told me today. She and colleagues were surprised that little or no biodegradation of the
dispersant substance had occurred.
The team analyzed concentrations of a molecule called DOSS (dioctyl sodium sulfoscuccinate), which makes up about 10 percent of the dispersant
solution. In May and June of last year, it was present in the oil plume in parts-per-million concentrations. More than 640,000 pounds of DOSS were
injected into the deep ocean from April to July.
By September, the plume had drifted 200 miles away from the wellhead, and concentrations of DOSS were detected there in parts-per-billion
concentrations. The finding suggests that the degradation of the molecule was insubstantial relative to other factors such as simple dilution,
While the researchers expected the molecule to degrade faster, they note that there is a dearth of data on the fate of the molecule in seawater and
dispersants in the deep ocean, making any interpretation scientifically tentative. Instead, they see this study as a foundation for future studies.
"By knowing how the dispersant was distributed in the deep ocean, we can begin to assess the subsurface biological exposure, and ultimately what
effects the dispersant the dispersant may have had," another study co-author, David Valentine from the University of California at Santa Barbara,
said in a statement. "The results indicate that an important component of the chemical dispersant injected into the deep ocean remained there and
resisted rapid biodegradation. This knowledge will ultimately help us understand the efficacy of the dispersant application as well as the biological
Valentine said that the decision to use the dispersants at the sea floor "was a classic choice between bad and worse," and that scientists will need
to do more studies on the chemicals' biological effects. "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," he said.
The existing scientific literature indicates that toxic concentrations of DOSS are about 1,000 times more concentrated than the highest concentration
Kujawinski and colleagues observed, which suggests the concentrations of the molecule they detected in the deep ocean are not toxic to the ecosystem
Kujawinski noted, however, that she's unclear on how long organisms were exposed to the chemical in those toxicity studies. In any case, most if not
all of those studies were conducted on coastal organisms such as blue crab.
"One of the concerns about this deepwater application is that it affects a different group of organisms, deep sea corals, deepwater fish, and so
on," she told me. "And the question is whether or not they would be as sensitive, more sensitive, or less sensitive, as the organisms that were
Findings were published online today in the American Chemical Society journal Environmental Science & Technology.