No disappearing act: Dispersant ingredient lives on months after BP oil disaster

Richard Denison, Ph.D., is a Senior Scientist.

Remember that old naïve saw, “Dilution is the Solution to Pollution”?   When it comes to the dispersants used last year to address the Deepwater Horizon disaster in the Gulf of Mexico, that axiom appears to be the operative mechanism.

Last week, researchers at Woods Hole Oceanographic Institute published data showing that a key component of the Corexit dispersant used by BP to address the oil spill, did not degrade – as had been predicted by just about everybody, including BP, the Coast Guard, the dispersant manufacturer Nalco and EPA.  In fact, it was still detectable when last looked for in September, 5 months after the spill began and at least two months after use of dispersants had ceased.

The researchers, led by chemist Elizabeth B. Kujawinski, report detecting dioctyl sodium sulfosuccinate (DOSS, CAS# 577-11-7) in samples taken from the residual oil and gas plume in the deep ocean.  In a release accompanying the study, they argue that the DOSS they detected most likely came from the subsurface application of dispersant, which was intended to mix with and disperse the oil before it reached the surface.

Nearly 800,000 gallons of DOSS-containing Corexit, BP’s dispersant of choice, had been applied below the surface by the time the well was finally capped last July 15.  That subsea use of dispersant was unprecedented, with Corexit having been approved in advance of the spill only for surface use.  Kujawinski and colleagues note that this amounted to 640,000 pounds of DOSS applied to deep ocean water in the Gulf between April and July.

DOSS was detected by the researchers 200 miles from the wellhead two to three months after dispersant use in the subsea, leading the researchers to conclude little degradation of DOSS was occurring.  Based on the concentrations detected, they conducted calculations that led them to conclude 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” (emphasis added)

The researchers said their methods were not able to differentiate between two possibilities:  that DOSS was present by itself, or that it was present on the surface of coated dispersed oil particles.  They also note that levels detected were well below published toxicity values for the dispersant ingredients.  But those levels are based on short-term effects testing using near-surface or coastal estuary-dwelling organisms.  The researchers cautioned that because “relatively little is known about the potential effects of this type of dispersant/hydrocarbon combination in the deep ocean,” much more study of potential toxicity is needed.

There goes yet another piece of conventional wisdom, which should remind us of that much less naïve axiom, “There is no away.”

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