Magazine article Oceanus

Finding a Drop in the Ocean: Sensitive Method Detects Tiny Traces of Dispersant in the Gulf

Magazine article Oceanus

Finding a Drop in the Ocean: Sensitive Method Detects Tiny Traces of Dispersant in the Gulf

Article excerpt

Marine chemist Elizabeth Kujawinski had developed her analytical method for entirely different research purposes. But she recognized that it could readily be adapted to track chemical components from the Deepwater Horizon oil spill, as well as the dispersant used to try to clean it up.

Kujawinski brought into play a device with a powerful 7-tesla magnet (seven times stronger than the average MRI) and an intimidating name: a Fourier transform ion cyclotron resonance mass spectrometer, or FT-ICR-MS. It can detect and measure vanishingly tiny amounts of an individual compound in a mixture containing tens of thousands of compounds.

Kujawinski spearheaded the grant proposal to install the FT-ICR-MS at Woods Hole Oceanographic Institution (WHOI) in 2007. Since then she and WHOI colleagues Melissa Kido Soule and Krista Longnecker have been using it to develop highly sensitive analytical methods to tease out the complex mishmash of organic matter dissolved in seawater. These molecules--either made or used by marine microbes and other organisms--are like bread crumbs that can guide researchers to find key biochemical pathways that allow living things to thrive and make the entire ecosystem run.

In research published online Jan. 26, 2010, in the journal Environmental Science & Technology (ES&T), Kujawinski and colleagues showed that the highly powerful mass spec and their method were also well-suited to detect, measure, and definitively identify minute quantities of chemical compounds from the Deepwater Horizon spill, including a compound in the dispersant Corexit. The dispersant has been used often on the ocean surface to break down oil clumps and make the oil easier to clean up. But never before had so much been used, and never before had the dispersant been released in the deep ocean.

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Kujawinski and colleagues' method is a thousand times more sensitive than that used by the U.S. Environmental Protection Agency to track Corexit and could be used to monitor the dispersant over longer time and distances, she said. As such, it provides a means to answer some key questions: What happened to the approximately 800,000 gallons of the dispersant released in the deep sea? Was it effective? Might it have impacts on the environment, deep-sea coral communities, and deep-water fish such as tuna?

The "metabolomics" of the ocean

Kujawinski received samples of seawater from in and around the oil spill collected in May, June, and September of 2010 by David Valentine, a scientist at the University of California, Santa Barbara, and co-author of the ES&T paper. Using their technique, Kujawinski and colleagues provided a first glimpse of what happened to the dispersant. They detected one of the dispersant's key components, called DOSS (dioctyl sodium sulfosuccinate)--in concentrations of parts per million. It was present months after it was injected into the depths, indicating that the dispersant had not been rapidly biodegraded by microbes.

The researchers also detected DOSS in even lower concentrations (parts per billion) in a plume of oil and natural gas that flowed 1,100 meters deep in a southwesterly direction away from the broken well. That indicated that the dispersant did not itself become randomly dispersed, but rather became trapped in the deep-water plume of oil and natural gas.

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"The decision to use chemical dispersants at the seafloor was a classic choice between bad and worse," Valentine said. "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. …

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