No S*&%t Sherlock, dispersants DON’T degrade quickly

Another disturbing paper about the BP oil spill was published this week.  The new study from Wood’s Hole researchers shows lingering traces of dispersant in the deepwater oil plume that spread out for 200 miles southwest of the Macondo well head.  The sampling took place over a number of months, showing that Corexit dispersant is slowly diluting and spreading out in Gulf of Mexico waters.

Kujawinski et al., 2010

…DOSS [a key ingredient of Corexit dispersants] was sequestered in deepwater hydrocarbon plumes at 1000-1200 m water depth and did not intermingle with surface dispersant applications. Further, its concentration distribution was consistent with conservative transport and dilution at depth and it persisted up to 300 km from the well, 64 days after deepwater dispersant applications ceased. We conclude that DOSS was selectively associated with the oil and gas phases in the deepwater plume, yet underwent negligible, or slow, rates of biodegradation in the affected waters.


Map view of DOSS concentrations at plume depth (∼1000-1200 m) in May/June (A) and in September (B) 2010. Color and size of dots indicate concentration magnitude in each plot. White = below detection; blue = <0.01 μg L-1; cyan = 0.011-0.1 μg L-1; green = 0.11-1.0 μg L-1; yellow = 1.0-9.0 μg L-1; red = >9.1 μg L-1. Black indicates samples taken at this location but not in plume depth horizon. The Deepwater Horizon oil spill site (MC-252) is denoted with a red star in both plots. The red hatched box in (B) denotes the subregion represented by (A). [Figure caption from Kujawinski et al. 2010

Why do I find this study disturbing?  Well first of all, the main argument in favour of dispersant use was their rapid degradation (public statements by BP and Corexit officials claimed this happened in DAYS).  But nope, dispersants are still there–any sea life swimming though the oil plume faces ongoing exposure to Corexit.  Second, it highlights the complex, ongoing consequences of such a large volume of oil in the Gulf.  A previous study showed that methane in the deepwater plume degraded rapidly.  Now it appears dispersant did not.  Crude oil is made up of hundreds of compounds, and the biological response and subsequent degradation of these compounds is not straightforward. We obviously lack enough scientific information to make long-term predictions–the Gulf of Mexico is a giant guinea pig in an unfortunate natural experiment.

Reference:  Kujawinski, EB et al. (2010) Fate of dispersants associated with the Deepwater Horizon Oil Spill.  Environmental Science &

Holly Bik (140 Posts)

I am a computational biologist at the University of California, Davis. My research uses DNA sequencing and genomics to study microbial eukaryotes (yeah, nematodes!) in marine ecosystems, with an emphasis on evolution and biodiversity in the deep-sea. I can neither confirm nor deny that I like Unix more than I like going to sea.

2 comments on “No S*&%t Sherlock, dispersants DON’T degrade quickly
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