Oil from Gulf of Mexico spill may still be present, particularly on the Gulf floor

Oil from Gulf of Mexico spill may still be present, particularly on the Gulf floor

Prior posts have noted that the dispersants used in the BP spill had a longer than anticipated life in the Gulf.  Additionally, prior posts have noted the evidence supporting the thesis that the oil was consumed by microbes unusually fast.  Recently published evidence indicates that the latter assertion may lack merit.

Underwater images show that, within 40 miles of the damaged wellhead, "huge" quantities of oil from the BP blowout taint the Gulf of Mexico seafloor.  The deposits are patchy, and range from small spots of oil to localized blankets several inches thick.  The oil is in the form of bacterial slime, mucus streamers that ranged from one millimeter to almost two meters long.  The key "ingredient" in the slime are surfactants which are secreted by many oil-eating bacteria, and render the oil easier for them to digest by breaking apart large globules of oil.  As the sticky slime picks up cells and other debris from the water, it becomes heavy and sinks.  The mucus streamers are distinct from oil that was chemically dispersed with Corexit, the commercial dispersant used by cleanup crews.  Corexit created an oil-water emulsion that looks like chocolate mousse under water, the researchers claim.

To test the hypothesis, the researchers collected a milliliter of oil from the BP well and added it to a liter of surface seawater that had been collected from an oil-free part of the Gulf.  After just one day, naturally occurring microbes in the water began growing on the oil. After a week, the cells formed blobs, held together by spit, that were so heavy they began sinking to the bottom of a jar. Two weeks later, large streamers of microbial slime and cells were evident. Brown dots visible inside the mix were emulsified oil.

When the researchers extracted cores of sediment from the Gulf's spill-impacted zones, the top sediment layers often showed signs of what appeared to be the microbial spit.  That layer also was devoid of living animals, forming an "invertebrate graveyard."  The researchers report seeing dead corals, crabs and sea stars in the affected seafloor areas.  Absent were sea cucumbers that are normally abundant in parts of the Gulf where natural petroleum seeps occur.  Damage was also evident above the seafloor.  Mortality in free-floating jellyfish and sea squirts proved especially high, researchers reported; also some worms had become nothing more than hollow tubes filled with the slimy goop that chemical fingerprinting methods showed had contained BP oil.

Also of interest was that oil was not the only spill-related pollution raining down onto the seabed.  Data also indicated that remnants of the burning of oil by spill-cleanup crews was also present on the seabed. Soot, which normally is not present in ocean sediment, turned up in the September 2010 water samples. Also found were an elevated ratio of certain combustion byproducts known as polycyclic aromatic hydrocarbons, or PAHs, in sediments directly under burn sites.

Information on the study can be found at http://www.boingboing.net/2011/02/23/highlights-from-aaas-1.html, http://www.nytimes.com/2011/03/22/science/22conversation.html, and http://blogs.discovermagazine.com/80beats/2010/09/14/bp-update-bottom-kill-nearly-complete-but-oil-found-on-seafloor/.