ETX.10.Gulf.spill - News | Focus BETWEENTHE DEVIL AND THE...

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News | Focus Dispersant is released off the coast of Houma, Louisiana, from a Basler BT-67 fixed-wing aircraft, 5 May 2010 (above). Surface oil (right, photographed 7 June 2010 off the coast of Pensacola, Florida) will—with wind, wave action, and other factors—naturally disperse to some degree. The addition of chemical dispersants enhances the process, allowing a large part of the surface slick to move into the water column in the form of tiny droplets. At press time, nearly 2 million gallons of dispersants have been applied to the Gulf of Mexico. About 42% of that has been applied subsea at depths where these chemicals have never been tested. DISPERSANTS IN THE GULF OF MEXICO BETWEEN THE DEVIL DEEP BLUE SEA AND THE A 338
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Focus | Between the Devil and the Deep Blue Sea As this article goes to press, the scope of the worst oil spill in U.S. history remains a moving target. The explosion and collapse of the BP-owned Deepwater Horizon oil rig on 20 April 2010 uncorked an underwater geyser that for 85 consecutive days shot an estimated daily load of 1.47–2.52 million gallons 1 —and possibly more—into the Gulf of Mexico. Caused by igniting gases leaking from API Well No. 60-817-44169, located 42 miles off the Louisiana coast and 5,000 feet underwater, the explosion killed 11 workers. At press time more than 600 miles of coastline was fouled by the oil, and about one-third of the Gulf’s fishing grounds were closed. 2 BP engineers stanched the flow on July 15 with a mechanical cap, but oil and methane seeps have since appeared near the wellhead, raising new questions about the integrity of the well and, indeed, of the seafloor. 2 No one knows what will happen next. The Deepwater Horizon spill has generated heart-wrenching scenes of dying birds, oil-fouled marshes and barrier islands, and traumatized coastal residents. But a key image from this story isn’t even visible: mysterious plumes of dispersed oil droplets flowing deep underwater. To some degree, these plumes arose from intense physical pressures at the mile-deep wellhead, which broke the oil A 339 Left: Stephen Lehmann/ U.S. Coast Guard. Below: © Brandon Kruse/ The Palm Beach Post /ZUMApress.com
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Focus | Between the Devil and the Deep Blue Sea A 340 VOLUME 118 | NUMBER 8 | August 2010 Environmental Health Perspectives into droplets that never reached the sur- face. But spill response workers also used chemical dispersants—mixtures of sol- vents, surfactants, and other proprietary additives—to achieve a similar effect. Sprayed from the air and applied direct- ly at the gushing wellhead, dispersants changed the oil’s physical and chemical properties, splitting it into tiny drop- lets that measure roughly 10 microns in diameter (naturally dispersed oil droplets are about 10 times larger). 3 Dispersed oil droplets get pulled (or “entrained”) into the water column, where they undergo a range of removal processes, mainly metab- olism by marine bacteria.
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