Sunday, 30 January 2011


As 42,000 gallons of crude oil a day erupt from the sea floor in the Gulf of Mexico at the site where an oil rig caught fire and sank, responders are working against the clock to contain and redirect the oil to keep it from hitting shore. But the degree to which this spill will be able to be cleaned up remains to be seen, according to experts.
One potentially helpful fact is that because the leak is around 50 miles offshore, teams have greater ability to protect the coastline than in the infamous 1989 spill in Prince William Sound, Alaska, when the oil tanker Exxon Valdez ran aground and dumped nearly 11 million gallons of crude oil along the coastline and killed tens of thousands of birds and other wildlife.
"No two oil spills are the same," said Stanley Rice of the National Oceanic and Atmospheric Administration in Juneau, Alaska, who has studied the aftermath of the Valdez spill for the last 20 years. 
Nonetheless, lessons learned and legislation passed following the Valdez spill will be guiding the efforts to contain the oil now spewing into the Gulf.
"I think one lesson over time is, to have the equipment and be ready for the spill," Rice said. "The other lesson is, once it gets into sediments or wetlands it's very difficult to deal with. There's going to be a lot of effort to keep it from getting to wetland shores."
"I think we're in really strong shape," said oil spill scientist Chris Reddy of the Woods Hole Oceanographic Institution in Woods Hole, Mass. As a result of the Oil Pollution Act of 1990, passed following the Valdez spill, stakeholders carry out practice drills in anticipation of spills and have a coordinated procedure for responding. "We're in really good hands," he said.
But he agrees every spill requires a tailored response that can't entirely be anticipated. "We have very little knowledge of deep water spills," he said, in contrast with a tanker spill where the oil is released at the surface. "You have the plume of oil coming upward. How it behaves at the surface depends on the type of oil, the currents, the water temperature."
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Clean Up: Natural and Human-Led
Crude oil is a complex mixture of chemicals. Evaporation will remove some of the oil components, including many of the most toxic compounds, Reddy explained.
Other crude oil components will dissolve into the water. This helps by diluting these chemicals into a larger volume -- the entire water column instead of just the surface -- but these compounds are often toxic and until they can be widely dispersed, they may reach concentrations high enough to kill ocean life.
Over time, other processes will play a role. "Nature's bacteria do a tremendously good job of cleaning up oil spills," Reddy said, by eating the oil for energy. "But there's usually some lag time before the bacteria kick in."
Meanwhile, human efforts at the beginning include setting out booms that surround the oil to keep it from spreading. Oil skimming boats can suck up the contained oil, and snares that look like cheerleaders' pom poms can be set out on the spill to soak up oil and then be removed.
Dispersants can be used to break the oil into droplets that can dissolve into the water. Although they remove oil from the surface where it threatens birds and mammals, their downside is that they bring the oil into the water where animals like fish and shrimp can be exposed.
The goal, Rice said, is to protect places where long-term contamination is likely: "The lesser of two evils is not to have the habitat affected," he said. "We're willing to absorb more acute mortalities in the short term. If the habitat gets contaminated we have this chronic situation where several species are affected over long periods of time."
Valdez Spill Lessons
Indeed, one of the lessons of the Valdez is that the effects of a spill can persist far longer than researchers anticipated. "We used to think of things in terms of a couple of years, Rice said. "Now we think of things in a couple of decades."
For instance, a recent study in Environmental Toxicology and Chemistry showed that harlequin ducks in Prince William Sound are still exposed to oil. These birds live in shallow water near the shore and eat mussels and snails, which makes them especially vulnerable to continued exposure to oil trapped in beach sands, said study lead author Daniel Esler of Simon Fraser University in Burnaby, British Columbia.
"Most of the residual oil and especially the stuff that's still potentially toxic to wildlife is buried in the sediment of the beaches." Esler said. "If you were there right after a storm or if an otter had just been there digging, the oil would still be liquid and still have an odor to it."
"The amount of oil that is there is a teeny fraction of what spilled," he added. "But a teeny fraction of 11 million gallons is still a lot of oil."
Salt marshes along the Gulf Coast, like the shallow shore areas of Prince William Sound, provide sediments and lots of little pockets where oil can be trapped and stay. "If it does make it to the beaches and the marshes, the lesson from the Exxon Valdez is that it's likely to be there for a while and it's not going to be good for wildlife," Esler said.
Another lesson from the Valdez is that certain approaches do more harm than good. Steam cleaning rocks on beaches after the Valdez spill killed barnacles and mussels, says ecologist Dee Boersma of the University of Washington in Seattle. She adds that many of the birds people tried to save by washing with soap to remove the oil died anyway -- with only the added stress of the washing and human handling to show for it.
"Washing sand or rocks or birds doesn't do a lot of good," Boersma told Discovery News. "It just makes us feel better."