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The Great Vanishing Oil Spill

Microbes may have eaten away at BP’s oil in deep water; now the marshland needs help.
August 27, 2010

Microbes may become the heroes of the Gulf of Mexico oil spill by gobbling up oil more rapidly than anyone expected. Now some experts suggest we ought to artificially stimulate such microbes in stricken marshland areas to aid their cleanup.

Crude crunching: Rod-shaped Oceanospirillales bacteria feed on a droplet of crude oil in this sample from a deep oil plume near BP’s spill. The bacteria was collected by researchers from the Lawrence Berkeley Laboratory.

Evidence published this week shows that deep-water microbes in the Gulf may be rapidly chewing up BP’s spilled crude. This could sway federal authorities to use petroleum-digesting microbes or fertilizer additives that can stimulate naturally occurring bacteria for future spills. Such measures were originally rejected for the BP spill.

Ralph Portier, a marine toxicologist at Louisiana State University, says the EPA approves of such measures in general, but they weren’t approved for the Gulf spill because it was thought they wouldn’t be necessary–a presumption that now appears to be correct.

Oil has disappeared from the Gulf’s surface waters since BP capped its blown-out well on August 15. Yet most of the estimated 4.9 million barrels of oil are unaccounted for. Some of BP’s oil, however, has reached more than 100 miles of sensitive Gulf marsh, and may remain lodged deep within sediments for years.

Portier says cleanup authorities are following a 2001 federal position paper arguing that stimulating biodegradation was unnecessary in the Gulf ecosystem. The Gulf already harbors microbes adapted to degrading the region’s naturally occurring underwater petroleum seeps, the federal paper said.

Microbial ecologist Terry Hazen, a bioremediation expert at the U.S. Department of Energy’s Lawrence Berkeley Laboratory, says that this reasoning is correct for dispersed oil. Hazen led a team that identified a strain of microbes rapidly breaking down oil at a depth of 1,100 meters and icy temperatures as low as 5 °C–conditions where biodegradation is expected to proceed slowly. The research appears this week in the journal Science.

Hazen’s team examined one of several plumes of oil droplets emanating from BP’s blowout, and observed rod-shaped bacteria feasting on the 10- to 60-micrometer droplets fast enough to halve the oil every two to six days. That rate contradicts a study of the same plume conducted by the Woods Hole Oceanographic Institution, and published in Science earlier this month, that found meager oxygen consumption (to be expected where large numbers of microbes are consuming oil) and concluded that the oil was therefore not being broken down.

The divergence, according to Hazen, is explained by the thin concentration of the oil. While immense, stretching over 35 kilometers, the oil in the studied plume maxed out at 10 parts-per-million. Oxygen depletion by microbes would thus be negligible, argues Hazen.

In recent weeks, Hazen’s group has detected no oil, although it’s possible the oil could simply have been carried out of view by Gulf currents. Federal incident commander Thad Allen told Technology Review on Wednesday that he needs a more rigorous measurement program to “get a handle on what is actually out there in the water.”

Hazen bets that the dispersed oil has indeed broken down, and says some credit for that goes to the 1.84 million gallons of dispersant sprayed on the spilling oil as part of the cleanup operation. This dispersant also likely acted as a bioremediation agent because the tiny droplets it created gave microbes more surface area to chew at.

Natural microbial activity, however, may fall short in marsh sediments where oil is concentrated and the supply of oxygen and nutrients is constrained, slowing microbial digestion to a crawl.

Artificial enhancements could speed up marsh recovery, says Portier. He says LSU scientists showed this to be true three years ago in a marsh in Lake Charles, LA, that was contaminated with heavy crude. They bolstered the marsh microbial community with an LSU-developed culture of oil-eating marsh microbes, along with diluted fertilizer. After 72 days, untreated sites still harbored more than half of their spilled oil, says Portier, whereas treated sites were clean enough to meet strict federal risk levels for residential areas.

Portier says he is working with a BP-backed research coalition of universities and state agencies that expects to have field trials underway in Gulf marshes next month.

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