Chemical dispersants were supposed to make it easier for undersea bacteria to digest the oil that poured into the Gulf of Mexico after the Deepwater Horizon blowout.
But scientists who've been studying the aftermath of the 2010 disaster now say the controversial chemicals were a bust: Instead of eating the dispersed hydrocarbons, oil-munching microbes appear uninterested when crude and dispersants are mixed together.
A type of bacteria that normally would be first in line at the hydrocarbon buffet — and which surged when exposed to oil alone — "clearly declined in the presence of dispersants," a new study found. And another microbe actually ate the dispersants, University of Georgia oceanographer Samantha Joye said.
"Instead of making a community that was more efficient at oil degradation, the dispersant created a community that was really efficient at degrading dispersant, but not very efficient at degrading oil," said Joye, who leads a research group examining the effects of the oil spill on the Gulf.
The latest research by Joye and her colleagues was published this week in Proceedings of the National Academy of Sciences, a leading peer-reviewed scientific journal. The authors recommend moving cautiously before spraying dispersants — which are toxic on their own, and appear to be more toxic when combined with oil — onto the next spill.
"We need to know what the effects of these dispersants are on microbial organisms under a variety of conditions before we consider broad application again," Joye said.
The study was an attempt to address one of the unsolved mysteries of the disaster: how a persistent "bathtub ring" of oily residue remains on the sea floor long after the oil rig Deepwater Horizon blew up and sank in April 2010, taking 11 men with it.
Well owner BP used more than 1.8 million gallons of dispersants in trying to corral the undersea gusher. That kept much of the 160 million-plus gallons of oil released from sloshing ashore on the Gulf Coast — but it left the dispersed crude suspended in the waters offshore.
"Just because the oil goes off the surface doesn't meant it's been biodegraded," Joye said. "It's not visible anymore to your eye. But it's in the water, and we need to do a much better job of tracking its fate quantitatively, because we didn't do a very good job of that in Deepwater Horizon."
But she added, "We've got a lot more data than we had in 2010, to be fair ... It was not an easy decision to make."
'But we're learning again and again, and this is another good example, that a lot of times if you just leave nature up to its own devices, it will solve the problem a lot faster than getting humans involved.'
A wide area around the ruptured wellhead has been covered by a "dirty blizzard" of organic material and hydrocarbon residue. A 2014 study concluded that an area nearly the size of Rhode Island was coated with sediment that contained high concentration of hopane, a crude component that doesn't break down.
"We know there was a big oil plume that was stuck in the deep sea for a long time. A lot of the oil that went to the surface ended up coming back down and ended up back down there," said Erik Cordes, a Temple University biologist who has studied the damage to coral colonies in the Gulf. "I think a lot of it's in the deep sea, and a lot of it is going to be in the deep sea for a long time."
The new study suggests that oil might have been broken down nearly twice as fast without dispersants, said Cordes, who is part of the same Gulf research group as Joye but wasn't involved in this study.
"I understand that for a lot of the people who were trying to react to this situation and clean up the mess that was caused, it's hard to be seen sitting there on your hands and not doing anything about it," Cordes said. "But we're learning again and again, and this is another good example, that a lot of times if you just leave nature up to its own devices, it will solve the problem a lot faster than getting humans involved."
Joye's researchers took water samples from more than 3,800 feet beneath the surface of the Gulf near a natural seep, where hydrocarbons bubble out of the seafloor. They kept the samples in a University of Georgia laboratory at temperatures comparable to those found at that depth, introduced oil and dispersant in some of them in concentrations comparable to those recorded during the spill. Then they used a radioactive tracer to look for chemicals that are produced when bacteria digests some of the chemicals that make up crude oil. They ran similar tests on oil-laced surface water taken from near a sunken oil platform off the mouth of the Mississippi River.
BP declined comment on the study. But the American Petroleum Institute called dispersants "the most effective technique for combating larger spills in offshorewaters," and questioned whether a laboratory study could reflect "what is experienced in the real world."
"Artificialities introduced in the laboratory environment, when left unexplained, only add confusion to the issue and may result in faulty or inadequate measures being put into place should a spill event occur in the future," the trade association said in a written statement to VICE News.
But Joye said her team "reproduced what happened in the actual environment to at T."
"We were incredibly thorough, and we thought about every possible way to improve this experiment and optimize it and make it as realistic as possible," she said.
The blowout is expected to cost BP well over $50 billion in cleanup costs, compensation, and penalties by the time all claims are settled. Scientists say marine life in the stricken area is still suffering: Shallow-water corals up to 67 miles north of the well "declined significantly after the spill," the National Oceanic and Atmospheric Administration reported in October.
"The corals that were impacted really heavily have continued to go downhill and die, and the ones that had fairly light impacts, some of them have been able to recover," Cordes said.
Follow Matt Smith on Twitter: @mattsmithatl
Watch the VICE News documentary Oil and Water here: