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Five years after the explosion of the Deepwater Horizon rig, no one knows for certain how much oil gushed into the Gulf of Mexico in the 87 days it took BP to seal its well.

At trial, lawyers for the oil giant argued only 3.26 million barrels leaked into the Gulf, while the U.S. government pegged the number closer to 5 million. A judge ultimately split the difference, settling on 4 million.

The difference between BP’s estimate and the government’s—1.74 million—is a big gap. Researchers at Florida State University recently reported finding that between 129,000 to 210,700 barrels of spilled oil wound up on the Gulf floor, about 60 miles southeast of the Mississippi Delta. It has seeped into the ground, which is both good (because it won’t be washing up on shore, where it can be a danger to birds) and bad (because it is contaminating worms, and threatening to poison the wider food chain, particularly fish).

Scientists arrived at the estimate—which accounts for somewhere between 3 to 5 percent of the total oil spilled in the 2010 disaster—after sampling sediment about 9,000 square miles around the Deepwater Horizon. Their findings were published in the latest edition of the journal Environmental Science and Technology.

Jeff Chanton, professor of oceanography at FSU and lead author on the study, believes the spill will continue to impact the Gulf ecosystem for years to come. “It’s a conduit for contamination into the food web,” Chanton said in last week.

The researchers caution that it’s hard to tell how much of the food chain will be affected because the crude is buried hundreds of meters below the surface. And they say there are other more immediate concerns for animals that suffered during the spill, such as Brown Pelicans, Northern Gannets, and herons.  

“There is coastal oil still around in the marshes that I'd be more concerned about in terms of bird life,” Chanton says.

Unfortunately, there’s not much more that can be done about that remnant oil. At this point, as much oil as can be cleaned from the marshes has been, says Chris Canfield, Լ����Ƶ VP of the Mississippi Flyway. "This is one big uncontrolled chemistry and biology experiment. We will be witnessing and trying to document this process for decades."

The fine BP will ultimately be forced to pay will be based on how much spilled, minus the amount it was able to recover through cleanup efforts. With roughly 800,000 barrels recovered, the remaining total is about 3.2 million. Just how much the company will have to pony up per barrel, though, remains to be determined. Under the Clean Water Act, it may have to pay as much as $4,300 per barrel of oil spilled. A shows that 70 percent of Americans think BP should pay the maximum fine allowed under the Act.  But ultimately a judge will decide after hearing arguments in the third and final portion of BP’s trial, which got underway last month.