Smoke billows from controlled oil burns near the site of the BP Plc Deepwater Horizon oil spill in the Gulf of Mexico off the coast of Louisiana, U.S., on Saturday, June 19, 2010.  (Derick E. Hingle/Bloomberg)

When the Deepwater Horizon oil rig exploded on April 20, 2010, the immediate victims were clear enough. Eleven employees died in the blaze. There was also the ocean itself, suddenly covered in approximately three million barrels of crude. Birds of the sea became fatally entangled in oil scum. Dead fish floated to the surface. Dolphin populations declined.

But the BP oil disaster also took another, slower toll. Thousands of men and women who had helped clean up the spill gradually became ill. Lungs began to burn. Skin began to blister.

Nearly five years after the worst offshore spill in U.S. history, a new study by researchers at the University of Alabama at Birmingham suggests that an oil dispersant widely used during the cleanup of the BP disaster is capable of causing damage to humans and marine animals alike.

In the study, published in PLOS ONE on April 2, scientists focused their attention on a dispersant called Corexit EC9500A.

Nearly two million gallons of Corexit were sprayed atop the oil spill to help break down the petroleum. But in their study, the UAB scientists found that the dispersant can seriously damage epithelial cells, such as those in the lungs of humans or the gills of marine animals.

“The evidence that Corexit causes structural and functional abnormalities in airway tissue includes dispersant-induced cell detachment, edema, contraction in cell diameter and increased permeability,” Prof. Veena Antony, M.D., the paper’s senior author, said in a UAB news release.

“There were some 48,000 workers involved in the cleanup operations, and it is possible that workers were exposed to Corexit via inhalation,” Antony said. “Cough, shortness of breath and sputum production were among symptoms expressed by workers.”

In a statement emailed to the Washington Post, BP responded:

“The paper published by the University of Alabama at Birmingham provides no data to suggest that response workers or aquatic life were exposed to harmful levels of dispersants in the wake of the Deepwater Horizon accident,” BP said. “The laboratory study focused not on whether dispersants had an impact in the Gulf, but on how a respiratory effect could occur and how any such effect could be counteracted.”

George Barisich, a Louisiana fisherman who spent weeks helping to skim oil from the waters he loved and relied upon for a living, was one of those who says he developed respiratory problems while working on the oil spill that later developed into pneumonia.

“After that, I found out that I couldn’t run,” he told the AP. “I couldn’t exert past a walk.” Barisich’s doctor declined to comment, according to the AP.

Barisich is one of potentially 200,000 people, according to the AP, who could take advantage of a medical settlement with BP regarding future negative health effects related to assisting in the cleanup.

In addition to noting that the study showed only that a respiratory effect could occur–rather than did occur–BP also said the Centers for Disease Control and Prevention had found no evidence dispersants caused health problems for cleanup workers.

“Federal agencies and BP did extensive monitoring, including collecting 30,000 air monitoring samples, and found that response workers and the public were not exposed to dispersant compounds at levels that would be expected to result in any significant adverse health effects,” BP’s statement continued. “Also, the multi-agency Operational Science Advisory Team collected and analyzed water and sediment samples and observed none that exceeded the EPA’s aquatic life benchmarks for dispersants.”

The UAB study is one of several to be published in preparation for the disaster’s fifth anniversary. A wider-ranging study from the National Wildlife Federation linked the 2010 oil spill to a four-fold increase in dolphin deaths along the Louisiana coast as well as dwindling populations of sea turtles, trout and pelicans. The NWF report, “Five Years and Counting: Gulf Wildlife in the Aftermath of the Deepwater Horizon Disaster,” looks at how no less than 20 species are faring after the massive oil spill.

“Wildlife from sperm whales to marsh ants are still feeling the effects of the disaster,” said Ryan Fikes, the NWF’s Gulf of Mexico restoration scientist.

BP has also disputed the NWF study, calling it  “a work of political advocacy.” In its own recently released study, BP determined that the region is rebounding.

“The science is showing that most of the environmental impact occurred immediately after the accident – during spring and summer 2010 – in areas near the wellhead and along oiled beaches and marshes,” according to BP’s report. “Areas that were affected are recovering and data BP has collected and analyzed to date do not indicate a significant long-term impact to the population of any Gulf species.”

The debate isn’t just academic. How badly the BP spill damaged the region is the big question in an ongoing federal lawsuit against the company. Prosecutors have called for a $13.7 billion penalty under the Clean Water Act, but the oil giant recently argued that any fine larger than $2.3 billion could threaten the future of its business in the U.S. A judge has yet to decide.

The explosion of another oil rig in the Gulf of Mexico last week has stirred memories of the 2010 spill, although this time there was no leak.

The possibility of a repeat wasn’t lost on the UAB scientists. Their study suggested a novel way of preventing lung damage from Corexit by boosting an enzyme affected by the dispersant.

“Unfortunately, the likelihood of another oil spill is high,” Antony concluded, “and the need to use dispersal agents will remain.”