Two years ago this week, the wellhead that ruptured on the sea floor of the Gulf of Mexico, sending 4.9 million barrels of oil into the water, was capped. After three months, the end of the largest oil spill in the industry's history was in sight.
With the help of nearly 2 million gallons of toxic chemicals known as dispersants, BP and government agencies involved in the response managed to prevent most of the oil from reaching the shoreline. But while the Gulf Coast's seafood and tourism industries are slowly recovering, the effects of those dispersants — used underwater for the first time ever — remain murky.
"My stomach churns when I hear people say, 'We dodged a bullet,' because I've heard it so many times, but we shouldn't be so quick to wave this off," said James Cowan, a professor at Louisiana State University's School of the Coast and Environment. "This notion of 'Come back to the Gulf, eat seafood, it's fine' is a problem."
The health risks of dispersants used in the response to the Deepwater Horizon spill are not yet fully known, said Cheryl Murphy, an environmental toxicologist at Michigan State University, in part because the contamination that began in phytoplankton may take years to rise up the food chain to the seafood eaten by humans.
Scientists are already spotting red flags. Cowan said the rates of dolphin and sea turtle deaths have risen to highly unusual levels in the Gulf of Mexico.
There is also clear evidence, he said, that contamination has been making strides up the food chain, with 2 to 5 percent of the gulf fish population affected. His greatest worry now, he said, is for fishermen who handle fish with lesions containing highly concentrated pathogens linked to the dispersants, which accelerate the breakup of oil.
Significant gaps remain in researchers' understanding of the dispersants' environmental consequences, according to a report released by the Government Accountability Office earlier this month. Despite $15.5 million in federal funding for studies on dispersants — including $8 million since the gulf spill — scientists have yet to answer basic questions about how the chemicals affect underwater environments and what their potential risks to human health may be as the chemicals and their combinations with oil droplets move up the food chain.
The main dispersant used in the spill response was Corexit, a cocktail of 57 chemicals manufactured by Illinois-based Nalco. It was neither the most effective nor the least toxic oil dispersants, and it is banned from use in oil spills in the United Kingdom and Canada. But BP claimed that only Nalco could provide the quantities of dispersant needed the week of the disaster. By the time the well was capped, about 1.1 million gallons of dispersants were sprayed at the wellhead in addition to the nearly 1 million gallons poured onto the surface.
On Aug. 2, 2010, the Environmental Protection Agency defended the use of dispersants, arguing that the threat they posed to the environment was no greater than that of the oil. But the picture is much more complicated than that, many scientists say.
When oil combines with the dispersant chemicals, the result is more toxic than either substance individually, and the depth at which dispersants were released raises concerns that currents are carrying their dangers far beyond the wellhead, Cowan said.