LSU AgCenter and Louisiana Sea Grant researchers Chris Green and Andy Nyman are studying the effects of dispersants used after the 2010 Deepwater Horizon oil spill. Photo by Olivia McClure/LSU AgCenter

LSU AgCenter and Louisiana Sea Grant researcher Chris Green holds a dish of FA-Glu, a microbe-based dispersant being used in experiments. Photo by Olivia McClure/LSU AgCenter

News Release Distributed 09/10/14

BATON ROUGE, La. – Four years ago, as nearly 5 million barrels of oil flowed into the Gulf of Mexico after the Deepwater Horizon oil rig exploded, desperate cleanup crews applied dispersants to break up the oil that people worried would have profoundly negative effects on coastal wetlands and wildlife.

But dispersants like COREXIT 9500A, which was used in 2010, may have made the oil even more dangerous to aquatic life, according to LSU AgCenter and Louisiana Sea Grant scientists who have been studying the effects of the Deepwater Horizon spill.

Dispersants break oil into smaller pieces so it spreads throughout the water column. The downside is that they also make oil easier for fish and other life in the Gulf to ingest and absorb, said Chris Green, associate professor at the AgCenter's Aquaculture Research Station.

Green and AgCenter wetlands biologist Andy Nyman tested hundreds of Gulf killifish, a popular baitfish, and found that oil becomes less toxic over time, partially because bacteria that live in the Gulf eat the toxins. While fish populations take a significant hit when oil first spills, they are able to survive later on, Green said.

That doesn't necessarily mean those fish are healthy, however.

"They still had signs of toxicity in their bodies," Green said. "That can cause stresses, but probably not death. The toxins build up in their bodies, and they can have developmental, endocrine and reproductive health problems."

Salinity, which increases as one moves farther away from the coast, also affects the oil’s toxicity, Nyman said. Greater salinity causes common surfactants, a main ingredient of dispersants, to become more toxic, affecting a fish's ability to regulate ions.

There are many kinds of surfactants, including those found in everyday items like toothpaste and shampoo, but dispersants containing them make oil more toxic, he said.

Nyman and Green are testing FA-Glu, a dispersant made by Modular Genetics from microbes rather than chemicals. Nyman said FA-Glu looks to be less toxic, although it is not commercially available yet.

Nyman said there might be a relationship between the shape of dispersant molecules and their toxicity and effectiveness. If so, scientists could genetically engineer better microbes to create safer, better dispersants.

"We can't make the oil less toxic, but we can make the dispersant less toxic," Nyman said. "If we can help figure out how to design less toxic surfactants and more effective oil spill dispersants, that could make a huge difference, if we ever have an oil spill again."

Nyman and Green's work is funded by a grant from the Gulf of Mexico Research Initiative and the U.S. Environmental Protection Agency.

Olivia McClure