Oil residue from Deepwater Horizon spill still detectable along Louisiana coast: Study

Traces of oil spilled in the 2010 Deepwater Horizon explosion remained in areas along the Gulf Coast, beyond the reach of cleanup efforts, a decade later, according to research published in the journal Frontiers in Marine Science. 

Researchers, led by retired Louisiana State University environmental chemist Edward Overton, analyzed about a decade of research on the aftereffects of the spill combined with their own data. The research was funded by the Gulf of Mexico Research Initiative, an independent research program created with BP funds in the wake of the spill. 

They determined that while about 90 percent of the oil degraded, evaporated or was broken down by bacteria in the first few months following the spill, 10 percent remained as solid residue that does not dissolve in water. Much of this sank as marine snow, the term for organic material that descends to the deeper ocean from near the surface. 

Meanwhile, a portion of the residue also washed up on shore. While the residue washing up on the beach could be cleaned up, the same was not true of the portion that ended up in wetlands, which are inaccessible by the equipment used for cleanup. Coastal marshes comprise about 10,700 square miles of the coastline, and the state has the most salt-marsh acreage of any state. 

While most of the residue stayed within the first 30 meters (about 98 feet) of marsh coastline, events such as hurricanes moved it farther into marshlands in some cases, Overton and his team found.  

“Most environmental consequences from oil spills are caused by hydrocarbon material whose composition has changed, to lesser or greater degree, when compared to the initial spilled material,” researchers added. “In many cases, the alterations represent significant compositional alterations affecting the residue material’s chemical, physical, toxic properties and affecting routes of exposure, and thus their potential for environmental impacts and remediations.”