Traces of the oil spilled during the Deepwater Horizon explosion in 2010 remained in areas along the Gulf Coast beyond the reach of cleanup efforts a decade later, according to a study published in the journal Frontiers in Marine Science.
Researchers, led by Edward Overton, a retired environmental chemist from Louisiana State University, analyzed about a decade of research into the aftermath 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 funds from BP following the spill.
They determined that while about 90% of the oil degraded, evaporated, or was broken down by bacteria in the first few months after the spill, 10% remained as solid residue that does not dissolve in the water. Much of it sank as marine snow, a term for organic matter that sinks to the depths of the ocean from the surface.
During this time, part of the tailings also washed up on the shore. If the residues washed up on the beach could be cleaned, it was not the same for the part which ended up in the humid environments, inaccessible by the equipment used for the cleaning. Coastal marshes comprise approximately 10,700 square miles of coastline, and the state has the largest area of salt marshes of any state.
While most tailings remained within the top 30 meters (about 98 feet) of the marsh shoreline, events such as hurricanes moved them farther into the marshes in some cases, Overton and his team found.
“[M]Most of the environmental consequences of oil spills are caused by hydrocarbons that have changed in composition, to a greater or lesser degree, from the material originally spilled,” the researchers added. “In many cases, the alterations represent significant compositional alterations affecting the chemical, physical and toxic properties of the residual material and affecting exposure pathways, and therefore their potential for environmental and remediation impacts.”