Just days after the publication of a study finding that chemical dispersants meant to clean up the 2010 Deepwater Horizon oil spill in the Gulf of Mexico actually made the oil more toxic, a study in Environmental Science & Technology reveals that the dispersants failed even at their primary goal: preventing oil from reaching the ocean surface.
The study was conducted by researchers from the University of Miami, Columbia University, Colorado School of Mines and SUNY at Stony Brook.
The 2010 blowout of the deep water Macondo well produced the worst gulf oil spill in U.S. history. As experts searched for a way to cap the rupture, the Environmental Protection Agency ordered the injection of chemical dispersants at the wellhead. This was the first time that such chemicals had been used in large quantities and over a prolonged period of time in deep water (they are designed for breaking up oil slicks on the surface of the water).
The idea was that the dispersants would break up and scatter the oil as it gushed from the rupture, thereby preventing oil from ever reaching the delicate coastal and marsh ecosystems at the ocean's surface.
Tracking the oil plumeThe new study is the first to examine the effectiveness of this unorthodox strategy. To test the effects of the dispersants, the researchers constructed a model and a three-dimensional simulation of the Deepwater Horizon spill. The model's accuracy was demonstrated through its ability to correctly predict various, unique elements of the oil plume, including its direction and "the strange layering of oxygen deficit anomalies that we observed during our field sampling," oceanographer Ajit Subramaniam said.
"For us, it was like being able to track the ghosts of the oil plume."
Using this model, the researchers tracked the motion and behavior of the oil plume both with and without the chemical dispersants.
"Regardless of whether you have the dispersant in the water mixture or not, the amount of oil reaching the sea surface remained relatively unchanged," lead researcher Claire Paris, said.
The dispersants may have failed because the oil was already gushing under so much pressure that individual droplets were already widely dispersed, Paris suggested.
"Deepwater drilling into large, high-pressure reservoirs of oil and gas located far offshore and hundreds of meters below the ocean's surface involves risks for which we were not adequately prepared," she said.
The study comes only days after a study in the journal Environmental Pollution reported that dispersants actually made the oil from the spill 52 times more toxic, rather than less. And in March, a study in Geographical Research Letters reported that oil bearing the unique chemical signature of the Macondo well was still entering the food chain up to a month after the gushing well was capped. Because the oil contaminated zooplankton which were in turn eaten by shrimp and baby fish, marine animals living far from the well site were found to be contaminated months later.
