New Study Found Deep Sea Chemical Dispersants To Be Ineffective for Deepwater Horizon Oil Spill

Credit: US Coast Guard.
On 20 April 2010, the Deepwater Horizon oil rig exploded, releasing 210 million gallons of crude oil into the Gulf of Mexico for a total of 87 days, making it the largest oil spill in US history.

A new study of the Deepwater Horizon response showed that massive quantities of chemically engineered dispersants injected at the wellhead—roughly 1,500 m beneath the surface—were unrelated to the formation of the massive deepwater oil plume.

A University of Miami Rosenstiel School of Marine and Atmospheric Science-led research team analyzed polycyclic aromatic hydrocarbons, the most toxic components of petroleum, based on the BP Gulf Science Data’s extensive water chemistry samples taken within a 10-km radius of the blowout site. The results of this analysis demonstrated that substantial amounts of oil continued to the surface near the response site, despite 3,000 tons of subsea dispersants injection—a new spill response strategy meant to curb the spread of oil and facilitate its degradation.

Dispersants application to manage surface oil spills has been shown to break the oil into small, easily dissolved droplets. However, the Deepwater Horizon was very different in that the oil entered the system at depth. The turbulent energy and pressure at such immense depths contributed to the rapid expansion of the spill and helped disperse oil in microdroplets and render the dispersant ineffective and unnecessary. 

“The results of this study are critically important,” said the study’s coauthor Samantha Joye from the University of Georgia. “This work shows clearly that the eruptive nature of the Macondo discharge was more than sufficient to generate the deepwater oil plume. Further, application of dispersant did not increase the amount of oil in the aqueous phase or change the distribution of oil over depth. These findings should change the way we think about spill response and calls for a reconsideration and reprioritization of response measures.”

The team’s research, led by Claire Paris, professor of ocean sciences at the University of Miami, founded on an unprecedented volume of data publicly available through the Gulf of Mexico Research Initiative Information and Data Cooperative, demonstrated that the formation of the massive deepwater oil plumes was unrelated to the new response. They further show, in agreement with previous studies, that plumes of oil persisted in the Gulf months after the spewing wellhead was capped 87 days later. The powerful chemical dispersant, called Corexit, may have added to the ecological damage by suppressing the growth of natural oil-degrading bacteria and by increasing the toxicity of the oil itself.

“Our earlier work using computer modeling and high-pressure experimental approaches suggested that pumping chemical dispersants at the spewing wellhead may have had little effect on the amount of oil that ultimately surfaced. But empirical evidence was lacking until the release of the BP Gulf Science Data. When completely different approaches converge to the same conclusion, it is time to listen,” Paris said. “There is no real trade-off because there is no upside in using ineffective measures that can worsen environmental disasters.”

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