Scientists are reporting that key chemical components of the 770,000 gallons of oil dispersants applied below the ocean surface in the Deepwater Horizon spill did mix with oil and gas spewing out of the damaged wellhead and remained in the deep ocean for two months or more without degrading. However, it was not possible to determine if the first deep ocean use of oil dispersants worked as planned in breaking up and dissipating the oil. Their study, the first peer-reviewed research published on the fate of oil dispersants added to underwater ocean environments, appears in ACS’ journal Environmental Science & Technology.
Elizabeth Kujawinski and colleagues note ongoing concern about the environmental fate of the 1.4 million gallons of dispersant applied to the ocean surface and the 770,000 gallons of dispersant pumped to the mile-deep well head during the oil spill in the Gulf of Mexico. Many studies show that dispersants added to surface oil spills prevent them from coating and harming sensitive coastal environments, but no large-scale applications of dispersants in deep water had been conducted until the Deepwater Horizon oil spill. Thus, no data exists on the environmental fate of dispersants in deep water, the scientists say.
The scientists collected and analyzed seawater samples from the Gulf of Mexico for the presence of a key dispersant ingredient, called DOSS (dioctyl sodium sulfosuccinate), during the active oil flow and again after the flow had ceased. They found DOSS became concentrated in the deepwater plumes of suspended oil and gas at depths of up to three-quarters of a mile and did not mix with the surface applications of dispersant. They also detected the dispersant ingredient at distances of nearly 200 miles from the well two months after deepwater dispersant applications ceased, indicating it was not rapidly biodegraded. Their data is not sufficient to resolve whether the dispersant was effective in dispersing the oil coming out of the wellhead. However, the scientists argue that the persistence of the dispersant over long distances and time periods justifies further study of the effects of chemical dispersant and oil mixture exposure.
The authors acknowledge funding from the National Science Foundation, the Gordon and Betty Moore Foundation and from the Woods Hole Oceanographic Institution.
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“Fate of Dispersants Associated with the Deepwater Horizon Oil Spill”
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