An active ingredient in the chemical dispersants pumped deep into the Gulf of Mexico after BP's oil spill didn't break down, but remained for several months in a deep layer of oil and gas, according to a study published Wednesday.
The study provides the first data about what happened to the 800,000 gallons of dispersants that were pumped into the oil and gas that gushed a mile below the surface from the broken BP well. Additional studies are under way to find out if there were toxic effects from the dispersants in the deep water.
Elizabeth Kujawinski, a chemist at the Woods Hole Oceanographic Institution in Massachusetts, and a team of colleagues analyzed samples from three research cruises: two near the wellhead while the oil was gushing, in late May to early June and again in mid-June, and a third in September in a location southwest of the well, where currents had carried a deep plume of oil and gas.
The scientists found a key compound of the dispersants, dioctyl sodium sulfosuccinate or DOSS, in concentrations of parts per million in May and June. They found lower concentrations, in parts per billion, in September, after the well was capped on July 15 and the use of dispersants ended.
Kujawinski said her team members were somewhat surprised to discover that the compounded had degraded at a low rate or not at all. Calculations showed the lower concentration in September was the result of dilution. If biodegradation had occurred, the concentration would have been much lower.
Environmental Protection Agency scientists previously reported that they detected no lingering dispersants in waters near shore. Kujawinski, however, said her team used a mass spectrometer that was 1,000 times more sensitive than the method used by the EPA.
"We can see it further and longer than the EPA can," she said in an interview.
Most toxicity studies of dispersants have assessed their toxicity on small fish and other animals that live in coastal waters, Kujawinski said. Her deep-water study found toxicity levels that were below the limits in these published reports. However, additional studies may be needed to nail down the environmental impact on the unique environment and organisms in the deep water.
Some of those studies on corals are under way, but "they're just inherently difficult and slow," said Charles Fisher, a professor of biology at Penn State University who's studied deep-sea corals in the Gulf of Mexico, at a conference on Wednesday at the University of Georgia.
It's also not known yet how effective the dispersants were in breaking down oil droplets in the deep water, Kujawinski said. She said her team's study would help scientists design further studies. It was published in the journal Environmental Science and Technology.