By Amanda Mascarelli
Almost three million litres of chemical dispersants were injected into the broken Deepwater Horizon oil well during last year's spill, and lingered for months after the well was successfully capped, researchers say.
The dispersants travelled
By Amanda Mascarelli
Almost three million litres of chemical dispersants were injected into the broken Deepwater Horizon oil well during last year's spill, and lingered for months after the well was successfully capped, researchers say.
The dispersants travelled with the deep-water oil plumes in the Gulf of Mexico at depths of 1,000-1,200 metres, and degraded very little between May and September, according to a study published this week in Environmental Science and Technology.
The finding has mixed implications. On the one hand, it is positive that the dispersants remained in deep waters and didn't float up through the water column, where they would have mingled with surface layers, says Elizabeth Kujawinski, a chemical oceanographer at the Woods Hole Oceanographic Institution in Massachusetts, who led the study. "But the bad news is that it stayed there. It didn't really go away as quickly as maybe they had thought it would."
The fate of the chemical dispersants has been one of the biggest wild cards of the spill's legacy. Prior to the Deepwater Horizon disaster, dispersants had been used only to treat oil slicks at the surface and had never been tested in deep subsurface environments.
Many researchers expressed concern (see 'Debate grows over impact of dispersed oil') early on, when the decision was made to apply dispersants on such a large scale in the deep ocean, because so little was known about how the chemicals might interact with the oil and gas spewing from the wellhead, or how long the chemical brew would stick around.
Indeed, the non-profit Project on Government Oversight in Washington DC revealed this week that e-mail exchanges between scientists from government agencies, including the US Environmental Protection Agency (EPA) and National Oceanic and Atmospheric Administration (NOAA), that were tasked with leading the response to the Deepwater Horizon crisis seem to show that the Obama administration "may have ignored" EPA suggestions to use more conservative language in relation to the success of the chemical dispersants.
Corexit 9500A, the main dispersant that BP applied, both at the surface and in deep water, is a mixture of surfactants and hydrocarbon-based solvents. Dispersant works by breaking oil down into tiny droplets, which aids in its degradation and weathering.
The researchers measured one of Corexit 9500A's main ingredients, a surfactant called dioctyl sodium sulphosuccinate (DOSS), on cruises in the Gulf in May and June, and again in September, two months after the well had been capped. Their technique involved extra