After the 2010 BP Deepwater Horizon explosion, unprecedented amounts (approx. 210 million gallons) of oil rushed into the Gulf of Mexico. In a desperate attempt to minimize the damage, BP authorized pouring 1.84 million gallons more chemicals on top of the oil spill.
An adhoc experimentIt was hoped that these chemicals, known as dispersants, would help the oil break up into small bits instead of forming slicks, and that this would reduce the availability of the toxic components in the oil to aquatic life and prevent oil slicks from fouling the beaches and delicate marshes along the coast.
At the time, we tried to put the toxicity of these dispersant chemicals into perspective, noting that the active ingredients in the dispersants "are regarded as being of low concern, because they biodegrade very rapidly." Regulators presumably pinned their hopes on that fact because they approved use of the chemicals in the face of other studies showing they can be quite toxic to single celled organism in the short term (the same property that helps a chemical bind oil and break it up in water makes it effective at breaking up the fatty cell wall that holds in that bubble of water with all the little cellular machines of life).
What we didn't know thenNow we find that the key dispersant ingredient DOSS, which stands for dioctyl sodium sulfosuccinate, does not disappear quickly from the environment. Four years after the spill, scientists are still detecting DOSS in the deep sea water column and in oil contaminated "sand patties" on the beached. The DOSS in the deep water does not surprise researchers so much, because degradation slows down in the dark, cold environment far below the surface.
But on the beaches, with air and sun and warmth to fuel the microorganisms that help clean contaminants out of the environment, it was predicted that the DOSS would have long since disappeared. The researchers developed new methods to detect the DOSS when it is bound up with oil and clinging to sand, causing sand patties to form.
Don't touch the sand pattiesGulf beaches still have signs posted, warning people not to touch the sand patties. Just how toxic are these reportedly low levels of dispersant that are left over along the coast? Lead author Helen White, who teaches chemistry at Haverford College, says:
It’s hard to say because we don’t know how toxic it might be. The EPA has determined what concentrations of DOSS may be harmful to marine life in the water, but the toxicity of DOSS in solid (non-aqueous) forms like sediments or sand patties is not known. We know that if you measure ‘x’ amount of this compound in ‘y’ amount of water, that’s toxic. But you can’t compare those numbers to what we’ve found in the sand patties because we’re looking at this compound in a mixture of sand and oil.
It should be remembered that these dispersants are an awful lot like the chemicals we discharge every day from cleaning tasks in our homes and industries, but the mixture of the oil residue with the dispersants may present entirely new hazards to the environment and the people who occupy it. On the other hand, the fact that the DOSS has not yet degraded suggests it may be adsorbed or otherwise fixed so tightly into the sand patties that it really presents little risk of exposure.
Studies like these are important to help emergency responders understand how best to react when disaster happens, and to further our understanding of the still evolving situation after the Deepwater Horizon disaster.