The fate of oil during the first day after an accidental oil spill is still poorly understood, with researchers often arriving on the scene only after several days. New findings from a field experiment carried out in the North Sea could help shape the emergency response in the immediate wake of disasters.
It is well known that oil and water don’t mix. Less well known is the fact that when petroleum is spilled onto a water surface, a fraction of the oil immediately begins to evaporate into the air or dissolve into the seawater. These dissolved toxic hydrocarbons can threaten aquatic species, while evaporated compounds may pose a risk to rescue workers or populations downwind of an accident site.
Following a spill, oil suddenly finds itself in a radically new environment – exposed to light, air, and the water surface after millions of years underground. “In its new environment, the oil immediately begins to change its composition, and much of that change happens on the first day,” explains Samuel Arey, a researcher at École Polytechnique Fédérale de Lausanne and the Swiss Federal Institute of Aquatic Science and Technology (Eawag) and corresponding author of the study. Oil is a complex mixture of many hydrocarbon compounds. Certain volatile compounds evaporate within hours, contaminating the overlying atmosphere. Others, such as toxic naphthalene, simultaneously dissolve into the seawater, posing a threat to aquatic life.
Especially since the Exxon Valdez catastrophe in 1990, which released over 40,000 cubic meters of oil into the ocean, researchers have sought to evaluate to what extent marine species in the vicinity of an oil spill are exposed to toxic hydrocarbons. But this question has largely remained debated, because many of the hydrocarbons are dispersed into the water or the overlying air well before scientists arrive at the site.
In order to collect data on the immediate aftermath of an oil spill, the researchers collaborated with emergency response specialists of the Dutch Rijkswaterstaat to recreate a four cubic meter oil spill in the North Sea, in a shipping zone already burdened by pollutants, 200 kilometers off the coast of the Netherlands. By studying this relatively small oil release, they were able to gain a better understanding of what goes on in much larger spills, with findings that could be useful to assess the risks to underwater life, as well as to emergency response team workers at the sea surface.
Thanks to a computer model that was tested against the data collected in the North Sea, the researchers are now able to extrapolate their findings to larger spills and other environmental conditions.