A field experiment in the North Sea has provided valuable insights that could help shape the emergency response in the immediate wake of an oil spill disaster.
It’s well known that oil and water don’t mix. Less well known is the fact that when petroleum is spilt 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 marine life, while evaporated compounds may pose a risk to rescue workers or populations downwind of an accident site.
A team of European and American researchers have shed new light on the poorly understood fate of hydrocarbons during the first 24 hours after an oil spill, as reported in the journal Environmental Science & Technology.
Oil ‘mutates’ within hours
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 (EPFL) and the Swiss Federal Institute of Aquatic Science and Technology (Eawag).
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, often several days after the spill.
Learning from a controlled oil spill
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. By studying this relatively small oil release – analysing the hydrocarbon compounds in samples collected from the oil slick and surrounding water – they gained a better understanding of what goes on in much larger spills. Their findings could help assess the risks to underwater life and 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. Results from the study will provide scientists with tools to better assess the immediate impact of future disasters on humans and the environment, as well as to plan the emergency response, even in settings that differ strongly from those encountered in the North Sea.