POCKETS of oil can survive for more than 30 years after an oil spill. It is unclear whether the oil could affect local ecosystems, but the finding has surprised researchers, suggesting that some oil spills may continue to pollute the environment indefinitely.
The discovery comes from the longest-running study of a major oil spill, which began shortly after the barge Florida ran aground off the coast of Massachusetts in September 1969, spilling 700,000 litres of diesel oil right into the backyard of the Woods Hole Oceanographic Institution. While that鈥檚 60 times less than the oil spilled by the Exxon Valdez, it became famous as one of the most closely studied oil spills in history thanks to the quality of the equipment and expertise in the area.
Seven years after the spill, plants had returned to the marshy coastline, and by 1989 the ecosystem was back on its feet. Studies of fish in the area showed elevated levels of enzymes that help them deal with oil in the water but, overall, the area seemed to be healthy. The marsh is still thriving today, and the oil spill seems but a distant memory.
Advertisement
However, more accurate analytical techniques have revealed oil trapped in the sediments at higher levels than thought. Chemist Christopher Reddy and his team at Woods Hole found up to 8 milligrams of oil per gram of soil 鈥� concentrations so high that you might be able to smell it 鈥� in layers 15 centimetres below the surface. That鈥檚 about the same as measurements taken seven years after the spill (Environmental Science and Technology, DOI: 10.1021/es020656n).
Even more surprising, the composition of that oily sludge hasn鈥檛 changed much over the years, indicating that bacteria have done very little to degrade the oil. 鈥淚t still looks like run-of-the-mill diesel fuel. We were flabbergasted,鈥� says Reddy.
The Woods Hole study sets a new benchmark for how long oil can linger in oxygen-deprived sediments, says Reddy. More worrying is that it suggests the contamination could persist indefinitely, he says, although both Reddy and Paul Boehm, an oceanographer with Battelle, an environment research consultancy in Massachusetts, point out that spills in other environments, such as rocky shorelines, are more likely to be scrubbed clean by the action of the wind and the waves.
And just because the oil is there doesn鈥檛 necessarily mean it鈥檚 harming life, says Boehm. Reddy hopes biologists will now investigate how burrowing creatures such as clams are faring in the area.