In the wake of hurricane Isaac, which first made landfall in the southeastern states last Wednesday, residents of the Louisiana and Alabama coasts started noticing tar balls along the beach. Locals and public officials were quick to suggest that the churned up oil stemmed from the 2010 Deepwater Horizon oil spill, a disaster which saw 4.9 million barrels of oil leak into the Gulf of Mexico from a blown-out well on the sea floor. Putting an end to the speculation, Louisiana State University chemist Edward Overton confirmed that at least some of the oil strewn along the coast last week did in fact stem from the BP oil spill, reports the Associated Press.
The link between the new oil and the the BP oil was made based on the oil’s chemical “fingerprint.” There are multiple techniques with which different oil samples can be tied to one another. Scientists can test for the oil’s isotopic composition, for instance, or identify the oil’s precise chemical mix.
Crude oil is not one single compound but a mixture of different hydrocarbons and carbon-based chemicals. By identifying the mixture from oil known to have streamed from the blown-out Macondo well, scientists can then use it as a reference against which they can compare unknown oil or tar balls, like those strewn up by Isaac. The Washington Post:
Petroleum consists of carbon atoms strung in chains, branches and rings, with many hydrogen atoms attached. It contains thousands of distinct chemical compounds. They range from simple ones that evaporate easily because they contain only a handful of carbon atoms, to 40-carbon behemoths that aren’t broken down by weather, sunlight and microbes and end up as baseball-heavy tar balls.
Chemists can identify both the presence and quantity of hundreds of compounds using procedures called gas chromatography and mass spectroscopy. The ratios of one compound to another (with many compounds compared) is often enough to distinguish one oil sample from another.
Such chemical fingerprinting helped scientists tie the seeping oil to the Macondo well in the first place and since then has helped track its flow through the ecosystem.