Diamondoids For Tracing Oil Spills

Forensic investigators searching for oil spill culprits have a new tool for tracking down whodunit. Researchers at Environment Canada, in Ottawa, characterized diamondoid compounds for use in fingerprinting spilled oil distillates of low or medium molecular weight, such as diesel and jet oil (Environ. Sci. Technol., DOI: 10.1021/es060675n).

When environmental chemists want to track down the origin of a spill, they compare−often using a combination of gas chromatography and mass spectrometry−the constituents of spill samples with suspected sources. Commonly used biomarkers for crude oil spills are high-molecular-weight terpanes and steranes that get removed during refining and are therefore not ideal for fingerprinting lighter distillates. But lighter distillates are often implicated in groundwater contamination from underground fuel receptacles at gas stations or military bases. Sinking ships also release light- to midrange distillates because they use diesel in fuel, either directly or as an agent to reduce fuel viscosity.

Enter the diamondoids, a family of rigid, three-dimensionally fused cyclohexyl alkanes such as diamantane. With cage structures that look, as one might suspect, like diamonds, the compounds are naturally occurring in oil.

The ratio of different diamondoid compounds provides a regional signature for the oil's origin, says study author Zhendi Wang. The flora and fauna in Saudi Arabia vary from those in Alberta, so when organic matter decomposes with heat and pressure, diamondoids are produced in varying amounts, providing a regional signature.

During refining, diamondoids are concentrated in petroleum products. To boot, the researchers find that higher-molecular-weight diamondoids are not easily removed by evaporative weathering or altered by microbial degradation. This means diamondoids remain a usable forensic standard over a long period of time.

"Previous methods leave a lot to be desired for light- to midrange spills," comments Jeffrey W. Short, a research chemist with the National Oceanic & Atmospheric Administration's National Marine Fisheries Service. "This new method fills a void."