Another piece of the Deepwater Horizon spill has fallen into place as scientists have determined the chemical makeup of the oil plume.

Using a sample from the very riser pipe that the plume escaped from, Woods Hole Oceanographic Institution chemist Christopher Reddy and his team ascertained that the plume was comprised of benzene, toluene, ethybenzene, and total xylenes – together, called BTEX – at concentrations of about 70 micrograms per liter.

By analyzing this particular sample, which was taken in June 2010, the scientists were able to determine what chemicals left the pipe before nature compromised it.

The discovery "helps explain and sheds light on the plume formation, and verifies much of what we thought about the plume's composition," Reddy in a news release about the researchers’ findings.

The BTEX in the plume was "significantly higher than background," Reddy stated. 

BTEX represented about 2 percent of the oil that came out of the well, but "nearly 100 percent of what was in the plume," Reddy said.

"A small, selective group of compounds took a right-hand turn" after exiting the well and formed the 3,000-foot-deep plume, he added.

The concentration of BTEX at such depths, and its effect on marine life, will remain for future study.

"In most instances the BTEX compounds are volatilized very quickly, such that exposure duration is very short," Woods Hole Oceanographic Institution scientist Judith McDowell said.

"The persistence of BTEX at depth poses an interesting question as to the potential effects of these compounds on mid-water organisms."

Gathering the sample

Along with an analysis of the plume’s composition, the research expedition utilized a number of special techniques for obtaining the unique sample.

An isobaric gas-tight sampler, developed by Woods Hole Oceanographic Institution geochemist Jeff Seewald and his colleagues, and intended for use collecting fluids from deep-sea hydrothermal vents, was used to gather a sample of the plume residue from the pipe.

The scientists had 12 hours to get a sample using an oil industry remotely operated vehicle with the gas-tight sampler attached.

The National Science Foundation funded the project through three Rapid Response Research grants. The research was also funded by the U.S. Coast Guard.

This study appears in the online edition of the journal Proceedings of the National Academy of Sciences.