It’s been more than a year since an explosion on BP’s Deepwater Horizon caused the worst offshore oil spill in the history of the United States, sending some 5 million barrels of oil into the Gulf of Mexico. Recovery efforts in the Gulf and its surrounding communities are still underway, and since the beginning, one of the biggest obstacles has been scientific uncertainty about how much oil spilled, what exactly the spill was made up of, and where it all went. But new research findings by the Woods Hole Oceanographic Institution explain just what came out of the Deepwater well, shedding light on what happened to it and how it affected the environment.

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Two months after the Deepwater explosion, Chris Reddy and colleagues from Woods Hole took their research vessel to the rig, which was still spewing oil and natural gas, to do something that had never been done before. Using a robot arm, they stuck a small bottle directly into the hot hydrocarbons to collect a sample. They needed to go right to the source to know what compounds were in the spill. Now, a year later, they finally have the results from the analysis, showing the exact chemical makeup of what came out of the well.

Some of the chemicals in the well react differently under the high pressure atmosphere right near the well than they do at the surface, which explains why only some of the chemicals made it into the 22-mile plume that spread over the Gulf. “We now have a far better understanding of how and why an oil ‘spill’ into the ocean from below differs from one from above. The significance of this work extends well beyond the Gulf of Mexico,” said Don Rice, director of the National Science Foundation’s chemical oceanography program in a statement. The NSF is funding Woods Hole’s continued research.

To collect a sample of the fluids and gas coming right out of the pipe, the team used a tool invented by a Woods Hole geochemist specifically to collect fluids from deep-sea hydrothermal vents. Popular Science explains what they found:

The team found a gas-to-oil ratio of 1,600 cubic feet of gas per barrel of oil, according to a paper on the findings published this week in the Proceedings of the National Academy of Sciences and funded by the NSF. Based on this ratio, and using the federal government’s estimate of 4.1 million barrels of oil, Reddy et. al estimate 1.7 × 1011 g of methane, ethane and propane leaked into the Gulf. That’s about 105 tons. That’s a lot of methane.

But perhaps more interesting is the makeup of the plume, which mostly comprised benzene, toluene, ethybenzene, and total xylenes, or BTEX. BTEX compounds only represented about 2 percent of the oil that came out of the well, but almost 100 percent of the deep-sea plume. They apparently took a right-hand turn 3,000 feet below sea level, whereas the other hydrocarbons — like methane — degraded, washed on shore, were eaten by bacteria, or were burned in the fires that Reddy experienced while gathering his sample.

The good news is that BTEX compounds are not toxic to marine life unless there is a much higher concentration than what was in the Gulf. But neurological damage can occur, and the team is still studying how the BTEX may have affected the ecosystem, and continues to collect samples from the shore line for evaluation.

Via Popular Science