With the explosion on the Deepwater Horizon Rig on April 20, 2010 in the Gulf of Mexico, a huge oil spill started that lasted till August 15, 2010. Some 4.4 million barrels (185 million gallons) of crude oil gushed out of the Macondo 252 well. A small fraction of the oil was collected from the riser pipe while the rest flowed onto the sea bottom. Burning of the crude oil collected by booms and the excess oil that cannot be processed otherwise was another technique used to mitigate the disaster. Initially the oil was seen on the surface as a sheen but over time tar balls washed up ashore in Louisiana and other Gulf states. The sheen was mostly emulsified oil, an intimate mixture of oil and water.
Crude oil commonly contains heavy metals such as vanadium, nickel, chromium, cadmium, and lead. Vanadium and nickel are usually in highest concentrations. Concentrations as high as 1600 parts per million (ppm) have been recorded for vanadium in crude oil. The nickel concentration is generally less than that of vanadium. These metals are known to be toxic at certain concentrations. The sulfur concentration in the BP oil is ca. 0.4%.
Crude oil samples collected from various locations along the Louisiana coast are being examined by synchrotron infrared Fourier transform spectro-microscopy, X-ray fluorescence spectrometry (XRF), X-ray absorption spectroscopy (XAS), tomography and small and wide angle X-ray scattering. Samples also include oil collected from the riser pipe and oil from in situ controlled burn. Most of these synchrotron based methods allow in situ measurements.
Semi-quantitative X-ray fluorescence analysis of the oil samples suggested less than 50 ppm of vanadium and nickel in the oil samples. The speciation of nickel is that of porphyrin in all samples except in the emulsified crude oil. Vanadium also showed a slight change in oxidation state upon emulsification. Small angle scattering suggests that asphaltene aggregate size increases with in situ burning. Wide angle scattering data suggest that the temperature rise during burning could not have been high. Tomography indicates the presence of an element with absorption edge in the range 8 to 18 keV; this is probably due to lead (LIII edge). Crude oil can be easily identified by infrared spectro-microscopy. The presence of sulfate in oil samples indicates degradation.