Tracking the 2010 BP Deepwater Horizon Oil Spill in the Gulf of Mexico through Trace Element Analysis of Oyster Shells

On April 20, 2010, 41 miles off the Louisiana coast, a wellhead blowout on the Deepwater Horizon (DH) drilling rig initiated the largest accidental oil spill in history, releasing over 200 million gallons of oil before it was capped on July 15, 2010. Past studies have suggested vanadium concentrations in biogenic carbonates as a straightforward proxy of oil contamination. Thus, being the largest spill of all time, the DH spill should produce a distinct vanadium signal in carbonates. Therefore, shells of the economically and ecologically important oyster Crassostrea virginica that lived through the DH spill were serially sampled through ontogeny and analyzed for concentrations of elements associated with hydrocarbon contamination (vanadium, chromium, cobalt, arsenic & lead) using LA-ICP-MS. Two shells collected prior to oil landfall in May 2010, shells collected from the Gulf coast in 1947 and 1970, and a shell from North Carolina were also analyzed for elemental concentrations to establish a baseline and to investigate the historical impacts of hydrocarbon exploration in the Gulf of Mexico. Pre- and post-spill soft tissue samples were also analyzed for trace metal concentrations to clarify the mechanisms and timing of hydrocarbon infiltration into Gulf coast food webs. Although vanadium concentrations were higher in post-spill shells and tissues, the results suggest that several poorly-understood factors can produce significant variability in vanadium concentrations of carbonates (as well as tissues), and that our understanding of these controls must be refined before a vanadium excursion recorded in biogenic carbonates can be attributed to any particular source.

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