TRACE ELEMENT PROXIES FOR HYDROCARBON EXPOSURE IN OYSTER SHELLS AFTER THE 2010 DEEPWATER HORIZON OIL SPILL

The 2010 Deepwater Horizon (DWH) well explosion led to the largest accidental oil spill in history, exceeded only by intentional releases into the Persian Gulf during the First Gulf War. To document longer-term impacts of The DWH spill on the Gulf of Mexico (GOM) coastal food webs, we are using sclerochronologic techniques to assess pathways and rates of incorporation of crude oil components from the DWH spill into major primary consumers. These techniques enable us to examine high-resolution chemical records preserved within the accretionary growth of molluscan shells. Because the GOM coast has been long influenced by anthropogenic effects and natural hydrocarbon seepage, we are using historical specimens from museums, baseline specimens collected in prior to shoreline impact of the DWH spill, and specimens collected after DWH spill landfall (August 2010).

Some trace metals, such as vanadium (V) and nickel (Ni), have high relative abundances in many crude oils, and incorporation of these metals into shell carbonate after exposure is well documented. Our preliminary results for the American oyster Crassostrea virginica indicate that V concentrations, determined using ICPMS, were elevated only in specimens collected post spill. Those specimens also exhibit elevated lead (Pb) concentrations, which also had elevated concentrations in GOM surface waters after the spill (EPA, Operations science Advisory Team data).

Generally, impacts beyond immediate and near-term devastation caused by fouling and toxic effects of oil spills are poorly constrained. Complicating efforts to documents such effects are potential additional impacts due to mitigation efforts, large-scale freshwater diversion into Louisiana coastal wetlands in the summer of 2010, and extensive application of chemical dispersants in both the subsurface and surface during the spill. An historical approach harnessing geochemical records of shell carbonate provides one avenue to begin to tease apart these effects.