Ongoing biodegradation of Deepwater Horizon oil in beach sands: Insights from tracing petroleum carbon into microbial biomass.

Abstract Heavily weathered petroleum residues from the Deepwater Horizon ( DwH ) disaster continue to be found on beaches along the Gulf of Mexico as oiled-sand patties. Here, we demonstrate the ongoing biodegradation of weathered Macondo Well (MW) oil residues by tracing oil-derived carbon into active microbial biomass using natural abundance radiocarbon ( 14 C). Oiled-sand patties and non-oiled sand were collected from previously studied beaches in Mississippi, Alabama, and Florida. Phospholipid fatty acid (PLFA) analyses illustrated that microbial communities present in oiled-sand patties were distinct from non-oiled sand. Depleted 14 C measurements of PLFA revealed that microbes on oiled-sand patties were assimilating MW oil residues five years post-spill. In contrast, microbes in non-oiled sand assimilated recently photosynthesized carbon. These results demonstrate ongoing biodegradation of weathered oil in sand patties and the utility of 14 C PLFA analysis to track the biodegradation of MW oil residues long after other indicators of biodegradation are no longer detectable.