Footprint, weathering, and persistence of synthetic-base drilling mud olefins in deep-sea sediments following the Deepwater Horizon disaster

Olefin-based synthetic-based drilling mud (SBM) was released into the Gulf of Mexico as a result of the Deepwater Horizon (DWH) disaster in 2010. We studied the composition of neat SBM and, using conventional GC-FID, the extent, concentration, and chemical character of SBM-derived olefins in >3600 seafloor sediments collected in 2010/2011 and 2014. SBM-derived (C14–C20) olefins occurred (up to 10cm deep) within a 6.5km2 “footprint” around the well. The olefin concentration in most sediments decreased an order of magnitude between 2010/2011 and 2014, at least in part due to biodegradation, evidenced by the preferential loss C16 and C18 linear (α- and internal) versus branched olefins. Based on their persistence for 4-years in sediments around the Macondo well, and 13-years near a former unrelated drill site (~62km away), weathered SBM-derived olefins released during the DWH disaster are anticipated to persist in deep-sea sediment for (at least) a comparable duration. •Synthetic-based mud measurably impacted 6.5km2 of the seafloor around the Macondo wellhead.•SBM-derived olefin concentrations in surface sediments decreased between 2010/2011 and 2014.•Preferential biodegradation of linear olefins over branched olefins was observed.•SBM-derived olefin residues at an unrelated drill site (62km away) persisted for 13years.•Biodegraded SBM residues in sediments near the Macondo well are likely to comparably persist.