Abstract
Sediment-oil-agglomerates (SOA) are one of the most common forms of contamination impacting shores after a major oil spill; and following the Deepwater Horizon (DWH) accident, large numbers of SOAs were buried in the sandy beaches of the northeastern Gulf of Mexico. SOAs provide a source of toxic oil compounds, and although SOAs can persist for many years, their long-term fate was unknown. Here we report the results of a 3-year in-situ experiment that quantified the degradation of standardized SOAs buried in the upper 50 cm of a North Florida sandy beach. Time series of hydrocarbon mass, carbon content, n-alkanes, PAHs, and fluorescence indicate that the decomposition of golf-ball-size DWH-SOAs embedded in beach sand takes at least 32 years, while SOA degradation without sediment contact would require more than 100 years. SOA alkane and PAH decay rates within the sediment were similar to those at the beach surface. The porous structure of the SOAs kept their cores oxygen-replete. The results reveal that SOAs buried deep in beach sands can be decomposed through relatively rapid aerobic microbial oil degradation in the tidally ventilated permeable beach sand, emphasizing the role of the sandy beach as an aerobic biocatalytical reactor at the land-ocean interface.
Highlights
After the 2010 Deepwater Horizon explosion, currents and waves moved approximately 22,000 tons of spilled MC252-oil[1] to the northeastern Gulf of Mexico shoreline[2,3], where this oil polluted an estimated 965 km of sandy beaches[4,5,6]
Petroleum hydrocarbon mass in the standardized MC525-SOAs (sSOAs) decreased over 3 years from 4.82 g (1 SD = 0.43 g) to 1.95 g (1 SD = 1.70 g) and at a similar rate as the total carbon content of the sSOAs (Fig. 2a,c, Petroleum hydrocarbon mass(t) (%) = 83.40e−0.00063d, R2 = 0.26, Carbon content(t) (%) = 7.583e−0.00057d, R2 = 0.72, p < 0.0009)
Since the organic and inorganic carbon content of the uncontaminated beach sand that makes up more than 80% of the SOA material is small (
Summary
After the 2010 Deepwater Horizon explosion, currents and waves moved approximately 22,000 tons of spilled MC252-oil[1] to the northeastern Gulf of Mexico shoreline[2,3], where this oil polluted an estimated 965 km of sandy beaches[4,5,6]. Since the organic and inorganic carbon content of the uncontaminated beach sand that makes up more than 80% of the SOA material is small (
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