The biodegradation of crude oil in the deep ocean

•Biodegradation of dispersed crude oil is prompt and extensive at 5 °C and a pressure equivalent to 1500 m.•The half-life of the hydrocarbons of 3 ppm dispersed oil was 16 days at 1500 m.•This is slightly slower than the half-life of 13 days measured at the surface.

Oil biodegradation at a simulated depth of 1500 m was studied in a high-pressure apparatus at 5 °C, using natural seawater with its indigenous microbes, and 3 ppm of an oil with dispersant added at a dispersant:oil ratio of 1:15. Biodegradation of the detectable hydrocarbons was prompt and extensive (> 70% in 35 days), although slower by about a third than under otherwise identical conditions equivalent to the surface. The apparent half-life of biodegradation of the total detectable hydrocarbons at 15 MPa was 16 days (compared to 13 days at atmospheric pressure), although some compounds, such as the four-ring aromatic chrysene, were degraded rather more slowly.

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