Biodegradability of Orimulsion in Saltwater and Freshwater Environments¹

Shake flask and respirometer experiments were executed to test the biodegradability of Orimulsion in freshwater and saltwater. For each experimental setup, two concentrations of the Orimulsion and the appropriate bacterial inoculum were added to artificial seawater and freshwater solutions, and the concentrations of Orimulsion hydrocarbons were monitored with time. Respirometers were used to monitor oxygen (O₂) uptake and carbon dioxide (CO₂) evolution to determine when to sample the shake flasks. Sampling of shake flasks occurred periodically by sacrificing triplicate flasks for each treatment. Residual hydrocarbons were extracted with dichloromethane and quantified by gas chromatography/mass spectrometry (GC/MS). The respirometry flasks were sacrificed on the last shake-flask sampling event and similarly evaluated for residual hydrocarbon content and for Microtox toxicity. Data reported confirm literature citations that Orimulsion is indeed biodegradable, at least to some extent. In the 10 g/L freshwater treatment, normal and branched alkanes present were degraded by 83.6% and PAHs by 59.8% after 183 days of incubation. In saltwater, the extent of alkane and PAH degradation was 93.5% and 81.4% after 183 days. Implications for cleanup are discussed.