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Aggregation between suspended oil droplets and suspended particulate matter (SPM), which leads to the formation of oil-SPM aggregates (OSAs), is recognized as an important process affecting the fate of spilled oil in fresh and marine water systems. It affects oil sedimentation and; thus, contamination of bottom sediments during oil spill events. This paper presents laboratory results from a multi-year research project to gain quantitative understanding of the factors controlling the formation and fate of OSAs formed with naturally and chemically dispersed oils. The results relate to the measurements of OSA's content in total petroleum hydrocarbon (TPH), size distribution, density and settling velocity. Oil sedimentation caused by negatively buoyant OSAs varied from 0.3 % to 56 %. The highest percentage of oil sedimentation was obtained with chemically dispersed oil. The size of OSAs varied from 40 to 700 μm. The median size varied between 115 and 240 μm. The effective density and settling velocity varied between 10 and 200 g/L and 0.3 and 3 mm/s, respectively. The study showed that sediment grain size and concentration have strong influence on OSA formation. For a relatively low sediment concentration of 100 mg/L, OSA formation can lead to significant enhancement of oil transfer from the water surface to bottom sediments. Overall, the study showed that the formation and physical properties of OSAs are similar to those of sediment flocs.
oil spill, oil sedimentation, oil-sediment interaction, oil-clay flocculation, oil-SPM interactions, oil-SPM aggregates, oil-fine interactions, oil-mineral aggregates, oil dispersion; contaminated sediments, oil in sediments
Emergencies Science and Technology Section, Operational Analytical Laboratories and Research Support Division, Science & Technology Branch, Environment Canada, Ottawa, ON