Fate of diluted bitumen spilled in the coastal waters of British Columbia, Canada

There is public concern about the behaviour of spilled diluted bitumen (dilbit) in marine and estuarine waters. We provide a preliminary assessment of the results of laboratory experiments and models, in the context of environmental conditions in the coastal waters of British Columbia. Most dilbit spilled within this region would likely float at the surface and be transported to shore by winds and currents. Fresh dilbit is too light to sink in coastal waters. Highly weathered dilbit could sink where salinity is less than 14, typically only near river mouths and in the top 1–3 m of fjords after heavy rainfall. Subsurface plumes of weathered dilbit could re-emerge at the surface. Sinking oil-particle aggregates are unlikely to form in coastal waters. However, dilbit could be entrained below the surface by wave mixing during storms and to depths of 150 m by coherent mixing in the Haro Strait tidal convergence zone. •Spilled diluted bitumen will mainly float in BC waters and wash up on the shoreline.•Near river mouths or nearshore after heavy rain, dilbit could sink ∼3 m and resurface.•Wave mixing or advection by tidal convergence could carry dilbit under water.•Dilbit weathers rapidly; its high density and viscosity limit traditional recovery.