Weathering of spilled oil and methods of accelerating

Oil spilled on water undergoes alteration by physical, chemical, and biological processes. Rapid physical processes include spreading, movement with winds and water currents, evaporation of volatile components, solution, water-in-oil emulsification, dispersion as small droplets into water, spray injection into the air, and sedimentation. As the oil spreads, less rapid biological and photochemical processes start. Biological processes include degradation by micro-organisms and uptake by larger organisms. The latter is followed by either discharge or metabolism of the ingested oil. Photooxidation destroys hydrocarbons, especially aromatics. Low-molecular-weight hydrocarbons rapidly evaporate, and the very small amounts of these that dissolve quickly evaporate from near-surface waters. Surface oil slicks can adversely affect birds, possibly sea otters, and can foul fishing gear. If oil strands, it is concentrated and can kill some shoreline species of plants and animals. Chemical dispersants can be used to change an oil slick into a dilute oil-in-water emulsion. Dispersed oil does not travel as far as in a slick, and shorelines are less threatened. Weathering processes of dispersed oil are accelerated, oil toxicity is more quickly reduced, and most of the known adverse effects from oil spills are lessened or eliminated. Bioassay testing of crude oils and petroleum products needs re-evaluation and research with more realistic hydrocarbon concentrations, compositions, and exposure durations.