Anne Mildped Br^vig , released 125,000 barrels of crude oil to the North Sea 

 almost instantaneously, but by the time local authorities had mobilized to 

 deal with the spill the oil was dissipating rapidly. The disappearance of 

 the oil was undoubtedly due to sinking. Whether it was the combination of 

 cold February weather and the high specific gravity of Iranian crude, or in- 

 teraction with suspended sediments, is not known, but little environmental 

 damage was recorded as a result of the accident. Evaporation of volatile 

 components of the No. 6 fuel oil released in the collision of the Avizona 

 Standard and the Oregon Standard under the Golden Gate Bridge in January 1971 

 resulted in an increase in specific gravity of the remaining oil, allowing 

 rapid dispersion of oil throughout the water column. How much of this pro- 

 cess was due to unaided sinking, and how much could be attributed to inter- 

 actions with the heavy suspended sediment load of San Francisco Bay, is not 

 clear. In the 1970 Arrow accident in Chedabucto Bay, Nova Scotia, a spill of 

 65,000 barrels of No. 6 fuel oil in rough, cold seas, investigators found 

 suspended oil particles (5 microns to 1 millimeter in size) widely distri- 

 buted in the water column as far as 250 kilometers away from the wreck. 

 Forrester (1971) estimated the flux of emulsified and particulate oil into 

 the water column at 40 to 50 barrels per day for the first 15 days after the 

 Apvow grounding. 



The interaction of oil with suspended sediments is an important dissipa- 

 tive process, as the sinking of the Anne Mvldred Br^vig's cargo and the Santa 

 Barbara Channel spill show. There are two major classes of suspended par- 

 ticulate matter in which a distinction has to be made regarding the type of 

 interaction that takes place with dissolved hydrocarbons. The first includes 

 clay minerals of the kaolinite or montmorillonite type (water layers alter- 

 nating between aluminosilicate layers) , which swell when exposed to water or 

 hydrocarbons, and easily accommodate bilayers of hydrocarbons between alumi- 

 nosilicate sheets (absorption) . The second type of suspended sediments 

 includes such materials as Si02, CaC03, and other nonporous solids. On these 

 materials, dissolved hydrocarbons can be adsorbed. Obviously, adsorption on 

 nonporous solids will not remove much oil from the water column, and thereby 

 allow more oil to diffuse in, unless there is a high density of finely di- 

 vided particles in the water column. The effects of suspended particulate 

 matter become much less obvious when one considers (1) oil micelles inter- 

 acting with particles, (2) collision between suspended particles and the 

 slick itself, and (3) the coalescence of particles that have become coated 

 with oil. These three processes, as nature would have it, are of primary 

 importance in the interactions of oil with suspended sediments, yet we know 

 little or nothing about these processes. 



3.1.2 Evaporation 



Evaporation from an oil slick is responsible for the loss of about one- 

 fourth of most crude oil spills, representing those components that volatil- 

 ize at temperatures below approximately 270°C. The principal difficulty in 

 predicting evaporation is that it cannot be done for actual oil spills for 

 more than a short period of time, because of the multicomponent nature of 

 petroleum. Even for such light materials as No. 2 fuels and gasoline, mass 

 transfer within the liquid phase will determine the rate at which certain 

 volatile components will reach the oil-air interface, and as the spill is 



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