3. INVESTIGATIONS OF CHEMICAL PROCESSES 

 3.1 Basic Chemistry of Spilled Oil 



The phrase "spilled oil" encompasses a wide variety of hydrocarbon 

 blends, including among others, crude oils, home heating oil, and heavy 

 residual fuels. Crude oils and petroleum products contain thousands of 

 individual chemical compounds, with a wide range of physical and chemical 

 properties. When spilled into the aquatic environment, light distillate 

 fuels, such as gasoline or jet fuels, do not behave in the same manner as do 

 heavy distillates or heavy residual (No. 6) fuels. The light fuels spread to 

 cover a large surface area with a thin film of oil, while the heavy fuels 

 tend to thicken and form "pancakes" of oil up to several inches thick. 

 Natural degradative processes are directly related to surface area of the 

 slick, and therefore remove oil from the sea surface much more rapidly in the 

 case of light oils than in the case of heavy products or crude oils. 



Knowledge regarding the degradation of oil in the marine environment is 

 limited. We know what the major degradative processes are, i.e., those 

 natural processes that operate to modify the physical and chemical character- 

 istics of spilled oil, changing its viscosity, solubility, toxicity, and so 

 on. But we cannot predict the rate at which a No. 2 fuel oil will enter the 

 water column under a given set of conditions. If "oil" were pure benzene or 

 hexane, for example, then it would be a straightforward task to develop a set 

 of physical-chemical descriptors, or mathematical algorithms, which would 

 enable us to predict the behavior and fate of such "oil" under all possible 

 environmental conditions. Unfortunately, such is not the case. One problem 

 associated with the multicomponent nature of petroleum is a phenomenon known 

 as "skinning." When oil forms thick lenses, from a centimeter to several 

 inches thick, the evaporation of volatile components through the top sUi.'^ace 

 (the air-oil interface) depletes the surface of the oil in light hydrocar- 

 bons, leaving behind heavier compounds characteristic of heavy fuel oils and 

 asphalts. These high-molecular-weight compounds form an essentially imper- 

 meable skin at the air-oil interface, precluding continued evaporation of the 

 lighter fraction from the interior of the oil lenses. This "skin" may be 

 broken up with sufficient turbulence, and the process of evaporation can then 

 restart. "Skinning" is only one of the many physical-chemical processes that 

 take place with increasing age of an oil slicK. Processes considered under 

 the collective appellation of "chemical" include: (1) interactions with 

 suspended sediments; (2) evaporation; (3) dissolution; (4) emulsif ication; 

 (5) photo-oxidation; and (6) microbial degradation. The individual processes 

 are not completely independent, photo-oxidation enhances the dissolution of 

 the aromatic fraction of oil by the formation of more soluble carboxylic 

 acids, and so on. Brief summaries of each of the major processes are pre- 

 sented below. 



3.1.1 Suspended Sediments 



During the Santa Barbara Channel blowout in 1969, an unusually large 

 influx of suspended clay minerals from the Ventura and Santa Clara Rivers 

 served to sink the oil on contact. A 1966 collision, involving the tanker 



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