exposed for 2 years in floating enclosures without effective degradation ( Davis and 

 Gibbs, 1975). An oil-in-water emulsion or dispersion results from the suspension of 

 small particles/ droplets of oil within the water column. Oil is physically forced into 

 the water column by turbulence at the surface, generally wave action. The degree of 

 turbulence determines the quantity and depth of mixing while oil density and parti- 

 cle size determine residence time in the water column (Forrester, 1971). 



Sedimentation is a process that determines the fate of some heavy oils in the 

 marine environment. In the case of a few spills involving Bunker C fuel oil, a signifi- 

 cant portion of the oil quickly dispersed within the water column in the form of drop- 

 lets or globules that had a specific gravity equal to or greater than the surface sea- 

 water (Conover, 1971). These particles can sink in the water column and be moved 

 about by subsurface currents (Conomos, 1975). Less dense crude and fuel oil drop- 

 lets dispersed in surface waters can be sedimented by adsorption to suspended miner- 

 al particles. This process could be particularly important in more turbid coastal 

 waters. Oil droplets may also be ingested by zooplankton and excreted in fecal pel- 

 lets that have density greater than sea water (Conover, 1971). 



Photochemical oxidation is probably the most important of the various abiotic 

 chemical reactions that occur during the weathering process. Ultraviolet radiation is 

 absorbed by selected molecules, especially aromatics, that react with oxygen to form 

 oxygenated intermediates such as hydroperoxides. These oxygenated intermediates 

 are generally much more soluble and toxic than the parent compound (Larson etal., 

 1976). Products that result from irradiation of oil include organic acids, alcohols, 

 esters, aldehydes, ketones, phenols, and sulfoxides (Parkeretal., 1971). Photochem- 

 ical and abiotic oxidation of crude oil during the weathering process may be largely 

 responsible for the high NSO and asphaltene content of some tarballsand tarry resi- 

 dues that are difficult to account for by simple evaporation and solution losses 

 (Frankenfeld. 1973). 



Biodegradation is an important process in the further weathering of oil that has 

 dispersed or dissolved in seawater. Although microbial degradation plays a far more 

 significant role in weathering, macroorganisms also degrade oil. Marine animals of 

 all sizes and genera may purposefully or accidentally ingest oil particles during 

 feeding. A portion of the oil is absorbed and incorporated into tissues while the bulk 

 is eliminated in the feces (Conover, 1971). Petroleum hydrocarbons are depurated 

 from tissues at various rates depending upon the type of tissue and organism. 



A broad spectrum of mcroorganisms is active in the metabolism of petroleum that 

 enters the marine environment. Cyanobacteria (blue-green algae) and microalgae 

 (Cernigliaetal., 1980), bacteria (Zobell, 1969), fungi (Walker et al., 1973), and yeasts 

 ( Klug and Markovetz, 1967) have been reported capable of degrading oil or oil com- 

 ponents. Hydrocarbon-utilizing microorganisms are ubiquitous in the oceans. How- 

 ever, their concentrations vary, with highest counts in areas of chronic petroleum 

 pollution (Walker and Colwell, 1976). Individual species differ in ability to grow on 

 petroleum hydrocarbons as a sole carbon source. Often a species may be able to uti- 

 lize a given aromatic ring structure while unable to grow on others. Maximum degra- 

 dation of petroleum is accomplished by the combined and sequential attack of a 

 mixed population (Horowitz et al., 1975). 



Numerous studies indicate preferential utilization of tt-alkanes during early stages 

 of microbial degradation of crude oils (Jobson et al., 1972). Isoprenoid hydrocar- 

 bons such as pristane and phytane are often degraded at a slower rate than /?-alkanes 

 (Westlake et al., 1974). Walker et al. (1976) report alkanes degraded to a greater 

 extent than cycloalkanes in two crude oils. A wide variety of aromatic and 

 naphtheno-aromatic compounds may also be utilized by microorganisms. A larger 

 percentage of aromatics were degraded than saturates in the study of Walker et al. 

 (1976). 



Microbial degradation rates in the ocean may become nutrient-limited. Nitrogen 

 ( NOi , N H 4 + ) and or phosphorus ( POT' 1 ) concentrations can determine degradation 

 rates especially in offshore areas. 



101 



