dispersants supposedly break oil into fairly homogeneous particles - 1 

 micron in diameter which have a rise velocity of zero (Canevari 1975). Dis- 

 persants that are not self-mixing produce oil particles that are heterogene- 

 ous and vary in size from 10 microns to several millimeters. These particles 

 will return to the water surface unless there is considerable wave action. 



ADVANTAGES AND DISADVANTAGES OF DISPERSANTS 



Research on dispersant effectiveness and on the biological effects of 

 dispersed oil has been limited. Most of the information available comes 

 from laboratory experiments which are often difficult to relate to field 

 conditions. Although statements of advantages and disadvantages of using 

 chemical oil dispersants are based on conclusions derived from inadequate 

 information (Exxon Production Research Company 1978), it is appropriate to 

 present the most commonly reported characteristics of dispersant use. 



The advantages of using dispersants to control oil spills include: 



1) Dispersants remove oil from the water surface by dispersing the 

 oil into the water column. This eliminates the fire hazard, air 

 pollution from volatilization, and the threat of serious oiling for 

 water birds; and accomplishes the cosmetic improvement of removing 

 the oil from sight. 



2) The dispersion of oil prevents the formation of water-in-oil 

 emulsions ("chocolate mousse") and tar balls. Water-in-oil emul- 

 sions are particularly difficult to deal with because the emulsi- 

 fied water causes an increase in the volume of oily material that 

 must be removed from shorelines and the emulsions do not respond 

 well to dispersants (Canevari 1975). 



3) Dispersed oil will not adhere as well to shorelines, plants, 

 and animals as will nondispersed oil. Dispersal, therefore, is 

 an important consideration when oil is expected to reach inter- 

 tidal areas, beaches, islands, or large concentrations of birds. 



4) Dispersants increase the surface area of the spilled oil, 

 permitting more rapid weathering and bioloqical deterioration 

 (Wells and Keizer 1975). 



The disadvantages of using dispersants to control oil spills include: 



1) Oil dispersants cause the concentration of oil in the water 

 column to increase rapidly, with a corresponding increase in 

 toxicity. The increase is temporary, but species not affected 

 by the floating oil may be affected by the dispersed oil (Swedmark 

 et al . 1973), Wells and Keizer 1975, Linden 1976, Dalla Venezia 

 and Fossato 1977, Trudel 1978), thus increasing the short-term 



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