190 



Table 1 S - Concentrations of oil in the water column resulting from natural and chemical dispersion at sea 



Details of spill 



Xatural dispersion 



ARROW, Chedabucto Bay, USA 

 April 1970 



AMOCO CADIZ, Brittany 

 March 1978 



DRUPA, Norway 

 February 1976 



Ekofisk Bravo blowout, 

 North Sea, April 1977 



Experimental 14 t sUck 



Experimental 7 I enclosed 

 slick 



Experir.iental V: t slick 



ELENl V, North Sea 

 May 1978 



Picnic Bay, Hong Kong 

 November 1973 



Chemical dispersion 



ELENl V, North Sea 

 May 1978 (near wreck) 



Heavy fuel oil •^ 

 Dasic Slickgone LTD 



0.2 



Law and Hall, 

 1978 



DRUPA, Norway 

 Experimental 230 1 slick 



Iranian crude + 

 Finasol GSR 2 



Fresh Kuwait crude + 

 BPlOO: 



Grahl-Nielsen 

 era/..1978 



Cormack and 

 Nichols. 1977b 



Experimental 7 1 enclosed 

 sUck 



Nonh Sea crude 

 + BP llOOX 



Ward and Davies, 

 1978 



to the concentrations which have been shown to be en- 

 countered initially following dispersion of a sUck. Where 

 the less toxic dispersants are used, the 100 min LC50 

 value is substantially higher than concentrations actually 

 measured under a chemically-dispersed slick. 



Observations at sea have demonstrated that subsequent 

 dilution is rapid; in Cormack's (1977) studies, the maxi- 

 mum concentration of chemically-dispersed oil fell from 



48 Ml r* jfter 2 min to below 2 (J 1'' after 100 min. 

 Therefoit dilution during the first 100 min is likely to 

 reduce iht dispersed oil concentration to between 0.01 

 and 0.001 of the 100 min LC50 value where the less toxic 

 products IK used. Weathering of fresh oil which is likely to 

 occur before spraying with dispersant will also tend to re- 

 duce the toxicity of the dispersed oil. Thus, provided 

 marine arg^nisms are not exposed repeatedly to concentra- 

 tions of dispersed oil and provided there is adequate water 



