UK Deepwater Drilling – implications of the Gulf of Mexico oil spill, UK Parliament, Commons Select Committee on Energy and Climate Change, October 21, 2010:
The contingency plan also includes a provision to use the controversial dispersant Corexit 9500 manufactured by American company Nalco.  Use of Corexit is restricted in the UK, after failure of the rocky shore tests required for its approval,  and there remain concerns over the overall effects on shore-based animals and wildlife as well as the general toxicity of the product and its effects particularly on fish and marine mammals.  Two million gallons of the product has been used in cleanup operations in the Gulf of Mexico despite a public outcry and major concerns by lead scientists.
 See for example: Andrew Rogersona and Jacques Berger, ‘The toxicity of the dispersant Corexit 9527 and oil-dispersant mixtures to ciliate protozoa’ Department of Zoology, University of Toronto, 24 November 1980. Concluded that: “Chemically dispersed oil was more toxic than either the dispersant or crude oil alone.” And US Environmental Protection Agency Office of Research and Development, ‘Analysis of Eight Oil Spill Dispersants Using In Vitro Tests for Endocrine and Other Biological Activity’, 30 June 2010 where Corexit ranks among the most cytotoxic of the eight dispersants in the study.
Cytotoxic: (i.e. toxic to cells) Treating cells with a cytotoxic compound can result in a variety of cell fates. The cells may undergo necrosis, in which they lose membrane integrity and die rapidly as a result of cell lysis. The cells can stop actively growing and dividing (a decrease in cell viability), or the cells can activate a genetic program of controlled cell death (apoptosis).