§ Mr. WallaceTo ask the Secretary of State for Transport if he will list the chemical composition of dispersants, including the half-life of biodegradable substances, used to date to disperse oil spilled from the MV Braer.
§ Mr. Curry[holding answer 14 January 1993]: I have been asked to reply.
In general, dispersants are a blend of surfactants and solvents which have the ability to modify surface tension between the oil and the water, promoting the formation of oil droplets and helping to prevent the oil reforming into one mass. Dispersion of the droplets in the water column makes the oil more accessible to the natural processes of degradation. The precise chemical composition of individual dispersants is subject to conditions of commercial confidentiality under which manufacturers have provided the information.
No specific tests are carried out on the biodegradability of the dispersants. However, data on the substances used indicate that they are not environmentally persistent and most would degrade within a few weeks.