A half century of oil spill dispersant development, deployment and lingering controversy

Abstract

Massive oil spills leading to ‘Black Tides’ have been sad features of the last half century, although fortunately of generally decreasing frequency. Such spills often led to massive bird mortality and enormous public pressure for mitigation. One unfortunately misunderstood response has been the development of chemical dispersants designed to move floating slicks into the water column as tiny droplets. These droplets become entrained in the water and dilute to levels below those of acute toxic concern within hours; equally importantly, they naturally biodegrade within weeks, and do not impact shorelines. Initial dispersants were not especially effective, but a deeper understanding of what controls the lowering of interfacial tension between oil and water has led to very effective modern products, exemplified by Corexit 9500 used in the Deepwater Horizon response. By getting oil off the sea surface, dispersants protect birds and animals from potentially lethal oiling and the likely fouling of shorelines with its attendant problems of human exposure to oil residues as shorelines are physically cleaned. And by increasing the surface area of the spilled oil they promote indigenous microbial biodegradation, which can consume oil droplets with a half-life of 1–3 weeks without the need for any additional intervention. Dispersants thus provide the most environmentally-beneficial bioremediation option for ameliorating potentially environmentally devastating oil spills (when they work), and it is disappointing that they are not always tried on a significant (not test) scale.