Three Widely-Available Dispersants Substantially Increase the Biodegradation of otherwise Undispersed Oil

Prince RC, Kelley BA and Butle

Abstract

Dispersants are essential tools for responding to large marine oil spills, both at the surface and in deep water at uncontrolled well-heads. By reducing the interfacial tension between oil and water, they allow turbulence from surface wavelets or well-head ejection to disperse oil as tiny droplets (<70m). Although the intrinsic density of the oil is unaffected, droplets are too small to rise rapidly, and minor turbulence and diffusive dilution impede droplet encounter and coalescence. Oil droplets disperse to very dilute concentrations, and provide substantial surface area for indigenous microbes to rapidly degrade the oil hydrocarbons. While the literature on this latter point is confused because few experiments have assessed biodegradation at environmentally relevant concentrations in natural seawater, we show here that three dispersants widely-available in international stockpiles effectively stimulate biodegradation when compared to oil in floating slicks, decreasing the residence time of the oil in the environment from many months (and potentially years if tarballs form or the oil reaches a shoreline) to a few weeks.