Dispersants in Ice
Chemical dispersants enhance natural dispersion by reducing the surface tension at the oil/water interface, making it easier for waves to create small oil droplets (generally less than 100 microns) that remain in suspension for long periods and are rapidly diluted in the water column to below toxicity thresholds of concern.
Studies show that oil-degrading microbes colonise the droplets within a few days if not sooner. Dispersed oil dilutes to concentrations in the parts per million range within a few hours of effective dispersant application and to concentrations in the parts per billion range in one or more days, depending upon the currents and wind dynamic.
Over the past two decades, a series of tank and basin tests and field experiments proved that cold temperatures do not reduce the dispersibility of many oils or the activity of the dispersant.
Importantly, research showed that the motion and interaction of broken ice pieces actually enhances – rather than detracts from – the dispersion process by providing surface turbulence at higher levels than would occur naturally with non-breaking waves in open water.
Studies found that dispersants are less toxic than both naturally dispersed and dispersant-treated oil. Additional studies at the University of Alaska Fairbanks (UAF) demonstrated that three Arctic marine species (two fish species and a copepod species) were no more sensitive to dispersed oil than their counterparts in southern waters.
Experiments in a laboratory at Point Barrow, Alaska, completed close to the launch of the JIP, demonstrated that indigenous Arctic microorganisms effectively degraded both fresh and weathered oil regardless of whether it was dispersed naturally or with the addition of dispersants. The researchers concluded that naturally available levels of nutrients and oxygen could sustain effective microbial degradation, in Arctic as well as temperate waters.
Dispersants provide an oil spill response option that combines high encounter rates, high effectiveness and greater responder safety than mechanical response. Subsea dispersant injection for well control events provides an additional tool that enhances contingency planning for offshore operations. In many cases, including in the Arctic, dispersants could prove to be the best response option to treat an oil spill before it has spread, broken apart, impacted marine mammals and birds become stranded.