Dispersant Effectiveness on Heavy Fuel Oil and Crude Oil in New Zealand

ABSTRACT The New Zealand (NZ) Maritime Safety Authority (MSA) recently identified seven crude oils and nine IFO-380 heavy fuel oils used or transported in NZ waters that had a high relative risk of being spilt. To determine the relative effectiveness of dispersants stocked by the MSA (Corexit 9527, Slickgone LTSW, Gamlen OSD LT, and Tergo R40) on the oils, effectiveness was tested using the Warren Spring Laboratory (WSL) LR 448 protocol. All testing was on fresh (unweathered) oil at 15°C, at a dispersant to oil ratio (DOR) of 1:25. Effective dispersion was considered to be equivalent to a WSL test result of ≥15%, as proposed in the work of Lunel & Davies (1996). Overall, the seven crude oils tested could be dispersed with MSA stocked dispersants; Corexit 9527 and Slickgone LTSW dispersing the greatest volume of oil, while Gamlen OSD LT and Tergo R40 were effective on the widest range of oils. For the nine IFO-380 heavy fuel oils, dispersant effectiveness was generally lower than for crude oils, and two oils could not be dispersed. Corexit 9527 was the most effective dispersant and worked on the widest range of fuel oils. Slickgone LTSW, Gamlen OSD LT, and Tergo R40 were less effective and worked on a smaller range of fuel oils. To assess whether other dispersants not currently stocked by the MSA offered a significantly improved capacity, two high performance products (Corexit 9500 and Slickgone EW) were tested on the same oils, and across a range of temperatures and DORs. Laboratory results showed that Corexit 9500 and Slickgone EW were significantly more effective on both the crude oils and the IFO-380 heavy fuel oils than existing MSA dispersant stocks. While the results of this study provide a good indication of the relative effectiveness of different dispersants, they do not indicate absolute levels of effectiveness, and field experiments are needed to define how laboratory effectiveness translates to effectiveness in the field.