ABSTRACT
Chemical dispersants can be used to reduce the interfacial tension of floating oil slicks so that the oils disperse more rapidly into the water column and thus pose less of a threat to shorelines, birds, and marine mammals. The laboratory test currently specified in federal regulations to measure dispersant effectiveness is not especially easy or inexpensive, and generates a rather large quantity of oily waste water. This paper describes the results of an effort by the U.S. Environmental Protection Agency (EPA) to identify a more suitable laboratory dispersant effectiveness test.
EPA evaluated three laboratory methods: the Revised Standard Dispersant Effectiveness Test currently used (and required by regulation) in the United States, the swirling flask test (developed by Environment Canada), and the IFP-dilution test (used in France and other European countries). Six test oils and three dispersants were evaluated; dispersants were applied to the oil at an average 1:10 ratio (dispersant to oil) for each of the three laboratory methods. Screening efforts were used to focus on the most appropriate oil/dispersant combination for detailed study. A screening criterion was established that required a combination that gave at least 20 percent effectiveness results. The selected combination turned out to be Prudhoe Bay crude oil (an EPA-American Petroleum Institute Standard Reference Oil) and the dispersant Corexit 9527. This combination was also most likely to be encountered in U. S. coastal waters. The EPA evaluation concluded that the three tests gave similar precision results, but that the swirling flask test was fastest, cheapest, simplest, and required least operator skill.
Further, EPA is considering conducting the dispersant effectiveness test itself, rather than having data submitted by a dispersant manufacturer, and establishing an acceptability criterion (45 percent efficiency) which would have to be met before a dispersant could be placed on the Product Schedule of the National Contingency Plan (NCP). Also under consideration by EPA is a sequential testing procedure for a dispersant being placed on the schedule, whereby successful effectiveness testing would be required before toxicity testing would begin.
Ten Years of Research by the U.S. Oil Industry to Evaluate the Ecological Issues of Dispersant Use: An Overview of the Past Decade
