A comparison of standard test methods for determining the laboratory effectiveness of oil spill dispersants: their benefits and drawbacks

A comparison of two standard test methods for determining the laboratory effectiveness of oil spill dispersants — ASTM F2059-17 «Standard Test Method for Laboratory Oil Spill Dispersant Effectiveness Using the Swirling Flask» and ASTM F3251-17 «Standard Test Method for Laboratory Oil Spill Dispersant Effectiveness Using the Baffled Flask» — is presented in this article. It is underlined that ASTM F2059-17 and ASTM F3251-17 are almost identical from the methodological and technical points of view. The main differences lie in specific design features of the applied test vessels and mixing energies created inside them. It is reasonably established that ASTM F2059-17 can be defined as a low-energy, but ASTM F3251-17 — as a high-energy laboratory test method. The specific examples of application of the test methods for determining the effectiveness of commercially available dispersants are given. It is also concluded that both test methods are necessary to apply for a correct understanding of the dispersant effectiveness. Herewith, the results obtained according to ASTM F2059-17 should be conditionally considered as the lower limit and those according to ASTM F3251-17 — the upper limit of effectiveness of the dispersant. Moreover, the use of gas chromatography with flame ionization detection (GC-FID) is emphasized to be sometimes impossible as a recommended in both ASTM F2059-17 and ASTM F3251-17 method for analyzing the oil extracts obtained during the test. The UV spectrophotometry is proposed instead of GC-FID as an alternative. However, its application is possible only after mandatory optimization of the measurement parameters for each specific oil.