A surface tension based method for measuring oil dispersant concentration in seawater

• Developed a new method for analyzing oil dispersants by measuring surface tension
• The method can accurately measure Corexit EC9500A and likely other dispersants.
• Minor changes in salinity, pH, and DOM do not alter surface tension measurements.
• Sediment exudates showed little interference with the method accuracy.
• The method accuracy was validated by comparing with TOC analysis.

This work developed a new method to determine concentration of Corexit EC9500A, and likely other oil dispersants, in seawater. Based on the principle that oil dispersants decrease surface tension, a linear correlation was established between the dispersant concentration and surface tension. Thus, the dispersant concentration can be determined by measuring surface tension. The method can accurately analyze Corexit EC9500A in the concentration range of 0.5–23.5 mg/L. Minor changes in solution salinity (< 0.3%), pH (7.9–9.0), and dissolved organic matter (< 2.0 mg/L as TOC) had negligible effects on the measurements. Moreover, effects of extracts from marine sediments were negligible, and thus, the method may be directly applied to seawater–sediment systems. The method accuracy was confirmed by comparing with direct TOC analysis. This simple, fast, economical method offers a convenient analytical tool for quantifying complex oil dispersants in water/seawater, which has been desired by the oil spill research community and industries.