Dispersion of Louisiana crude oil in salt water environment by Corexit 9500A in the presence of natural coastal materials

• Effectiveness of Corexit 9500A for dispersing Louisiana crude oil was studied.
• Variables were dispersant-to-oil ratio (DOR), salinity, and natural materials.
• Both salinity and DOR had significant effects on dispersant effectiveness.
• Dispersant effectiveness was high at 17 ppt salinity and DOR range 1:15–1:10.
• Dispersant effectiveness was significantly low in the salinity range of 34–51 ppt.

Effectiveness of Corexit 9500A for dispersing Louisiana crude oil was evaluated in salt water solutions containing natural materials in relation to salinity and dispersant-to-oil ratio (DOR). Experimental results showed that both salinity and DOR had significant effects on dispersion of Louisiana crude oil in the presence of different natural materials. The natural materials added to the salt water solutions included sea sand (South Beach, Miami, Florida), red mangrove leaves (Rhizophora mangle), seaweed (Sargassum natans), and sea grass (Halodule wrightii). Dispersant effectiveness (amount of oil dispersed into the water) was reduced significantly with increasing salinity with the minimum effectiveness observed in the salinity range between 30 and 50 ppt in all aqueous samples containing natural materials. When significant amounts of floating oil were present, the partially submerged natural materials enhanced the transfer of oil into the water column, which improved the dispersion effectiveness. However, dispersant effectiveness was significantly reduced when the amount of floating oil was relatively small and could not be released back to the water column. Surface tension may not be an adequate parameter for monitoring the effectiveness of dispersants in salt water environment. When distilled water was used (i.e., zero salinity), surface tension was significantly reduced with increasing dispersant concentration. However, there was no clear trend in the surface tension of the salt water solutions (17–51 ppt) containing crude oil and natural materials with increasing dispersant concentration.

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