Biosurfactant-based dispersants for oil spill remediation: Salinity effects and mechanistic insights

Salinity variations, particularly in dynamic environments such as estuaries, may significantly affect the dispersion effectiveness (DE) of oil spill dispersants. While bio-based dispersants are gaining attention as alternatives to chemical dispersants, limited research exists on their adaptability to varying salinity conditions and their associated molecular mechanism and ecological impact. This study evaluated the DE of bio-based dispersants formulated with two biosurfactants (BS); Surfactin (SUC) and Rhamnolipid (RAM), either individually or in combination with Tween 80 (TWE), referred to as BS/TWE, across salinity levels of 10, 20, and 34 psu. The DE of each bio-based dispersant was compared to the chemical dispersant Corexit 9500A under various environmental conditions, including dispersant-to-oil ratios, temperature variations, and mixing energy levels simulating turbulence in natural aquatic environments. The SUC-based dispersant achieved high DE (88 %) with smallest oil droplets size around 5.08 microm at 10 psu but exhibited reduced performance at 34 psu. In contrast, the BS/TWE dispersant showed 90 % DE with droplets size of 10.45 microm at 34 psu, as a result of synergistic surfactant interactions. Molecular dynamics simulation revealed that salinity affects surfactant-water interactions, with SUC-based dispersant losing efficiency at high salinity due to lack of ion bridging, while BS/TWE dispersant remaining effective through reduced electrostatic interactions. Toxicity assessments exhibited minimal inhibitory effects of bio-based dispersants on algal growth, Dunaliella tertiolecta, highlighting their potential for environmental applications. The findings highlight the potential of these dispersants as effective, and environmentally friendly solutions for oil spill response in diverse marine environments.