Unraveling the resuspension and transformation of stranded oil: Mechanisms driving oil-particle aggregate formation in intertidal zones

The intertidal zone, serving as a dynamic interface, presents a challenging environment for understanding the transport of spilled oil. This study explores the resuspension of stranded oil and the formation of suspended oil-particle aggregates (OPAs) under varying sediment properties, water chemistry, hydrodynamic forces, and biodegradation conditions. Findings reveal that sediment grain size and mineralogical structure influence oil resuspension and OPA formation but function through distinct mechanisms. Mixed sediments exhibit variable oil-mineral interaction regimes and sediment cohesiveness, which together govern oil resuspension and OPA formation. An increase in ionic strength can largely constrain the resuspension of stranded oil by promoting the swelling of the montmorillonite interlayer space and reducing the electrostatic repulsion among oil-contaminated particles, particularly at low ionic concentrations where oil resuspension is highly sensitive to changes in ionic strength. Both natural and commercial amphiphilic compounds facilitated oil resuspension; however, excessive concentrations of commercial amphiphilic compounds hindered oil resuspension. Stronger hydrodynamic disturbances promoted OPA fragmentation while simultaneously driving oil resuspension, potentially expanding contamination areas. Biodegradation altered oil composition, thereby improving its adhesion to sediments and reducing resuspension, but it may pose challenges for sediment cleanup due to its increased recalcitrance. These findings highlight the complexity of stranded oil behavior in intertidal zones and contribute to the development of targeted cleanup strategies for specific conditions of affected intertidal zones.