Interactions among microplastics, spilled oil and dispersant: Impacts of marine environmental conditions

Marine oil spill accidents are serious environmental disasters. The nearshore waters and shipping channels where oil spills occur occasionally are often hotspot areas for microplastics (MPs) pollution. Few researchers have focused on the impacts of marine environmental conditions on oil spill migration and transformation behaviors when MPs and chemical dispersant coexist. This study investigated the effects of MPs and dispersant on oil dispersion and sedimentation under a range of oscillation frequencies, temperatures, and salinities. The results indicated that the presence of dispersant increased the mass of oil dispersed into the water column and reduced the size of the dispersed oil. Regardless of the presence of MPs, the increase in the value of environmental variables enhanced the above trends. Dispersant enhanced the interaction between MPs and oil to form MPs-oil-dispersant agglomerates (MODA), thereby promoting the sedimentation of oil. Except for temperature, the increase in oscillation frequency (from 140 rpm to 180 rpm) and salinity (from 20 ‰ to 35 ‰) increased the density of the sunken MODA by 21.9 and 14.5 kg/m, respectively. The morphology of MODA also changed with the variation of environmental conditions. One type of MODA was formed by oil coating the MPs, with no obvious MPs on the surface; the other type was formed by MPs embedding into the oil, and MPs of which were clearly visible on the surface. The results of this experimental study may improve the knowledge on the fate and transport of marine oil spill in the presence of MPs.