Biological/physical particles interact to degrade marine oil spills.

After marine oil spills, suspended physical particles and extracellular polymeric substances (EPS) secreted by bacteria can aggregate with oil to form marine oil snow (MOS), which determines the vertical migration and biodegradation processes of the submerged oil. Here, we investigated the biodegradation of oil spills during the formation of MOS under different average energy dissipation rates (ε) and different ratios of particles. Furthermore, we elucidated the biodegradation mechanism of oil spills from a spatiotemporal perspective. The ε plays a major role (either promoting or inhibiting) in the biodegradation effect of oil spills, and there is a proportional threshold for biological/physical particles, which can regulate the ε's effect on degradation. The oil-water interfacial tension, the encapsulation of oil droplets by particles, hydrogen bonds, and the vertical distribution of oil droplets (suspended or deposited) will also jointly affect the particles threshold on this basis, thereby influencing the biodegradation of oil spills. When the proportion of XG exceeds the threshold (kaolinite: XG = 1:3 at 150 rpm and 1:1 at 200 rpm), the originally promotive role of ε on n-alkane degradation shifts to inhibition, while its inhibition impact on PAHs biodegradation shifts to enhancement, respectively. Notably, in nearshore and extreme environments (storm or strong wave conditions), particles are more conducive to the degradation of n-alkanes and PAHs, respectively. This study will further broaden the research perspective on the environmental behavior of marine oil spills in the presence of MOS and providing a theoretical basis for predicting the fate of oil spills in nearshore environments.