Microplastic-oil-dispersant agglomerates in the marine environment: Formation mechanism and impact on oil dispersion

Microplastics (MPs) can interact with spilled oil to form MP-oil-dispersant agglomerates (MODAs) in oceans. This study investigated the MODA formation mechanism and its impact on oil dispersion during marine oil spill responses. Two types of agglomerates, MODA-1 (MP-in-oil) and MODA-2 (MP-oil droplet-embedded), were identified. The 12 pm-MPs only formed MODA-1, while 45 pm-MPs and 125 pm-MPs formed MODA-1 and MODA-2 due to the surface free energy minimization principle. Impacts of MODA on oil dispersion under different mixing energy levels and seawater salinities were explored. We found that MODA reduced oil dispersion effectiveness under different mixing energy levels. Among three MP sizes, 12 pm-MPs caused the greatest reduction in dispersion effectiveness due to the formation of MODA-1. Pristine 12 pm-MPs reduced dispersion effectiveness by 21.95% under 5.62 x 10-1 W/kg, while pristine 45 pm-MPs and pristine 125 pm-MPs decreased it by 5.85% and 1.83%, respectively. In addition, MODA formed by pristine MPs has a larger impact on oil dispersion effectiveness than that of aged MPs under different salinities. Under 20psu, pristine 12 pm-MPs reduced dispersion effectiveness by 33.68%, while aged 12 pm-MPs decreased it by 24.61%. This study is the first report on the MODA formation mechanism, which is essential for exploring MODA transport and toxicity through marine trophic levels.

Automated summary

This study investigated the formation mechanism of microplastic-oil-dispersant agglomerates (MODAs) in the ocean and found two different types of agglomerates. The results showed that MODA reduced oil dispersion effectiveness, and the impact varied with the size of the microplastics. Additionally, the salinity and aging status of the microplastics also affected the effectiveness of MODA on oil dispersion.