Aggregation of microplastics with marine biogenic particles

Although microplastics have dramatically accumulated in the marine environment, knowledge of their impact on organisms and biological processes in marine ecosystems is very scarce. The present study aimed at testing the hypothesis that microplastics participate in biogenic particle aggregation processes within the marine water column. For this purpose, interactions of polystyrene microplastics (700-900 µm) with biogenic particles, primarily phytoplankton, were investigated in laboratory experiments. Together with biogenic particles, microplastics formed relatively large aggregates. In the presence of microplastics, particle aggregation was faster and more pronounced compared to aggregation between biogenic particles only. At the end of the experiments, microplastics were covered by biofilms containing bacteria and microalgae. No aggregate formation took place in control experiments with microplastics and either filtered or artificial seawater. The aggregation of biogenic particles with biofilm-covered microplastics was much faster than that of biogenic particles with microplastics without biofilms. These results suggest that (1) microplastics interact with biogenic particles and are strongly involved in natural particle aggregation processes in the water column and (2) biofilm formation increases the microplastics’ aggregation potential.