How Microplastics Cross the Buoyancy Barrier

Microplastic (MP) particles in the environment are covered by a so-called eco-corona. The eco-corona is made up of natural organic matter (NOM) like biomolecules, humic substances and other natural molecules. NOM substantially changes the surface properties of MP particles and therefore the interaction with other surfaces in the aqueous environment influencing their heteroaggregation behaviour.Using Colloidal Probe-AFM we studied the interactions of eco-corona covered MP particles with model sand particles on the nanoscale. Measurements were performed in different ionic concentrations to mimic changing environmental conditions. We found that the eco-corona is able to *pull* at the model sand colloidal probe by macromolecular bridging. Simulations verified the stability of these heteroaggregates under flow. With heteroaggregation experiments and following Raman-Imaging we verified the presence and stability of these aggregates on the microscale.In conclusion, we present macromolecular bridging as an eco-corona mediated heteroaggregation mechanism. It is present at monovalent salt concentrations > 1 mM and dependent on the eco-corona surface coverage. This mechanism is able to contribute substantially to MP particle heteroaggregation in the aqueous environment and explains how MPs cross the buoyancy barrier.