Plastic wastes including microplastics can become the carriers of hydrophobic organic contaminants (HOCs) in the aquatic environment, thus affecting the bioavailability and environmental behavior of HOCs. However, little is known about the fate of contaminants after adsorption, especially under the influence of biofilm formation in field conditions. In this study, we used polyethylene (PE) to pre-absorb different concentrations of benzo[a]pyrene (BaP), a non-polar contaminant, and deployed in-situ at two stations in the Haihe River estuary, China. Based on the desorption kinetics of BaP from PE, a mass transfer model for desorption of non-polar contamination from PE under the influence of biofilm formation was developed. This study proved that biofilm formation, as an intermediate medium connecting the polymer with the aquatic environment, did not become a sink for contaminants during the desorption process in field conditions, but accelerated the desorption of highly hydrophobic contaminants by reducing the partition coefficient between the polymer and the boundary layer, where mass transfer process is mainly limited by the boundary layer. Furthermore, the effects of biofilm formation on the fate of other non-polar and weakly polar contaminants (including additives) in PE were predicted. The results of this study highlight the need for future studies on the mass transfer kinetics of plastic- combined contaminants in field conditions and the release degree of the sorbed contaminants, except focusing on the occurrence and equilibrium partitioning of plastic-combined contaminants.

Microplastic,,absorption,biofilm,Marine environment