Biofilm-mediated mass transfer of sorbed benzo[a]pyrene from polyethylene to seawater

Plastic waste, including microplastics (MPs), often serves as a carrier for hydrophobic organic contaminants (HOCs) and additives in aquatic environments. However, little is known about the fate of contaminants in plastics, especially under the influence of biofilm in field conditions. In this study, polyethylene (PE) was pre-sorbed with varying concentrations of benzo[a]pyrene (BaP), a non-polar contaminant, and deployed in situ to study desorption kinetics under natural biofilm colonization. Based on the desorption kinetics of BaP from PE, a mass transfer model was developed to describe the desorption of non-polar contaminants from PE under the influence of biofilm formation. This study proved that biofilm, acting as an intermediary between plastics and the aquatic environment, did not serve as a sink for plastic-sorbed BaP, but accelerated the desorption process of BaP by reducing the partition coefficient between the plastic and the boundary layer. Furthermore, based on our developed model (IABL-ODD), the effects of biofilm on the fate of other non-polar and weakly polar contaminants in PE were predicted. This study highlights the influence of biofilm on the desorption of hydrophobic contaminants from plastics in field conditions and also informs future work on more relevant processes such as additive leaching.