Hydrodynamic transport modes drive the mechanism of copper adsorption on polyethylene terephthalate microplastic...

The capacity of microplastics (MPs) to adsorb metals is widely regarded as an additional adverse impact of MPs in natural environments, as they can act as vectors for contaminant transport. Natural aquatic systems exhibit a broad range of turbulence levels associated with different hydrodynamic transport modes, which can play a critical role in controlling metal adsorption onto microplastic surfaces. Through a series of controlled laboratory experiments, this study examines how metal adsorption (using Cu as a metal model) is mediated by turbulence, with a particular focus on Cu²⁺ adsorption onto polyethylene terephthalate (PET) MPs. High turbulence conditions resulted in an increased adsorption capacity due to sustained interactions between Cu²⁺ ions and PET particle surfaces. In contrast, low turbulence conditions promoted the settling of PET particles, thereby reducing Cu²⁺ adsorption as particle PET surfaces became partially or entirely shielded from the flow once deposited at the bottom of the water column. Additionally, experiments conducted using PET MPs with sizes ranging from 45 μm to 250 μm demonstrated that smaller MPs of 45 μm exhibited an additional 70% of Cu²⁺ adsorption than the larger MPs of 250 μm, highlighting the significant role of small-sized MPs in the transport of contaminants.