Influence of micro- and nano-plastics on phenanthrene adsorption at the root-water interface

The adsorption of organic pollutants onto plant root surfaces is an initial crucial stage in the transfer of these pollutants from aqueous or soil solutions to plant systems. This study explored the potential influence of micro- and nano-plastics (MNPs) (0.1–100 μm) on the process of phenanthrene (Phe) adsorption at the root–water interface. The findings indicate that MNPs can exhibit either promotional or inhibitory effects on the root adsorption of organic pollutants, depending on both their particle size and content. Specifically, both the sorption capability of MNPs for Phe and their tendency to accumulate on or within root tissues increase with decreasing particle size. These dual effects facilitate the accumulation of nanoscale MNPs (0.1–6 μm in this work) within roots, which function as efficient carriers for Phe and increase Phe accumulation in root tissues. In contrast, MNPs with larger particle sizes (1–100 μm in this work) exhibit reduced affinity for roots and are more prone to remain in solution, thereby exerting more pronounced competitive inhibition against the adsorption of Phe by roots. However, when the concentration of nano-plastics in the root water system exceeded the retention capacity of the roots, the excess nano-plastics could compete with the roots for Phe, potentially reducing overall Phe sorption by the roots. These conditional effects of MNPs as either competitors or facilitators (vectors) in the root adsorption processes of organic pollutants may account for the different roles observed in previous studies where MNPs exhibited varying effects on the plant accumulation of organic pollutants.