Clay minerals limit nanoplastic uptake in wheat plant

The effects of nanoplastics (NPs) on crop plants are receiving increasing attention. Studies have demonstrated that many crop plants can internalize and transport NPs to their aboveground tissues. However, the effect of ubiquitous soil clay minerals on NP uptake remains unclear. This study investigated the interaction between two common clay minerals (kaolinite and montmorillonite) and 200 nm polystyrene (PS) NPs during uptake by wheat seedlings. Our results revealed that both kaolinite and montmorillonite formed heterogeneous aggregates with PS NPs in the rhizosphere. Furthermore, clay minerals were observed to co-localize with NPs within lateral root cracks, suggesting potential competition for entry pathways. Quantification of PS NPs demonstrated that co-exposure with clay minerals significantly reduced NP accumulation: specifically, kaolinite decreased root and shoot accumulation by 44.9 % and 17.4 %, respectively, while montmorillonite induced greater reductions of 69.1 % in roots and 17.5 % in shoots. Sequential exposure (clay minerals followed by NPs) also resulted in decreased uptake, with reductions of 37.5 % (roots) and 4.7 % (shoots) for kaolinite, and 44.4 % (roots) and 7.2 % (shoots) for montmorillonite. The stronger uptake limitation observed with montmorillonite, compared to kaolinite, is attributed to its larger aggregate size and greater surface area. These findings demonstrate that both kaolinite and montmorillonite reduce the uptake of 200 nm PS-NPs in wheat seedlings through dual mechanisms: (1) hetero-aggregation in the rhizosphere and (2) competitive occupation of lateral root crack-entry pathways. This study reveals the important role of clay minerals in mitigating NP uptake by crop plants, provides insights into how clay minerals can alter the environmental risk posed by NPs, and establishes a foundation for future research on plant interactions with complex environmental particles.