Size-Selective Uptake, Translocation, and Accumulation of Polyethylene Microplastics in Maize: Implications for Agricultural Sustainability

Microplastics (MPs) are environmental pollutants that have attracted widespread concern. However, the effects of particle size on the uptake, translocation, and tissue distribution of polyethylene microplastics (PE-MPs), the dominant polymer in agricultural mulch film residues, in maize plants remain insufficiently understood. To investigate the size-dependent PE-MP migration and distribution in maize plants, we conducted hydroponic experiments using maize seedlings. By combining confocal laser scanning microscopy, scanning electron microscopy, and pyrolysis–gas chromatography–mass spectrometry, we investigated the uptake, transport, and accumulation of PE-MPs with four particle sizes (0.1, 1.0, 10.0, and 100.0 μm) in maize plants. The results showed that maize roots exhibited particle-size selectivity in the PE-MP uptake and transport. Small-sized particles (0.1 and 1.0 μm) were detected within the root tissues and aboveground parts, while large-sized particles (10.0 and 100.0 μm) were detected mainly on the root surface. The small-sized PE-MPs were observed at the junctions between primary and lateral roots and were also detected in root vascular tissues. The PE-MP accumulation pattern across plant tissues was root > leaf > stem. The 1.0 μm PE-MPs exhibited a numerically higher apparent translocation to aboveground tissues than the 0.1 μm particles. Particle aggregation is one plausible explanation for the higher root retention of 0.1 μm PE-MPs, while the underlying mechanisms remain to be further verified. The observed distribution patterns were consistent with a potential contribution of the apoplastic pathway to PE-MP translocation through the root vascular system. These findings demonstrate particle-size-dependent differences in PE-MP uptake, distribution, and accumulation in maize and provide a basis for further investigation of the environmental behavior of MPs in soil–plant systems. These findings deepen the understanding of PE-MP environmental behavior in crop systems, and provide basic scientific evidence for the sustainable management of agricultural mulch film residues, microplastic risk assessment in agro-ecosystems, and agricultural product safety prevention and control.