Stress impacts of different types of micro- and nanomaterials on vegetable crops†

Nanotechnology has revolutionized industries, but the unique properties of nanoparticles, such as small size, large surface area, and stability, enable them to bypass natural defence systems, complicating toxicity assessments. This study investigated the toxic effects and migration of micro- or nanoparticles, specifically polystyrene (PS; 100 nm and 300 nm), graphene quantum dots (GQDs), and single-walled carbon nanotubes (SWCNTs), in hydroponically grown cherry radishes and lettuce. In cherry radishes, nanoparticles disrupted cellular processes, breaking down starch and protein into soluble sugars and proteins, increasing their concentrations by 11.9–18.8% and 44.8–75.5%, respectively, depending on the nanoparticle type and concentration. The increase in small molecule content raised cell sap concentration, enhancing cell osmotic pressure and promoting water absorption. Root dehydrogenase activity (DHA) decreased significantly under 50 mg L⁻¹ treatments of PS100, PS300, GQDs, and SWCNTs by 47.3%, 26.3%, 60.3%, and 36.9%, respectively, leading to reduced root vitality. In lettuce, nanoparticles induced antioxidative responses, significantly increasing hydrogen peroxide (H₂O₂) levels. Under 10 mg L⁻¹ treatments, the H₂O₂ content rose by 30.6%, 1.1%, 28.5%, and 67.4% for PS100, PS300, GQDs, and SWCNTs, respectively, and by 76.4%, 1.1%, 43.2%, and 29.5% under 50 mg L⁻¹ treatments. Microplastics caused higher H₂O₂ accumulation than GQDs and SWCNTs. Elevated malondialdehyde (MDA) levels indicated severe lipid peroxidation, with GQDs causing the most damage, reducing the lipid content by 63.2% and 38.2%. Micro- or nanoparticles can penetrate plant cells, accumulating in the fleshy root cells of cherry radishes. In lettuce, PS300 particles can migrate from roots to leaves through transpiration, while SWCNTs can induce cytoplasmic and cell wall separation. Micro- or nanoparticles accumulate in directly exposed lettuce roots, but whether they can migrate to unexposed roots of the same plant still requires further investigation.