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Early-exposure legacy effects of polystyrene nanoplastics on lettuce: Trait-specific non-monotonic responses mask ionomic and antioxidant disruption
Summary
Lettuce seedlings briefly exposed to tiny plastic particles (nanoplastics) during germination looked perfectly healthy weeks later—growing normally in size and leaf area—but hidden beneath that normal appearance was serious internal damage, including disrupted mineral balance (way too much calcium, too little phosphate) and stress responses lingering long after the plastic exposure ended. This matters because it means a lettuce plant could look fine on the outside while being nutritionally compromised on the inside, suggesting that current safety checks based on how crops look may not be enough to catch contamination from nanoplastics that are incre
The prevalence of polystyrene nanoplastics (PS-NPs) in agricultural ecosystems necessitates a detailed understanding of their impacts on crop development, physiology, and nutritional quality. However, while toxicological effects of nanoplastics are increasingly documented, the integrated and dose-dependent consequences of short-term early exposure across later developmental stages remain poorly understood. In this study, the morphological, biochemical, and ionomic responses of hydroponically grown lettuce (Lactuca sativa L. cv. ‘Red Little Gem’) to 50 nm PS-NPs were investigated at concentrations of 0, 1, 10, and 100 mg/L. Importantly, plants were exposed to PS-NPs only during the initial 7-day germination phase and were then transferred to a clean hydroponic system for a further 28 days, allowing the assessment of early-exposure legacy effects or stress memory. A low dose of exposure (1 mg/L) improved early germination kinetics while increasing seedling vigor, shoot biomass, and root fresh weight. Exposure to high quantities (100 mg/L) caused significant physiological stress, including reduced antioxidant capacity, increased catalase activity, and proline buildup. Furthermore, mineral analysis revealed a severe disruption of ion homeostasis under high exposure, including a dose-dependent depletion of phosphate and a five-fold increase in calcium. At 100 mg/L, visible development, including sustained root biomass and maximum leaf area growth, disguised significant internal stress signs and nutritional deficits. The findings show that focusing solely on macroscopic morphological criteria is insufficient to establish crop safety and that multi-domain physiological and ionomic frameworks must be employed to estimate actual agricultural dangers of nanoplastic contamination.