Silicon dioxide nanoparticles mitigate cadmium sulfide phytotoxicity in spinach: a metabolomic and physiological investigation.

The widespread application of cadmium sulfide (CdS) nanoparticles (NPs) in various fields inevitably leads to their release into the environment, where they can negatively affect plants and, consequently, pose risks to human health through the food chain. Over the past two decades, the increasing release of NPs into soils, resulting from production, consumption and waste disposal, has raised significant environmental concerns. Current research focuses on understanding NPs interactions with plants to enable sustainable agriculture. Therefore, the present study examines how CdS NPs affect spinach growth and whether silicon dioxide (SiO2) NPs can alleviate CdS NPs induced stress. Three-week-old spinach plants were treated for 4 weeks with either 1 mg/l CdS NPs alone or in co-exposure with three concentrations (1, 20 and 100 mg/l) of SiO2 NPs. The central methods applied included measuring metal content, transmission electron microscopy (TEM) for cellular uptake visualization, analysis of biochemical stress markers and a metabolomic analysis to identify altered metabolic pathways. Key results demonstrated that SiO2 NPs, particularly at 1 and 100 mg/l concentrations, significantly reduced Cd content by up to 40.72% and enhanced the uptake of essential nutrients (Zn, Co, Ca, Fe). TEM imaging confirmed reduced cellular internalization of CdS NPs. The treatment also induced a strong antioxidant response and increased chlorophyll content by up to 170.10%. Metabolomic analysis revealed significant alterations in metabolites (53-75%), primarily affecting pathways related to amino acids, carbohydrates, oxidative phosphorylation and sulphur metabolism. SiO2 NPs effectively detoxify CdS NPs in spinach through a dual mechanism: limiting cellular uptake and biochemically triggering a robust antioxidant and metabolic defence system. This study provides critical insights into the application of SiO2 NPs as a nano-enabled strategy to enhance crop safety in heavy metal-contaminated environments.