Application of SiO2 nanoparticles to address CdS NPs contamination in spinach

Abstract

Rising cadmium (Cd) contamination poses significant threats to crop productivity, quality, and human health. To address this, nano-enabled techniques have recently gained attention for their potential to enhance crop yields and remediate contamination due to heavy metals. This study explores the efficacy of silicon dioxide nanoparticles (SiO₂ NPs) in mitigating the effects of cadmium sulfide (CdS) NPs in spinach. Field experiments were conducted growing spinach plants subjected to cultivation with 1 mg/L CdS NPs contamination, with foliar application of SiO₂ NPs at concentrations of 1, 20, and 100 mg/L. The phenotypic, biochemical, and metabolic responses of the plants to stress conditions were examined following exposure to CdS and SiO₂ for four weeks. The results showed that SiO₂ NPs increased the fresh and dry weights of both roots and shoots. Furthermore, CdS NPs exposure reduced chlorophyll content by 66.76 %, whereas SiO₂ NPs co-exposure increased chlorophyll levels by up to 42 % compared to the CdS NPs and control groups. However, elevated malondialdehyde (MDA) levels were observed in leaves for the CdS-only group and roots for all treatments indicating oxidative stress was most pronounced for the CdS case. Results demonstrated that SiO₂ application significantly reduced Cd accumulation in spinach by up to 34.92 %. Also, enhanced mineral accumulations were recorded in both roots and shoots, whereas decreased levels were found in the co-exposure groups, except for Zn. The exposure to SiO₂ resulted in upregulation of metabolites including galactonic acid, d-aspartic acid and others, and UDP-d-galactose was downregulated in the group exposed only to CdS NPs. The upregulation of these metabolites by SiO₂ NPs demonstrates their mitigating effect against CdS NPs induced stress. This work enhances understanding of phenotypic and metabolic alterations induced in spinach by CdS and SiO₂ NPs, and independently and through their co-exposure. Overall, our findings indicate that Cd contamination can be reduced in spinach using SiO₂ NPs when applied at low levels, and the mechanisms are discussed.