Quantification of metal uptake in Spinacia oleracea irrigated with water containing a mixture of CuO and ZnO nanoparticles

An extensive application and potential release of nanoparticles (NPs) through wastewater treatment plants to agricultural lands have created an urgent necessity to evaluate food safety. The study here grew Spinacia oleracea until maturity in the soil and irrigated with CuO and ZnO NPs (as single and as a binary mixture). The plants were grown in soil containing pots and were exposed to NPs (CuO and ZnO) and ions (Cu²⁺ and Zn²⁺) (concentration = 1.2 × 10⁻⁴, 1.2 × 10⁻³, 1.2 × 10⁻² mol/Kg of soil); a binary mixture (CuO + ZnO and Cu²⁺+Zn²⁺) concentration = 1.2 × 10⁻⁴+1.2 × 10⁻⁴ mol/Kg of soil, respectively. At maturity, plant fresh weight, root length, and elemental content (Cu and Zn) were quantified.Results showed significant adverse effects on plant biomass exposed at 1.2 × 10⁻² mol/Kg of soil (percentage reduction = 36%, 26% and 45% for CuO, ZnO, and CuO + ZnO NPs, respectively). The interaction of toxicity between two NPs and ions on reduction in fresh weight was observed to be additive. Desorption studies were performed for determining root-surface adsorbed CuO and ZnO NPs using three different concentrations of Na₄EDTA. The estimated internal uptake of Cu and Zn was found to be 0.4 mg Cu/g dry weight and 0.7 mg Zn/g dry weight in the shoot portion of the plant and 3.06 mg Cu/g dry weight and 3.4 mg Zn/g dry weight in the root portion of the plant, respectively. (at 1.2 × 10-2 mol/Kg of soil). Exposure of metal ions has shown a higher reduction in biomass and higher uptake in plants as compared to NPs. The projected hazard quotient values for the intake of NPs by children was found to be greater than 1 indicating risks to children. Given the importance of food safety, determination of the potential risk of consuming contaminated plants, irrigated using nanoparticles containing wastewater is advised.