Zinc oxide nanoparticles and nano-hydroxyapatite enhanced Cd immobilization, activated antioxidant activity, improved wheat growth, and minimized dietary health risks in soil-wheat system

Abstract

Cadmium (Cd) accumulation in alkaline soils has posed a serious global food safety and health threat. In this work, the effects of zinc oxide nanoparticles (ZnO NPs) and nano-hydroxyapatite (n-HAP) on Cd uptake by wheat in Cd-contaminated soils were evaluated by potting experiments. Results revealed that wheat grain yield increased with the application of nanomaterials (NPs), particularly at higher concentrations. The addition of ZnO NPs or n-HAP reduced Cd concentrations in wheat grains, shoots, and roots by 8.40∼44.54 %, 34.50∼57.28 %, 9.32∼41.26 % and 6.72∼14.29 %, 18.18∼32.19 %, and 1.08∼11.02 % compared with those in controls, respectively, while simultaneously increasing leaf antioxidative activity of SOD, POD, and CAT and decreasing MDA content. Soil pH increased and exchangeable Cd was transformed into more stable organically-bound and residual-bound Cd, thereby reducing soil available Cd content (0.1 g/kg ZnO NPs:16.97 %; 2.0 g/kg n-HAP:14.98 %). As a result, Cd enrichment in wheat tissues was reduced significantly by 0.1 g/kg ZnO NPs or 2.0 g/kg n-HAP. The health risk was assessed, and the Target Hazard Quotient (THQ) value was <1 with 0.1 g/kg ZnO NPs, which was within the safe range (P<0.05). Principal component analysis (PCA) suggested that ZnO NPs were more effective than n-HAP in preventing Cd from entering plant roots. Furthermore, soil availability Cd was most affected by soil fractionation, whereas Cd concentrations in wheat tissues had the greatest effect on grain Cd accumulation. These results provide a key basis for the safe and sustainable application of nanoparticles and indicate that type and concentration should be fully considered when selecting nanomaterials to control Cd stress.