Uptake and Fate of Silver and Zinc Engineered Nanoparticles in Maize under Single and Binary Dosing Soil Ecosystems

Recent agricultural applications of engineered metallic nanoparticles (ENPs) have raised concerns about their uptake and fate in plants. To understand this critical issue, this study investigated the fate and uptake of silver (Ag) and zinc oxide (ZnO) ENPs in maize (Zea mays L.) after single or binary ENP exposure in soil. Results indicated that both Zn and Ag elemental concentrations in roots increased with increasing ENP dosage. Ag NPs in the tissues were detected, but not Zn NPs. Ag NP concentration was 3 times higher in the roots than in the shoots at low Ag NP dosing, while Ag NP size increased with dosing and became 20% smaller in the shoots. ENP uptake by maize was predominantly through fine root hair breaches. The coexisting ZnO NPs in general reduced the total dissolved Ag concentration by >42.9% in roots and >54.9% in shoots. However, particulate Ag (Ag NP) concentration was found to be 88.7% higher in roots with the 100 mg/kg ZnO NPs + 50 mg/kg Ag NPs treatment compared to the Ag NP-only group at 50 mg/kg. A higher ZnO NP dosage elevated maize height and shoot biomass, with significant effects observed at 200 mg/kg ZnO NPs. A moderate Ag NP dose at 50 mg/kg increased both height and biomass. Notably, the 50 mg/kg ZnO NPs + 25 mg/kg Ag NPs treatment significantly increased shoot biomass (>49.0%) compared to the control and the corresponding single ENP groups. ENP treatment also altered the micronutrient status in plants. ZnO NPs decreased Cu content but Ag NPs elevated Mo level in roots. The findings provide the first evidence of Ag NP–ZnO NP interactions in the soil–plant ecosystem, highlighting implications for nanoagrochemical efficacy, safety, and crop productivity.