Potential Threat of Lead Oxide Nanoparticles for Food Crops: Comprehensive Understanding of the Impacts of Different Nanosized PbO_x (x = 1, 2) on Maize (Zea mays L.) Seedlings In Vivo

PbOx (PbO2 and PbO, x = 1, 2) nanoparticles are emerging contaminants in dust, soil, and water due to extensive application of commercial lead products. As far as we know, the current studies are first conducted to understand the phytotoxic effects of PbO2 (10 ± 3 nm) and PbO NPs (20 ± 5 nm) on maize (Zea mays L.) grown in hydroponic treatments. The exposure assays indicated that phytotoxic effects were dose- and size-dependent on PbOx NPs. Water uptake would be the crucial mechanism to govern the effects of PbOx on maize seed germination and root elongation, while the nanosize of particles and water transpiration processes would control maize growth and biomass production. PbOx NPs significantly influenced the macro- and micronutrients in roots and shoots of maize and significantly affected the maize growth and grain development. Our findings provide clear-cut evidence that PbO/PbO2 NPs can bioaccumulate in maize cell organelles via apoplastic and symplastic routes from the seed and root pathways along with water uptake and transportation. The significance of this research elucidates the impacts of PbO/PbO2 NPs on food security and indicates the threat of emerging PbO/PbO2 NPs to human dietary health.