Machine learning was applied to predict the plant uptake and transport of engineered nanoparticles (ENPs). A back propagation neural network (BPNN) was used to predict the root concentration factor (RCF) and translocation factor (TF) of ENPs from their essential physicochemical properties (e.g., composition and size) and key external factors (e.g., exposure time and plant species). The relative importance of input variables was determined by sensitivity analysis, and gene-expression programming (GEP) was used to generate predictive equations. The BPNN model satisfactorily predicted the RCF and TF in both hydroponic and soil systems, with an R 2 higher than 0.8 for all simulations. Inclusion of the initial ENP concentration as an input variable further improved the accuracy of the BPNN for soil systems. Sensitivity analysis indicated that the composition of ENPs (e.g., metals vs metal oxides) is a major factor affecting RCF and TF values in a hydroponic system. However, the soil organic matter and clay contents are more dominant in a soil system. The GEP model (R 2 = 0.8088 and 0.8959 for RCF and TF values) generated more accurate predictive equations than the conventional regression model (R 2 = 0.5549 and 0.6664 for RCF and TF values) in a hydroponic system, which could guide the sustainable design of ENPs for agricultural applications.

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A greenhouse study extending to the life cycle of rice was conducted to evaluate the effect of copper oxide nanoparticles (CuONPs), copper ions (Cu2+), or CuO bulk particles (CuOBPs) at 100 mg/kg on As accumulation and speciation in rice. Cu amendments significantly lowered the total As in rice shoots at the maximum tillering stage by 38–64%; however, the total As concentration in rice shoots treated with CuOBPs was significantly higher than in other treatments at the mature stage, which had comparable As in their shoots. Although Cu amendments did not significantly alter the total As accumulation in rice grains, they all significantly lowered the As­(III) to total As ratio in rice grains by 21–65%. The possible modification of iron plaque by Cu amendments was investigated as one of the potential mechanisms for altered As accumulation and speciation in rice due to its known role in As retention. Interestingly, even though the formation of iron plaque was unaffected by the Cu amendments, CuONPs significantly increased the As/Fe ratio in iron plaque by 71%, while Cu2+ significantly decreased the As retention in iron plaque by 30% at the mature stage. Our study showed that Cu amendments affected As uptake and speciation in rice tissues, and the modification of iron plaque played a role in this process.

This study examined the effect of three forms of zinc fertilizers on arsenic (As) accumulation and speciation in rice tissues over the life cycle of this cereal crop in a paddy soil. The formation and properties of iron plaque on rice roots at the maximum tillering stage and the mature stage were also determined. Elevated As at 5 mg/kg markedly lowered the rice yield by 86%; however, 100 mg/kg Zn fertilizers significantly increased the rice yield by 354–686%, regardless of the Zn form. Interestingly, only Zn2+ significantly lowered the total As in rice grains by 17% to 3.5 mg/kg and As­(III) by 64% to around 0.5 mg/kg. Zinc amendments substantially hindered and, in the case of zinc oxide bulk particles (ZnOBPs), fully prevented the crystallization of iron oxides (Fe3O4 and Fe2O3) and silicon oxide (SiO2) and altered the composition of iron plaques on rice roots. SiO2 was first reported to be a significant component of iron plaque. Overall, ZnOBPs, ZnO nanoparticles, and Zn2+ displayed significant yet distinctive effects on the properties of iron plaque and As accumulation in rice grains, providing a fresh perspective on the potentially unintended consequences of different Zn fertilizers on food safety.

Novel nano-based fertilizers, pesticides, sensors, and nutrient delivery systems for agricultural applications have been widely reported. However, several key questions remain regarding nanoparticle (NP)−plant interactions, such as the impact of interactions of co-existing NPs on their accumulation in plants, especially in plants grown in soil systems. In this study, soil-grown lettuce was exposed to different concentrations of silver nanoparticles (AgNPs) alone (0−200 mg/kg) or in combination with 100 mg/kg cerium oxide nanoparticles (CeO 2 NPs) in a greenhouse study. As expected, the concentrations of AgNPs and CeO 2 NPs in plant tissues were markedly increased in plant tissues grown in NP-treated soil. Surprisingly, the size of AgNPs in roots was much smaller than those in shoots and in freshly prepared suspensions, suggesting that smaller AgNPs were preferably taken up by plant roots and then aggregated into large NPs in lettuce shoots. The noticeably smaller AgNPs might stem from the dissolution of AgNPs in the rhizosphere or the formation of transformed Ag-containing NPs from dissolved Ag + . CeO 2 NPs significantly modified the uptake and in planta distribution of AgNPs in lettuce. For example, the co-presence of CeO 2 NPs in soil notably increased the concentration of AgNPs in lettuce shoots but significantly reduced their concentration in roots, compared with 100 mg/kg AgNPs treatment alone. The total concentrations of zinc (Zn) and copper (Cu) in plant tissues were determined as representative micronutrients and compared with those of the control; 100 mg/kg AgNPs diminished the Zn and Cu concentrations in lettuce, but there was no significant effect when AgNPs and CeO 2 NPs were co-available in the soil. These results shed new light on plant−NP interactions in soil ecosystems exposed to multiple NPs at the same time.