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Nanoparticles (NPs) are increasingly being used in medical, electronic, energy, and agricultural applications due to their unique properties that often arise due to the high surface area-to-volume ratio. However, this characteristic along with the high reactivity of NPs make these materials highly dynamic in environmental settings. Thus, several transformations can take place when these materials enter the environment that determines their transport, toxicity, and fate of them in our environment. These transformations, and more specifically oxidative dissolution and sulfidation, are directly impacted by the characteristics that a NP has in addition to the surrounding environmental conditions. Therefore, this review aims to summarize how NP characteristics (size, coatings, etc.) and other important environmentally relevant conditions (oxic/anoxic waters, natural organic matter, etc.) impact the oxidative dissolution and sulfidation of several metal and metal oxide NPs. The impact of these factors is crucial to understanding and predicting the environmental risks of these materials in a wide range of applications. 

There is a need to develop new and sustainable agricultural technologies to help provide global food security, and nanoscale materials show promising results in this area. In this study, mesoporous silica nanoparticles (MSNs) and chitosan-coated mesoporous silica nanoparticles (CTS-MSNs) were synthesized and applied to soybeans (Glycine max) by two different strategies in greenhouse and field studies to study the role of dissolved silicic acid and chitosan in enhancing plant growth and suppressing disease damage caused by Fusarium virguliforme. Plant growth and health were assessed by measuring the soybean biomass and chlorophyll content in both healthy and Fusarium-infected plants at harvest. In the greenhouse study, foliar and seed applications with 250 mg/L nanoparticle treatments were compared. A single seed treatment of MSNs reduced disease severity by 30% and increased chlorophyll content in both healthy and infected plants by 12%. Based on greenhouse results, seed application was used in the follow-up field study and MSNs and CTS-MSNs reduced disease progression by 12 and 15%, respectively. A significant 32% increase was observed for chlorophyll content for plants treated with CTS-MSNs. Perhaps most importantly, nanoscale silica seed treatment significantly increased (23–68%) the micronutrient (Zn, Mn, Mg, K, B) content of soybean pods, suggesting a potential sustainable strategy for nano-enabled biofortification to address nutrition insecurity. Overall, these findings indicate that MSN and CTS-MSN seed treatments in soybeans enable disease suppression and increase plant health as part of a nano-enabled strategy for sustainable agriculture. 

Increasing the capacity of biological nitrogen fixation (BNF) is an effective strategy to enhance food security while simultaneously reducing the carbon and nitrogen footprint of agriculture. Nanotechnology offers several pathways to enhance BNF successfully. 

The potential of biochar and nanoparticles to serve as effective delivery agents for beneficial bacteria to crops was investigated. Application of nanoparticles and biochar as carriers for beneficial bacteria improved not only the amount of nitrogen-fixing and phosphorus-solubilizing bacteria in soil, but also improved chlorophyll content (1.2–1.3 times), cell viability (1.1–1.5 times), and antioxidative properties (1.1–1.4 times) compared to control plants. Treatments also improved content of phosphorus (P) (1.1–1.6 times) and nitrogen (N) (1.1–1.4 times higher) in both tomato and watermelon plants. However, the effect of biochars and nanoparticles were species-specific. For example, chitosan-coated mesoporous silica nanoparticles with adsorbed bacteria increased the phosphorus content in tomato by 1.2 times compared to a 1.1-fold increase when nanoclay with adsorbed bacteria was applied. In watermelon, the situation was reversed: 1.1-fold increase in the case of chitosan-coated mesoporous silica nanoparticles and 1.2 times in case of nanoclay with adsorbed bacteria. Our findings demonstrate that use of nanoparticles and biochar as carriers for beneficial bacteria significantly improved plant growth and health. These findings are useful for design and synthesis of novel and sustainable biofertilizer formulations.