Recent investigations show that carbon-based and metal-based engineered nanomaterials (ENMs), components of consumer goods and agricultural products, have the potential to build up in sediments and biosolid-amended agricultural soils. In addition, reports indicate that both carbon-based and metal-based ENMs affect plants differently at the physiological, biochemical, nutritional, and genetic levels. The toxicity threshold is species-dependent and responses to ENMs are driven by a series of factors including the nanomaterial characteristics and environmental conditions. Effects on the growth, physiological and biochemical traits, production and food quality, among others, have been reported. However, a complete understanding of the dynamics of interactions between plants and ENMs is not clear enough yet. This review presents recent publications on the physiological and biochemical effects that commercial carbon-based and metal-based ENMs have in terrestrial plants. This document focuses on crop plants because of their relevance in human nutrition and health. We have summarized the mechanisms of interaction between plants and ENMs as well as identified gaps in knowledge for future investigations.

A B S T R A C TGiven increasing use of copper-based nanomaterials, particularly in applications with direct release, it is imperative to understand their human and ecological risks. A comprehensive and systematic approach was used to determine toxicity and fate of several Cu nanoparticles (Cu NPs). When used as pesticides in agriculture, Cu NPs effectively control pests. However, even at low (5-20 mg Cu/plant) doses, there are metabolic effects due to the accumulation of Cu and generation of reactive oxygen species (ROS). Embedded in antifouling paints, Cu NPs are released as dissolved Cu + 2 and in nano-and micron-scale particles. Once released, Cu NPs can rapidly (hours to weeks) oxidize, dissolve, and form CuS and other insoluble Cu compounds, depending on water chemistry (e.g. salinity, alkalinity, organic matter content, presence of sulfide and other complexing ions). More than 95% of Cu released into the environment will enter soil and aquatic sediments, where it may accumulate to potentially toxic levels (> 50-500 μg/L). Toxicity of Cu compounds was generally ranked by high throughput assays as: Cu + 2 > nano Cu(0) > nano Cu(OH) 2 > nano CuO > micron-scale Cu compounds. In addition to ROS generation, Cu NPs can damage DNA plasmids and affect embryo hatching enzymes. Toxic effects are observed at much lower concentrations for aquatic organisms, particularly freshwater daphnids and marine amphipods, than for terrestrial organisms. This knowledge will serve to predict environmental risks, assess impacts, and develop approaches to mitigate harm while promoting beneficial uses of Cu NPs.

With increasing global population, innovations in agriculture will be essential for a sustainable food supply. We compare commercial CuO NP to synthesized Cu 3 (PO 4 ) 2 •3H 2 O nanosheets to determine the influence of coordinating anion, particle morphology, and dissolution profile on Fusarium oxysporum f. sp. niveum induced disease in watermelon. Copper dissolution in organic acid solutions that mimic complexing agents found in plants was increased by 2 orders of magnitude relative to water. Cu 3 (PO 4 ) 2 •3H 2 O nanosheets showed a rapid initial dissolution, with equilibration after 24 h; CuO NP exhibited continuous particle dissolution. In a greenhouse study, Cu 3 (PO 4 ) 2 •3H 2 O nanosheets at 10 mg/L significantly repressed fungal disease as measured by yield and by a 58% decrease in disease progress. Conversely, CuO NP only yielded significant effects on disease at 1000 mg/L. In field studies, similar enhanced disease suppression was noted for Cu 3 (PO 4 ) 2 •3H 2 O nanosheets, although biomass and yield effects were variable. The method of application was a significant factor in treatment success, with the dip method being more effective than foliar spray; this is likely due to homogeneity of coverage during treatment. The data show that Cu-based nanoscale materials can be an effective and sustainable strategy in the crop disease management but that particle characteristics such as morphology, coordination environment, and dissolution profile will be important determinants of success.