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The use of engineered nanomaterial (ENMs) has increased dramatically and the possible interaction of these materials with soil-borne organic co-contaminants is largely unknown. Imidacloprid (IMDA) is a neonicotinoid insecticide and one of the most widely used pesticides in the United States and significant concerns have risen due to unknown role of these insecticides in pollinator decline. As such, understanding ENM interactions with these agrochemicals is important. In this study, the bioaccumulation, translocation, and toxicity of IMDA (10 mg/kg) to Cucurbita pepo L (zucchini) was evaluated upon simultaneous exposure to CeO2 or Ag in bulk (CeBulk or AgBulk) or nanoparticle (CeNP or AgNP) form at 100 mg/kg under soil-grown conditions. Additionally, expression analysis of seven genes (related to stress, photosynthesis, and elemental transport) previously identified as putative biomarkers of nanoparticle (NPs) exposure in zucchini was also performed. Total IMDA and metabolites accumulation in plant root and aerial tissues (shoot-stem and leaf, flower, and stamen) was equivalent to controls (soil with IMDA minus NPs) in both CeO2 exposures. However, co-exposure to AgBulk and AgNP significantly suppressed IMDA accumulation in zucchini aerial tissues by 30% and 33%, respectively. The Ag and Ce concentration in aerial tissues exposed to NPs alone were 85.4% and 79.2%, respectively, higher than plants co-exposed to NPs with IMDA. The expression level of the seven genes studied shows that the response mechanisms of zucchini to IMDA and NPs are different. Moreover, no synergistic effects were observed in gene expression upon IMDA-NPs co-exposure. These findings show that ENMs may not only affect the bioavailability and translocation of currently used pesticides but that the reverse is true as well; these interactions should be considered when assessing the exposure and risk of these materials in the environment.

Soil organic matter plays a major role in determining the fate of the engineered nanomaterials (ENMs) in the soil matrix and effects on the residing plants. In this study, kidney bean plants were grown in soils varying in organic matter content and amended with 0-500mg/kg cerium oxide nanoparticles (nano-CeO2) under greenhouse condition. After 52days of exposure, cerium accumulation in tissues, plant growth and physiological parameters including photosynthetic pigments (chlorophylls and carotenoids), net photosynthesis rate, transpiration rate, and stomatal conductance were recorded. Additionally, catalase and ascorbate peroxidase activities were measured to evaluate oxidative stress in the tissues. The translocation factor of cerium in the nano-CeO2 exposed plants grown in organic matter enriched soil (OMES) was twice as the plants grown in low organic matter soil (LOMS). Although the leaf cover area increased by 65-111% with increasing nano-CeO2 concentration in LOMS, the effect on the physiological processes were inconsequential. In OMES leaves, exposure to 62.5-250mg/kg nano-CeO2 led to an enhancement in the transpiration rate and stomatal conductance, but to a simultaneous decrease in carotenoid contents by 25-28%. Chlorophyll a in the OMES leaves also decreased by 27 and 18% on exposure to 125 and 250mg/kg nano-CeO2. In addition, catalase activity increased in LOMS stems, and ascorbate peroxidase increased in OMES leaves of nano-CeO2 exposed plants, with respect to control. Thus, this study provides clear evidence that the properties of the complex soil matrix play decisive roles in determining the fate, bioavailability, and biological transport of ENMs in the environment.

Iron and copper nanomaterials are widely used in environmental remediation and agriculture. However, their effects on physiological parameters and nutritional quality of terrestrial plants such as lettuce (Lactuca sativa) are still unknown. In this research, 18-day-old hydroponically grown lettuce seedlings were treated for 15 days with core-shell nanoscale materials (Fe/Fe(3)O(4), Cu/CuO) at 10 and 20mg/L, and FeSO(4)·7H(2)O and CuSO(4)·5H(2)O at 10mg/L. At harvest, Fe, Cu, micro and macronutrients were determined by ICP-OES. Also, we evaluated chlorophyll content, plant growth, and catalase (CAT) and ascorbate peroxidase (APX) activities. Our results showed that iron ions/NPs did not affect the physiological parameters with respect to water control. Conversely, Cu ions/NPs reduced water content, root length, and dry biomass of the lettuce plants. ICP-OES results showed that nano-Cu/CuO treatments produced significant accumulation of Cu in roots compared to the CuSO(4)·5H(2)O treatment. In roots, all Cu treatments increased CAT activity but decreased APX activity. In addition, relative to the control, nano-Cu/CuO altered the nutritional quality of lettuce, since the treated plants had significantly more Cu, Al and S but less Mn, P, Ca, and Mg.

Quantum dots (QDs) are used in an array of applications from electronic devices to medicine, leading to environmental release and accumulation in landfills and agricultural soils. However, their effects on plants have been least studied among other engineered nanomaterials. In the current study, soybean seedlings were exposed to 50–200 mg/L cadmium sulfide quantum dots (CdS-QDs) to elucidate their bioaccumulation and biological response in comparison to Cd2+ ions and bulk-CdS. To understand the role of surface coatings on QD stability, uptake, translocation, subcellular localization and cellular response, bare CdS-QDs were capped with ligands varying in polarity and surface charge. Four common ligands, including trioctylphosphine oxide, polyvinylpyrrolidone, mercaptoacetic acid, and glycine were used to synthesize QD-TOPO, QD-PVP, QD-MAA, and QD-GLY, respectively. In aqueous suspension, QD-MAA particles were most stable, maintaining their size at 332 nm with least Cd2+ dissolution (9%) after 14 d, whereas QD-TOPO formed large aggregates of size 3861 nm with 27% Cd2+ dissolution. Upon exposure to 100 mg/L bare and coated CdS-QDs in vermiculite for 14 d, soybean roots accumulated Cd, ranging from 568 (QD-MAA) to 1010 (QD-PVP) μg/g tissue dry weight (DW); statistically equivalent to bulk-CdS treatment (639 μg/g DW). In the roots, Cd from CdCl2, bulk- CdS, QD-MAA and QD-GLY accumulated primarily in the cell wall (~40–55%) followed by organelles (28–40%), suggesting apoplastic pathway; whereas in QD-TOPO, dissolved Cd2+ ions accumulated mainly in the membranes. The exception was QD-PVP, which sequestered Cd mainly in the organelles (49%) in roots, potentially via symplastic pathway and translocated to shoots, resulting in reduced leaf biomass. Results suggested that peroxidases play the predominant role in quenching the oxidative stress caused by CdS-QD exposure. At the highest CdS-QD treatment (200 mg/L), root lignification allowed the plants to restrict Cd accumulation, except in QD-PVP, where lignification was reduced by 21% leading to higher Cd content in shoots. Increased amino acid content in the leaves was noted as a stress tolerance mechanism by the plants exposed to 200 mg/L QD treatments. This study highlights the significant influence that surface coating exerts on QDs fate and effects in a planted system.