Potential of Novel Magnesium Nanomaterials to Manage Bacterial Spot Disease of Tomato in Greenhouse and Field Conditions.

Bacterial spot of tomato is among the most economically relevant diseases affecting tomato plants globally. In previous studies, non-formulated magnesium oxide nanoparticles (nano-MgOs) significantly reduced the disease severity in greenhouse and field conditions. However, the aggregation of nano-MgO in liquid suspension makes it challenging to use in field applications. Therefore, we formulated two novel MgO nanomaterials (SgMg #3 and SgMg #2.5) and one MgOH2 nanomaterial (SgMc) and evaluated their physical characteristics, antibacterial properties, and disease reduction abilities. Among the three Mg nanomaterials, SgMc showed the highest efficacy against copper-tolerant strains of Xanthomonas perforans in vitro, and provided disease reduction in the greenhouse experiments compared with commercial Cu bactericide and an untreated control. However, SgMc was not consistently effective in field conditions. To determine the cause of its inconsistent efficacy in different environments, we monitored particle size, zeta potential, morphology, and crystallinity for all three formulated materials and nano-MgOs. The MgO particle size was determined by the scanning electron microscopy (SEM) and dynamic light scattering (DLS) techniques. An X-ray diffraction (XRD) study confirmed a change in the crystallinity of MgO from a periclase to an Mg(OH)2 brucite crystal structure. As a result, the bactericidal activity correlated with the high crystallinity present in nano-MgOs and SgMc, while the inconsistent antimicrobial potency of SgMg #3 and SgMg #2.5 might have been related to loss of crystallinity. Future studies are needed to determine which specific variables impair the performance of these nanomaterials in the field compared to under greenhouse conditions. Although SgMc did not lead to significant disease severity reduction in the field, it still has the potential to act as an alternative to Cu against bacterial spot disease in tomato transplant production.

Copper Oxide Nanomaterial Fate in Plant Tissue: Nanoscale Impacts on Reproductive Tissues.

A thorough understanding of the implications of chronic low-dose exposure to engineered nanomaterials through the food chain is lacking. The present study aimed to characterize such a response in Cucurbita pepo L. (zucchini) upon exposure to a potential nanoscale fertilizer: copper oxide (CuO) nanoparticles. Zucchini was grown in soil amended with nano-CuO, bulk CuO (100 mg Kg-1), and CuSO4 (320 mg Kg-1) from germination to flowering (60 days). Nano-CuO treatment had no impact on plant morphology or growth nor pollen formation and viability. The uptake of Cu was comparable in the plant tissues under all treatments. RNA-seq analyses on vegetative and reproductive tissues highlighted common and nanoscale-specific components of the response. Mitochondrial and chloroplast functions were uniquely modulated in response to nanomaterial exposure as compared with conventional bulk and salt forms. X-ray absorption spectroscopy showed that the Cu local structure changed upon nano-CuO internalization, suggesting potential nanoparticle biotransformation within the plant tissues. These findings demonstrate the potential positive physiological, cellular, and molecular response related to nano-CuO application as a plant fertilizer, highlighting the differential mechanisms involved in the exposure to Cu in nanoscale, bulk, or salt forms. Nano-CuO uniquely stimulates plant response in a way that can minimize agrochemical inputs to the environment and therefore could be an important strategy in nanoenabled agriculture.

Influence of Single and Combined Mixtures of Metal Oxide Nanoparticles on Eggplant Growth, Yield, and Verticillium Wilt Severity.

Verticillium wilt, caused by Verticillium dahliae, is one of the major diseases of eggplants. Nanoparticles (NPs) of CuO, Mn2O3, and ZnO were sprayed alone onto leaves of young eggplants and in different combinations and rates, and then seedlings were transplanted into soil infested with V. dahliae in the greenhouse and field between 2015 and 2018. All combinations of NPs were consistently less effective than CuO NPs applied alone at 500 µg/ml at increasing disease suppression, biomass, and fruit yield. CuO NPs were associated with an increase in fruit yield (17 and 33% increase) and disease suppression (28 and 22% reduction) in 2016 and 2017, respectively, when compared with untreated controls. However, this effect was negated in the greenhouse and field experiments when CuO NPs were combined with Mn2O3. Combining NPs of CuO with ZnO resulted in variable effects; amendments increased growth and suppressed disease in greenhouse experiments, but results were mixed in the field. Leaf tissue analyses from the greenhouse experiments showed that Cu concentration in leaves was reduced when CuO NPs were combined with other NPs, even when application rates were the same amount. A simple competition for entry sites may explain why combinations of CuO NPs and Mn2O3 NPs reduced efficacy but does not explain the lack of inhibition between Cu and Zn. NPs of CuO performed better than their larger bulk equivalent, and studies on application rate found 500 µg/ml was optimal. No phytotoxicity, as determined, by leaf burning, necrotic spots, or dead apical buds was noted even at the highest combined rates of 1,500 µg/ml.

Advanced material modulation of nutritional and phytohormone status alleviates damage from soybean sudden death syndrome.

Customized Cu3(PO4)2 and CuO nanosheets and commercial CuO nanoparticles were investigated for micronutrient delivery and suppression of soybean sudden death syndrome. An ab initio thermodynamics approach modelled how material morphology and matrix effects control the nutrient release. Infection reduced the biomass and photosynthesis by 70.3 and 60%, respectively; the foliar application of nanoscale Cu reversed this damage. Disease-induced changes in the antioxidant enzyme activity and fatty acid profile were also alleviated by Cu amendment. The transcription of two dozen defence- and health-related genes correlates a nanoscale Cu-enhanced innate disease response to reduced pathogenicity and increased growth. Cu-based nanosheets exhibited a greater disease suppression than that of CuO nanoparticles due to a greater leaf surface affinity and Cu dissolution, as determined computationally and experimentally. The findings highlight the importance and tunability of nanomaterial properties, such as morphology, composition and dissolution. The early seedling foliar application of nanoscale Cu to modulate nutrition and enhance immunity offers a great potential for sustainable agriculture.

Seed Biofortification by Engineered Nanomaterials: A Pathway To Alleviate Malnutrition?

Micronutrient deficiencies in global food chains are a significant cause of ill health around the world, particularly in developing countries. Agriculture is the primary source of nutrients required for sound health, and as the population has continued to grow, the agricultural sector has come under pressure to improve crop production, in terms of both quantity and quality, to meet the global demands for food security. The use of engineered nanomaterial (ENM) has emerged as a promising technology to sustainably improve the efficiency of current agricultural practices as well as overall crop productivity. One promising approach that has begun to receive attention is to use ENM as seed treatments to biofortify agricultural crop production and quality. This review highlights the current state of the science for this approach as well as critical knowledge gaps and research needs that must be overcome to optimize the sustainable application of nano-enabled seed fortification approaches.

Nanoparticle treatment of maize analyzed through the metatranscriptome: compromised nitrogen cycling, possible phytopathogen selection, and plant hormesis.

BACKGROUND: The beneficial use of nanoparticle silver or nanosilver may be confounded when its potent antimicrobial properties impact non-target members of natural microbiomes such as those present in soil or the plant rhizosphere. Agricultural soils are a likely sink for nanosilver due to its presence in agrochemicals and land-applied biosolids, but a complete assessment of nanosilver's effects on this environment is lacking because the impact on the natural soil microbiome is not known. In a study assessing the use of nanosilver for phytopathogen control with maize, we analyzed the metatranscriptome of the maize rhizosphere and observed multiple unintended effects of exposure to 100 mg kg-1 nanosilver in soil during a growth period of 117 days. RESULTS: We found several unintended effects of nanosilver which could interfere with agricultural systems in the long term. Firstly, the archaea community was negatively impacted with a more than 30% decrease in relative abundance, and as such, their involvement in nitrogen cycling and specifically, nitrification, was compromised. Secondly, certain potentially phytopathogenic fungal groups showed significantly increased abundances, possibly due to the negative effects of nanosilver on bacteria exerting natural biocontrol against these fungi as indicated by negative interactions in a network analysis. Up to 5-fold increases in relative abundance have been observed for certain possibly phytopathogenic fungal genera. Lastly, nanosilver exposure also caused a direct physiological impact on maize as illustrated by increased transcript abundance of aquaporin and phytohormone genes, overall resulting in a stress level with the potential to yield hormetically stimulated plant root growth. CONCLUSIONS: This study indicates the occurrence of significant unintended effects of nanosilver use on corn, which could turn out to be negative to crop productivity and ecosystem health in the long term. We therefore highlight the need to include the microbiome when assessing the risk associated with nano-enabled agriculture. Video Abstract.

Metalloid and Metal Oxide Nanoparticles Suppress Sudden Death Syndrome of Soybean.

Soybeans (Glycine max) (V3 stage) were sprayed once with nanoparticles (NPs) of AgO, B, CeO, CuO, MnO, MoO3, SiO, TiO, or ZnO and exposed to Fusarium virguliforme, the cause of sudden death syndrome. Up to 80% root rot was observed in greenhouse experiments. However, NP CuO, B, MoO3, or ZnO reduced the root rot severity by 17-25%. Infected roots and shoots had significant changes in B, Mg, P, S, Si, and Zn, but NP treatment restored levels to that of the healthy control. For example, the increased root Mg and Mn contents induced by disease were reversed by NP B and Mn amendments. In vitro assays found that the NPs did not inhibit the pathogen. This, along with the restoration of altered nutrient levels in the plant tissue, suggests that modulated plant nutrition increased disease defense. Treatment of seedlings with nanoscale micronutrients may be a new tool in promoting soybean health.

Co-exposure to the food additives SiO2 (E551) or TiO2 (E171) and the pesticide boscalid increases cytotoxicity and bioavailability of the pesticide in a tri-culture small intestinal epithelium model: Potential health implications.

Many toxicity investigations have evaluated the potential health risks of ingested engineered nanomaterials (iENMs); however, few have addressed the potential combined effects of iENMs and other toxic compounds (e.g. pesticides) in food. To address this knowledge gap, we investigated the effects of two widely used, partly nanoscale, engineered particulate food additives, TiO2 (E171) and SiO2 (E551), on the cytotoxicity and cellular uptake and translocation of the pesticide boscalid. Fasting food model (phosphate buffer) containing iENM (1% w/w), boscalid (10 or 150 ppm), or both, was processed using a simulated in vitro oral-gastric-small intestinal digestion system. The resulting small intestinal digesta was applied to an in vitro tri-culture small intestinal epithelium model, and effects on cell layer integrity, viability, cytotoxicity and production of reactive oxygen species (ROS) were assessed. Boscalid uptake and translocation was also quantified by LC/MS. Cytotoxicity and ROS production in cells exposed to combined iENM and boscalid were greater than in cells exposed to either iENM or boscalid alone. More importantly, translocation of boscalid across the tri-culture cellular layer was increased by 20% and 30% in the presence of TiO2 and SiO2, respectively. One possible mechanism for this increase is diminished epithelial cell health, as indicated by the elevated oxidative stress and cytotoxicity observed in co-exposed cells. In addition, analysis of boscalid in digesta supernatants revealed 16% and 30% more boscalid in supernatants from samples containing TiO2 and SiO2, respectively, suggesting that displacement of boscalid from flocculated digestive proteins by iENMs may also contribute to the increased translocation.

Bioaccumulation of CeO2 Nanoparticles by Earthworms in Biochar-Amended Soil: A Synchrotron Microspectroscopy Study.

The interactions of nanoparticles (NPs) with biochar and soil components may substantially influence NP availability and toxicity to biota. In the present study, earthworms ( Eisenia fetida) were exposed for 28 days to a residential or agricultural soil amended with 0-2000 mg of CeO2 NP/kg and with biochar (produced by the pyrolysis of pecan shells at 350 and 600 °C) at various application rates [0-5% (w/w)]. After 28 days, earthworms were depurated and analyzed for Ce content, moisture content, and lipid peroxidation. The results showed minimal toxicity to the worms; however, biochar (350 or 600 °C) was the dominant factor, accounting for 94 and 84% of the variance for the moisture content and lipid peroxidation, respectively, in the exposed earthworms. For both soils with 1000 mg of CeO2/kg at 600 °C, biochar significantly decreased the accumulation of Ce in the worm tissues. Amendment with 350 °C biochar had mixed responses on Ce uptake. Analysis by micro X-ray fluorescence (µ-XRF) and micro X-ray absorption near edge structure (µ-XANES) was used to evaluate Ce localization, speciation, and persistence in CeO2- and biochar-exposed earthworms after depuration for 12, 48, and 72 h. Earthworms from the 500 mg of CeO2/kg and 0% biochar treatments eliminated most Ce after a 48 h depuration period. However, in the same treatment and with 5% BC-600 (biochar pyrolysis temperature of 600 °C), ingested biochar fragments (∼50 µm) with Ce adsorbed to the surfaces were retained in the gut after 72 h. Additionally, Ce remained in earthworms from the 2000 mg of CeO2/kg and 5% biochar treatments after depuration for 48 h. Analysis by µ-XANES showed that, within the earthworm tissues, Ce remained predominantly as Ce4+O2, with only few regions (2-3 µm2) where it was found in the reduced form (Ce3+). The present findings highlight that soil and biochar properties have a significant influence in the internalization of CeO2 NPs in earthworms; such interactions need to be considered when estimating NP fate and effects in the environment.

Soil mixture composition alters Arabidopsis susceptibility to Pseudomonas syringae infection.

Pseudomonas syringae is a gram-negative bacterial pathogen that causes disease on more than 100 different plant species, including the model plant Arabidopsis thaliana. Dissection of the Arabidopsis thaliana-Pseudomonas syringae pathosystem has identified many factors that contribute to successful infection or immunity, including the genetics of the host, the genetics of the pathogen, and the environment. Environmental factors that contribute to a successful interaction can include temperature, light, and the circadian clock, as well as the soil environment. As silicon-amended Resilience soil is advertised to enhance plant health, we sought to examine the extent to which this soil might affect the behavior of the A. thaliana-P. syringae model pathosystem and to characterize the mechanisms through which these effects may occur. We found that plants grown in Si-amended Resilience soil displayed enhanced resistance to bacteria compared to plants grown in non-Si-amended Sunshine soil, and salicylic acid biosynthesis and signaling were not required for resistance. Although silicon has been shown to contribute to broad-spectrum resistance, our data indicate that silicon is not the direct cause of enhanced resistance and that the Si-amended Resilience soil has additional properties that modulate plant resistance. Our work demonstrates the importance of environmental factors, such as soil in modulating interactions between the plant and foliar pathogens, and highlights the significance of careful annotation of the environmental conditions under which plant-pathogen interactions are studied.

Effect of Metalloid and Metal Oxide Nanoparticles on Fusarium Wilt of Watermelon.

This study explored the use of foliar sprays with nanoparticles (NP) of B, CuO, MnO, SiO, TiO, and ZnO to protect watermelon against Fusarium wilt. Leaves of young watermelon plants were sprayed (1 to 2 ml per plant) with NP suspensions (500 to 1,000 µg/ml) and were planted in potting mix infested with Fusarium oxysporum f. sp. niveum. In five of eight greenhouse experiments, CuO NP suppressed disease and, in six of eight experiments, CuO NP increased biomass or yield more than in untreated controls or other tested NP. More root Cu was detected in CuO NP-treated plants than other treatments (P = 0.015). In Griswold, CT, plants treated with CuO NP yielded 39% more fruit than untreated controls. In Hamden, CT, treatment with CuO NP produced 53% more fruit when compared with controls (P = 0.02) and was superior to other Cu fungicides. Gene expression in watermelon roots revealed strong upregulation of polyphenol oxidase (PPO) and PR1 genes when CuO NP and F. oxysporum f. sp. niveum were both present. Enzymatic assays for PPO supported the gene expression results. CuO NP may serve as a highly effective delivery agent for this micronutrient to suppress disease.

An integrated methodology for assessing the impact of food matrix and gastrointestinal effects on the biokinetics and cellular toxicity of ingested engineered nanomaterials.

BACKGROUND: Engineered nanomaterials (ENMs) are increasingly added to foods to improve their quality, sensory appeal, safety and shelf-life. Human exposure to these ingested ENMs (iENMS) is inevitable, yet little is known of their hazards. To assess potential hazards, efficient in vitro methodologies are needed to evaluate particle biokinetics and toxicity. These methodologies must account for interactions and transformations of iENMs in foods (food matrix effect) and in the gastrointestinal tract (GIT) that are likely to determine nano-biointeractions. Here we report the development and application of an integrated methodology consisting of three interconnected stages: 1) assessment of iENM-food interactions (food matrix effect) using model foods; 2) assessment of gastrointestinal transformations of the nano-enabled model foods using a three-stage GIT simulator; 3) assessment of iENMs biokinetics and cellular toxicity after exposure to simulated GIT conditions using a triculture cell model. As a case study, a model food (corn oil-in-water emulsion) was infused with Fe2O3 (Iron(III) oxide or ferric oxide) ENMs and processed using this three-stage integrated platform to study the impact of food matrix and GIT effects on nanoparticle biokinetics and cytotoxicity . METHODS: A corn oil in phosphate buffer emulsion was prepared using a high speed blender and high pressure homogenizer. Iron oxide ENM was dispersed in water by sonication and combined with the food model. The resulting nano-enabled food was passed through a three stage (mouth, stomach and small intestine) GIT simulator. Size distributions of nano-enabled food model and digestae at each stage were analyzed by DLS and laser diffraction. TEM and confocal imaging were used to assess morphology of digestae at each phase. Dissolution of Fe2O3 ENM along the GIT was assessed by ICP-MS analysis of supernatants and pellets following centrifugation of digestae. An in vitro transwell triculture epithelial model was used to assess biokinetics and toxicity of ingested Fe2O3 ENM. Translocation of Fe2O3 ENM was determined by ICP-MS analysis of cell lysates and basolateral compartment fluid over time. RESULTS: It was demonstrated that the interactions of iENMs with food and GIT components influenced nanoparticle fate and transport, biokinetics and toxicological profile. Large differences in particle size, charge, and morphology were observed in the model food with and without Fe2O3 and among digestae from different stages of the simulated GIT (mouth, stomach, and small intestine). Immunoflorescence and TEM imaging of the cell culture model revealed markers and morphology of small intestinal epithelium including enterocytes, goblet cells and M cells. Fe2O3 was not toxic at concentrations tested in the digesta. In biokinetics studies, translocation of Fe2O3 after 4 h was <1% and ~2% for digesta with and without serum, respectively, suggesting that use of serum proteins alters iENMs biokinetics and raises concerns about commonly-used approaches that neglect iENM - food-GIT interactions or dilute digestae in serum-containing media. CONCLUSIONS: We present a simple integrated methodology for studying the biokinetics and toxicology of iENMs, which takes into consideration nanoparticle-food-GIT interactions. The importance of food matrix and GIT effects on biointeractions was demonstrated, as well as the incorporation of these critical factors into a cellular toxicity screening model. Standardized food models still need to be developed and used to assess the effect of the food matrix effects on the fate and bioactivity of iENMs since commercial foods vary considerably in their compositions and structures.

Exposure of agricultural crops to nanoparticle CeO2 in biochar-amended soil.

Biochar is seeing increased usage as an amendment in agricultural soils but the significance of nanoscale interactions between this additive and engineered nanoparticles (ENP) remains unknown. Corn, lettuce, soybean and zucchini were grown for 28 d in two different soils (agricultural, residential) amended with 0-2000 mg engineered nanoparticle (ENP) CeO2 kg-1 and biochar (350 °C or 600 °C) at application rates of 0-5% (w/w). At harvest, plants were analyzed for biomass, Ce content, chlorophyll and lipid peroxidation. Biomass from the four species grown in residential soil varied with species and biochar type. However, biomass in the agricultural soil amended with biochar 600 °C was largely unaffected. Biochar co-exposure had minimal impact on Ce accumulation, with reduced or increased Ce content occurring at the highest (5%) biochar level. Soil-specific and biochar-specific effects on Ce accumulation were observed in the four species. For example, zucchini grown in agricultural soil with 2000 mg CeO2 kg-1 and 350 °C biochar (0.5-5%) accumulated greater Ce than the control. However, for the 600 °C biochar, the opposite effect was evident, with decreased Ce content as biochar increased. A principal component analysis showed that biochar type accounted for 56-99% of the variance in chlorophyll and lipid peroxidation across the plants. SEM and µ-XRF showed Ce association with specific biochar and soil components, while µ-XANES analysis confirmed that after 28 d in soil, the Ce remained largely as CeO2. The current study demonstrates that biochar synthesis conditions significantly impact interactions with ENP, with subsequent effects on particle fate and effects.

Weathering in soil increases nanoparticle CuO bioaccumulation within a terrestrial food chain.

This study evaluates the bioaccumulation of unweathered (U) and weathered (W) CuO in NP, bulk and ionic form (0-400 mg/kg) by lettuce exposed for 70 d in soil co-contaminated with field incurred chlordane. To evaluate CuO trophic transfer, leaves were fed to crickets (Acheta domestica) for 15 d, followed by insect feeding to lizards (Anolis carolinensis). Upon weathering, the root Cu content of the NP treatment increased 214% (327 ± 59.1 mg/kg) over unaged treatment. Cu root content decreased in bulk and ionic treatments from 70-130 mg/kg to 13-26 mg/kg upon aging in soil. Micro X-ray fluorescence (µ-XRF) analysis of W-NP-exposed roots showed a homogenous distribution of Cu (and Ca) in the tissues. Additionally, micro X-ray absorption near-edge (µ-XANES) analysis of W-NP-exposed roots showed near complete transformation of CuO to Cu (I)-sulfur and oxide complexes in the tissues, whereas in unweathered treatment, most root Cu remained as CuO. The expression level of nine genes involved in Cu transport shows that the mechanisms of CuO NPs (and bulk) response/accumulation are different than ionic Cu. The chlordane accumulation by lettuce upon co-exposure to CuO NPs significantly increased upon weathering. Conversely, bulk and ionic exposures decreased pesticide accumulation by plant upon weathering. The Cu cricket fecal content from U-NP-exposed insects was significantly greater than the bulk or ion treatments, suggesting a higher initial NP accumulation followed by significantly greater elimination during depuration. In the lizard, Cu content in the intestine, body and head did not differ as a function of weathering. This study demonstrates that CuO NPs may undergo transformation processes in soil upon weathering that subsequently impact NPs availability in terrestrial food chains.

Molecular Response of Crop Plants to Engineered Nanomaterials.

Functional toxicology has enabled the identification of genes involved in conferring tolerance and sensitivity to engineered nanomaterial (ENM) exposure in the model plant Arabidopsis thaliana (L.) Heynh. Several genes were found to be involved in metabolic functions, stress response, transport, protein synthesis, and DNA repair. Consequently, analysis of physiological parameters, metal content (through ICP-MS quantification), and gene expression (by RT-qPCR) of A. thaliana orthologue genes were performed across different plant species of agronomic interest to highlight putative biomarkers of exposure and effect related to ENMs. This approach led to the identification of molecular markers in Solanum lycopersicum L. and Cucurbita pepo L. (tomato and zucchini) that might not only indicate exposure to ENMs (CuO, CeO2, and La2O3) but also provide mechanistic insight into response to these materials. Through Gene Ontology (GO) analysis, the target genes were mapped in complex interatomic networks representing molecular pathways, cellular components, and biological processes involved in ENM response. The transcriptional response of 38 (out of 204) candidate genes studied varied according to particle type, size, and plant species. Importantly, some of the genes studied showed potential as biomarkers of ENM exposure and effect and may be useful for risk assessment in foods and in the environment.

Terrestrial Trophic Transfer of Bulk and Nanoparticle La2O3 Does Not Depend on Particle Size.

The bioaccumulation and trophic transfer of bulk and nanoparticle (NP) La2O3 from soil through a terrestrial food chain was determined. To investigate the impact of growth conditions, lettuce (Lactuca sativa) was grown in 350 or 1200 g of bulk/NP amended soil. Leaf tissues were fed to crickets (Acheta domesticus) or darkling beetles (Tenebrionoidea); select crickets were fed to mantises. In the small pot (350 g), La2O3 exposure reduced plant biomass by 23-30% and La tissue content did not differ with particle size. In the large pot (1200 g), biomass was unaffected by exposure and La content in the tissues were significantly greater with bulk particle treatment. Darkling beetles exposed to bulk and NP La2O3-contaminated lettuce contained La at 0.18 and 0.08 mg/kg; respectively (significantly different, P < 0.05). Crickets fed bulk or NP La2O3-exposed lettuce contained 0.53 and 0.33 mg/kg, respectively (significantly different, P < 0.05) with 48 h of depuration. After 7 d of depuration, La content did not differ with particle size, indicating that 48 h may be insufficient to void the digestive system. Mantises that consumed crickets from bulk and NP-exposed treatments contained La at 0.05-0.060 mg/kg (statistically equivalent). These results demonstrate that although La does trophically transfer, biomagnification does not occur and NP levels are equivalent or less than the bulk metal.

Impact of non-functionalized and amino-functionalized multiwall carbon nanotubes on pesticide uptake by lettuce (Lactuca sativa L.).

The effect of non-functionalized and amino-functionalized multiwall carbon nanotube (CNT) exposure, as well as the impact of CNT presence on coexistent pesticide accumulation, was investigated in lettuce (Lactuca sativa L.). Lettuce seeds were sown directly into CNT-amended vermiculite (1000 mg L(-1)) to monitor phytotoxicity during germination and growth. During growth, lettuce seedlings were subsequently exposed to chlordane (cis-chlordane [CS], trans-chlordane [TC] and trans-nonachlor [TN]) and p,p'-DDE (all at 100 ng/L) in the irrigation solution for a 19-d growth period. CNT exposure did not significantly influence seed germination (82-96%) or plant growth. Similarly, pesticide exposure had no impact on plant growth, total pigment production or tissue lipid peroxidation. After 19 d, the root content of total chlordane and p,p'-DDE was 390 and 73.8 µg g(-1), respectively; in plants not exposed to CNTs, the shoot levels were 1.58 and 0.40 µg g(-1), respectively. The presence and type of CNT significantly influenced pesticide availability to lettuce seedlings. Non-functionalized CNT decreased the root and shoot pesticide content by 88% and 78%, respectively, but amino-functionalized CNT effects were significantly more modest, with decreases of 57% in the roots and 23% in the shoots, respectively. The presence of humic acid completely reversed the reduced accumulation of pesticides induced by amino-functionalized CNT, likely due to strong competition over adsorption sites on the nanomaterial (NM). These findings have implications for food safety and for the use of engineered NMs in agriculture, especially with leafy vegetables.

Particle-size dependent accumulation and trophic transfer of cerium oxide through a terrestrial food chain.

The accumulation and trophic transfer of nanoparticle (NP) or bulk CeO2 through a terrestrial food chain was evaluated. Zucchini (Cucurbita pepo L.) was planted in soil with 0 or 1228 µg/g bulk or NP CeO2. After 28 d, zucchini tissue Ce content was determined by ICP-MS. Leaf tissue from each treatment was used to feed crickets (Acheta domesticus). After 14 d, crickets were analyzed for Ce content or were fed to wolf spiders (family Lycosidae). NP CeO2 significantly suppressed flower mass relative to control and bulk treatments. The Ce content of zucchini was significantly greater when exposure was in the NP form. The flowers, leaves, stems, and roots of zucchini exposed to bulk CeO2 contained 93.3, 707, 331, and 119,000 ng/g, respectively; NP-exposed plants contained 153, 1510, 479, and 567 000 ng/g, respectively. Crickets fed NP CeO2-exposed zucchini leaves contained significantly more Ce (33.6 ng/g) than did control or bulk-exposed insects (15.0-15.2 ng/g). Feces from control, bulk, and NP-exposed crickets contained Ce at 248, 393, and 1010 ng/g, respectively. Spiders that consumed crickets from control or bulk treatments contained nonquantifiable Ce; NP-exposed spiders contained Ce at 5.49 ng/g. These findings show that NP CeO2 accumulates in zucchini at greater levels than equivalent bulk materials and that this greater NP intake results in trophic transfer and possible food chain contamination.

Multiwalled carbon nanotubes and c60 fullerenes differentially impact the accumulation of weathered pesticides in four agricultural plants.

The effect of multiwalled carbon nanotubes (MWCNT) or C60 fullerenes on the uptake of weathered chlordane or DDx (DDT + metabolites) by Cucurbita pepo (zucchini), Zea mays (corn), Solanum lycopersicum (tomato), and Glycine max (soybean) was investigated. The plants were grown in 50 g of soil with weathered chlordane (2150 ng/g) and DDx (118 ng/g) that was amended with 0, 500, 1000, or 5000 mg/kg MWCNT or C60. After 28 d, the root and shoot content of chlordane components and DDx was determined by GC-MS. Zucchini and tomato growth were unaffected by carbon nanomaterial coexposure, although C60 at 500 mg/kg reduced corn and soybean biomass by 36.5-45.0%. Total chlordane content ranged from 1490 (tomato) to 4780 (zucchini) ng; DDx amounts ranged from 77.8 (corn) to 395 ng (zucchini). MWCNT coexposure decreased chlordane and DDx accumulation 21-80% across all crops, depending on species and nanotube concentration. Conversely, C60 had species- and contaminant-specific effects on pesticide uptake, ranging from complete suppression of DDx uptake (corn/tomato) to 34.9% increases in chlordane accumulation (tomato/soybean). The data show that pesticide accumulation varies greatly with crop species and carbon nanomaterial type/concentration. These findings have implications for food safety and for the use of engineered nanomaterials in agriculture.

Impact of Ag nanoparticle exposure on p,p'-DDE bioaccumulation by Cucurbita pepo (zucchini) and Glycine max (soybean).

The effect of nanoparticle (NP), bulk, or ionic Ag exposure on dichlorodiphenyldichloroethylene (p,p'-DDE; DDT metabolite) accumulation by Glycine max L. (soybean) and Cucurbita pepo L. (zucchini) was investigated. The plants were grown in 125-mL jars of vermiculite amended with 500 or 2000 mg/L of bulk or NP Ag; ion controls at 5 and 20 mg/L were established. During 19 d of growth, plants were amended with solution containing 100 ng/mL of p,p'-DDE. Total shoot p,p'-DDE levels in non-Ag exposed G. max and C. pepo were 500 and 970 ng, respectively; total root DDE content was 13,700 and 20,300 ng, respectively. Ag decreased the p,p'-DDE content of G. max tissues by up to 40%, with NP exposure resulting in less contaminant uptake than bulk Ag. Total Ag content of exposed G. max ranged from 50.5 to 373 µg; NP-exposed plants had 1.9-2.2 times greater overall Ag than corresponding bulk particle treatments and also significantly greater relative Ag transport to shoot tissues. Bulk and NP Ag at 500 mg/L suppressed DDE uptake by C. pepo by 21-29%, although Ag exposure at 2000 mg/L had no impact on contaminant uptake. Similar to G. max , C. pepo whole plant Ag content ranged from 50.5 to 182 µg, with tissue element content generally being greater for NP exposed plants. These findings show that the Ag may significantly alter the accumulation and translocation of cocontaminants in agricultural systems. Notably, the cocontaminant interactions vary both with Ag particle size (NP vs bulk) and plant species. Future investigations will be needed to clarify the mechanisms responsible for the cocontaminant interactions and assess the impact on overall exposure and risk.