Exposure of tomato (<i>Lycopersicon esculentum</i>) to silver nanoparticles and silver nitrate: physiological and molecular response

Silver nanoparticles (AgNPs) are among the most widely used nanomaterials, with applications in sectors as diverse as communications, energy, medicine, and agriculture. This diverse application of AgNPs increases the risk of the release of these materials into the environment and raises the potential for transfer into plants and, subsequently, the human body. To better understand the effects of NPs in agricultural systems, this study investigates plant physiological and molecular responses upon exposure to AgNPs in comparison to silver nitrate (AgNO3). Tomato seedlings (Lycopersison esculentum) were exposed to 10, 20, or 30 mg/L silver (Ag), AgNO3, or AgNPs in hydroponic media for 7 days. A number of endpoints were measured, including plant growth, photosynthetic pigments, oxidative and antioxidant responses. The results showed 2–7 times lower growth rate in plants exposed to silver compared to the control. H2O2 and malondialdehyde as oxidative stress indicators were, respectively, 1.7 and 4 times higher in plants exposed to all forms of silver compared to the control. The antioxidative responses increased significantly in plants exposed to Ag and AgNPs compared to the control. However, plants exposed to AgNO3 showed up to 50% lower enzymatic antioxidant activity. At the molecular level, the expression of genes involved in defense responses, including ethylene-inducing xylanase (EIX), peroxidase 51 (POX), and phenylalanine ammonia lyase, were significantly upregulated upon exposure to silver. The molecular and physiological data showed exposure to all forms of silver resulted in oxidative stress and exposure to AgNPs induced antioxidative and defense responses. However, exposure to AgNO3 resulted in phytotoxicity and failure in antioxidative responses. It indicates the higher reactivity and phytotoxicity of the ionic form of silver compared to NPs. The findings of this study add important information to efforts in attempting to characterize the exposure and risk associated with the release of nanomaterials in the environment.</p

Impact of Ag Nanoparticle Exposure on <i>p,p′</i>-DDE Bioaccumulation by Cucurbita pepo (Zucchini) and Glycine max (Soybean)

The effect of nanoparticle (NP), bulk, or ionic Ag exposure on dichlorodiphenyldichloroethylene (<i>p,p′</i>-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 <i>p,p′</i>-DDE. Total shoot <i>p,p′</i>-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 <i>p,p′</i>-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

Fullerene-Enhanced Accumulation of <i>p</i>,<i>p</i>′‑DDE in Agricultural Crop Species

The effect of C60 fullerene exposure on the accumulation of dichlorodiphenyldichloroethylene (p,p′-DDE; DDT metabolite) by Cucurbita pepo L. (zucchini), Glycine max L. (soybean), and Solanum lycopersicum L. (tomato) was determined. The plants were grown in 125 mL jars of vermiculite amended with 0 or 40 mg of C60 fullerenes. Prior to planting, the jars were amended with 40 mL solution containing 100 ng/mL of p,p′-DDE with 0 or 100 mg/L humic acid. During three weeks of growth, plants were watered with the same p,p′-DDE containing solutions. Total shoot p,p′-DDE levels in nonfullerene exposed tomato, soybean, and zucchini were 26.9, 131, and 675 ng, respectively; total root DDE content for the three plants was 402, 5970, and 5830 ng, respectively. Fullerenes increased the shoot p,p′-DDE content of zucchini by 29%; contaminant levels in soybean shoots were decreased by 48% but tomato shoot content was unaffected. The root and total plant p,p′-DDE content of all three species was significantly increased by fullerene exposure; enhanced contaminant uptake ranged from 30 to 65%. Humic acid, regardless of fullerene presence or plant type, significantly decreased the p,p′-DDE uptake. Fullerenes were detected in the roots of all plants but were not detected in plant shoots in the initial study. In a follow up study with zucchini designed to maximize biomass for extraction, over half the analyzed stems contained fullerenes at 60.5 to 4490 ng/g. These findings show that the carbon-based nanomaterials may significantly alter the accumulation and potentially the toxicity of cocontaminants in agricultural systems

Fullerene-Enhanced Accumulation of <i>p</i>,<i>p</i>′‑DDE in Agricultural Crop Species

The effect of C₆₀ fullerene exposure on the accumulation of dichlorodiphenyldichloroethylene (<i>p</i>,<i>p</i>′-DDE; DDT metabolite) by <i>Cucurbita pepo</i> L. (zucchini), <i>Glycine max</i> L. (soybean), and <i>Solanum lycopersicum</i> L. (tomato) was determined. The plants were grown in 125 mL jars of vermiculite amended with 0 or 40 mg of C₆₀ fullerenes. Prior to planting, the jars were amended with 40 mL solution containing 100 ng/mL of <i>p</i>,<i>p</i>′-DDE with 0 or 100 mg/L humic acid. During three weeks of growth, plants were watered with the same <i>p</i>,<i>p</i>′-DDE containing solutions. Total shoot <i>p</i>,<i>p</i>′-DDE levels in nonfullerene exposed tomato, soybean, and zucchini were 26.9, 131, and 675 ng, respectively; total root DDE content for the three plants was 402, 5970, and 5830 ng, respectively. Fullerenes increased the shoot <i>p</i>,<i>p</i>′-DDE content of zucchini by 29%; contaminant levels in soybean shoots were decreased by 48% but tomato shoot content was unaffected. The root and total plant <i>p</i>,<i>p</i>′-DDE content of all three species was significantly increased by fullerene exposure; enhanced contaminant uptake ranged from 30 to 65%. Humic acid, regardless of fullerene presence or plant type, significantly decreased the <i>p</i>,<i>p</i>′-DDE uptake. Fullerenes were detected in the roots of all plants but were not detected in plant shoots in the initial study. In a follow up study with zucchini designed to maximize biomass for extraction, over half the analyzed stems contained fullerenes at 60.5 to 4490 ng/g. These findings show that the carbon-based nanomaterials may significantly alter the accumulation and potentially the toxicity of cocontaminants in agricultural systems

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, <i>P</i> < 0.05). Crickets fed bulk or NP La₂O₃-exposed lettuce contained 0.53 and 0.33 mg/kg, respectively (significantly different, <i>P</i> < 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

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 (<i>Cucurbita pepo</i> 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 (<i>Acheta domesticus</i>). 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