Trophic Transfer and Transformation of CeO2 Nanoparticles along a Terrestrial Food Chain: Influence of Exposure Routes

Evidence for low bioavailability of dietary nanoparticulate cerium in a freshwater food chain

Radioactive 141Ce in ionic (I-Ce), nano (N-Ce, 11 ± 9 nm mean primary particle size ± standard deviation) and micron-sized (M-Ce, 530 ± 440 µm) forms associated with natural and artificial diets in natural river water and synthetic freshwater were used to measure the real-time biokinetics of dietary 141Ce assimilation in a freshwater food chain. The model food chain consisted of microalgae (Raphidocelis subcapitata), snails (Potamopyrgus antipodarum) and prawns (Macrobrachium australiense). Pulse-chase experiments showed that 91-100 % of all forms of cerium associated with all diets and water types were eliminated from the digestive system of the snail and prawn within 24 h, with no detectable cerium assimilation. The prawn and snail median elimination times (ET50) and elimination rates (Ke) for all cerium forms ranged from 0.05 to 1.7 d, and 30 to >100 % per d, respectively. The pulse-chase results were supported by the autoradiographic evidence for N-Ce and M-Ce that confirmed no detectable assimilation and translocation within the tissue of the prawn over time. In contrast, the more soluble I-Ce was found to be associated in low quantities with the hepatopancreas in the prawn confirming that the lack of dissolution by N-Ce and M-Ce in the digestive environment of these organisms makes these forms less bioavailable. In addition, hetero-agglomeration of N-Ce and M-Ce resulted in particles that did not dissociate in digestive fluids and were too large to be assimilated thereby making them non-bioavailable. Based on the results from this study and from the literature review, the risk of N-Ce biomagnification and chronic dietary toxicity in freshwater ecosystems is no greater than the risk associated with M-Ce or I-Ce.

Phytotoxicity of single and mixed rare earth element (La, Nd and Sm) exposures on Lactuca sativa seed germination and growth

The mode of action, bioaccumulation potential and toxicity of Rare Earth Elements (REE), with several applications in the technology, medical and agricultural fields, are still understudied. The nitrates acute effects on single exposures, binary and ternary mixtures of lanthanum (La), neodymium (Nd) and samarium (Sm) on Lactuca sativa lettuce seed germination and wet biomass in an artificial soil (AS) and an Ultisol were assessed. Germination (EC50), wet biomass (IC50) and germination inhibition (% GI) were evaluated. EC50 values show La was the most toxic in Ultisol, Sm in AS, and Nd appears with intermediate values on both substrates. The IC50, both single and mixed, decreased from 3- to 181-fold with increasing test concentrations in relation to the control in AS, while increases in Ultisol were observed, followed by decreases at higher doses which may be associated with the low-dose stimulation effect (hormesis). Our findings may be used to subsidize REE risk assessment studies and reinforce the hormesis effect to prevent the use of high application of REE fertilizers, avoiding the accumulation of REE in agricultural soils.

Differential Leaf-to-Root Movement, Trophic Transfer, and Tissue-Specific Biodistribution of Metal-Based and Polymer-Based Nanoparticles When Present Singly and in Mixture

The transfer of nanoparticles (NPs) through the terrestrial food chain via foliar uptake presents poorly understood risks, especially in scenarios involving copollution and plant translocation. Herein, we exposed the radishes to single and mixed foliar doses of CeO2 NPs and deuterated polystyrene (DPS), investigating the trophic transfer of NPs from radish shoots/roots to snails. Compared to single treatments, mixture treatments increased Ce uptake by plants but had no effect on DPS uptake. Additionally, mixture treatments did not affect the movement of Ce and DPS from shoots to roots. Under NP mixture exposure, trophic transfer efficiencies (TTF) for Ce (2.09 × 10-2) and DPS (2.54 × 10-2) significantly decreased in shoot-feeding snails. In root-feeding snails, TTF for Ce (3.32 × 10-1) also showed a significant decrease, while TTF for DPS remained unchanged. Mixture treatments exhibited differential impacts on different snail body parts, particularly leading to biomagnification of DPS in the digestive glands and soft tissues (TTF > 1) of snails consuming roots exposed to mixtures. Both CeO2 and DPS displayed a sudden increase in assimilation efficiency following translocation to the roots. This study provides insights into changes during trophic transfer due to coexposure and plant translocation processes associated with nanoparticles, enhancing our comprehension regarding their environmental risks.

Trophic Transfer of Metal Oxide Nanoparticles in the Tomato-Helicoverpa armigera Food Chain: Effects on Phyllosphere Microbiota, Insect Oxidative Stress, and Gut Microbiome

Understanding the trophic transfer and ecological cascade effects of nanofertilizers and nanopesticides in terrestrial food chains is crucial for assessing their nanotoxicity and environmental risks. Herein, the trophic transfer of La2O3 (nLa2O3) and CuO (nCuO) nanoparticles from tomato leaves to Helicoverpa armigera (Lepidoptera: Noctuidae) caterpillars and their subsequent effects on caterpillar growth and intestinal health were investigated. We found that 50 mg/L foliar nLa2O3 and nCuO were transferred from tomato leaves to H. armigera, with particulate trophic transfer factors of 1.47 and 0.99, respectively. While nCuO exposure reduced larval weight gain more (34.7%) than nLa2O3 (11.3%), owing to higher oxidative stress (e.g., MDA and H2O2) and more serious intestinal pathological damage (i.e., crumpled columnar cell and disintegrated goblet cell) by nCuO. Moreover, nCuO exposure led to a more compact antagonism between the phyllosphere and gut microbiomes compared to nLa2O3. Specifically, nCuO exposure resulted in a greater increase in pathogenic bacteria (e.g., Mycobacterium, Bacillus, and Ralstonia) and a more significant decrease in probiotics (e.g., Streptomyces and Arthrobacter) than nLa2O3, ultimately destroying larval intestinal immunity. Altogether, our findings systematically revealed the cascade effect of metal oxide nanomaterials on higher trophic consumers through alteration in the phyllosphere and insect gut microbiome interaction, thus providing insights into nanotoxicity and environmental risk assessment of nanomaterials applied in agroecosystems.

Temporal Dynamics of Copper-Based Nanopesticide Transfer and Subsequent Modulation of the Interplay Between Host and Microbiota Across Trophic Levels

During agricultural production, significant quantities of copper-based nanopesticides (CBNPs) may be released into terrestrial ecosystems through foliar spraying, thereby posing a potential risk of biological transmission via food chains. Consequently, we investigated the trophic transfer of two commonly available commercial CBNPs, Reap2000 (RP) and HolyCu (HC), in a plant-caterpillar terrestrial food chain and evaluated impacts on host microbiota. Upon foliar exposure (with 4 rounds of spraying, totaling 6.0 mg CBNPs per plant), leaf Cu accumulation levels were 726 ± 180 and 571 ± 121 mg kg-1 for RP and HC, respectively. HC exhibited less penetration through the cuticle compared to RP (RP: 55.5%; HC: 32.8%), possibly due to size exclusion limitations. While caterpillars accumulated higher amounts of RP, HC exhibited a slightly higher trophic transfer factor (TTF; RP: 0.69 ± 0.20; HC: 0.74 ± 0.17, p > 0.05) and was more likely to be transferred through the food chain. The application of RP promoted the dispersal of phyllosphere microbes and perturbed the original host intestinal microbiota, whereas the HC group was largely host-modulated (control: 65%; RP: 94%; HC: 34%). Integrating multiomics analyses and modeling approaches, we elucidated two pathways by which plants exert bottom-up control over caterpillar health. Beyond the direct transmission of phyllosphere microbes, the leaf microbiome recruited upon exposure to CBNPs further influenced the ingestion behavior and intestinal microbiota of caterpillars via altered leaf metabolites. Elevated Proteobacteria abundance benefited caterpillar growth with RP, while the reduction of Proteobacteria with HC increased the risk of lipid metabolism issues and gut disease. The recruited Bacteroidota in the RP phyllosphere proliferated more extensively into the caterpillar gut to enhance stress resistance. Overall, the gut microbes reshaped in RP caterpillars exerted a strong regulatory effect on host health. These findings expand our understanding of the dynamic transmission of host-microbiota interactions with foliar CBNPs exposure, and provide critical insight necessary to ensure the safety and sustainability of nanoenabled agricultural strategies.

Foliar Exposure of Deuterium Stable Isotope-Labeled Nanoplastics to Lettuce: Quantitative Determination of Foliar Uptake, Transport, and Trophic Transfer in a Terrestrial Food Chain

Nanoplastics (NPs) are widely detected in the atmosphere and are likely to be deposited on plant leaves. However, our understanding of their foliar uptake, translocation, and trophic transfer profiles is limited due to a lack of quantitative analytical tools to effectively probe mechanisms of action. Here, using synthesized deuterium (2H) stable isotope-labeled polystyrene nanoplastics (2H-PSNPs), the foliar accumulation and translocation of NPs in lettuce and the dynamics of NP transfer along a lettuce-snail terrestrial food chain were investigated. Raman imaging and scanning electron microscopy demonstrated that foliar-applied NPs aggregated on the leaf surface, entered the mesophyll tissue via the stomatal pathway, and eventually translocated to root tissues. Quantitative analysis showed that increasing levels of foliar exposure to 2H-PSNPs (0.1, 1, and 5 mg/L in spray solutions, equivalent to receiving 0.15, 1.5, and 7.5 μg/d of NPs per plant) enhanced NP accumulation in leaves, with concentrations ranging from 0.73 to 15.6 μg/g (dw), but only limited translocation (<5%) to roots. After feeding on 5 mg/L 2H-PSNP-contaminated lettuce leaves for 14 days, snails accumulated NPs at 0.33 to 10.7 μg/kg (dw), with an overall kinetic trophic transfer factor of 0.45, demonstrating trophic dilution in this food chain. The reduced ingestion rate of 3.18 mg/g/day in exposed snails compared to 6.43 mg/g/day can be attributed to the accumulation of 2H-PSNPs and elevated levels of chemical defense metabolites in the lettuce leaves, which decreased the palatability for snails and disrupted their digestive function. This study provides critical quantitative information on the characteristics of airborne NP bioaccumulation and the associated risks to terrestrial food chains.

Mixed effects and co-transfer of CeO2 NPs and arsenic in the pakchoi-snail food chain

Nanomaterial application in agriculture offers novel solutions for soil arsenic (As) pollution control, yet safety along the food chain is of concern. We comprehensively assessed CeO2 nanoparticles (NPs) foliar application effects on As uptake by pakchoi and their presence in the pakchoi-snail food chain. CeO2 NPs reduced As transfer from pakchoi roots to shoots by 37.9%, lowered As in snail foot by 39%, and halved human As exposure risk. The NPs alleviated pakchoi shoot As toxicity by regulating antioxidants, enhancing water use efficiency, and photosynthesis. CeO2 +As treatment raised GSH/GSSG ratios by 38.92%- 167.54%, leading to an increased AsIII/AsV ratio and inorganic As detoxification compared to As alone. Metabolomics revealed CeO2's rapid As response via phosphatidylinositol signaling. The enzyme-like activity of CeO2 NPs may drive these effects. While CeO2 foliar application accumulated Ce on pakchoi leaves, > 99% of Ce was excreted following snail consumption. Ce transfer from pakchoi leaves to snail foot was minimal (trophic transfer factor ∼0.00007) due to limited bioavailability. The target hazard quotient of Ce in pakchoi shoot (1.21 ± 0.18) and snails (0.0016 ± 0.0004) indicated low exposure risk, suggesting a 'risk filter' effect for CeO2. Our results contribute to the safe and sustainable application of CeO2 NPs in the future implication.

Mass-based trophic transfer of polystyrene nanoplastics in the lettuce-snail food chain

To investigate the potential transfer of nanoplastics (NPs) from water to plants and subsequently to a higher trophic level, we established a food chain and evaluated the trophic transfer of polystyrene (PS) NPs based on mass concentrations by pyrolysis gas chromatography-mass spectrometry. Lettuce plants were cultivated in Hoagland solution with varying concentrations of PS-NPs (0.1, 1, 10, 100 and 1000 mg/L) for a period of 60 d and then a total of 7 g lettuce shoot was fed to snails for 27 d. Shoot biomass exposed at 1000 mg/L PS-NPs was reduced by 36.1 %. No significant change in root biomass was observed, however, root volume was reduced by 25.6 % at 100 mg/L. Moreover, PS-NPs were detected in both lettuce roots and shoots across all concentrations. Additionally, PS-NPs were transferred to snails and primarily found in feces (>75 %). Only 28 ng/g of PS-NPs were detected in the soft tissue of snails indirectly exposed at 1000 mg/L. Although PS-NPs were bio-diluted when transferred to species at higher trophic levels, they significantly inhibited the growth of snails, indicating that their potential risk to high trophic levels cannot be ignored. This study provides key information on trophic transfer and patterns of PS-NPs in food chains and helps to evaluate risk of NPs in terrestrial ecosystem.

Trophic transfer of nanomaterials and their effects on high-trophic-level predators

Nanotechnology offers great opportunities for numerous sectors in society. One important challenge in sustainable nanotechnology is the potential of trophic transfer of nanomaterials (NMs), which may lead to unintentional impacts on environmental and human health. Here, we highlight the key advances that have been made in recent 15 years with respect to trophic transfer of heterogeneous NMs, including metal-based NMs, carbon-based NMs and nanoplastics, across various aquatic and terrestrial food chains. Particle number-based trophic transfer factors (TTFs), rather than the variable mass-based TTFs, capture the particle-specific transfer, for which NMs exhibit dynamic and complex biotransformation (e.g., dissolution, sulfidation, reduction, and corona formation). Trophic transfer of NMs has toxicological significance to predators at molecular (e.g., increased oxidative stress and modified metabolites), physiological (e.g., feeding inhibition) and population (e.g., reproduction inhibition) levels. However, linking NM exposure and toxicity remains a challenge, partly due to the dynamic biotransformation along the food chain. Although NMs have been used to increase crop yield in agriculture, they can exert detrimental impacts on crop yield and modify crop quality, depending on NMs type, exposure dose, and crop species, with unknown consequences to human health via crop consumption. Given this information, we describe the challenges and opportunities in understanding the significance of NMs trophic transfer to develop more sustainable, effective and safer nanotechnology.

Averaging Strategy for Interpretable Machine Learning on Small Datasets to Understand Element Uptake after Seed Nanotreatment

Understanding plant uptake and translocation of nanomaterials is crucial for ensuring the successful and sustainable applications of seed nanotreatment. Here, we collect a dataset with 280 instances from experiments for predicting the relative metal/metalloid concentration (RMC) in maize seedlings after seed priming by various metal and metalloid oxide nanoparticles. To obtain unbiased predictions and explanations on small datasets, we present an averaging strategy and add a dimension for interpretable machine learning. The findings in post-hoc interpretations of sophisticated LightGBM models demonstrate that solubility is highly correlated with model performance. Surface area, concentration, zeta potential, and hydrodynamic diameter of nanoparticles and seedling part and relative weight of plants are dominant factors affecting RMC, and their effects and interactions are explained. Furthermore, self-interpretable models using the RuleFit algorithm are established to successfully predict RMC only based on six important features identified by post-hoc explanations. We then develop a visualization tool called RuleGrid to depict feature effects and interactions in numerous generated rules. Consistent parameter-RMC relationships are obtained by different methods. This study offers a promising interpretable data-driven approach to expand the knowledge of nanoparticle fate in plants and may profoundly contribute to the safety-by-design of nanomaterials in agricultural and environmental applications.

Trophic transfer of silver nanoparticles shifts metabolism in snails and reduces food safety

Food security and sustainable development of agriculture has been a key challenge for decades. To support this, nanotechnology in the agricultural sectors increases productivity and food security, while leaving complex environmental negative impacts including pollution of the human food chains by nanoparticles. Here we model the effects of silver nanoparticles (Ag-NPs) in a food chain consisting of soil-grown lettuce Lactuca sativa and snail Achatina fulica. Soil-grown lettuce were exposed to sulfurized Ag-NPs via root or metallic Ag-NPs via leaves before fed to snails. We discover an important biomagnification of silver in snails sourced from plant root uptake, with trophic transfer factors of 2.0-5.9 in soft tissues. NPs shifts from original size (55-68 nm) toward much smaller size (17-26 nm) in snails. Trophic transfer of Ag-NPs reprograms the global metabolic profile by down-regulating or up-regulating metabolites for up to 0.25- or 4.20- fold, respectively, relative to the control. These metabolites control osmoregulation, phospholipid, energy, and amino acid metabolism in snails, reflecting molecular pathways of biomagnification and pontential adverse biological effects on lower trophic levels. Consumption of these Ag-NP contaminated snails causes non-carcinogenic effects on human health. Global public health risks decrease by 72% under foliar Ag-NP application in agriculture or through a reduction in the consumption of snails sourced from root application. The latter strategy is at the expense of domestic economic losses in food security of $177.3 and $58.3 million annually for countries such as Nigeria and Cameroon. Foliar Ag-NP application in nano-agriculture has lower hazard quotient risks on public health than root application to ensure global food safety, as brought forward by the United Nations Sustainable Development Goals.

Emerging Nanoparticles in Food: Sources, Application, and Safety

Nanoparticles (NPs) are small-sized, with high surface activity and antibacterial and antioxidant properties. As a result, some NPs are used as functional ingredients in food additives, food packaging materials, nutrient delivery, nanopesticides, animal feeds, and fertilizers to improve the bioavailability, quality, and performance complement or upgrade. However, the widespread use of NPs in the industry increases the exposure risk of NPs to humans due to their migration from the environment to food. Nevertheless, some NPs, such as carbon dots, NPs found in various thermally processed foods, are also naturally produced from the food during food processing. Given their excellent ability to penetrate biopermeable barriers, the potential safety hazards of NPs on human health have attracted increased attention. Herein, three emerging NPs are introduced including carbon-based NPs (e.g., CNTs), nanoselenium NPs (SeNPs), and rare earth oxide NPs (e.g., CeO₂ NPs). In addition, their applications in the food industry, absorption pathways into the human body, and potential risk mechanisms are discussed. Challenges and prospects for the use of NPs in food are also proposed.

Toxicokinetics and Particle Number-Based Trophic Transfer of a Metallic Nanoparticle Mixture in a Terrestrial Food Chain

Herein, we investigated to which extent metallic nanoparticles (MNPs) affect the trophic transfer of other coexisting MNPs from lettuce to terrestrial snails and the associated tissue-specific distribution using toxicokinetic (TK) modeling and single-particle inductively coupled plasma mass spectrometry. During a period of 22 days, snails were fed with lettuce leaves that were root exposed to AgNO3 (0.05 mg/L), AgNPs (0.75 mg/L), TiO2NPs (200 mg/L), and a mixture of AgNPs and TiO2NPs (equivalent doses as for single NPs). The uptake rate constants (ku) were 0.08 and 0.11 kg leaves/kg snail/d for Ag and 1.63 and 1.79 kg leaves/kg snail/d for Ti in snails fed with NPs single- and mixture-exposed lettuce, respectively. The elimination rate constants (ke) of Ag in snails exposed to single AgNPs and mixed AgNPs were comparable to the corresponding ku, while the ke for Ti were lower than the corresponding ku. As a result, single TiO2NP treatments as well as exposure to mixtures containing TiO2NPs induced significant biomagnification from lettuce to snails with kinetic trophic transfer factors (TTFk) of 7.99 and 6.46. The TTFk of Ag in the single AgNPs treatment (1.15 kg leaves/kg snail) was significantly greater than the TTFk in the mixture treatment (0.85 kg leaves/kg snail), while the fraction of Ag remaining in the body of snails after AgNPs exposure (36%) was lower than the Ag fraction remaining after mixture exposure (50%). These results indicated that the presence of TiO2NPs inhibited the trophic transfer of AgNPs from lettuce to snails but enhanced the retention of AgNPs in snails. Biomagnification of AgNPs from lettuce to snails was observed in an AgNPs single treatment using AgNPs number as the dose metric, which was reflected by the particle number-based TTFs of AgNPs in snails (1.67, i.e., higher than 1). The size distribution of AgNPs was shifted across the lettuce-snail food chain. By making use of particle-specific measurements and fitting TK processes, this research provides important implications for potential risks associated with the trophic transfer of MNP mixtures.

The impact of engineered nanomaterials on the environment: Release mechanism, toxicity, transformation, and remediation

The presence and longevity of nanomaterials in the ecosystem, as well as their properties, account for environmental toxicity. When nanomaterials in terrestrial and aquatic systems are exposed to the prevailing environmental conditions, they undergo various transformations such as dissociation, dissolution, and aggregation, which affects the food chain. The toxicity of nanomaterials is influenced by a variety of factors, including environmental factors and its physico-chemical characteristics. Bioaccumulation, biotransformation, and biomagnification are the mechanisms that have been identified for determining the fate of nanomaterials. The route taken by nanomaterials to reach living cells provides us with information about their toxicity profile. This review discusses the recent advances in the transport, transformation, and fate of nanomaterials after they are released into the environment. The review also discusses how nanoparticles affect lower trophic organisms through direct contact, the impact of nanoparticles on higher trophic organisms, and the possible options for remediation.

Trophic transfer of Cu nanoparticles in a simulated aquatic food chain

The goal of the current study was to quantify the trophic transfer of copper nanoparticles (CuNPs) in a food chain consisting of the microalga Pseudokirchneriella subcapitata as the representative of primary producer, the grazer Daphnia magna, and the omnivorous mysid Limnomysis benedeni. To quantify the size and number concentration of CuNPs in the biota, tissue extraction with tetramethylammonium hydroxide (TMAH) was performed and quantification was done by single particle inductively coupled plasma mass spectrometry (sp-ICP-MS). The bioconcentration factor (BCF) of the test species for CuNPs varied between 10² - 10³ L/kg dry weight when expressing the internal concentration on a mass basis, which was lower than BCF values reported for Cu²⁺ (10³ - 10⁴ L/kg dry weight). The particle size of CuNPs determined by sp-ICP-MS ranged from 22 to 40 nm in the species. No significant changes in the particle size were measured throughout the food chain. Moreover, the measured number of CuNPs in each trophic level was in the order of 10¹³ particles/kg wet weight. The calculated trophic transfer factor (mass concentration basis) was > 1. This indicates biomagnification of particulate Cu from P. subcapitata to L. benedeni. It was also found that the uptake of particulate Cu (based on the particle number concentration) was mainly from the dietary route rather than from direct aqueous exposure. Furthermore, dietary exposure to CuNPs had a significant effect on the feeding rate of mysid during their transfer from daphnia to mysid and from alga through daphnia to mysid. This work emphasizes the importance of tracing the particulate fraction of metal-based engineered nanoparticles when studying their uptake and trophic transfer.

Greater Bioaccessibility of Silver Nanoparticles in Earthworm than in Soils

The buildup of silver nanoparticles (AgNPs) in soil has raised mounting concerns on their impact on human health. Human are exposed to AgNPs in soils via hand-to-mouth activities (direct exposure) and food consumption (indirect exposure). However, the bioaccessibility of AgNPs under these exposure scenarios remains largely unknown. We used a physiologically based extraction test (PBET) to assess Ag bioaccessibility in AgNP-containing soils and in earthworms (Pheretima guillemi) cultured in these soils. Silver bioaccessibility was 1.2 - 8.4% and 8.1 - 78.7% upon direct exposure and indirect exposure, respectively. These results indicated greater Ag bioaccessibility in earthworms than in soils. Moreover, particle size decreased upon direct exposure, but remained constant upon indirect exposure in wetland soil, as revealed by single particle inductively coupled plasma-mass spectrometry (spICP-MS) analysis. Our results highlight the importance of indirect exposure to NPs.

Effects of subchronic dietary exposure to the engineered nanomaterials SiO2 and CeO2 in C57BL/6J and 5xFAD Alzheimer model mice

BACKGROUND

There is an increasing concern about the neurotoxicity of engineered nanomaterials (NMs). To investigate the effects of subchronic oral exposures to SiO2 and CeO2 NMs on Alzheimer's disease (AD)-like pathology, 5xFAD transgenic mice and their C57BL/6J littermates were fed ad libitum for 3 or 14 weeks with control food pellets, or pellets dosed with these respective NMs at 0.1% or 1% (w/w). Behaviour effects were evaluated by X-maze, string suspension, balance beam and open field tests. Brains were analysed for plaque load, beta-amyloid peptide levels, markers of oxidative stress and neuroinflammation.

RESULTS

No marked behavioural impairments were observed in the mice exposed to SiO2 or CeO2 and neither treatment resulted in accelerated plaque formation, increased oxidative stress or inflammation. In contrast, the 5xFAD mice exposed to 1% CeO2 for 14 weeks showed significantly lower hippocampal Aβ plaque load and improved locomotor activity compared to the corresponding controls.

CONCLUSIONS

The findings from the present study suggest that long-term oral exposure to SiO2 or CeO2 NMs has no neurotoxic and AD-promoting effects. The reduced plaque burden observed in the mice following dietary CeO2 exposure warrants further investigation to establish the underlying mechanism, given the easy applicability of this administration method.

Cross-examination of engineered nanomaterials in crop production: Application and related implications

The review presents the current knowledge on the development and implementation of nanotechnology in crop production, giving particular attention to potential opportunities and challenges of the use of nano-sensors, nano-pesticides, and nano-fertilizers. Due to the size-dependent properties, e.g. high reactivity, targeted and controlled delivery of active ingredients, engineered nanomaterials (ENMs) are expected to be more efficient agrochemicals than conventional agents. Growing production and usage of ENMs result in the spread of ENMs in the environment. Because plants constitute an important component of the agri-ecosystem, they are subjected to the ENMs activity. A number of studies have confirmed the uptake and translocation of ENMs by plants as well as their positive/negative effects on plants. Here, these endpoints are briefly summarized to show the diversity of plant responses to ENMs. The review includes a detailed molecular analysis of ENMs-plant interactions. The transcriptomics, proteomics and metabolomics tools have been very recently employed to explore ENMs-induced effects in planta. The omics approach allows a comprehensive understanding of the specific machinery of ENMs occurring at the molecular level. The summary of data will be valuable in defining future studies on the ENMs-plant system, which is crucial for developing a suitable strategy for the ENMs usage.

Influence of extracellular polymeric substances on the heteroaggregation between CeO2 nanoparticles and soil mineral particles

Interaction with soil mineral particles (SMPs) and organic matters can significantly determine the fate of nanoparticles (NPs) in the environment such as waters, sediments, and soils. In this study, the heteroaggregation of CeO₂ NPs with different soil minerals (kaolinite, montmorillonite, goethite and hematite) and the influence of extracellular polymeric substance (EPS) were studied. The obvious heteroaggregation between CeO₂ NPs with different SMPs were demonstrated via co-settling and aggregation kinetics experiments. The variety in the heteroaggregation between CeO₂ NPs with different SMPs is mainly induced by the difference in their surface properties, such as surface charge, specific surface areas and surface complexation. The presence of EPS can result in great inhibition on the heteroaggregation between CeO₂ NPs with the positive charged goethite by enhancing the electrostatic repulsion between NPs and mineral colloids. However, the influence of EPS on the interaction between CeO₂ NPs with negative charged SMPs is more dependent on the steric stabilization. The presence of EPS may promote the migration of CeO₂ NPs in environment and then increase their risks to human health and ecosystems. These findings contribute to better understanding interactions between NPs and SMPs and have important implications on predicting the behaviors and risks of NPs in the natural environment.

Trophic Transfer and Toxicity of (Mixtures of) Ag and TiO2 Nanoparticles in the Lettuce-Terrestrial Snail Food Chain

The increasing application of biosolids and agrochemicals containing silver nanoparticles (AgNPs) and titanium dioxide nanoparticles (TiO2NPs) results in their inevitable accumulation in soil, with unknown implications along terrestrial food chains. Here, the trophic transfer of single NPs and a mixture of AgNPs and TiO2NPs from lettuce to snails and their associated impacts on snails were investigated. Both AgNPs and TiO2NPs were transferred from lettuce to snails with trophic transfer factors (defined as the ratio of the Ag/Ti concentration in snail tissues to the Ag/Ti concentration in lettuce leaves) of 0.2-1.1 for Ag and 3.8-47 for Ti. Moreover, the majority of Ag captured by snails in the AgNP-containing treatments was excreted via feces, whereas more than 70% of Ti was distributed in the digestive gland of snails in the TiO2NP-containing treatments. Additionally, AgNP-containing treatments significantly inhibited the activity of snails, while TiO2NP-containing treatments significantly reduced feces excretion of snails. Furthermore, the concurrent application of AgNPs and TiO2NPs did not affect the biomagnification and distribution patterns of Ag and Ti in snails, whereas their co-existence exhibited more severe inhibition of the growth and activity of snails than in the case of applying AgNPs or TiO2NPs alone. This highlights the possibility of nanoparticle transfer to organisms of higher trophic levels via food chains and the associated risks to ecosystem health.

Copper nanoclusters promote tomato (Solanum lycopersicum L.) yield and quality through improving photosynthesis and roots growth

The innovative and sustainable technologies are highly needed to decrease serious environmental problems from current agriculture. Herein, the green and biosafe copper-based nano-agriculture was described for tomato production. Prepared Cu nanoclusters (NCs) showed small size (3.0 ± 0.5 nm) and high bioavailability. At low concentration (1 mg kg^-1) in soil, Cu NCs improved the activities of antioxidant enzymes (superoxide dismutase, catalase and peroxidase) in the tomato plants, which could help to slow down leaf aging, increase photosynthesis and carbohydrates content by 19.4 % and 14.9 %, respectively. Cu NCs promoted the roots' growth, especially increasing the root tip' number, which might contribute to the increase in absorption of macronutrients (K, Mg and P) and micronutrients (B, Mn, Cu and Zn). The Cu NCs (1 mg kg^-1) promoted tomato growth and increased the tomato fruit yields by 12.2 % compared to the control. Moreover, the tomato fruit qualities had been improved meanwhile the accumulation of Cu in fruits was not observed. These findings indicate that the Cu NCs have potential to be safely applied for tomato production.

Effects of surface modification on toxicity of CeO2 nanoparticles to lettuce

Phytotoxicity of nanoceria (nCeO2) has been reported, but there are few studies on how to reduce its phytotoxicity. In the present study, we modified nCeO2 with two organophosphates (nCeO2@ATMP and nCeO2@EDTMP) and compared their toxicity to lettuce with that of uncoated nCeO2. The results showed that bare nCeO2 significantly inhibited the root growth of lettuce, leading to oxidative damages and root cell death. In contrast, after surface modification, the toxicity of nCeO2@ATMP to lettuce was weakened, while nCeO2@EDTMP was nontoxic to lettuce. It was found that the surface properties of the modified materials have been changed, resulting in sharp decreases in their bioavailability. Although nCeO2 with and without surface coatings were all transformed when interacting with plants, the absolute contents of Ce(III) in roots treated with modified nCeO2 decreased significantly, which may be the main reason for the reduction of toxicity. This study indicates that it is feasible to reduce the phytotoxicity of nanomaterials through surface coating.

Cytotoxicity of functionalized CeO2 nanoparticles towards Escherichia coli and adaptive response of membrane properties

The cytotoxicity and mechanisms of cerium oxide nanoparticles (CeO₂-NPs) on organisms have attracted great concerns recently, while that of CeO₂-NPs with functional groups remains unclear. This study investigated cytotoxic effects and mechanisms of CeO₂-NPs with hydroxyl, carboxyl, or amino functional groups towards a strain Escherichia coli (E. Coli). Results showed that CeO₂-NPs produced a stronger cytotoxicity in NaCl medium than in PBS medium at the concentrations of 10-400 mg/L. The toxicity followed the order of CeO₂-COOH > CeO₂-NH₂ > CeO₂-OH. Exposing to CeO₂-NPs increased cell membrane permeability and reduced membrane fluidity. The membrane phospholipid fatty acid compositions also varied greatly as a response to the stress of CeO₂-NPs, with the proportion of unsaturated fatty acids increased and saturated fatty acids decreased. Both intracellular reactive oxygen species (ROS) level and malonaldehyde (MDA) level declined, suggesting the oxidative stress from ROS may be not the primary reason for the membrane damage. Other mechanisms such as direct membrane oxidation by Ce⁴⁺ or physical penetration based on a close contact between nanoparticles and microbes might contribute to the membrane damages and cell viability loss. The present study provides a significant insight into the influence of functionalized CeO₂-NPs on a gram-negative bacterium.

Growing Rice (Oryza sativa) Aerobically Reduces Phytotoxicity, Uptake, and Transformation of CeO2 Nanoparticles

This study compared the impact and uptake of root-administered CeO₂ nanoparticles (NPs) in rice growing under flooded and aerobic soil conditions, which are two water regimes commonly used for rice cultivation. CeO₂ NPs at 100 mg/kg improved photosynthesis and plant growth by reducing the oxidative damage and enhancing plant tolerance to stress, while a higher concentration (500 mg/kg) of CeO₂ NPs negatively affected plant growth. More significant effects were observed under the flooded condition than under the aerobic condition. CeO₂ NPs of 100 and 500 mg/kg resulted in 78% and 70% higher accumulation of Ce in shoots under the flooded condition compared to the aerobic condition. CeO₂ NPs partially transformed to Ce(III) species in soils and plants under both conditions. A higher extent of transformation under the flooded condition, which was partly attributed to the lower soil pH and redox potential under the flooded condition, leads to higher plant uptake of Ce. A higher extent of transformation in rhizosphere soil was observed. A higher plant transpiration rate (TR) under flooded conditions resulted in a higher accumulation of CeO₂ species in shoots. This study, for the first time, reported that water regimes influenced the biotransformation of CeO₂ NPs and their uptake and impact in rice plants.

Comparative toxicity of rod-shaped nano-CeO2 and nano-CePO4 to lettuce

The influence of morphology on the biological effects of nanomaterials (NMs) has not been well understood. In the present study, we compared the phytotoxicity of rod-shaped nano-cerium dioxide (R-CeO2) and nano-cerium phosphate (R-CePO4) to lettuce plants. The results showed that R-CeO2 significantly inhibited the root elongation of lettuce, induced oxidative damages, and caused cell death, while R-CePO4 was nontoxic to lettuce. The different distribution and speciation of Ce in plant tissues were determined by transmission electron microscopy (TEM) and X-ray absorption near edge spectroscopy (XANES) combined with linear combination fitting (LCF). The results showed that in the R-CeO2 group, part of Ce was transformed from Ce(IV) to Ce(III), while only Ce(III) was present in the R-CePO4 group. When interacting with plants, R-CeO2 is easier to be dissolved and transformed than R-CePO4, which might be the reason for their different phytotoxicity. Although both are Ce-based NMs and have the same morphology, the toxicity of R-CeO2 seems to come from the released Ce3+ ions rather than its shape. This research emphasizes the importance of chemical composition and reactivity of NMs to their toxicological effects.

Ingestion and effects of cerium oxide nanoparticles on Spodoptera frugiperda (Lepidoptera: Noctuidae)

The objective of this study was to evaluate the biological and nutritional characteristics of Spodoptera frugiperda (Lepidoptera: Noctuidae), an arthropod pest widely distributed in agricultural regions, after exposure to nano-CeO₂ via an artificial diet and to investigate the presence of cerium in the body of this insect through X-ray fluorescence mapping. Nano-CeO₂, micro-CeO₂, and Ce(NO₃)₃ were incorporated into the diet (0.1, 1, 10, and 100 mg of Ce L^-1). Cerium was detected in caterpillars fed with diets containing nano-CeO₂ (1, 10 and 100 mg of Ce L^-1), micro-CeO₂ and Ce(NO₃)₃, and in feces of caterpillars from the first generation fed diets with nano-CeO₂ at 100 mg of Ce L^-1 as well. The results indicate that nano-CeO₂ caused negative effects on S. frugiperda. After it was consumed by the caterpillars, the nano-CeO₂ reduced up to 4.8% of the pupal weight and 60% of egg viability. Unlike what occurred with micro-CeO₂ and Ce(NO₃)₃, nano-CeO₂ negatively affected nutritional parameters of this insect, as consumption rate two times higher, increase of up to 80.8% of relative metabolic rate, reduction of up to 42.3% efficiency of conversion of ingested and 47.2% of digested food, and increase of up to 1.7% of metabolic cost and 8.7% of apparent digestibility. Cerium caused 6.8-16.9% pupal weight reduction in second generation specimens, even without the caterpillars having contact with the cerium via artificial diet. The results show the importance of new ecotoxicological studies with nano-CeO₂ for S. frugiperda in semi-field and field conditions to confirm the toxicity.

Effects of ceria nanoparticles and CeCl3 on growth, physiological and biochemical parameters of corn (Zea mays) plants grown in soil

The release of toxic ions from metal-based nanoparticles (NPs) may play an important role in biological effects of NPs. In this life cycle study, physiological and biochemical responses of soil-grown corn (Zea mays) plants exposed to ceria NPs and its ionic counterparts Ce³⁺ ions at 0, 25, 75 and 225 mg Ce/kg were investigated. Both treatments tended to reduce the fresh weight and height of the plants at 28 days after sowing (DAS), and delay silk appearance and finally decrease fruit weight at harvest. Uptake and distribution of some mineral nutrients, Ca, P, Fe, B, Zn and Mn in the plants were disturbed. None of the treatments significantly affected activities of antioxidant enzymes and MDA contents in the roots and leaves at 28 DAS. At 90 DAS, ceria NPs and Ce³⁺ ions disturbed the homeostasis of antioxidative systems in the plants, Ce³⁺ ions at all concentrations provoked significant oxidative damage in the roots and significantly increased MDA levels as compare to the control. The results indicate that the effects of ceria NPs and Ce³⁺ ions on corn plants varied with different growth stages and ceria NPs had similar but less severe impacts than Ce³⁺ ions. Speciation analysis revealed there was mutual transformation between CeO₂ and Ce³⁺ in the soil-plant system. It is speculated that Ce³⁺ ions play a key role in toxicity. To the authors' knowledge, this is the first report of a life cycle study on comparative toxicity of CeO₂ NPs and Ce³⁺ ions on corn plants.

Surface Properties and Environmental Transformations Controlling the Bioaccumulation and Toxicity of Cerium Oxide Nanoparticles: A Critical Review

Increasing production and utilization of cerium oxide nanoparticles (CNPs) in recent years have raised wide concerns about their toxicity. Numerous studies have been conducted to reveal the toxicity of CNPs, but the results are sometimes contradictory. In this review, the most important factors in mediating CNPs toxicity are discussed, including (1) the roles of physicochemical properties (size, morphology, agglomeration condition, surface charge, coating and surface valence state) on CNPs toxicity; (2) the phase transfer and transformation process of CNPs in various aqueous, terrestrial, and airborne environments; and (3) reductive dissolution of CNPs core and their chemical reactions with phosphate, sulfate/S^2-, and ferrous ions. The physicochemical properties play key roles in the interactions of CNPs with organisms and consequently their environmental transformations, reactivity and toxicity assessment. Also, the speciation transformations of CNPs caused by reactions with (in)organic ligands in both environmental and biological systems would further alter their fate, transport, and toxicity potential. Thus, the toxicity mechanisms are proposed based on the physical damage of direct adsorption of CNPs onto the cell membrane and chemical inhibition (including oxidative stress and interaction of CNPs with biomacromolecules). Finally, the current knowledge gaps and further research needs in identifying the toxicological risk factors of CNPs under realistic environmental conditions are highlighted, which might improve predictions about their potential environmental influences. This review aims to provide new insights into cost-effectiveness of control options and management practices to prevent environmental risks from CNPs exposure.

Ecological Drawbacks of Nanomaterials Produced on an Industrial Scale: Collateral Effect on Human and Environmental Health

Currently, hundreds of different nanomaterials with a broad application in products that make daily lives a little bit easier, in every aspect, are being produced on an industrial scale at thousands of tons per year. However, several scientists, researchers, politics, and ordinary citizens have stated their concern regarding the life cycle, collateral effects, and final disposal of these cutting-edge materials. This review summarizes, describes, and discusses all manuscripts published in the Journal Citation Reports during the last 10 years, which studied the toxicity or the effects of nanomaterials on human and environmental health. It was observed that 23.62% of the manuscripts analyzed found no ecological or human risks; 54.39% showed that several nanomaterials have toxicological effects on the ecosystems, human, or environmental health. In comparison, only 21.97% stated the nanomaterials had a beneficial impact on those. Although only 54.39% of the manuscripts reported unfavorable effects of nanomaterials on ecosystems, human, or environmental health, it is relevant because the potential damage is invaluable. Therefore, it is imperative to make toxicological studies of nanomaterials with holistic focus under strictly controlled real conditions before their commercialization, to deliver to the market only innocuous and environmentally friendly products.

Toxicity of engineered nanomaterials to aquatic and land snails: A scientometric and systematic review

The emerging growth of nanotechnology has attracted great attention due to its application in the parasite and intermediate host control. However, the knowledge concerning the mechanism of action (MoA) and toxicity of nanomaterials (NMs) to snails remain unclear. In this context, the present study revised the historical use of snails as experimental models in nanotoxicological studies and summarized the MoA and toxicity of NMs in aquatic and land snails. The data concerning the bioaccumulation, reproductive and transgenerational toxicity, embryotoxicity, genotoxicity and potential molluscicidal activity of NMs were revised. Furthermore, the data about the experimental conditions, such as exposure time, concentrations, cell and tissue-specific responses, snail species and nanoparticle types are discussed. Revised data showed that the toxic effects of NMs were reported for 21 snail species with medical, veterinary and ecological importance. The NM toxicity to snails is dependent on the physical and chemical properties of NMs, as well as their environmental transformation and experimental design. The NM bioaccumulation on snails was related to several toxic effects, such as reactive oxygen species (ROS) production, oxidative stress, following by oxidative damage to DNA, lipids and proteins. The NM metabolism in snails remains unknown. Results showed the potential use of NMs in the snail control program. Also, significant research gaps and recommendations for future researches are indicated. The present study confirms that snails are suitable invertebrate model system to assess the nanotoxicity.

Bioavailability and translocation of metal oxide nanoparticles in the soil-rice plant system

To determine the bioavailability and translocation of metal oxide nanoparticles (MONPs) in the soil-rice plant system, we examined the accumulation and micro-distribution of ZnO nanoparticles (NPs), CuO NPs and CeO₂ NPs (50, 100 and 500 mg/kg) in the paddy soil and rice plants under flooded condition for 30 days using single-step chemical extraction and diffusive gradients in thin films (DGT) technique combined with micro X-ray fluorescence spectroscopy (μ-XRF). The results show that various MONPs changed the soil properties, especially the redox potential was enhanced to -165.33 to -75.33 mV compared to the control. The extraction efficiency of Zn, Cu and Ce in the paddy soil from high to low was EDTA, DTPA, CaCl₂ and DGT. Moreover, exposure to 500 mg/kg CuO NPs and CeO₂ NPs induced the primary accumulation of Cu and Ce elements in rice roots as high as 235.48 mg Cu/kg and 164.84 mg Ce/kg, respectively, while the Zn concentration in shoots was up to 313.18 mg/kg under highest ZnO NPs with a 1.5 of translocation factor. The effect of MONPs on the plant growth was mainly related to the chemical species and solubility of MONPs. Micro-XRF analysis shows that Zn was mostly located in the root cortex while Cu was primarily accumulated in the root exodermis and few Ce distributed in the root. Pearson correlation coefficients indicate that only DTPA-extracted metals in soil were significantly and well correlated to the Zn, Cu and Ce accumulation in rice seedlings exposed to MONPs. This work is of great significance for evaluating the environmental risks of MONPs in soil and ensuring the safety of agricultural products.

Untargeted Metabolic Pathway Analysis as an Effective Strategy to Connect Various Nanoparticle Properties to Nanoparticle-Induced Ecotoxicity

Elucidation of the relationships between nanoparticle properties and ecotoxicity is a fundamental issue for environmental applications and risk assessment of nanoparticles. However, effective strategies to connect the various properties of nanoparticles with their ecotoxicity remain largely unavailable. Herein, an untargeted metabolic pathway analysis was employed to investigate the environmental risk posed by 10 typical nanoparticles (AgNPs, CuNPs, FeNPs, ZnONPs, SiO₂NPs, TiO₂NPs, GO, GOQDs, SWCNTs, and C₆₀) to rice (a staple food for half of the world's population). Downregulation of carbohydrate metabolism and upregulation of amino acid metabolism were the two dominant metabolic effects induced by all tested nanoparticles. Partial least-squares regression analysis indicated that a zerovalent metal and high specific surface area positively contributed to the downregulation of carbohydrate metabolism, indicating strong abiotic stress. In contrast, the carbon type, the presence of a spherical or sheet shape, and the absence of oxygen functional groups in the nanoparticles positively contributed to the upregulation of amino acid metabolism, indicating adaptation to abiotic stress. Moreover, network relationships among five properties of nanoparticles were established for these metabolic pathways. The results of the present study will aid in the understanding and prediction of environmental risks and in the design of environmentally friendly nanoparticles.

Relatively Low Dosages of CeO2 Nanoparticles in the Solid Medium Induce Adjustments in the Secondary Metabolism and Ionomic Balance of Bean (Phaseolus vulgaris L.) Roots and Leaves

Nanoparticles (NPs) are known to significantly alter plant metabolism in a dose-dependent manner, with effects ranging from stimulation to toxicity. The metabolic adjustment and ionomic balance of bean (Phaseolus vulgaris L.) roots and leaves gained from plants grown in a solid medium added with relatively low dosages (0, 25, 50, and 100 mg/L) of CeO₂ NPs were investigated. Ce accumulated in the roots (up to 287.91 mg/kg dry weight) and translocated to the aerial parts (up to 2.78% at the highest CeO₂ dosage), and ionomic analysis showed that CeO₂ NPs interfered with potassium, molybdenum, and zinc. Unsupervised hierarchical clustering analysis from metabolomic profiles suggested a dose-dependent and tissue-specific metabolic reprogramming induced by NPs. The majority of differential metabolites belonged to flavonoids and other phenolics, nitrogen-containing low molecules (such as alkaloids and glucosinolates), lipids, and amino acids.

Detection, occurrence, and fate of emerging contaminants in agricultural environments (2019)

A review of 82 papers published in 2018 is presented. The topics ranged from detailed descriptions of analytical methods, to fate and occurrence studies, to ecological effects and sampling techniques for a wide variety of emerging contaminants likely to occur in agricultural environments. New methods and studies on veterinary pharmaceuticals, microplastics, and engineered nanomaterials in agricultural environments continue to expand our knowledge base on the occurrence and potential impacts of these compounds. This review is divided into the following sections: Introduction, Analytical Methods, Fate and Occurrence, Pharmaceutical Metabolites, Anthelmintics, Microplastics, and Engineered Nanomaterials. PRACTITIONER POINTS: New research describes innovative new techniques for emerging contaminant detection in agricultural settings. Newer classes of contaminants include human and veterinary pharmaceuticals. Research in microplastics and nanomaterials shows that these also occur in agricultural environments and will likely be topics of future work.

Soybean Interaction with Engineered Nanomaterials: A Literature Review of Recent Data

With a continuous increase in the production and use in everyday life applications of engineered nanomaterials, concerns have appeared in the past decades related to their possible environmental toxicity and impact on edible plants (and therefore, upon human health). Soybean is one of the most commercially-important crop plants, and a perfect model for nanomaterials accumulation studies, due to its high biomass production and ease of cultivation. In this review, we aim to summarize the most recent research data concerning the impact of engineered nanomaterials on the soya bean, covering both inorganic (metal and metal-oxide nanoparticles) and organic (carbon-based) nanomaterials. The interactions between soybean plants and engineered nanomaterials are discussed in terms of positive and negative impacts on growth and production, metabolism and influences on the root-associated microbiota. Current data clearly suggests that under specific conditions, nanomaterials can negatively influence the development and metabolism of soybean plants. Moreover, in some cases, a possible risk of trophic transfer and transgenerational impact of engineered nanomaterials are suggested. Therefore, comprehensive risk-assessment studies should be carried out prior to any mass productions of potentially hazardous materials.

Influence of Surface Charge on the Phytotoxicity, Transformation, and Translocation of CeO2 Nanoparticles in Cucumber Plants

The physiochemical properties of nanoparticles (NPs), including surface charge, will affect their uptake, transformation, translocation, and final fate in the environment. In this study, we compared the phytoxoxicity and transport behaviors of nano CeO₂ (nCeO₂) functionalized with positively charged (Cs-nCeO₂) and negatively charged (PAA-nCeO₂) coatings. Cucumber seedlings were hydroponically exposed to 0-1000 mg/L of Cs-nCeO₂ and PAA-nCeO₂ for 14 days and the contents, distribution, translocation, and transformation of Ce in plants were analyzed using inductively coupled plasma mass spectrometry, micro X-ray fluorescence (μ-XRF), and X-ray absorption near-edge spectroscopy (XANES), respectively. Results showed that the seedling growth and Ce contents in plant tissues were functions of exposure concentrations and surface charge. Cs-nCeO₂ was adsorbed strongly on a negatively charged root surface, which led to significantly higher Ce contents in the roots and lower translocation factors of Ce from the roots to shoots in Cs-nCeO₂ group than in PAA-nCeO₂ group. The results of μ-XRF showed that Ce elements were mainly accumulated at the root tips and lateral roots, as well as in the veins and at the edge of leaves. XANES results revealed that the proportion of Ce(III) was comparable in the plant tissues of the two groups. We speculated that Cs-nCeO₂ and PAA-nCeO₂ were partially dissolved under the effect of root exudates, releasing Ce³⁺ ions as a result. Then, the Ce³⁺ ions were transported upward in the form of Ce(III) complexes along the vascular bundles and eventually accumulated in the veins. The other portion of Cs-nCeO₂ and PAA-nCeO₂ entered the roots through the gap of a Casparian strip at root tips/lateral roots and was transported upward as intact NPs and finally accumulated at the edge of the blade. This study will greatly advance our information on how the properties of NPs influence their phytotoxicity, uptake, and subsequent trophic transfer in terrestrial food webs.

Discerning the Sources of Silver Nanoparticle in a Terrestrial Food Chain by Stable Isotope Tracer Technique

The increasing use of silver-containing nanoparticles (NPs) in commercial products has led to NP accumulation in the environment and potentially in food webs. Identifying the uptake pathways of different chemical species of NPs, such as Ag2S-NP and metallic AgNPs, into plants is important to understanding their entry into food chains. In this study, soybean Glycine max L. was hydroponically exposed to Ag2S-NPs via their roots (10-50 mg L-1) and stable-isotope-enriched 109AgNPs via their leaves [7.9 μg (g fresh weight)-1]. Less than 29% of Ag in treated leaves (in direct contact with 109AgNP) was accumulated from root uptake of Ag2S-NPs, whereas almost all of the Ag in soybean roots and untreated leaves sourced from Ag2S-NPs. Therefore, Ag2S-NPs are phytoavailable and translocate upward. During trophic transfer the Ag isotope signature was preserved, indicating that accumulated Ag in snails most likely originated from Ag2S-NPs. On average, 78% of the Ag in the untreated leaves was assimilated by snails, reinforcing the considerable trophic availability of Ag2S-NPs via root uptake. By highlighting the importance of root uptake of Ag2S-NPs in plant uptake and trophic transfer to herbivores, our study advances current understanding of the biogeochemical fate of Ag-containing NPs in the terrestrial environment.