Single particle ICP-MS method development for the determination of plant uptake and accumulation of CeO2 nanoparticles

Advancing Simultaneous Extraction and Sequential Single-Particle ICP-MS Analysis for Metallic Nanoparticle Mixtures in Plant Tissues

Engineered nanoparticles (ENPs) have been increasingly used in agricultural operations, leading to an urgent need for robust methods to analyze co-occurring ENPs in plant tissues. In response, this study advanced the simultaneous extraction of coexisting silver, cerium oxide, and copper oxide ENPs in lettuce shoots and roots using macerozyme R-10 and analyzed them by single-particle inductively coupled plasma-mass spectrometry (ICP-MS). Additionally, the standard stock suspensions of the ENPs were stabilized with citrate, and the long-term stability (up to 5 months) was examined for the first time. The method performance results displayed satisfactory accuracies and precisions and achieved low particle concentration and particle size detection limits. Significantly, the oven drying process was proved not to impact the properties of the ENPs; therefore, oven-dried lettuce tissues were used in this study, which markedly expanded the applicability of this method. This robust methodology provides a timely approach to characterize and quantify multiple coexisting ENPs in plants.

Evaluation of the effect of nanoparticles on the cultivation of edible plants by ICP-MS: a review

Nanoparticle (NP) applications aiming to boost plant biomass production and enhance the nutritional quality of crops hae proven to be a valuable ally in enhancing agricultural output. They contribute to greater food accessibility for a growing and vulnerable population. These nanoscale particles are commonly used in agriculture as fertilizers, pesticides, plant growth promoters, seed treatments, opportune plant disease detection, monitoring soil and water quality, identification and detection of toxic agrochemicals, and soil and water remediation. In addition to the countless NP applications in food and agriculture, it is possible to highlight many others, such as medicine and electronics. However, it is crucial to emphasize the imperative need for thorough NP characterization beyond these applications. Therefore, analytical methods are proposed to determine NPs' physicochemical properties, such as composition, crystal structure, size, shape, surface charge, morphology, and specific surface area, detaching the inductively coupled plasma mass spectrometry (ICP-MS) that allows the reliable elemental composition quantification mainly in metallic NPs. As a result, this review highlights studies involving NPs in agriculture and their consequential effects on plants, with a specific focus on analyses conducted through ICP-MS. Given the numerous applications of NPs in this field, it is essential to address their presence and increase in the environment and humans since biomagnification and biotransformation effects are studies that should be further developed. In light of this, the demand for rapid, innovative, and sensitive analytical methods for the characterization of NPs remains paramount.

Unraveling the micro- and nanoplastic predicament: A human-centric insight

Micro- and nanoplastics are vast anthropogenic pollutants in our direct surroundings with a robust environmental stability and a potential for a long-lasting and increasing global circulation. This has raised concerns among the public and policy makers for human health upon exposure to these particles. The micro- and nanoplastic burden on humans is currently under debate, along with criticism on the experimental approaches used in hazard assessment. The present review presents an overview of the human-relevant aspects associated with the current micro-and nanoplastic burden. We focus on environmental circulation and the estimation of exposure quantities to humans, along with a state-of-the-art overview of particle accumulation in over 15 human organs and other specimen. Additionally, data regarding particle characteristics used in toxicity testing was extracted from 91 studies and discussed considering their environmental and human relevance.

Dynamic Transformation of Nano-MoS2 in a Soil-Plant System Empowers Its Multifunctionality on Soybean Growth

Molybdenum disulfide (nano-MoS2) nanomaterials have shown great potential for biomedical and catalytic applications due to their unique enzyme-mimicking properties. However, their potential agricultural applications have been largely unexplored. A key factor prior to the application of nano-MoS2 in agriculture is understanding its behavior in a complex soil-plant system, particularly in terms of its transformation. Here, we investigate the distribution and transformation of two types of nano-MoS2 (MoS2 nanoparticles and MoS2 nanosheets) in a soil-soybean system through a combination of synchrotron radiation-based X-ray absorption near-edge spectroscopy (XANES) and single-particle inductively coupled plasma mass spectrometry (SP-ICP-MS). We found that MoS2 nanoparticles (NPs) transform dynamically in soil and plant tissues, releasing molybdenum (Mo) and sulfur (S) that can be incorporated gradually into the key enzymes involved in nitrogen metabolism and the antioxidant system, while the rest remain intact and act as nanozymes. Notably, there is 247.9 mg/kg of organic Mo in the nodule, while there is only 49.9 mg/kg of MoS2 NPs. This study demonstrates that it is the transformation that leads to the multifunctionality of MoS2, which can improve the biological nitrogen fixation (BNF) and growth. Therefore, MoS2 NPs enable a 30% increase in yield compared to the traditional molybdenum fertilizer (Na2MoO4). Excessive transformation of MoS2 nanosheets (NS) leads to the overaccumulation of Mo and sulfate in the plant, which damages the nodule function and yield. The study highlights the importance of understanding the transformation of nanomaterials for agricultural applications in future studies.

Transport of Nanoparticles into Plants and Their Detection Methods

Nanoparticle transport into plants is an evolving field of research with diverse applications in agriculture and biotechnology. This article provides an overview of the challenges and prospects associated with the transport of nanoparticles in plants, focusing on delivery methods and the detection of nanoparticles within plant tissues. Passive and assisted delivery methods, including the use of roots and leaves as introduction sites, are discussed, along with their respective advantages and limitations. The barriers encountered in nanoparticle delivery to plants are highlighted, emphasizing the need for innovative approaches (e.g., the stem as a new recognition site) to optimize transport efficiency. In recent years, research efforts have intensified, leading to an evendeeper understanding of the intricate mechanisms governing the interaction of nanomaterials with plant tissues and cells. Investigations into the uptake pathways and translocation mechanisms within plants have revealed nuanced responses to different types of nanoparticles. Additionally, this article delves into the importance of detection methods for studying nanoparticle localization and quantification within plant tissues. Various techniques are presented as valuable tools for comprehensively understanding nanoparticle-plant interactions. The reliance on multiple detection methods for data validation is emphasized to enhance the reliability of the research findings. The future outlooks of this field are explored, including the potential use of alternative introduction sites, such as stems, and the continued development of nanoparticle formulations that improve adhesion and penetration. By addressing these challenges and fostering multidisciplinary research, the field of nanoparticle transport in plants is poised to make significant contributions to sustainable agriculture and environmental management.

Fate and distribution of orally-ingested CeO2-nanoparticles based on a mouse model: Implication for human health

The use of nanoparticles in agrichemical formula and food products as additives has increased their chances of accumulation in humans via oral intake. Due to their potential toxicity, it is critical to understand their fate and distribution following oral intake. Cerium oxide nanoparticle (CeO2NP) is commonly used in agriculture and is highly stable in the environment. As such, it has been used as a model chemical to investigate nanoparticle's distribution and clearance. Based on their estimated human exposure levels, 0.15-0.75 mg/kg body weight/day of CeO2NPs with different sizes and surface charges (30-50 nm with negative charge and <25 nm with positive charge) were gavaged into C57BL/6 female mice daily. After 10-d, 50% of mice in each treatment were terminated, with the remaining being gavaged with 0.2 mL of deionized water daily for 7-d. Mouse organ tissues, blood, feces, and urine were collected at termination. At the tested levels, CeO2NPs displayed minimal overt toxicity to the mice, with their accumulation in various organs being negligible. Fecal discharge as the predominant clearance pathway took less than 7-d regardless of charges. Single particle inductively coupled plasma mass spectrometry analysis demonstrated minimal aggregation of CeO2NPs in the gastrointestinal tract. These findings suggest that nanoparticle additives >25 nm are unlikely to accumulate in mouse organ after oral intake, indicating limited impacts on human health.

Arsenic as hazardous pollutant: Perspectives on engineering remediation tools

Arsenic (As) is highly toxic metal (loid) that impairs plant growth and proves fatal towards human population. It disrupts physiological, biochemical and molecular attributes of plants associated with water/nutrient uptake, redox homeostasis, photosynthetic machineries, cell/membrane damage, and ATP synthesis. Numerous transcription factors are responsive towards As through regulating stress signaling, toxicity and resistance. Additionally, characterization of specific genes encoding uptake, translocation, detoxification and sequestration has also explained their underlying mechanisms. Arsenic within soil enters the food chain and cause As-poisoning. Plethora of conventional methods has been used since decades to plummet As-toxicity, but the success rate is quite low due to environmental hazards. Henceforth, exploration of effective and eco-friendly methods is aimed for As-remediation. With the technological advancements, we have enumerated novel strategies to address this concern for practicing such techniques on global scale. Novel strategies such as bioremediation, phytoremediation, mycorrhizae-mediated remediation, biochar, algal-remediation etc. possess extraordinary results. Moreover, nitric oxide (NO), a signaling molecule has also been explored in relieving As-stress through reducing oxidative damages and triggering antioxidative responses. Other strategies such as role of plant hormones (salicylic acid, indole-3-acetic acid, jasmonic acid) and micro-nutrients such as selenium have also been elucidated in As-remediation from soil. This has been observed through stimulated antioxidant activities, gene expression of transporters, defense genes, cell-wall modifications along with the synthesis of chelating agents such as phytochelatins and metallothioneins. This review encompasses the updated information about As toxicity and its remediation through novel techniques that serve to be the hallmarks for stress revival. We have summarised the genetic engineering protocols, biotechnological as well as nanotechnological applications in plants to combat As-toxicity.

Current Methods and Prospects for Analysis and Characterization of Nanomaterials in the Environment

Analysis and characterization of naturally occurring and engineered nanomaterials in the environment are critical for understanding their environmental behaviors and defining real exposure scenarios for environmental risk assessment. However, this is challenging primarily due to the low concentration, structural heterogeneity, and dynamic transformation of nanomaterials in complex environmental matrices. In this critical review, we first summarize sample pretreatment methods developed for separation and preconcentration of nanomaterials from environmental samples, including natural waters, wastewater, soils, sediments, and biological media. Then, we review the state-of-the-art microscopic, spectroscopic, mass spectrometric, electrochemical, and size-fractionation methods for determination of mass and number abundance, as well as the morphological, compositional, and structural properties of nanomaterials, with discussion on their advantages and limitations. Despite recent advances in detecting and characterizing nanomaterials in the environment, challenges remain to improve the analytical sensitivity and resolution and to expand the method applications. It is important to develop methods for simultaneous determination of multifaceted nanomaterial properties for in situ analysis and characterization of nanomaterials under dynamic environmental conditions and for detection of nanoscale contaminants of emerging concern (e.g., nanoplastics and biological nanoparticles), which will greatly facilitate the standardization of nanomaterial analysis and characterization methods for environmental samples.

Attenuation mechanisms of arsenic induced toxicity and its accumulation in plants by engineered nanoparticles: A review

The excessive arsenic (As) accumulation in plant tissues enforced toxic impacts on growth indices. So, the utilization of As-contaminated food leads to risks associated with human health. For the reduction of As concentrations in foods, it is obligatory to fully apprehend the take up, accretion, transportation and toxicity mechanisms of As within plant parts. This metalloid impairs the plant functions by disturbing the metabolic pathways at physio-biochemical, cellular and molecular levels. Though several approaches were utilized to reduce the As-accumulation and toxicity in soil-plant systems. Recently, engineered nanoparticles (ENPs) such a zinc oxide (ZnO), silicon dioxide or silica (SiO₂), iron oxide (FeO) and copper oxide (CuO) have emerged new technology to reduce the As-accumulation or phytotoxicity. But, the mechanistic approaches with systematic explanation are missing. By knowing these facts, our prime focus was to disclose the mechanisms behind the As toxicity and its mitigation by ENPs in higher plants. ENPs relives As toxicity and its oxidative damages by regulating the transporter or defense genes, modifying the cell wall composition, stimulating the antioxidants defense, phytochelatins biosynthesis, nutrients uptake, regulating the metabolic processes, growth improvement, and thus reduction in As-accumulation or toxicity. Yet, As-detoxification by ENPs depends upon the type and dose of ENPs or As, exposure method, plant species and experimental conditions. We have discussed the recent advances and highlight the knowledge or research gaps in earlier studies along with recommendations. This review may help scientific community to develop strategies such as applications of nano-based fertilizers to limit the As-accumulation and toxicity, thus healthy food production. These outcomes may govern sustainable application of ENPs in agriculture.

Determination of metallic nanoparticles in biological samples by single particle ICP-MS: a systematic review from sample collection to analysis

A systematic review of the use of single particle ICP-MS to analyse engineered nanomaterials (ENMs) in biological samples (plants, animals, body fluids) has highlighted that efforts have focused on a select few types of ENMs (e.g., Ag and TiO₂) and there is a lack of information for some important tissues (e.g., reproductive organs, skin and fatty endocrine organs). The importance of sample storage is often overlooked but plays a critical role. Careful consideration of the ENM and matrix composition is required to select an appropriate protocol to liberate ENMs from a tissue whilst not promoting the transformation of them, or genesis of new particulates. A 'one size fits all' protocol, applicable to all possible types of ENM and biological matrices, does not seem practical. However, alkaline-based extractions would appear to show greater promise for wide applicability to animal tissues, although enzymatic approaches have a role, especially for plant tissues. There is a lack of consistency in metrics reported and how they are determined (e.g. size limit of detection, and proportions of recovery), making comparison between some studies more difficult. In order to establish standardised protocols for regulatory use, effort is needed to: develop certified reference materials, achieve international agree on nomenclature and the use of control samples, and to create a decision tree to help select the best sample preparation for the type of tissue matrix.

Sample preparation for the analysis of nanoparticles in natural waters by single particle ICP-MS

With the significant increase in the production and use of nanoparticles (NP), concern is increasing over their release into their environment. Single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) is emerging as one of the best techniques for detecting the very small NP at very low concentrations in natural waters. However, there is no unified protocol for the preparation of natural water samples for SP-ICP-MS analysis. In order to minimize nebulizer blockage, filtration is often used with the expectation that 0.45 μm membranes will not remove significant quantities of 1-100 nm NP. Nonetheless, there are limited data on its effect on the concentrations or size distributions of the NP. To that end, we examined the interactions between six different membrane filters and silver (Ag) and cerium oxide (CeO₂) NP in aqueous samples. For Ag NP, the highest recoveries were observed for polypropylene membranes, where 55% of the pre-filtration NP were found in rainwater and 75% were found in river waters. For CeO₂ NP, recoveries for the polypropylene membrane attained 60% in rainwater and 75% in river water. Recoveries could be increased to over 80% by pre-conditioning the filtration membranes with a multi-element solution. Similar recoveries were obtained when samples were centrifuged at low centrifugal forces (≤1000×g).

Quantifying Chemical Composition and Reaction Kinetics of Individual Colloidally Dispersed Nanoparticles

To control a nanoparticle's chemical composition and thus function, researchers require readily accessible and economical characterization methods that provide quantitative in situ analysis of individual nanoparticles with high throughput. Here, we established dual analyte single-particle inductively coupled plasma quadrupole mass spectrometry to quantify the chemical composition and reaction kinetics of individual colloidal nanoparticles. We determined the individual bimetallic nanoparticle mass and chemical composition changes during two different chemical reactions: (i) nanoparticle etching and (ii) element deposition on nanoparticles at a rate of 300+ nanoparticles/min. Our results revealed the heterogeneity of chemical reactions at the single nanoparticle level. This proof-of-concept study serves as a framework to quantitatively understand the dynamic changes of physicochemical properties that individual nanoparticles undergo during chemical reactions using a commonly available mass spectrometer. Such methods will broadly empower and inform the synthesis and development of safer, more effective, and more efficient nanotechnologies that use nanoparticles with defined functions.

Cloud point extraction (CPE) combined with single particle -inductively coupled plasma-mass spectrometry (SP-ICP-MS) to analyze and characterize nano-silver sulfide in water environment

Silver Nanoparticles (Ag-NPs), an emerging type of pollutant, might occur various physical and chemical transformations, which would affect its environmental fate, transformation and biological effects. Sulfurization is the most common conversion of Ag-NPs, accompanied by the formation of nano-silver sulfide (Ag₂S-NPs). The method of Ag₂S-NPs analysis and characterization is of great significance for assessing the environmental risks of Ag. In this study, cloud point extraction (CPE) and Single Particle-Inductively Coupled Plasma-Mass Spectrometry (SP-ICP-MS) were used in combination to establish a simple and reliable analysis method to quantify Ag₂S-NPs in water, with the morphology unchanged. Non-Ag₂S-NPs were dissociated into Ag⁺ firstly, and Ag₂S-NPs and Ag⁺ were separated by CPE, followed by SP-ICP-MS analysis. The extraction rate based on particle number concentration was between (76.19 ± 0.56) % to (106.35 ± 0.00) % in environmental waters. Compared with the (76.96 ± 2.18) nm Ag₂S-NPs spiked, the particle size extracted increased slightly with (94.19 ± 2.72) nm- (97.25 ± 0.22) nm as the large-size Ag₂S-NPs originally presented in waters, instead of agglomeration. This method could be generally applicable to the analysis of Ag₂S-NPs in waters, and provide ideas for other metal sulfide nanoparticles (MS-NPs), which has certain significance.

Dissolution and Retention Process of CeO2 Nanoparticles in Soil with Dynamic Redox Conditions

The time-course association of soil physicochemical properties and fate of CeO₂ nanoparticles (NPs) is not well understood. This study for the first time investigated the dissolution and retention of CeO₂ NPs (<25 nm) during soil short-term (6 h) and long-term (30 d) aging processes with dynamic redox conditions. Under the additional reductant-induced initial reductive condition, theoretically, up to 220‰ of Ce(IV) was temporarily reductively dissolved within 10 min, accompanied by a slow retention process (180 min) of Ce species in soil solutions. Conversely, the dissolution and slow retention of Ce species were not significant in soil solutions without added reductant. X-ray absorption near edge spectroscopy (XANES) shows that most of Ce species were present as Ce(IV) (94.0%-97.8%) in all soils after a long-term aging process. These results indicate that the soil dynamic redox conditions induced by oxidant/reductant intrinsically determined the different time-course dissolution and retention of CeO₂ NPs, highlighting the occasional reductive condition in soil solution that may contribute to the migration and diffusion of Ce species. The time-course study should be also adopted to develop a comprehensive understanding of the nano-soil interactions.

Uptake and Translocation of Mesoporous SiO2-Coated ZnO Nanoparticles to Solanum lycopersicum Following Foliar Application

Nanoparticles composed of ZnO encapsulated in a mesoporous SiO₂ shell (nZnO@SiO₂) with a primary particle diameter of ∼70 nm were synthesized for delivery of Zn, a micronutrient, by foliar uptake. Compared to the rapid dissolution of bare nZnO (90% Zn dissolution after 4 h) in a model plant media (pH = 5), nZnO@SiO₂ released Zn more slowly (40% Zn dissolution after 3 weeks), thus enabling sustained Zn delivery over a longer period. nZnO@SiO₂, nZnO, and ZnCl₂ were exposed to Solanum lycopersicum by dosing 40 μg of Zn micronutrient (in a 20 μL suspension) on a single leaf. No Zn uptake was observed for the nZnO treatment after 2 days. Comparable amounts of Zn uptake were observed 2 days after ZnCl₂ (15.5 ± 2.4 μg Zn) and nZnO@SiO₂ (11.4 ± 2.2 μg Zn) dosing. Single particle inductively coupled plasma mass spectrometry revealed that for foliar applied nZnO@SiO₂, almost all of the Zn translocated to upper leaves and the stem were in nanoparticulate form. Our results suggest that the SiO₂ shell enhances the uptake of ZnO nanoparticles in Solanum lycopersicum. Sustained and controlled micronutrient delivery in plants through foliar application will reduce fertilizer, energy, and water use.

Separation and Analysis of Nanoscale Zero-Valent Iron from Soil

Nanoscale zero-valent iron (nZVI) has become one of the most used engineered nanoparticles for soil remediation. However, isolating nZVI particles from a complex soil matrix for their accurate particle characterizations and transport distance measurements is still challenging. Here, this study established a new analysis approach combining ultrasound-assisted solvent extraction, magnetic separation, and single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) analysis to isolate nZVI particles from soils and quantify their concentration and size. The interference from natural Fe-containing substances on nZVI analysis could be efficiently minimized by magnetic separation and dilution. After the optimization of extraction solvent type/concentration (i.e., 2.5 mM tetrasodium pyrophosphate) and ultrasonication time (i.e., 30 min), acceptable recoveries in both particle number (62.0 ± 10.8%-96.1 ± 4.8%) and Fe mass (70.6 ± 12.0%-119 ± 18%) could be achieved for different sizes (50 and 100 nm) and concentrations (50, 100, and 500 μg g^-1) of spiked nZVI from six soils. The detection limits of particle size and concentration were approximately 43.1 nm and 50 μg nZVI per gram soil, respectively. These results provide a feasible approach to quantify the nZVI concentration and size in complex soil matrices, which will allow the improvements to characterize and track the nZVI particles in the field, promote the use of nZVI particles for soil remediation, and better assess their environmental implications.

Enzyme digestion combined with SP-ICP-MS analysis to characterize the bioaccumulation of gold nanoparticles by mustard and lettuce plants

Plants can absorb and accumulate engineered nanomaterials (ENMs) through water and soil, providing a potential way for nanoparticles to be enriched in humans through the food chain. In this paper, a combination of enzymatic digestion method and SP-ICP-MS analysis was used to quantitatively characterize the enriched AuNPs in mustard and lettuce plants. The results showed that Macerozyme R-10 enzyme can extract AuNPs from plants without obvious aggregation/dissolution. Both mustard and lettuce plants can absorb and enrich the complete AuNPs to the above-ground organs, and the particle number concentrations detected are 1.24 × 107 particles L-1 and 4.39 × 107 particles L-1, respectively. With different exposure level of AuNPs(0.5 mg L-1,), a particle number concentration of 2.32 × 107 particles L-1 was detected in the stems of lettuce plants, while the mustard failed to transport AuNPs to the above-ground organs. The transport efficiency of Au ions by plants is higher than that of AuNPs, and the plants have stronger bioavailability for ions.

Effect of nano cerium oxide on soybean (Glycine max L. Merrill) crop exposed to environmentally relevant concentrations

This study evaluated the uptake and translocation of cerium nanoparticles (CeO2 NPs) and soluble Ce(NO3)3 by soybean plants (Glycine max L. Merrill) under the whole plant life-cycle and relevant environmental concentrations, 0.062 and 0.933 mg kg-1, which represent maximal values for 2017 in agricultural soils and sludge treated soils, respectively. The experiments were carried out using a nutrient solution. Cerium was detected in the soybean roots epidermis and cortex, leaves, and grains, but it neither impaired plant development nor grain yield. The concentration of Ce in the shoot increased as a function of time for plants treated with Ce(NO3)3, while it remained constant for plants treated with CeO2 NPs. It means that CeO2 NPs were absorbed in the same rate as biomass production, which suggests that they are taken up and transported by water mass flow. Single-particle inductively coupled plasma mass spectrometry revealed clusters of CeO2 NPs in leaves of plants treated with 25 nm CeO2 NPs (ca. 30-45 nm). The reprecipitation of soluble cerium from Ce(NO3)3 within the plant was not confirmed. Finally, bioconcentration factors above one were found for the lowest concentrated treatments. Since soybean is a widespread source of protein for animals, we draw attention to the importance of evaluating the effects of Ce entrance in the food chain and its possible biomagnification.

Metal-Containing Nanoparticles in Low-Rank Coal-Derived Fly Ash from China: Characterization and Implications toward Human Lung Toxicity

Characterization of nanoparticles (NPs) in coal fly ashes (CFAs) is critical for better understanding the potential health-related risks resulting from coal combustion. Based on single-particle (SP)-inductively coupled plasma mass spectrometry (ICP-MS) coupled with transmission electron microscopy techniques, this study is the first to determine the concentrations and sizes of metal-containing NPs in low-rank coal-derived fly ashes. Despite only comprising a minor component of the studied CFAs by mass, NPs were the dominant fraction by particle number. Fe- and Ti-containing NPs were identified as the dominant NPs with their particle number concentration ranging from 2.5 × 10⁷ to 2.5 × 10⁸ particles/mg. In addition, the differences of Fe-/Ti-containing NPs in various CFAs were regulated by the coalification degree of feed coals and combustion conditions of all of the low-rank CFAs tested. In the cases where these NPs in CFAs become airborne and are inhaled, they can be taken up in pulmonary interstitial fluids. This study shows that in Gamble's solution (a lung fluid simulant), 51-87% of Fe and 63-89% of Ti (ratio of the mass of Fe-/Ti-containing NPs to the total mass of Fe/Ti) exist in the NP form and remain suspended in pulmonary fluid simulants. These NPs are bioavailable and may induce lung tissue damage.

Green Analysis: Rapid-Throughput Analysis of Volatile Contaminants in Plants by Freeze-Thaw-Equilibration Sample Preparation and SPME-GC-MS Analysis

Emerging and fugitive contaminants (EFCs) can be introduced into the food chain through plants, particularly crop plants, and have threatened food safety and human health. The method for determination of volatile EFCs in plant tissues remains challenging. A new rapid, simple, precise, and accurate freeze-thaw-equilibration followed by head space (HS)-solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS) analytical method was developed in this study for high-throughput analysis of 1,4-dioxane and 1,2,3-trichloropropane (TCP) in tissues of three representative crop plants, corn, wheat, and tomato. The samples were treated by a freeze-thaw procedure, then equilibrated in a saturated sodium sulfate solution, and analyzed by HS-SPME-GC-MS method. Method detection limits ranged from 0.6 to 16 ng/g. The calibration showed good linearity (R² > 0.9). Recoveries of spiked analytes in the three plant species ranged from 82.69 to 106.3%. The ability of plant uptake of the compounds from soil has been investigated. As demonstrated in this study, this method is used to measure the concentrations of volatile contaminants in the stems of crop plants. This method should also be applicable for other plant tissues and therefore will contribute significantly to the sight of EFC transport in plants and to assess the potential risks EFCs pose to food safety and human health.

Inorganic arsenic toxicity and alleviation strategies in rice

Direct or indirect exposure to inorganic arsenic (iAs) in the forms of AsIII (arsenite) and AsV (arsenate) through consumption of As-contaminated food materials and drinking water leads to arsenic poisoning. Rice (Oryza sativa L.) plant potentially accumulates a high amount of iAs from paddy fields than any other cereal crops. This makes it to be a major source of iAs especially among the population that uses it as their dominant source of diet. The accumulation of As in human bodies poses a serious global health risk to the human population. Various conventional methods have been applied to reduce the arsenic accumulation in rice plant. However, the success rate of these techniques is low. Therefore, the development of efficient and effective methods aimed at lowering iAs toxicity is a very crucial public concern. With the current advancement in technology, new strategies aimed at addressing this concern are being developed and utilized in various parts of the world. In this review, we discuss the recent advances in the management of iAs in rice plants emphasizing the use of nanotechnology and biotechnology approaches. Also, the prospects and challenges facing these approaches are described.

A Sensitive Single Particle-ICP-MS Method for CeO2 Nanoparticles Analysis in Soil during Aging Process

The increasing prevalence of products that incorporate engineered nanoparticles (ENPs) has prompted efforts to investigate the potential release, environmental fate, and exposure of the ENPs. However, the investigation of cerium dioxide nanoparticles (CeO₂ NPs) in soil has remained limited, owing to the analytical challenge from the soil's complex nature. In this study, this challenge was overcome by applying a novel single particle-inductively coupled plasma-mass spectrometry (SP-ICP-MS) methodology to detect CeO₂ NPs extracted from soil, utilizing tetrasodium pyrophosphate (TSPP) aqueous solution as an extractant. This method is highly sensitive for determining CeO₂ NPs in soil, with detection limits of size and concentration of 15 nm and 194 NPs mL^-1, respectively. Extraction efficiency was sufficient in the tested TSPP concentration range from 1 mM to 10 mM at a soil-to-extractant ratio 1:100 (g mL^-1) for the extraction of CeO₂ NPs from the soil spiked with CeO₂ NPs. The aging study demonstrated that particle size, size distribution, and particle concentration underwent no significant change in the aged soils for a short period of one month. This study showed an efficient method capable of extracting and accurately determining CeO₂ NPs in soil matrices. The method can serve as a useful tool for nanoparticle analysis in routine soil tests and soil research.

A novel method to estimate cellular internalization of nanoparticles into gram-negative bacteria: Non-lytic removal of outer membrane and cell wall

Bacteria efficiently take up small organic molecules and ions. However, the internalization of particulate forms, specifically nanoparticles (NPs) has been understudied and is a newly-emerging area of interest. However, determination of true cellular internalization is challenging owing to the difficulty of separating the aqueous phase from bacteria-associated NPs and, more importantly, of differentiating between internalized and NPs sorbed on bacteria surfaces. In this work, we developed and validated an extraction method which can operationally estimate internalization of metal NPs into Gram-negative bacteria. The outer cell membrane and cell wall, collectively called the periplasm, was successfully removed from bacteria using ethylenediaminetetraacetic acid (EDTA) at an optimized exposure period and concentration, without lysis of bacteria. This was followed by standard digestion and metal measurements. Verification of each step of the methodology was conducted by assessing both cellular and metal behavior. Specifically, the combined approaches of live/dead staining of bacteria, optical density measurements, transmission electron microscopy (TEM) and metal analyses of the supernatant indicated that the method operationally separated externally-sorbed NPs from those internalized actually localized within the bacterial cytoplasm. However, this new method is ideally used alongside other methods in a multi-method approach, to provide improved data quality. Therefore, it should be used with CSLM, FACS, TEM and other available methods.

Germination and Early Development of Three Spontaneous Plant Species Exposed to Nanoceria (nCeO2) with Different Concentrations and Particle Sizes

This study aimed to provide insight regarding the influence of Ce oxide nanoparticles (nCeO₂) with different concentrations and two different particle sizes on the germination and root elongation in seedlings of spontaneous terrestrial species. In a bench-scale experiment, seeds of the monocot, Holcus lanatus and dicots Lychnis-flos-cuculi and Diplotaxis tenuifolia were treated with solutions containing nCeO₂ 25 nm and 50 nm in the range 0-2000 mg Ce L^-1. The results show that nCeO₂ enters within the plant tissues. Even at high concentration, nCeO₂ have positive effects on seed germination and the development of the seedling roots. This study further demonstrated that the particle size had no influence on the germination of L. flos-cuculi, while in H. lanatus and D. tenuifolia, the germination percentage was slightly higher (+10%) for seeds treated with nCeO₂ 25 nm with respect to 50 nm. In summary, the results indicated that nCeO₂ was taken up by germinating seeds, but even at the highest concentrations, they did not have negative effects on plant seedlings. The influence of the different sizes of nCeO₂ on germination and root development was not very strong. It is likely that particle agglomeration and ion dissolution influenced the observed effects.

Measurement of CeO2 Nanoparticles in Natural Waters Using a High Sensitivity, Single Particle ICP-MS

As the production and use of cerium oxide nanoparticles (CeO₂ NPs) increases, so does the concern of the scientific community over their release into the environment. Single particle inductively coupled plasma mass spectrometry is emerging as one of the best techniques for NP detection and quantification; however, it is often limited by high size detection limits (SDL). To that end, a high sensitivity sector field ICP-MS (SF-ICP-MS) with microsecond dwell times (50 µs) was used to lower the SDL of CeO₂ NPs to below 4.0 nm. Ag and Au NPs were also analyzed for reference. SF-ICP-MS was then used to detect CeO₂ NPs in a Montreal rainwater at a concentration of (2.2 ± 0.1) × 10⁸ L⁻¹ with a mean diameter of 10.8 ± 0.2 nm; and in a St. Lawrence River water at a concentration of ((1.6 ± 0.3) × 10⁹ L⁻¹) with a higher mean diameter (21.9 ± 0.8 nm). SF-ICP-MS and single particle time of flight ICP-MS on Ce and La indicated that 36% of the Ce-containing NPs detected in Montreal rainwater were engineered Ce NPs.

Unveil early-stage nanocytotoxicity by a label-free single cell pH nanoprobe

Single-cell analysis is an emerging research area that aims to reveal delicate cellular status and underlying mechanisms by conquering the intercellular heterogeneity. Current single-cell research methods, however, are highly dependent on cell-destructive protocols and cannot sequentially display the progress of cellular events. A recently developed pH nanoprobe in our lab conceptually showed its ability to detect intracellular pH (pHi) without cell labeling or disruption. In the present study, we took the cytotoxicity of nanoparticles (NPs) as a typical example of cell heterogeneity, to testify the practicality of the pH nanoprobe in interpreting cell status. Three types of NPs (CeO2, TiO2, and SiO2) were employed to generate varied toxic effects. Results showed that the traditional assays - including cell viability, intracellular ROS generation, and mitochondrial inner membrane depolarization - not only failed to report the nanotoxicity accurately and timely, but also drew confusing or misleading conclusions. The pH nanoprobe revealed explicit pHi changes induced by the NPs, which corresponded well with the cell damages found by the transmission electron microscopic (TEM) imaging. Besides, our results unveiled an unexpectedly devastating effect of SiO2 NPs on cells during the early stage NP-cell interaction. The developed novel pH nanoprobe demonstrated a rapid sensing capability at single-cell resolution with minimum invasiveness. Therefore, it may become a promising alternative for a wide range of applications in areas such as single-cell research and precision medicine.

Methanol-based extraction protocol for insoluble and moderately water-soluble nanoparticles in plants to enable characterization by single particle ICP-MS

The detection and characterization of soluble metal nanoparticles in plant tissues are an analytical challenge, though a scientific necessity for regulating nano-enabled agrichemicals. The efficacy of two extraction methods to prepare plant samples for analysis by single particle ICP-MS, an analytical method enabling both size determination and quantification of nanoparticles (NP), was assessed. A standard enzyme-based extraction was compared to a newly developed methanol-based approach. Au, CuO, and ZnO NPs were extracted from three different plant leaf materials (lettuce, corn, and kale) selected for their agricultural relevance and differing characteristics. The enzyme-based approach was found to be unsuitable because of changes in the recovered NP size distribution of CuO NP. The MeOH-based extraction allowed reproducible extraction of the particle size distribution (PSD) without major alteration caused by the extraction. The type of leaf tissue did not significantly affect the recovered PSD. Total metal losses during the extraction process were largely due to the filtration step prior to analysis by spICP-MS, though this did not significantly affect PSD recovery. The methanol extraction worked with the three different NPs and plants tested and is suitable for studying the fate of labile metal-based nano-enabled agrichemicals.

Fates of Au, Ag, ZnO, and CeO2 Nanoparticles in Simulated Gastric Fluid Studied using Single-Particle-Inductively Coupled Plasma-Mass Spectrometry

The increasing use of engineered nanoparticles (ENPs) in many industries has generated significant research interest regarding their impact on the environment and human health. The major routes of ENPs to enter the human body are inhalation, skin contact, and ingestion. Following ingestion, ENPs have a long contact time in the human stomach. Hence, it is essential to know the fate of the ENPs under gastric conditions. This study aims to investigate the fate of the widely used nanoparticles Ag-NP, Au-NP, CeO2-NP, and ZnO-NP in simulated gastric fluid (SGF) under different conditions through the application of single-particle inductively coupled plasma-mass spectrometry (SP-ICP-MS). The resulting analytical methods have size detection limits for Ag-NP, Au-NP, ZnO-NP, and CeO2-NP from 15 to 35 nm, and the particle concentration detection limit is 135 particles/mL. Metal ions corresponding to the ENPs of interest were detected simultaneously with detection limits from 0.02 to 0.1 μg/L. The results showed that ZnO-NPs dissolved completely and rapidly in SGF, whereas Au-NPs and CeO2-NPs showed apparent aggregation and did not dissolve significantly. Both aggregation and dissolution were observed in Ag-NP samples following exposure to SGF. The size distributions and concentrations of ENPs were affected by the original ENP concentration, ENP size, the contact time in SGF, and temperature. This work represents a significant advancement in the understanding of ENP characteristics under gastric conditions.

Analysis of cerium oxide and copper oxide nanoparticles bioaccessibility from radish using SP-ICP-MS

BACKGROUND

The transformation of nanoparticles (NPs) internalized in plant tissues is the human digestive system that can provide a better understanding of the impact of NPs on the human system. The presented methodology was developed to study the bioaccessibility of cerium oxide (CeO₂ ) and copper oxide (CuO) NPs from radish after the in vitro simulation of gastrointestinal digestion using single-particle inductively coupled plasma mass spectrometry (SP-ICP-MS).

RESULTS

Radish plants were cultivated hydroponically in a growth medium containing: (i) CeO₂ NPs and (ii) CuO NPs. Both cerium (Ce) and copper (Cu) were found in all organs of the radish plants after analysis by standalone ICP-MS. This confirms the bioaccumulation of CeO₂ and CuO NPs and the translocation of their Ce and Cu to the aerial parts of the plant. Less Ce (4.095 μg g^-1 ) has been detected in leaves than in roots (1.156 mg g^-1 ) while Cu content in leaves was 5.245 μg g^-1 and in roots was 10.41 μg g^-1 . Analysis of the digestive extracts obtained after the in vitro simulation of gastro (pepsin) and gastrointestinal (pancreatin) digestion showed that Ce has easy access to human system at least by 73%.

CONCLUSION

The size of CeO₂ NPs in digestive extracts showed no significant changes. However, the results obtained for CuO NPs digestion were variable and suggested that CuO NPs dissolved during the digestion process. The CuO NPs were observed in roots after the gastrointestinal digestion concluding that CuO NPs recovered after the initial dissolution. © 2020 Society of Chemical Industry.

La2O3 Nanoparticles: Study of Uptake and Distribution in Pfaffia glomerata (Spreng.) Pedersen by LA-ICP-MS and μ-XRF

The production and use of nanoparticles (NPs) in different fields increased in the last years. However, some NPs have toxicological properties, making these materials potential emerging pollutants. Therefore, it is important to investigate the uptake, transformation, translocation, and deposition of NPs in plants. In this work, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and micro X-ray fluorescence (μ-XRF) were used to investigate the uptake and translocation of La₂O₃ NPs to stem and leaves of Pfaffia glomerata (Spreng.) Pedersen after in vitro cultivation of plants in the presence of 400 mg L^-1 of La₂O₃ NPs. By using LA-ICP-MS and μ-XRF, image of the spatial distribution of La in the leaves was obtained, where higher concentration of La was observed in the main veins. Differences in the signal profile of La in leaves of plants cultivated in the presence of bulk La₂O₃ (b-La₂O₃) and La₂O₃ NPs were observed. Sharp peaks of La indicated that NPs were transported to the stems and leaves of plants treated with La₂O₃ NPs. Both LA-ICP-MS and μ-XRF techniques have shown to be useful for detecting NPs in plants, but LA-ICP-MS is more sensitive than μ-XRF and allowed better detection and visualization of La distribution in the whole leaf.

Uptake, translocation, size characterization and localization of cerium oxide nanoparticles in radish (Raphanus sativus L.)

Due to their unique physical and chemical properties, the production and use of cerium oxide nanoparticles (CeO₂ NPs) in different areas, especially in automotive industry, is rapidly increasing, causing their presence in the environment. Released CeO₂ NPs can undergo different transformations and interact with the soil and hence with plants, providing a potential pathway for human exposure and leading to serious concerns about their impact on the ecosystem and human organism. This study investigates the uptake, bioaccumulation, possible translocation and localization of CeO₂ NPs in a model plant (Raphanus sativus L.), whose edible part is in direct contact with the soil where contamination is more likely to happen. The stability of CeO₂ NPs in plant growth medium as well as after applying a standard enzymatic digestion procedure was tested by single particle ICP-MS (SP-ICP-MS) showing that CeO₂ NPs can remain intact after enzymatic digestion; however, an agglomeration process was observed in the growth medium already after one day of cultivation. An enzymatic digestion method was next used in order to extract intact nanoparticles from the tissues of plants cultivated from the stage of seeds, followed by size characterization by SP-ICP-MS. The results obtained by SP-ICP-MS showed a narrower size distribution in the case of roots suggesting preferential uptake of smaller nanoparticles which led to the conclusion that plants do not take up the CeO₂ NPs agglomerates present in the medium. However, nanoparticles at higher diameters were observed after analysis of leaves plus stems. Additionally, a small degree of dissolution was observed in the case of roots. Finally, after CeO₂ NPs treatment of adult plants, the spatial distribution of intact CeO₂ NPs in the radish roots was studied by laser ablation ICP-MS (LA-ICP-MS) and the ability of NPs to enter and be accumulated in root tissues was confirmed.

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.

Differential impacts of copper oxide nanoparticles and Copper(II) ions on the uptake and accumulation of arsenic in rice (Oryza sativa)

Arsenic (As) in rice grains is a serious food safety concern. Some coexisting engineered nanoparticles (ENPs) were shown to alter the accumulation and speciation of As in rice grains. However, investigation on the effects of copper oxide nanoparticles (CuO NPs), a popular ingredient in pesticides, on the uptake and accumulation of As is rare. We explored the potentially different impact of CuO NPs and corresponding Cu(II) ions on the accumulation of two As species in rice seedlings in a hydroponic system. Rice seedlings were treated with a combinations of 1 mg/L of arsenite (As(III)) or arsenate (As(V)) and 100 mg/L of CuO NPs or Cu(II) for 6 days. Both forms of Cu significantly reduced the accumulation of total As in rice tissues, with Cu(II) exhibiting significantly greater effect than CuO NPs. As speciation in rice roots was markedly affected by both forms of Cu, and the impacts were Cu-form dependent. For example, the co-existence of As(V) with CuO NPs led to a 45% decrease of As(V) in rice roots, while the co-existence of As(V) with Cu(II) caused a 47% increase in As(V) in rice roots. As speciation in rice shoots was less affected by co-present Cu than in rice roots. Co-occurring As(III) or As(V) lowered Cu concentration in rice roots by 40% and 50% in treatments with CuO NPs, but did not affect Cu content in rice roots co-exposed to Cu(II). The study confirmed the reciprocal effect of co-occurring CuO NPs or Cu(II) and As in rice paddies and highlighted the unique "nano-effect" of CuO NPs. The results alsos showed that the initial oxidation state of As plays an important role in the interactions between As and Cu. The results shed light on the current debate on the safe applications of nano-enabled agrichemicals vs. conventional metal salts in agriculture.

Polypropylene-MWCNT composite degradation, release, detection, and toxicity of MWCNT during accelerated aging

Nanomaterials (NM) are incorporated into polymers to enhance their properties. However, there are a limited number of studies on the aging of these nanocomposites and the resulting potential release of NM. To characterize NM at critical points in their life cycles, polypropylene (PP) and multiwall carbon nanotube filled PP (PP-MWCNT) plates with different thicknesses (from 0.25 mm to 2 mm) underwent accelerated weathering in a chamber that simulates solar irradiation and rainfall. The physicochemical changes of the plates depended on the radiation exposure, the plate thickness, and the presence of CNT fillers. Photodegradation increased with aging time, making the exposed surface more hydrophilic, decreasing the surface hardness and creating surface stress-cracks. Aged surface and cross-section showed crazing due to the polymer bond scission and the formation of carbonyls. The degradation was higher near the UV-exposed surface as the intensity of the radiation and oxygen diffusion decreased with increasing depth of the plates, resulting in an oxidation layer directly proportional to oxygen diffusion. Thus, sample thickness determines the kinetics of the degradation reaction and the transport of reactive species. Plastic fragments, which are less than 1 mm, and free CNTs were released from weathered MWCNT-PP. The concentrations of released NM that were estimated using ICP-MS, increased with prolonged aging time. Various toxicity tests, including reactive oxygen species generation and cell activity/viability, were performed on the released CNTs. The toxicity of the released fragments and CNTs to A594 adenocarcinomic human alveolar basal epithelial cells was observed. The released polymer fragments and CNTs did not show significant toxicity under the experimental conditions in this study. This study will help manufacturers, users of consumer products with nanocomposites and policymakers in the development of testing guidelines, predictive models, and risk assessments and risk based-formulations of NM exposure.

Gold Nanoparticle Uptake in Tumor Cells: Quantification and Size Distribution by sp-ICPMS

Gold nanoparticles (AuNPs) are increasingly studied for cancer treatment purposes, as they can potentially improve both control and efficiency of the treatment. Intensive research is conducted in vitro on rodent and human cell lines to objectify the gain of combining AuNPs with cancer treatment and to understand their mechanisms of action. However, using nanoparticles in such studies requires thorough knowledge of their cellular uptake. In this study, we optimized single particle ICPMS (sp-ICPMS) analysis to qualify and quantify intracellular AuNP content after exposure of in vitro human breast cancer cell lines. To this aim, cells were treated with an alkaline digestion method with 5% TMAH, allowing the detection of gold with a yield of 97% on average. Results showed that under our experimental conditions, the AuNP size distribution appeared to be unchanged after internalization and that the uptake of particles depended on the cell line and on the exposure duration. Finally, the comparison of the particle numbers per cell with the estimates based on the gold masses showed excellent agreement, confirming the validity of the sp-ICPMS particle measurements in such complex samples.

Strategies for robust and accurate experimental approaches to quantify nanomaterial bioaccumulation across a broad range of organisms

One of the key components for environmental risk assessment of engineered nanomaterials (ENMs) is data on bioaccumulation potential. Accurately measuring bioaccumulation can be critical for regulatory decision making regarding material hazard and risk, and for understanding the mechanism of toxicity. This perspective provides expert guidance for performing ENM bioaccumulation measurements across a broad range of test organisms and species. To accomplish this aim, we critically evaluated ENM bioaccumulation within three categories of organisms: single-celled species, multicellular species excluding plants, and multicellular plants. For aqueous exposures of suspended single-celled and small multicellular species, it is critical to perform a robust procedure to separate suspended ENMs and small organisms to avoid overestimating bioaccumulation. For many multicellular organisms, it is essential to differentiate between the ENMs adsorbed to external surfaces or in the digestive tract and the amount absorbed across epithelial tissues. For multicellular plants, key considerations include how exposure route and the role of the rhizosphere may affect the quantitative measurement of uptake, and that the efficiency of washing procedures to remove loosely attached ENMs to the roots is not well understood. Within each organism category, case studies are provided to illustrate key methodological considerations for conducting robust bioaccumulation experiments for different species within each major group. The full scope of ENM bioaccumulation measurements and interpretations are discussed including conducting the organism exposure, separating organisms from the ENMs in the test media after exposure, analytical methods to quantify ENMs in the tissues or cells, and modeling the ENM bioaccumulation results. One key finding to improve bioaccumulation measurements was the critical need for further analytical method development to identify and quantify ENMs in complex matrices. Overall, the discussion, suggestions, and case studies described herein will help improve the robustness of ENM bioaccumulation studies.

Synthesis and characterization of isotopically-labeled silver, copper and zinc oxide nanoparticles for tracing studies in plants

In parallel to technological advances and ever-increasing use of nanoparticles in industry, agriculture and consumer products, the potential ecotoxicity of nanoparticles and their potential accumulation in ecosystems is of increasing concern. Because scientific reports raise a concern regarding nanoparticle toxicity to plants, understanding of their bioaccumulation has become critical and demands more research. Here, the synthesis of isotopically-labeled nanoparticles of silver, copper and zinc oxide is reported; it is demonstrated that while maintaining the basic properties of the same unlabeled ("regular") nanoparticles, labeled nanoparticles enable more sensitive tracing of nanoparticles within plants that have background elemental levels. This technique is particularly useful for working with elements that are present in high abundance in natural environments. As a benchmark, labeled and unlabeled metal nanoparticles (Ag-NP, Cu-NP, ZnO-NP) were synthesized and compared, and then exposed in a series of growth experiments to Arabidopsis thaliana; the NPs were traced in different parts of the plant. All of the synthesized nanoparticles were characterized by TEM, EDS, DLS, ζ-potential and single particle ICP-MS, which provided essential information regarding size, composition, morphology and surface charge of nanoparticles, as well as their stability in suspensions. Tracing studies with A. thaliana showed uptake/retention of nanoparticles that is more significant in roots than in shoots. Single particle ICP-MS, and scanning electron micrographs and EDS of plant roots showed presence of Ag-NPs in particular, localized areas, whereas copper and zinc were found to be distributed over the root tissues, but not as nanoparticles. Thus, nanoparticles in any natural matrix can be replaced easily by their labeled counterparts to trace the accumulation or retention of NPs. Isotopically-labeled nanoparticles enable acquisition of specific results, even if there are some concentrations of the same elements that originate from other (natural or anthropogenic) sources.

Elucidating the Effects of Cerium Oxide Nanoparticles and Zinc Oxide Nanoparticles on Arsenic Uptake and Speciation in Rice ( Oryza sativa) in a Hydroponic System

The accumulation of arsenic (As) in rice grains depends greatly on the redox chemistry in rice rhizosphere. Intentional or accidental introduction of strong oxidizing or reducing agents, such as metallic engineered nanoparticles (ENPs) into the plant-soil ecosystem, can change As speciation and plant uptake. However, investigation on the effects of ENPs on plant uptake of co-occurring redox sensitive heavy metals and their speciation in plant tissues is scarce. We investigated the mutual effects of two commonly encountered ENPs, cerium oxide nanoparticles (CeO₂ NPs) and zinc oxide nanoparticles (ZnO NPs), and two inorganic species of As on their uptake and accumulation in rice seedlings in a hydroponic system. Rice seedlings were exposed to different combinations of 1 mg/L of As(III) or As(V) and 100 mg/L of CeO₂ NPs and ZnO NPs for 6 days about 40 days after germination. ZnO NPs significantly reduced the accumulation of As(III) in rice roots by 88.1 and 96.7% and in rice shoots by 71.4 and 77.4% when the initial As was supplied as As(III) and As(V), respectively. ZnO NPs also reduced As(V) in rice roots by 68.3 and 52.3% when the As was provided as As(III) and As(V), respectively. However, the As(V) in rice shoots was unaffected by ZnO NPs regardless of the initial oxidation state of As. Neither the total As nor the individual species of As in rice tissues was significantly changed by CeO₂ NPs. The co-presence of As(III) and As(V) increased Ce in rice shoots by 6.5 and 2.3 times but did not affect plant uptake of Zn. The results confirmed the active interactions between ENPs and coexisting inorganic As species, and the extent of their interactions depends on the properties of ENPs as well as the initial oxidation state of As.

Study of the uptake and bioaccumulation of palladium nanoparticles by Sinapis alba using single particle ICP-MS

In recent years, increased palladium content has been found in the environment, due to its wide use in various fields, especially as catalytic converters. Palladium can be emitted as a range of soluble and insoluble compounds and in the form of palladium nanoparticles (PdNPs). The level of toxicity is equally dependent on concentration and form of palladium and hence, it is important to determine not only the total content of this element, but also its forms of occurrence. This study for the first time investigates the uptake degree and distribution of PdNPs by model plant Sinapis alba, in comparison with a platinum salt (Pd(NO₃)₂). An enzymatic digestion method which allows the extraction of PdNPs from the different plant tissues without altering their properties was applied. After extraction, samples were analysed by single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) to provide information about the presences of palladium in nanoparticulated or dissolved form, the nanoparticle size and the nanoparticle number concentration. Significant amounts of PdNPs were found even in aboveground organs, but no significant changes in plant morphology were observed. Size distributions of PdNPs found in all tissues presented lower diameters than size distribution of the PdNPs stock suspension, suggesting that bigger nanoparticles are not taken up by the plant. The average size found is in good agreement between the different organs. Moreover, dissolved palladium was found in all samples, with the biggest contribution, in relative terms, observed in leaves followed by stems and roots.

Optimizing critical parameters for the directly measurement of particle flow with PF-SIBS

A novel measurement technology named as particle flow-spark induced breakdown spectroscopy (PF-SIBS) was reported for real-time measurement of solid materials. Critical measurement parameters of PF-SIBS were optimized and a set of fly ashes with different carbon content were measured for evaluation of measurement performance. Four electrode materials, tungsten, copper, molybdenum and platinum, were compared in the aspects of signal stability, line interference and electrode durability. Less line interference and better signal stability were obtained with W and Cu electrode, while W electrode has better durability. Quartz sand with diameters from 48 μm to 180 μm were tested to investigate the influence of particle size. As the particle diameter increased, the intensity of Si 288.16 nm line decreased while that of ambient air constituents increased. To reduce the particle effect, the sum intensity from sample and ambient air were introduced to correct. The RSD of line intensity between the five diameters were reduced from 67.30% to 16.59% with Cu electrodes and from 63.21% to 13.64% with W electrodes. With the optimal measurement parameters and correction, fly ash samples with different carbon content were tested and the correlation coefficients R² of multivariate calibration achieved 0.987.

The impact of cerium oxide nanoparticles on the physiology of soybean (Glycine max (L.) Merr.) under different soil moisture conditions

The ongoing global climate change raises concerns over the decreasing moisture content in agricultural soils. Our research investigated the physiological impact of two types of cerium oxide nanoparticles (CeO2NPs) on soybean at different moisture content levels. One CeO2NP was positively charged on the surface and the other negatively charged due to the polyvinylpyrrolidone (PVP) coating. The results suggest that the effect of CeO2NPs on plant photosynthesis and water use efficiency (WUE) was dependent upon the soil moisture content. Both types of CeO2NPs exhibited consistently positive impacts on plant photosynthesis at the moisture content above 70% of field capacity (θfc). Similar positive impact of CeO2NPs was not observed at 55% θfc, suggesting that the physiological impact of CeO2NPs was dependent upon the soil moisture content. The results also revealed that V Cmax (maximum carboxylation rate) was affected by CeO2NPs, indicating that CeO2NPs affected the Rubisco activity which governs carbon assimilation in photosynthesis. In conclusion, CeO2NPs demonstrated significant impacts on the photosynthesis and WUE of soybeans and such impacts were affected by the soil moisture content. Graphical abstract Soil moisture content affects plant cerium oxide nanoparticle interactions.

Impact of TiO2 and ZnO nanoparticles on an aquatic microbial community: effect at environmentally relevant concentrations

To investigate effects of engineered nanoparticles (ENPs) at environmentally relevant concentrations to aquatic microbial communities, TiO₂ at 700 µg/L and ZnO at 70 µg/L were spiked to river water samples either separately or combined. Compared to controls where no ENPs were added, the addition of TiO₂ ENPs alone at the tested concentration had no statistically significant effect on both the bacterial and eukaryotic communities. The presence of added ENPs: ZnO or ZnO + TiO₂ led to significant shift of the microbial community structure and genus distribution. This shift was more obvious for the bacteria than the eukaryotes. Based on results from single particle - inductively coupled plasma - mass spectrometry (SP-ICP-MS), all ENPs aggregated rapidly in water and resulted in much larger particles sizes than the original counterparts. "Dissolved" (including particles smaller than the size detection limits and dissolved ions) concentrations of Ti and Zn increased, too in treatment groups vs. the controls.

David JF, Nelson BC, Xing B. Multiple Method Analysis of TiO2 Nanoparticle Uptake in Rice (Oryza sativa L.) Plants

Understanding the translocation of nanoparticles (NPs) into plants is challenging because qualitative and quantitative methods are still being developed and the comparability of results among different methods is unclear. In this study, uptake of titanium dioxide NPs and larger bulk particles (BPs) in rice plant (Oryza sativa L.) tissues was evaluated using three orthogonal techniques: electron microscopy, single-particle inductively coupled plasma mass spectroscopy (spICP-MS) with two different plant digestion approaches, and total elemental analysis using ICP optical emission spectroscopy. In agreement with electron microscopy results, total elemental analysis of plants exposed to TiO₂ NPs and BPs at 5 and 50 mg/L concentrations revealed that TiO₂ NPs penetrated into the plant root and resulted in Ti accumulation in above ground tissues at a higher level compared to BPs. spICP-MS analyses revealed that the size distributions of internalized particles differed between the NPs and BPs with the NPs showing a distribution with smaller particles. Acid digestion resulted in higher particle numbers and the detection of a broader range of particle sizes than the enzymatic digestion approach, highlighting the need for development of robust plant digestion procedures for NP analysis. Overall, there was agreement among the three techniques regarding NP and BP penetration into rice plant roots and spICP-MS showed its unique contribution to provide size distribution information.