A framework to measure the availability of engineered nanoparticles in soils: Trends in soil tests and analytical tools

Particle morphology and soil properties affect the retention of copper oxide nanoparticles in agricultural soils

The interaction between nanoscale copper oxides (nano-CuOs) and soil matrix significantly affects their fate and transport in soils. This study investigates the retention of nano-CuOs and Cu2+ ions in ten typical agricultural soils by employing the Freundlich adsorption model. Retention of nano-CuOs and Cu2+ in soils was well fitted by the Freundlich model. The retention parameters (KD, KF, and N) followed an order of CuO NTs > CuO NPs > Cu2+, highlighting significant impact of nano-CuOs morphology. The KF and N values of CuO NPs/Cu2+ were positively correlated with soil pH and electrical conductivity (EC), but exhibited a weaker correlation for CuO NTs. Soil pH and/or EC could be used to predict KF and N values of CuO NPs or CuO NTs, with additional clay content should be included for Cu2+.The different relationship between retention parameters and soil properties may suggest that CuO NTs retention mainly caused by agglomeration, whereas adsorption and agglomeration were of equal importance to CuO NPs. The amendment of Ca2+ at low and medium concentration promoted retention of nano-CuOs in alkaline soils, but reduced at high concentration. These findings provided critical insights into the fate of nano-CuOs in soil environments, with significant implications for environmental risk assessment and soil remediation strategies.

Microbial bioprocess performance in nanoparticle-mediated composting

Microbial composting is one of the most cost-effective techniques for degradation, remediation, nutrition, etc. Currently, there is faster growth and development in nanotechnology in different sectors. This development leads nanoparticles (NPs) to enter into the composts in different ways. First, unintentional entry of NPs into the composts via: waste discharge, buried solid waste, surface runoff, direct disposal into wastes (consumer goods, food, pharmaceuticals, and personal care products). Second, intentional mediation of the NPs in the composting process is a novel approach developed to enhance the degradation rate of wastes and as a nutrient for plants. The presence of NPs in the composts can cause nanotoxicity. Conversely, their presence might also be beneficial, such as soil reclamations, degradation, etc. Alternatively, metal NPs are also helpful for all living organisms, including microorganisms, in various biological processes, such as DNA replication, precursor biosynthesis, respiration, oxidative stress responses, and transcription. NPs show exemplary performance in multiple fields, whereas their role in composting process is worth studying. Consequently, this article aids the understanding of the role of NPs in the composting process and how far their presence can be beneficial. This article reviews the significance of NPs in: the composting process, microbial bioprocess performance during nano composting, basic life cycle assessment (LCA) of NP-mediated composting, and mode of action of the NPs in the soil matrix. This article also sheds insight on the notion of nanozymes and highlights their biocatalytic characterization, which will be helpful in future composting research.

Unlocking the Potential of Nano-Enabled Precision Agriculture for Efficient and Sustainable Farming

Nanotechnology has attracted remarkable attention due to its unique features and potential uses in multiple domains. Nanotechnology is a novel strategy to boost production from agriculture along with superior efficiency, ecological security, biological safety, and monetary security. Modern farming processes increasingly rely on environmentally sustainable techniques, providing substitutes for conventional fertilizers and pesticides. The drawbacks inherent in traditional agriculture can be addressed with the implementation of nanotechnology. Nanotechnology can uplift the global economy, so it becomes essential to explore the application of nanoparticles in agriculture. In-depth descriptions of the microbial synthesis of nanoparticles, the site and mode of action of nanoparticles in living cells and plants, the synthesis of nano-fertilizers and their effects on nutrient enhancement, the alleviation of abiotic stresses and plant diseases, and the interplay of nanoparticles with the metabolic processes of both plants and microbes are featured in this review. The antimicrobial activity, ROS-induced toxicity to cells, genetic damage, and growth promotion of plants are among the most often described mechanisms of operation of nanoparticles. The size, shape, and dosage of nanoparticles determine their ability to respond. Nevertheless, the mode of action of nano-enabled agri-chemicals has not been fully elucidated. The information provided in our review paper serves as an essential viewpoint when assessing the constraints and potential applications of employing nanomaterials in place of traditional fertilizers.

Extraction and Quantification of Nanoparticulate Mercury in Natural Soils

Nanoparticulate mercury (Hg-NPs) are ubiquitous in nature. However, the lack of data on their concentration in soils impedes reliable risk assessments. This is due to the analytical difficulties resulting from low ambient Hg concentrations and background interferences of heterogeneous soil components. Here, coupled to single particle inductively coupled plasma-mass spectrometry (spICP-MS), a standardized protocol was developed for extraction and quantification of Hg-NPs in natural soils with a wide range of properties. High particle number-, particle mass-, and total mass-based recoveries were obtained for spiked HgS-NPs (74-120%). Indigenous Hg-NPs across soils were within 10⁷-10¹¹ NPs g^-1, corresponding to 3-40% of total Hg on a mass basis. Metacinnabar was the primary Hg species in extracted samples from the Wanshan mercury mining site, as characterized by X-ray absorption spectroscopy and transmission electron microscopy. In agreement with the spICP-MS analysis, electron microscopy revealed comparable size distribution for nanoparticles larger than 27 nm. These indigenous Hg-NPs contributed to 5-65% of the measured methylmercury in soils. This work paves the way for experimental determinations of indigenous Hg-NPs in natural soils, which is critical to understand the biogeochemical cycling of mercury and thereby the methylation processes governing the public exposure to methylmercury.

Measuring ZnO nanoparticles available concentrations in contaminated soils using the diffusive gradient in thin-films (DGT) technique

A major gap in understanding nanomaterials behaviour in the environment is a lack of reliable tools to measure their available concentrations. In this research we use diffusive gradients in thin films (DGT) for measuring concentrations of zinc oxide nanoparticles (ZNO NPs) in soils. Available nanoparticle concentrations were assessed by difference, using paired DGT devices with and without 1000 MWCO dialysis membranes to exclude NPs. We used ZnO because its toxic effects are accelerated through dissolution to Zn²⁺. Our test soils had different pH and organic matter (OM) contents, which both affect the dissolution rate of ZnO NPs. Woburn (pH ≈ 6.9, OM ≈ 1.8%) and Lufa (pH ≈ 5.9, OM ≈ 4.2%) soils were spiked to a single concentration of 500 mg of ZnO NPs per 1 kg of soil and the available concentrations of ZnO NPs and dissolved zinc were evaluated in 3, 7, 14, 21, 28, 60, 90, 120, 150 and 180 day intervals using DGT. The results showed that the dissolution of ZnO NPs, as well as the available concentrations of both dissolved and nanoparticulate Zn, was much higher in Lufa soil than in Woburn. This work demonstrates that DGT can be used as a simple yet reliable technique for determining concentrations of ZnO NPs in soils and probing its dissolution kinetics.

Dissolution of copper oxide nanoparticles is controlled by soil solution pH, dissolved organic matter, and particle specific surface area

Dissolution is the primary process affecting the bioavailability and toxicity of nanoscale copper oxide (nano-CuO) to plants and soil organisms. In this study, particle morphology, organic acid, and soil properties were considered to understand the dissolution characteristics of nano-CuO in soil solutions. The results showed that the copper ions (Cu²⁺) released from spherical nano-CuO (CuO NPs), tubular nano-CuO (CuO NTs), and spherical microsized CuO (CuO MPs) in the ten soil solutions were 26.6-4194.0 μg/L, 4.90-217.1 μg/L, and 10.8-326.0 μg/L, respectively. The concentration of Cu²⁺ was negatively correlated with the pH of the soil solution and positively correlated with the contents of dissolved organic carbon (DOC), aluminum, and manganese. Multivariate stepwise regression analysis indicated that the dissolution of CuO NPs could be well predicted by pH and DOC contents of the soil solutions. In the GD soil solution (acidic), 4- and 8-fold of the DOC content amendments significantly promoted the dissolution of the three sizes of CuOs, resulting in an increase of Cu²⁺ 4.55-11.3 and 5.67-16.2 times, respectively. In the CQ soil solution (neutral), 8-fold DOC amendments increase the release of Cu²⁺ 2.13-16.6 times. While in the SD soil solution (alkaline), promoting effect on the dissolution was only observed for nano-CuOs, with Cu²⁺ elevated by factors of 1.56-4.64 and 1.38-4.48. The amendments of Al³⁺ and Mn²⁺ in soil solution increased the amounts of Cu²⁺ 1.13-4.80 and 1.02-1.46 times in the GD soil solution. In comparison, no significant promoting effects were observed in CQ and SD soil solutions due to their stronger buffering capacities. These findings offer insight into the dissolution behavior of nano-CuOs in soils and be helpful to evaluate their environmental risks.

Risks and phyto-uptake of micro-nano size particulates bound with potentially toxic metals in Pb-contaminated alkaline soil (NW China): The role of particle size fractions

The fate and risk in the environment of potentially toxic metals (PTMs) pollutants depends on the size-fractions of contaminated soil. In this study, the variable micro-nano size-fractions of 50-250 μm, 5-50 μm, 1-5 μm, <1 μm in long-term Pb-contaminated alkaline soil (NW China) were obtained by Sequential Wet Sieving Separation Procedure (SWSSP). The chemical speciation, mobility and risk of PTMs in micro-nano particle fractions as well as their uptaken and translocation in Maize (Zea mays L.) plant were systematically determined. The results demonstrated that higher accumulation of both investigated PTMs was observed in the fine fractions of <1 μm. The metallic Pb predominantly occurred in all size-fractions (65%-86%) identified by XPS, and the reducible forms of lead oxide (Ⅱ,Ⅳ) would also likely preferred to enrich in the fine fraction of <1 μm. The mobility and bioaccessibility of PTMs in fine fraction of <1 μm were higher than other fractions, which were identified by the multi-indices, enrichment factor (EF), accumulation factor (AF), mobility factor (MF), potential ecological risk index of single metal (E_rⁱ) and the comprehensive potential ecological risk index (RI). The scenario for phyto-uptake of Pb and Cu in <1 μm soil nanoparticles under pot tests indicated that the Pb and Cu enriched in <1 μm with high ecological risk were inclined to translocate into the Maize roots and shoots with nano size fractions. The results implied that further environmental management should be needed in order to prevent the risk of PTMs from Pb-bearing micro-nano size fractions in the industrial contaminated alkaline soil.

Laser-induced breakdown spectroscopy as a straightforward bioimaging tool for plant biologists; the case study for assessment of photon-upconversion nanoparticles in Brassica oleracea L. plant

The main purpose of this work is to thoroughly describe the implementation protocol of laser-induced breakdown spectroscopy (LIBS) method in the plant analysis. Numerous feasibility studies and recent progress in instrumentation and trends in chemical analysis make LIBS an established method in plant bioimaging. In this work, we present an easy and straightforward phytotoxicity case study with a focus on LIBS method. We intend to demonstrate in detail how to manipulate with plants after exposures and how to prepare them for analyses. Moreover, we aim to achieve 2D maps of spatial element distribution with a good resolution without any loss of sensitivity. The benefits of rapid, low-cost bioimaging are highlighted. In this study, cabbage (Brassica oleracea L.) was treated with an aqueous dispersion of photon-upconversion nanoparticles (NaYF₄ doped with Yb³⁺ and Tm³⁺ coated with carboxylated silica shell) in a hydroponic short-term toxicity test. After a 72-hour plant exposure, several macroscopic toxicity end-points were monitored. The translocation of Y, Yb, and Tm across the whole plant was set by employing LIBS with a lateral resolution 100 µm. The LIBS maps of rare-earth elements in B.oleracea plant grown with 50 μg/mL nanoparticle-treated and ion-treated exposures showed the root as the main storage, while the transfer via stem into leaves was minimal. On the contrary, the LIBS maps of plants exposed to the 500 μg/mL nanoparticle-treated and ion-treated uncover slightly different trends, nanoparticles as well as ions were transferred through the stem into leaves. However, the main storage organ was a root as well.

Dissolution of Ag Nanoparticles in Agricultural Soils and Effects on Soil Exoenzyme Activities

To assess environmental risks related to the mobility and toxicity of AgNPs, the chemical availability of AgNPs and polyvinylpyrrolidone-coated AgNPs (PVP-AgNPs) in three agricultural soils was quantified in a pot experiment. Porewater collection and soil extractions with 0.01 M CaCl2, 0.4 M Glycine (pH 1.5) and 0.05 M NH4-EDTA were performed. The effect on soil exoenzyme activities was also assessed. Porewater concentration was low (<0.4% and <0.04% of dosed Ag, for AgNPs and PVP-AgNPs, respectively) and only detected in acidic soils (pH 4.4 and 4.9). The PVP-coating reduced the downward mobility of AgNPs in soil and possibly also their dissolution rate (and subsequent release of dissolved Ag+ ions into porewater). The effect of variation in organic matter on soil enzymatic activity was larger than that of AgNPs, as no significant additional inhibitory effect from Ag could be observed. Only at low pH and in the presence of complexing ligands that form very stable Ag complexes (0.4 M Glycine extraction at pH 1.5) up to 58% of the Ag added to soil was released (independently of PVP coating). An extraction with glycine is proposed as a useful indicator of potentially available Ag in soils.

Investigation of pore water and soil extraction tests for characterizing the fate of poorly soluble metal-oxide nanoparticles

Here we compared the efficiency of Cu extraction (dissolved + particulate) from two soils dosed with CuO nanoparticles (NPs) at 50 or 250 mg kg^-1 by pore water collection, and single- and multi-step soil extraction tests. Pore water collection recovered low levels of Cu (<0.18%, regardless of soil type or Cu dose). Single soil extraction by either CaCl₂ or DI water led to higher Cu recovery than pore water collection, but still <3% of total dose. These methods were useful for assessing the labile Cu ions pool. This fraction is controlled by Cu²⁺ dissolved from CuO NPs and it varies with time and soil type. Particulate Cu was poorly retrieved (<0.7%) by pore water extraction and by single-step soil extraction using CaCl₂ solution or water. Multi-step extraction including dispersing and metal-chelating agents allowed for simultaneous characterization of dissolved Cu (total ionic Cu²⁺, 24-49% of dosed Cu), extractable CuO NPs (reversibly attached, 15-26% of dosed Cu), and non-extractable CuO NPs (irreversibly attached, 36-50% of dosed Cu), and it could describe the aging of NPs along 30 d. This method extracted a significantly higher concentration of Cu than pore water collection and was less sensitive to method parameters (e.g. filtration). This multi-step method can reduce pore water extraction-related factors that may confound the interpretation of environmental exposure data in NPs studies, and describe upper limits of both exchangeable Cu²⁺ and dispersible CuO NPs in soil that can potentially become bioavailable to plants and organisms and thus provide a sounder basis for risks evaluations.

The chronic effects of CuO and ZnO nanoparticles on Eisenia fetida in relation to the bioavailability in aged soils

The bioavailability and bioaccumulation of metal-based engineered nanoparticles (ENPs) in soils need to be evaluated in environmentally relevant scenarios. The aim of this study was an analysis of potentially available metal-component ENPs (nano-ZnO and nano-CuO) in soils. Earthworms (Eisenia fetida) were used to examine the bioaccumulation potential of ENPs. Micro-particles (micro-ZnO and micro-CuO) and metal salts (ZnCl₂ and CuCl₂) were used to evaluate the nano-effect and the activity of dissolved ions, respectively. Zn- and Cu-compounds were added to sandy loam and silt loam at a concentration of 10 mg kg^-1. The bioavailable fractions of metals were extracted from soil using H₂O, MgCl₂ with CH₃COONa or EDTA. EDTA was the most effective extractant of Zn and Cu (10.06-11.65 mg Zn kg^-1 and 2.69-3.52 mg Cu kg^-1), whereas the H₂O-extractable metal concentration was at the lowest level (1.98-2.12 mg Zn kg^-1 and 0.54-0.82 Cu mg kg^-1). The bioavailable metal concentrations were significantly higher in silt loam than sandy loam soil, which was related to the higher pH value of silt. There were no significant differences between the Zn content in the earthworms incubated in the two soils, which may confirm the auto-regulation of the Zn content by earthworms. However, the bioaccumulation of Cu was strongly correlated with the extractable Cu concentrations. The juvenile earthworms accumulated Cu and Zn more than adults. Based on our results, aging neutralized the differences between the ionic and particulate effects of metal-compounds.

Analysis of complex particle mixtures by asymmetrical flow field-flow fractionation coupled to inductively coupled plasma time-of-flight mass spectrometry

Asymmetrical flow field-flow fractionation (AF4) hyphenated with inductively coupled plasma-mass spectrometry (ICP-MS) has been widely used to characterize metal containing particles. This study demonstrates the advantages of coupling AF4 with ICP-time-of-flight mass spectrometry (ICP-TOFMS) in standard and single particle modes to determine size distribution, elemental composition, and number concentration of composite particles. The coupled system was used to characterize two complex particle mixtures. The first mixture consisted of particles extracted from micro-alloyed steels with two size populations of different elemental composition. The second mixture consisted of particles extracted from soil spiked with various engineered nanoparticles (ENPs). The equivalent hydrodynamic sizes of individual micro-alloyed steel particles were up to 6 times larger than the sizes determined by single particle (sp)-ICP-TOFMS. The larger AF4 sizes were attributed to the presence of a surface coating, which is not reflected in the core size determined by sp-ICP-TOFMS. Two particle populations could not be separated by AF4 due to their broad size distributions but were resolved by sp-ICP-TOFMS using their unique elemental signatures. Multi-angle light scattering and ICP-TOFMS signals of soil suspensions increased with the spiked ENP concentrations. However, only after conducting full element screening and single particle fingerprinting by ICP-TOFMS could this increase be attributed to enhanced extraction efficiency of natural particles and the risk for false conclusions be eliminated. In this study, we describe how AF4 coupled to ICP-TOFMS can be applied to study complex samples of inorganic particles which contain organic compounds.

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.

Impact of TiO2 and ZnO Nanoparticles on Soil Bacteria and the Enantioselective Transformation of Racemic-Metalaxyl in Agricultural Soil with Lolium perenne: A Wild Greenhouse Cultivation

The effects of TiO₂ and ZnO nanoparticles on soil bacteria and enantioselective transformation of racemic-metalaxyl (rac-metalaxyl) in agricultural soil with or without Lolium perenne were investigated in an outdoor greenhouse. After a 70-day exposure to 2‰ ZnO, microbial biomass carbon decreased by 66% and bacterial community composition significantly changed. Meanwhile, ZnO decreased chlorophyll cumulation in L. perenne by 34%. ZnO also inhibited the enantioselective transformation of metalaxyl enantiomers and changed the enantiomer fraction of metalaxyl. TiO₂ showed similar effects but to a lesser extent. L. perenne promoted the transformation of rac-metalaxyl and ingested TiO₂ and ZnO. L. perenne changed the bacterial co-occurrence networks and biomarkers in native soil and soil exposed to TiO₂ and ZnO. L. perenne reduced the inhibition effects of TiO₂ and ZnO on the transformation of rac-metalaxyl. The decrease in the relative abundance of soil keystone taxa such as Acidobacteria and Gemmatimonas might respond to the corresponding slow transformation of rac-metalaxyl in soils exposed to TiO₂ and ZnO, regardless of L. perenne. Our results demonstrated the existence of mutual interactions among the impact of engineered nanoparticles on different components (microbes, plants, and coexisting pollutants) in the terrestrial ecosystem.

Nanoparticle Charge and Size Control Foliar Delivery Efficiency to Plant Cells and Organelles

Fundamental and quantitative understanding of the interactions between nanoparticles and plant leaves is crucial for advancing the field of nanoenabled agriculture. Herein, we systematically investigated and modeled how ζ potential (-52.3 mV to +36.6 mV) and hydrodynamic size (1.7-18 nm) of hydrophilic nanoparticles influence delivery efficiency and pathways to specific leaf cells and organelles. We studied interactions of nanoparticles of agricultural interest including carbon dots (CDs, 0.5 and 5 mg/mL), cerium oxide (CeO₂, 0.5 mg/mL), and silica (SiO₂, 0.5 mg/mL) nanoparticles with leaves of two major crop species having contrasting leaf anatomies: cotton (dicotyledon) and maize (monocotyledon). Biocompatible CDs allowed real-time tracking of nanoparticle translocation and distribution in planta by confocal fluorescence microscopy at high spatial (∼200 nm) and temporal (2-5 min) resolution. Nanoparticle formulations with surfactants (Silwet L-77) that reduced surface tension to 22 mN/m were found to be crucial for enabling rapid uptake (<10 min) of nanoparticles through the leaf stomata and cuticle pathways. Nanoparticle-leaf interaction (NLI) empirical models based on hydrodynamic size and ζ potential indicate that hydrophilic nanoparticles with <20 and 11 nm for cotton and maize, respectively, and positive charge (>15 mV), exhibit the highest foliar delivery efficiencies into guard cells (100%), extracellular space (90.3%), and chloroplasts (55.8%). Systematic assessments of nanoparticle-plant interactions would lead to the development of NLI models that predict the translocation and distribution of nanomaterials in plants based on their chemical and physical properties.

A Review of Metal and Metal-Oxide Nanoparticle Coating Technologies to Inhibit Agglomeration and Increase Bioactivity for Agricultural Applications

Coatings offer a means to control nanoparticle (NP) size, regulate dissolution, and mitigate runoff when added to crops through soil. Simultaneously, coatings can enhance particle binding to plants and provide an additional source of nutrients, making them a valuable component to existing nanoparticle delivery systems. Here, the surface functionalization of metal and metal-oxide nanoparticles to inhibit aggregation and preserve smaller agglomerate sizes for enhanced transport to the rooting zone and improved uptake in plants is reviewed. Coatings are classified by type and by their efficacy to mitigate agglomeration in soils with variable pH, ionic concentration, and natural organic matter profiles. Varying degrees of success have been reported using a range of different polymers, biomolecules, and inorganic surface coatings. Advances in zwitterionic coatings show the best results for maintaining nanoparticle stability in solutions even under high salinity and temperature conditions, whereas coating by the soil component humic acid may show additional benefits such as promoting dissolution and enhancing bioavailability in soils. Pre-tuning of NP surface properties through exposure to select natural organic matter, microbial products, and other biopolymers may yield more cost-effective nonagglomerating metal/metal-oxide NPs for soil applications in agriculture.

Transformation pathways and fate of engineered nanoparticles (ENPs) in distinct interactive environmental compartments: A review

The ever increasing production and use of nano-enabled commercial products release the massive amount of engineered nanoparticles (ENPs) in the environment. An increasing number of recent studies have shown the toxic effects of ENPs on different organisms, raising concerns over the nano-pollutants behavior and fate in the various environmental compartments. After the release of ENPs in the environment, ENPs interact with various components of the environment and undergoes dynamic transformation processes. This review focus on ENPs transformations in the various environmental compartments. The transformation processes of ENPs are interrelated to multiple environmental aspects. Physical, chemical and biological processes such as the homo- or hetero-agglomeration, dissolution/sedimentation, adsorption, oxidation, reduction, sulfidation, photochemically and biologically mediated reactions mainly occur in the environment consequently changes the mobility and bioavailability of ENPs. Physico-chemical characteristics of ENPs (particle size, surface area, zeta potential/surface charge, colloidal stability, and core-shell composition) and environmental conditions (pH, ionic strength, organic and inorganic colloids, temperature, etc.) are the most important parameters which regulated the ENPs environmental transformations. Meanwhile, in the environment, organisms encountered multiple transformed ENPs rather than the pristine nanomaterials due to their interactions with various environmental materials and other pollutants. Thus it is the utmost importance to study the behavior of transformed ENPs to understand their environmental fate, bioavailability, and mode of toxicity.

Energy reserves and respiration rate in the earthworm Eisenia andrei after exposure to zinc in nanoparticle or ionic form

The energy budget is an indicator of an organism's overall condition. Changes in energy reserves and/or energy consumption have been used as biomarkers of toxic stress. To understand the effects of different forms and concentrations of Zn and the costs of effective Zn regulation by the earthworm Eisenia andrei, we performed a toxicokinetic experiment in which individuals were sampled over time to determine the available energy reserves (total carbohydrate, protein, and lipid content), energy consumption (measured at the cellular level and as the whole-animal respiration rate), and internal Zn concentration. The earthworms were exposed to ZnCl2 or zinc nanoparticles (ZnO-NPs) in Lufa 2.2 soil for 21 days (contamination phase), followed by 14 days of elimination in clean soil (decontamination phase). Carbohydrates were the only energy reserves with significantly lower levels following ZnO-NP 1000 treatment than following other treatments (p ≤ 0.00001) in the contamination phase. The total available energy reserves and protein content did not differ among treatments, but a significant effect of exposure time was observed (p ≤ 0.0001). Exposure to Zn (both ions and NPs) increased energy consumption at the cellular level, reflecting the high energy demand of the stress response. The results indicated that E. andrei can regulate internal Zn concentrations efficiently, regardless of form or concentration, without considerable impact on energy reserves or respiration rate.

CuO Nanoparticle Dissolution and Toxicity to Wheat ( Triticum aestivum) in Rhizosphere Soil

It has been suggested, but not previously measured, that dissolution kinetics of soluble nanoparticles such as CuO nanoparticles (NPs) in soil affect their phytotoxicity. An added complexity is that such dissolution is also affected by the presence of plant roots. Here, we measured the rate of dissolution of CuO NPs in bulk soil, and in soil in which wheat plants ( Triticum aestivum) were grown under two soil NP dosing conditions: (a) freshly added CuO NPs (500 mg Cu/kg soil) and (b) CuO NPs aged for 28 d before planting. At the end of the plant growth period (14 d), available Cu was measured in three different soil compartments: bulk (not associated with roots), loosely attached to roots, and rhizosphere (soil firmly attached to roots). The labile Cu fraction increased from 17 mg/kg to 223 mg/kg in fresh treatments and from 283 mg/kg to 305 mg/kg in aged treatments over the growth period due to dissolution. Aging CuO NPs increased the toxicity to Triticum aestivum (reduction in root maximal length). The presence of roots in the soil had opposite and somewhat compensatory effects on NP dissolution, as measured in rhizosphere soil. pH increased 0.4 pH units for fresh NP treatments and 0.6 pH units for aged NPs. This lowered CuO NP dissolution in rhizosphere soil. Exudates from T. aestivum roots also increased soluble Cu in pore water. CaCl₂ extractable Cu concentrations increaed in rhizosphere soil compared to bulk soil, from 1.8 mg/kg to 6.2 mg/kg in fresh treatment and from 3.4 mg/kg to 5.4 mg/kg in aged treatments. Our study correlated CuO NP dissolution and the resulting Cu ion exposure profile to phytotoxicity, and showed that plant-induced changes in rhizosphere conditions should be considered when measuring the dissolution of CuO NPs near roots.

Uptake of Engineered Nanoparticles by Food Crops: Characterization, Mechanisms, and Implications

With the rapidly increasing demand for and use of engineered nanoparticles (NPs) in agriculture and related sectors, concerns over the risks to agricultural systems and to crop safety have been the focus of a number of investigations. Significant evidence exists for NP accumulation in soils, including potential particle transformation in the rhizosphere and within terrestrial plants, resulting in subsequent uptake by plants that can yield physiological deficits and molecular alterations that directly undermine crop quality and food safety. In this review, we document in vitro and in vivo characterization of NPs in both growth media and biological matrices; discuss NP uptake patterns, biotransformation, and the underlying mechanisms of nanotoxicity; and summarize the environmental implications of the presence of NPs in agricultural ecosystems. A clear understanding of nano-impacts, including the advantages and disadvantages, on crop plants will help to optimize the safe and sustainable application of nanotechnology in agriculture for the purposes of enhanced yield production, disease suppression, and food quality.

Impact of Nanoparticle Surface Properties on the Attachment of Cerium Oxide Nanoparticles to Sand and Kaolin

Soil texture has been found to be a critical factor in regulating the fate and transport of cerium oxide nanoparticles (CeONPs) in the terrestrial environment. However, the underlying mechanisms for the interactions between CeONPs and different components of soil are still poorly understood. The attachment of CeONPs onto two typical components of soil (sand and kaolin) in batch experiments were investigated to provide insights into the retention and bioavailability of CeONPs in soil. Surface properties of CeONPs, including surface charge and surface coating condition, had strong impacts on the interactions between CeONPs and soil particles. Positively charged CeONPs [CeONPs(+)] displayed the greatest attachment onto kaolin, whereas the negatively charged CeONPs [CeONPs(-)] showed poorest attachment onto sand. The attachment of CeONPs onto kaolin was significantly greater than onto sand, irrespective of surface charge. Homoaggregation of CeONPs increased the size of CeONPs on the surface of sand and kaolin. Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) calculations agreed with the experimental observations that surface charge and coating condition of CeONPs played a vital role in the homoaggregation and adsorption of CeONPs. For CeONPs(-) coated with polyvinylpyrrolidone (PVP), the steric repulsion between soil particles and CeONPs increases rapidly with the increase of maximum surface concentration of PVP. Adsorption isothermal fittings indicated that the adsorption of CeONPs onto sand and kaolin can be properly described by the Dubinin-Radushkevich isotherm. The results obtained in this study are crucial for the understanding of the fate and transport of engineered nanomaterials in the environment.

In Vivo Tracking of Copper-64 Radiolabeled Nanoparticles in Lactuca sativa

Engineered nanoparticles (NPs) are increasingly used in commercial products including automotive lubricants, clothing, deodorants, sunscreens, and cosmetics and can potentially accumulate in our food supply. Given their size it is difficult to detect and visualize the presence of NPs in environmental samples, including crop plants. New analytical tools are needed to fill the void for detection and visualization of NPs in complex biological and environmental matrices. We aimed to determine whether radiolabeled NPs could be used as a noninvasive, highly sensitive analytical tool to quantitatively track and visualize NP transport and accumulation in vivo in lettuce (Lactuca sativa) and to investigate the effect of NP size on transport and distribution over time using a combination of autoradiography, positron emission tomography (PET)/computed tomography (CT), scanning electron microscopy (SEM), and transition electron microscopy (TEM). Azide functionalized NPs were radiolabeled via a "click" reaction with copper-64 (64Cu)-1,4,7-triazacyclononane triacetic acid (NOTA) azadibenzocyclooctyne (ADIBO) conjugate ([64Cu]-ADIBO-NOTA) via copper-free Huisgen-1,3-dipolar cycloaddition reaction. This yielded radiolabeled [64Cu]-NPs of uniform shape and size with a high radiochemical purity (>99%), specific activity of  2.2 mCi/mg of NP, and high stability (i.e., no detectable dissolution) over 24 h across a pH range of 5-9. Both PET/CT and autoradiography showed that [64Cu]-NPs entered the lettuce seedling roots and were rapidly transported to the cotyledons with the majority of the accumulation inside the roots. Uptake and transport of intact NPs was size-dependent, and in combination with the accumulation within the roots suggests a filtering effect of the plant cell walls at various points along the water transport pathway.

Engineered nano particles: Nature, behavior, and effect on the environment

Increased application of engineered nano particles (ENPs) in production of various appliances and consumer items is increasing their presence in the natural environment. Although a wide variety of nano particles (NPs) are ubiquitously dispersed in ecosystems, risk assessment guidelines to describe their ageing, direct exposure, and long-term accumulation characteristics are poorly developed. In this review, we describe what is known about the life cycle of ENPs and their impact on natural systems and examine if there is a cohesive relationship between their transformation processes and bio-accessibility in various food chains. Different environmental stressors influence the fate of these particles in the environment. Composition of solid media, pore size, solution chemistry, mineral composition, presence of natural organic matter, and fluid velocity are some environmental stressors that influence the transformation, transport, and mobility of nano particles. Transformed nano particles can reduce cell viability, growth and morphology, enhance oxidative stress, and damage DNA in living organisms.

Assessing the Risk of Engineered Nanomaterials in the Environment: Development and Application of the nanoFate Model

We developed a dynamic multimedia fate and transport model (nanoFate) to predict the time-dependent accumulation of metallic engineered nanomaterials (ENMs) across environmental media. nanoFate considers a wider range of processes and environmental subcompartments than most previous models and considers ENM releases to compartments (e.g., urban, agriculture) in a manner that reflects their different patterns of use and disposal. As an example, we simulated ten years of release of nano CeO₂, CuO, TiO₂, and ZnO in the San Francisco Bay area. Results show that even soluble metal oxide ENMs may accumulate as nanoparticles in the environment in sufficient concentrations to exceed the minimum toxic threshold in freshwater and some soils, though this is more likely with high-production ENMs such as TiO₂ and ZnO. Fluctuations in weather and release scenario may lead to circumstances where predicted ENM concentrations approach acute toxic concentrations. The fate of these ENMs is to mostly remain either aggregated or dissolved in agricultural lands receiving biosolids and in freshwater or marine sediments. Comparison to previous studies indicates the importance of some key model aspects including climatic and temporal variations, how ENMs may be released into the environment, and the effect of compartment composition on predicted concentrations.

Time and Nanoparticle Concentration Affect the Extractability of Cu from CuO NP-Amended Soil

We assess the effect of CuO nanoparticle (NP) concentration and soil aging time on the extractability of Cu from a standard sandy soil (Lufa 2.1). The soil was dosed with CuO NPs or Cu(NO3)2 at 10 mg/kg or 100 mg/kg of total added Cu, and then extracted using either 0.01 M CaCl₂ or 0.005 M diethylenetriaminepentaacetic acid (DTPA) (pH 7.6) extraction fluid at selected times over 31 days. For the high dose of CuO NPs, the amount of DTPA-extractable Cu in soil increased from 3 wt % immediately after mixing to 38 wt % after 31 days. In contrast, the extractability of Cu(NO₃)₂ was highest initially, decreasing with time. The increase in extractability was attributed to dissolution of CuO NPs in the soil. This was confirmed with synchrotron X-ray absorption near edge structure measurements. The CuO NP dissolution kinetics were modeled by a first-order dissolution model. Our findings indicate that dissolution, concentration, and aging time are important factors that influence Cu extractability in CuO NP-amended soil and suggest that a time-dependent series of extractions could be developed as a functional assay to determine the dissolution rate constant.

Physiological and biochemical responses of sunflower (Helianthus annuus L.) exposed to nano-CeO2 and excess boron: Modulation of boron phytotoxicity

Little is known about the interaction of nanoparticles (NPs) with soil constituents and their effects in plants. Boron (B), an essential micronutrient that reduces crop production at both deficiency and excess, has not been investigated with respect to its interaction with cerium oxide NPs (nano-CeO₂). Considering conflicting results on the nano-CeO₂ toxicity and protective role as antioxidant, their possible modulation on B toxicity in sunflower (Helianthus annuus L.) was investigated. Sunflower was cultivated for 30 days in garden pots containing original or B-spiked soil amended with nano-CeO₂ at 0-800 mg kg^-1. At harvest, Ce and B concentrations in tissues, biomass, and activities of stress enzymes in leaves were determined. Results showed that in the original soil, Ce accumulated mainly in roots, with little translocation to stems and leaves, while reduced root Ce was observed in plants from B-spiked soil. In the original soil, higher levels of nano-CeO₂ reduced plant B concentration. Although morphological effects were not visible, changes in biomass and oxidative stress response were observed. Sunflower leaves from B-spiked soil showed visible symptoms of B toxicity, such as necrosis and chlorosis in old leaves, as well as an increase of superoxide dismutase (SOD) activity. However, at high nano-CeO₂ level, SOD activity decreased reaching values similar to that of the control. This study has shown that nano-CeO₂ reduced both the B nutritional status of sunflower in original soil and the B phytotoxicity in B-spiked soil.