Uptake and toxicity of nano-ZnO in the plant-feeding nematode, Xiphinema vuittenezi: the role of dissolved zinc and nanoparticle-specific effects

Influence of dissolution on the uptake of bimetallic nanoparticles Au@Ag-NPs in soil organism Eisenia fetida

A key aspect in the safety testing of metal nanoparticles (NPs) is the measurement of their dissolution and of the true particle uptake in organisms. Here, based on the tendency of Ag-NP to dissolve and Au-NP to be inert in the environment, we exposed the earthworm Eisenia fetida to Au core-Ag shell NPs (Au@Ag-NPs, Ag-NPs with a Au core) and to both single and combined exposures of non-coated Au-NPs, Ag-NPs, Ag⁺ and Au⁺ ions in natural soil. Our hypothesis was that the Ag shell would partially or completely dissolve from the Au@Ag-NPs and that the Au core would thereby behave as a tracer of particulate uptake. Au and Ag concentrations were quantified in all the soils, in soil extract and in organisms by inductively coupled plasma mass spectrometry (ICP-MS). The earthworm exposed to Au@Ag-NPs, and to all the combinations of Ag and Au, were analyzed by single particle inductively coupled plasma time-of-flight mass spectrometry (spICP-TOFMS) to allow the quantification of the metals that were truly part of a bimetallic particle. Results showed that only 5% of the total metal amounts in the earthworm were in the bimetallic particulate form and that the Ag shell increased in thickness, suggesting that biotransformation processes took place at the surface of the NPs. Additionally, the co-exposure to both metal ions led to a different uptake pattern compared to the single metal exposures. The study unequivocally confirmed that dissolution is the primary mechanism driving the uptake of (dissolving) metal NPs in earthworms. Therefore, the assessment of the uptake of metal nanoparticles is conservatively covered by the assessment of the uptake of their ionic counterpart.

How the Physicochemical Properties of Manufactured Nanomaterials Affect Their Performance in Dispersion and Their Applications in Biomedicine: A Review

The growth in novel synthesis methods and in the range of possible applications has led to the development of a large variety of manufactured nanomaterials (MNMs), which can, in principle, come into close contact with humans and be dispersed in the environment. The nanomaterials interact with the surrounding environment, this being either the proteins and/or cells in a biological medium or the matrix constituent in a dispersion or composite, and an interface is formed whose properties depend on the physicochemical interactions and on colloidal forces. The development of predictive relationships between the characteristics of individual MNMs and their potential practical use critically depends on how the key parameters of MNMs, such as the size, shape, surface chemistry, surface charge, surface coating, etc., affect the behavior in a test medium. This relationship between the biophysicochemical properties of the MNMs and their practical use is defined as their functionality; understanding this relationship is very important for the safe use of these nanomaterials. In this mini review, we attempt to identify the key parameters of nanomaterials and establish a relationship between these and the main MNM functionalities, which would play an important role in the safe design of MNMs; thus, reducing the possible health and environmental risks early on in the innovation process, when the functionality of a nanomaterial and its toxicity/safety will be taken into account in an integrated way. This review aims to contribute to a decision tree strategy for the optimum design of safe nanomaterials, by going beyond the compromise between functionality and safety.

Effects of silicon dioxide, zinc oxide and titanium dioxide nanoparticles on Meloidogyne incognita, Alternaria dauci and Rhizoctonia solani disease complex of carrot

Foliar spray of silicon dioxide (SiO₂ NPs), zinc oxide (ZnO NPs) and titanium dioxide (TiO₂ NPs) nanoparticles were used for the management of Meloidogyne incognita, Alternaria dauci and Rhizoctonia solani disease complex of carrot. Foliar spray of SiO₂ NPs/ZnO NPs or TiO₂ NPs increased plant growth attributes, chlorophyll and carotenoid of carrot. Foliar spray of 0.10 mg ml^-1 SiO₂ NPs caused the highest increase in plant growth, chlorophyll and carotenoid content of leaves followed by spray of 0.10 mg ml^-1 ZnO NPs_, 0_.05 mg ml^-1 SiO₂ NPs, 0.05 mg ml^-1 ZnO NPs, 0.10 mg ml^-1 TiO₂ NPs and 0.05 mg ml^-1 TiO2 NPs. Use of SiO₂ NPs caused a higher reduction in root galling, nematode multiplication and disease indices followed by ZnO NPs and TiO₂ NPs. Two principal components analysis showed a total of 97.84% overall data variance in plants inoculated with single pathogen and 97.20% in plants inoculated with two or more pathogens. Therefore, foliar spray of SiO₂ NPs appears interesting for the management of disease complex of carrot.

Toxicity mitigation by N-acetylcysteine and synergistic toxic effect of nano and bulk ZnO to Panagrellus redivivus

To better understand the nanosize-relevant toxic effects and underlying mechanisms, N-acetylcysteine (NAC), as a mitigation agent, an ionic form of Zn (ZnCl₂), and the binary mixture of ZnO with different particle sizes (15 nm and 140 nm), was used in toxicity assays with the nematode Panagrellus redivivus. The ZnCl₂ concentrations were applied to show the amount of dissolved Zn ions present in the test system. Reactive oxygen species (ROS) measuring method was developed to fit the used test system. Our studies have shown that NAC can mitigate the toxic effects of both studied particle sizes. In the applied concentrations, ZnCl₂ was less toxic than both of the ZnO particles. This finding indicates that not only ions and ROS produced by the dissolution are behind the toxic effects of the ZnO NPs, but also other particle size-dependent toxic effects, like the spontaneous ROS generation, are also relevant. When the two materials were applied in binary mixtures, the toxic effects increased significantly, and the dissolved zinc content and the ROS generation also increased. It is assumed that the chemical and physical properties of the materials have been mutually reinforcing to form a more reactive mixture that is more toxic to the P. redivivus test organism. Our findings demonstrate the importance of using mitigation agent and mixtures to evaluate the size-dependent toxicity of the ZnO.

Toxicity and uptake of nanoparticulate and bulk ZnO in nematodes with different life strategies

Despite the increasing number and quantity of nanomaterials released in the environment, our knowledge on their bioavailability and possible toxicity to organisms is rather limited. Thus, we know quite little about sensitivity of various nematode feeding types and life strategies to treatments with nano metal oxides. The toxicity of zinc oxide nanoparticles (nano-ZnO) (with a particle size of 25 nm) and the bulk counterpart was investigated in two free-living nematode species of different life strategies: Xiphinema vuittenezi, a K-strategist plant-feeder nematode and Panagrellus redivivus, an r-strategist bacterivor nematode. The internal zinc concentration and the concentration of minor and trace elements were determined by total reflection X-ray fluorescence spectrometry. Concentration-dependent mortality in both nematode species was observed following a 24-h exposure both to nano-ZnO and bulk ZnO. The zinc concentration of the treating suspension had a significant effect on the internal zinc content of the animals in both cases. Particle size did not influence the internal zinc content. Our results show that nano and bulk ZnO have a similar dose-response effect on mortality of the bacterivor P. redivivus. In contrast, the nano-ZnO has stronger toxic effect on the mortality of X. vuittenezi. In general, X. vuittenezi did not react more sensitively to the treatments than P. redivivus, but appeared sensitive to the nano-ZnO treatment compared to bulk ZnO.

Metallic nanoparticles influence the structure and function of the photosynthetic apparatus in plants

The applications of nanoparticles continue to expand into areas as diverse as medicine, bioremediation, cosmetics, pharmacology and various industries, including agri-food production. The widespread use of nanoparticles has generated concerns given the impact these nanoparticles - mostly metal-based such as CuO, Ag, Au, CeO₂, TiO₂, ZnO, Co, and Pt - could be having on plants. Some of the most studied variables are plant growth, development, production of biomass, and ultimately oxidative stress and photosynthesis. A systematic appraisal of information about the impact of nanoparticles on these processes is needed to enhance our understanding of the effects of metallic nanoparticles and oxides on the structure and function on the plant photosynthetic apparatus. Most nanoparticles studied, especially CuO and Ag, had a detrimental impact on the structure and function of the photosynthetic apparatus. Nanoparticles led to a decrease in concentration of photosynthetic pigments, especially chlorophyll, and disruption of grana and other malformations in chloroplasts. Regarding the functions of the photosynthetic apparatus, nanoparticles were associated with a decrease in the photosynthetic efficiency of photosystem II and decreased net photosynthesis. However, CeO₂ and TiO₂ nanoparticles may have a positive effect on photosynthetic efficiency, mainly due to an increase in electron flow between the photosystems II and I in the Hill reaction, as well as an increase in Rubisco activity in the Calvin and Benson cycle. Nevertheless, the underlying mechanisms are poorly understood. The future mechanistic work needs to be aimed at characterizing the enhancing effect of nanoparticles on the active generation of ATP and NADPH, carbon fixation and its incorporation into primary molecules such as photo-assimilates.

Evaluation of zinc oxide nanoparticles on lettuce (Lactuca sativa L.) growth and soil bacterial community

The wide spread of nanoparticles (NPs) has caused tremendous concerns on agricultural ecosystem. Some metallic NPs, such as zinc oxide (ZnO), can be utilized as a nano-fertilizer when used at optimal doses. However, little is known about the responses of plant development and concomitant soil bacteria community to ZnO NPs. The present pot experiment studied the impacts of different doses of ZnO NPs and bulk ZnO (0, 1, 10, 100 mg ZnO/kg), on the growth of lettuce (Lactuca sativa L.) and the associated rhizospheric soil bacterial community. Results showed that at a dose of 10 mg/kg, ZnO NPs and bulk ZnO, enhanced the lettuce biomass and the net photosynthetic rate; whereas, the Zn content in plant tissue was higher in NPs treatment than in their bulk counterpart at 10 mg/kg dose or higher. For the underground observations, 10 mg/kg treatment doses (NPs or bulk) significantly changed the soil bacterial community structure, despite the non-significant variations in alpha diversity. Taxonomic distribution revealed that some lineages within Cyanobacteria and other phyla individually demonstrated similar or different responses to ZnO NPs and bulk ZnO. Moreover, some lineages associated with plant growth promotion were also influenced to different extents by ZnO NPs and bulk ZnO, suggesting the distinct microbial processes occurring in soil. Collectively, this study expanded our understanding of the influence of ZnO NPs on plant performance and the associated soil microorganisms.