Tracking the Transport of Silver Nanoparticles in Soil: a Saturated Column Experiment

Silver nanoparticles in plant health: Physiological response to phytotoxicity and oxidative stress

Silver nanoparticles (AgNPs) have gained significant attention in various fields due to their unique properties, but their release into the environment has raised concerns about their environmental and biological impacts. Silver nanoparticles can enter plants following their exposure to roots or via stomata following foliar exposure. Upon penetrating the plant cells, AgNPs interact with cellular components and alter physiological and biochemical processes. One of the key concerns associated with plant exposure to AgNPs is the potential of these materials to induce oxidative stress. Silver nanoparticles can also suppress plant growth and development by disrupting essential plant physiological processes, such as photosynthesis, nutrient uptake, water transport, and hormonal regulation. In crop plants, these disruptions may, in turn, affect the productivity and quality of the harvested components and therefore represent a potential threat to agricultural productivity and ecosystem stability. Understanding the phytotoxic effects of AgNPs is crucial for assessing their environmental implications and guiding the development of safe nanomaterials. By delving into the phytotoxic effects of AgNPs, this review contributes to the existing knowledge regarding their environmental risks and promotes the advancement of sustainable nanotechnological practices.

Nano-antivirals: A comprehensive review

Nanoparticles can be used as inhibitory agents against various microorganisms, including bacteria, algae, archaea, fungi, and a huge class of viruses. The mechanism of action includes inhibiting the function of the cell membrane/stopping the synthesis of the cell membrane, disturbing the transduction of energy, producing toxic reactive oxygen species (ROS), and inhibiting or reducing RNA and DNA production. Various nanomaterials, including different metallic, silicon, and carbon-based nanomaterials and nanoarchitectures, have been successfully used against different viruses. Recent research strongly agrees that these nanoarchitecture-based virucidal materials (nano-antivirals) have shown activity in the solid state. Therefore, they are very useful in the development of several products, such as fabric and high-touch surfaces. This review thoroughly and critically identifies recently developed nano-antivirals and their products, nano-antiviral deposition methods on various substrates, and possible mechanisms of action. By considering the commercial viability of nano-antivirals, recommendations are made to develop scalable and sustainable nano-antiviral products with contact-killing properties.

Micro- and nanoplastics retention in porous media exhibits different dependence on grain surface roughness and clay coating with particle size

The presence and/or coating of natural colloids (e.g., clays and metal oxides or hydroxides) on collector surfaces has frequently been demonstrated to enhance the retention of engineered colloids that are negatively charged due to favorable electrostatic interactions. However, this work demonstrates that the presence of natural clay coating can lead to reduced or nonmonotonic retention of micro- and nanoplastics (MNPs). Column experiments were carried out to systematically investigate the transport of MNPs with different sizes in relatively smooth and rough sands that had various clay coating fractions. These coating fractions on the collector were found to significantly influence MNP retention in a complex manner that changed with the colloid size and the roughness properties of the sand. This observation was attributed to the impact of clay coatings on the roughness and morphology properties of collector surfaces that were dominant over surface charge. Scanning electron microscopy and interaction energy calculations on surfaces with pillars or valleys indicate that mechanisms that contributed to MNP retention changed with the colloid size. In particular, retention of nanosized plastics was mainly controlled by interactions on convex/concave locations that changed with the solution chemistry, whereas microsized plastics were also strongly influenced by the applied hydrodynamic torque and straining processes. Additionally, the significant sensitivity of MNP retention under a low-level ionic strength also reflects the importance of roughness and charge heterogeneities. These observations are important for investigating the mechanisms of colloid transport in natural systems that ubiquitously exhibit clay coating on their surfaces.

The Physical Modeling Analysis of Fate and Transport of Silver Nanoparticles Dispersed by Water Flow

The release of silver nanoparticles (AgNPs) from consumer products into an environment has become a central issue for many countries. Despite that the fate and behaviors of AgNPs incorporated into a wastewater have been investigated by building a model of wastewater treatment process, the transport and retention behaviors of AgNPs influenced by the water flow in a river must be understood. The physical model of simulated river to mimic a natural flow of river was proposed to investigate the behaviors of AgNP transport in the river. The results showed that the large amount of AgNPs deposited on the riverbed as Ag sediment with only 1.26% of AgNPs remained in the water flow. The elemental content of Ag freely dispersed across the riverbed increases from the upstream to downstream area of the simulated river. Verification of the spatial distribution of Ag dispersed along the water flow may contribute to a better understanding of the fate and transport of AgNPs in the aquatic environment.

Transport and retention of polymeric and other engineered nanoparticles in porous media

Increasing applications of nanoparticles (NPs) in agriculture have raised potential risks to soil and aquatic ecosystems. A comparative study examining the transport of commonly used NPs in porous media is of critical significance for their application and regulation in agroecosystems. In this study, laboratory column leaching experiments were conducted to investigate the transport and retention of polysuccinimide NPs (PSI-NPs) in two saturated porous media with different grain sizes, as compared with multi-walled carbon nanotubes (MWCNTs), nano-Ag and nano-TiO₂. Zeta potential of the NPs was negative at pH_6.3 and decreased in an order of PSI-NPs > nano-TiO₂ > MWCNTs > nano-Ag. The coarse and fine sands used in this study had negative charges with similar zeta potentials. The movement of NPs was affected by grain size, with larger sizes facilitating mobility while finer sizes favoring retention of NPs in the porous matrix. The retention profile significantly varied between the two sand columns, with more NPs transported to deeper layers in the coarse sand than the fine sand. The relative percentage of NPs detected in leachate was found to be positively correlated with the zeta potential of NPs (r = 0.931). Among the NPs, nano-Ag had the most negative zeta potential, and therefore was the most mobile, followed by MWCNTs and nano-TiO₂. Having the least negative zeta potential, PSI-NPs had the lowest mobility, as compared with other NPs regardless of matrix grain size. This work reveals grain size and zeta potential of NPs are major factors that influence transport of NPs along the vertical porous profile, as well as demonstrating the relative unimportance of NP composition, which could serve as important guideline in nanomaterials application, risk assessment, and waste management in agroecosystems.

Zinc oxide nanoparticles: potential effects on soil properties, crop production, food processing, and food quality

The use of zinc oxide nanoparticles (ZnO NPs) is expected to increase soil fertility, crop productivity, and food quality. However, the potential effects of ZnO NP utilization should be deeply understood. This review highlights the behavior of ZnO NPs in soil and their interactions with the soil components. The review discusses the potential effects of ZnO NPs on plants and their mechanisms of action on plants and how these mechanisms are related to their physicochemical properties. The impact of current applications of ZnO NPs in the food industry is also discussed. Based on the literature reviewed, soil properties play a vital role in dispersing, aggregation, stability, bioavailability, and transport of ZnO NPs and their release into the soil. The transfer of ZnO NPs into the soil can affect the soil components, and subsequently, the structure of plants. The toxic effects of ZnO NPs on plants and microbes are caused by various mechanisms, mainly through the generation of reactive oxygen species, lysosomal destabilization, DNA damage, and the reduction of oxidative stress through direct penetration/liberation of Zn2+ ions in plant/microbe cells. The integration of ZnO NPs in food processing improves the properties of the relative ZnO NP-based nano-sensing, active packing, and food/feed bioactive ingredients delivery systems, leading to better food quality and safety. The unregulated/unsafe discharge concentrations of ZnO NPs into the soil, edible plant tissues, and processed foods raise environmental/safety concerns and adverse effects. Therefore, the safety issues related to ZnO NP applications in the soil, plants, and food are also discussed.

Evidence on enhanced transport and release of silver nanoparticles by colloids in soil due to modification of grain surface morphology and co-transport

Natural soils have frequently been considered to decrease the mobility of engineered nanoparticles (NPs) in comparison to quartz sand due to the presence of colloids that provide additional retention sites. In contrast, this study demonstrates that the transport and release of silver nanoparticles (AgNPs) in sandy clay loam and loamy sand soils were enhanced in the presence of soil colloids that altered soil grain surface roughness. In particular, we found that the retention of AgNPs in purified soils (colloid-free and acid-treated) was more pronounced than in raw (untreated) soils or soils treated to remove organic matter (H₂O₂ or 600 °C treated). Chemical analysis and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy demonstrated that the grain surfaces of raw and organic matter-removed soils were abundant with metal oxides and colloids compared to purified soil. Column transport and release experimental results, SEM images, and interaction energy calculations revealed that a significant amount of concave locations on purified soils hindered AgNP release by diffusion or ionic strength (IS) reduction due to deep primary energy minima. Conversely, AgNPs that were retained in soils in the presence of soil colloids were more susceptible to release under IS reduction because the primary minimum was shallow on the tops of convex locations created by attached soil colloids. Additionally, a considerable fraction of retained AgNPs in raw soil was released after cation exchange followed by IS reduction, while no release occurred for purified soil under the same conditions. The AgNP release was highly associated with soil colloids and co-transport of AgNPs and soil colloids was observed. Our work is the first to show that the presence of soil colloids can inhibit deposition and facilitate the release and co-transport of NPs in soil by alteration of the soil grain surface morphology and shallow primary minimum interactions.

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.

Nano-Fertilization as an Emerging Fertilization Technique: Why Can Modern Agriculture Benefit from Its Use?

There is a need for a more innovative fertilizer approach that can increase the productivity of agricultural systems and be more environmentally friendly than synthetic fertilizers. In this article, we reviewed the recent development and potential benefits derived from the use of nanofertilizers (NFs) in modern agriculture. NFs have the potential to promote sustainable agriculture and increase overall crop productivity, mainly by increasing the nutrient use efficiency (NUE) of field and greenhouse crops. NFs can release their nutrients at a slow and steady pace, either when applied alone or in combination with synthetic or organic fertilizers. They can release their nutrients in 40–50 days, while synthetic fertilizers do the same in 4–10 days. Moreover, NFs can increase the tolerance of plants against biotic and abiotic stresses. Here, the advantages of NFs over synthetic fertilizers, as well as the different types of macro and micro NFs, are discussed in detail. Furthermore, the application of NFs in smart sustainable agriculture and the role of NFs in the mitigation of biotic and abiotic stress on plants is presented. Though NF applications may have many benefits for sustainable agriculture, there are some concerns related to the release of nanoparticles (NPs) from NFs into the environment, with the subsequent detrimental effects that this could have on both human and animal health. Future research should explore green synthesized and biosynthesized NFs, their safe use, bioavailability, and toxicity concerns.

Silver-Based Nanomaterials as Therapeutic Agents Against Coronaviruses: A Review

Since the identification of the first human coronavirus in the 1960s, a total of six coronaviruses that are known to affect humans have been identified: 229E, OC43, severe acute respiratory syndrome coronavirus (SARS-CoV), NL63, HKU1, and Middle East respiratory syndrome coronavirus (MERS-CoV). Presently, the human world is affected by a novel version of the coronavirus family known as SARS-CoV-2, which has an extremely high contagion rate. Although the infection fatality rate (IFR) of this rapidly spreading virus is not high (ranging from 0.00% to 1.54% across 51 different locations), the increasing number of infections and deaths has created a worldwide pandemic situation. To provide therapy to severely infected patients, instant therapeutic support is urgently needed and the repurposing of already approved drugs is presently in progress. In this regard, the development of nanoparticles as effective transporters for therapeutic drugs or as alternative medicines is highly encouraged and currently needed. The size range of the viruses is within 60-140 nm, which is slightly larger than the diameters of nanoparticles, making nanomaterials efficacious tools with antiviral properties. Silver-based nanomaterials (AgNMs) demonstrate antimicrobial and disinfectant effects mostly by generating reactive oxygen species (ROS) and are presently considered as a versatile tool for the treatment of COVID-19 patients. Other metal-based nanoparticles have been primarily reported as delivery agents or surface modifying agents, vaccine adjuvant against coronavirus. The present review summarizes and discusses the possible effectiveness of various surface-modified AgNMs against animal coronaviruses and presents a concept for AgNM-based therapeutic treatment of SARS-CoV-2 in the near future.

Bioturbation of Ag2S-NPs in soil columns by earthworms

Sewage sludge contains Ag₂S-NPs causing NP exposure of soil fauna when sludge is applied as soil amendment. Earthworm bioturbation is an important process affecting many soil functions. Bioturbation may be affected by the presence of Ag₂S-NPs, but the earthworm activity itself may also influence the displacement of these NPs that otherwise show little transport in the soil. The aim of this study was to determine effects of Ag₂S-NPs on earthworm bioturbation and effect of this bioturbation on the vertical distribution of Ag₂S-NPs. Columns (12 cm) of a sandy loamy soil with and without Lumbricus rubellus were prepared with and without 10 mg Ag kg^-1, applied as Ag₂S-NPs in the top 2 cm of the soil, while artificial rainwater was applied at ∼1.2 mm day^-1. The soil columns were sampled at three depths weekly for 28 days and leachate collected from the bottom. Total Ag measurements showed more displacement of Ag to deeper soil layers in the columns with earthworms. The application of rain only did not significantly affect Ag transport in the soil. No Ag was detected in column leachates. X-ray tomography showed that changes in macro porosity and pore size distribution as a result of bioturbation were not different between columns with and without Ag₂S-NPs. Earthworm activity was therefore not affected by Ag₂S-NPs at the used exposure concentration. Ag concentrations along the columns and the earthworm density allowed the calculation of the bioturbation rate. The effect on the Ag transport in the soil shows that earthworm burrowing activity is a relevant process that must be taken into account when studying the fate of nanoparticles in soils.