AgNPs In Soils Research Articles

Greater Bioaccessibility of Silver Nanoparticles in Earthworm than in Soils.

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

Biological transfer of silver under silver nanoparticle exposure and nitrogen transfer via a collembolan-predatory mite food-chain and ecotoxicity of silver sulfide

The development of nanotechnology has accelerated the use of silver nanoparticles (AgNPs) in household chemicals and the accumulation of Ag in sewage treatment systems. The application of sewage sludge products to soils raises concerns over the safety of Ag in the function and biogeochemical cycles of the soil belowground ecosystem. Here, we assess the potential risk of the accumulation and transfer of Ag under AgNPs exposure and its effects on the trophic transfer of nitrogen (N) through a soil animal food chain (Folsomia candida-Hypoaspis aculeifer). The formation of stable silver sulfide (Ag2S) was also studied via a single species test using F. candida. Concentrations of Ag in F. candida increased with increasing AgNPs concentration, as did those in the predator H. aculeifer, but the Ag bioaccumulation factors of both animals were < 1. Folsomia candida body tissue 15N abundance declined markedly compared with that of H. aculeifer. Silver sulfide did have adverse effects on the survival and reproduction of F. candida. The Ag concentrations of F. candida increased with increasing Ag2S concentration in sludge-treated soils. Silver sulfide showed ecotoxicity to the collembolan, therefore ecotoxicity resulting from the transformation and fate of AgNPs in soils needs to be considered before biosolid products are applied to agricultural soils.

Significant contribution of metastable particulate organic matter to natural formation of silver nanoparticles in soils

Particulate organic matter (POM) is distributed worldwide in high abundance. Although insoluble, it could serve as a redox mediator for microbial reductive dehalogenation and mineral transformation. Quantitative information on the role of POM in the natural occurrence of silver nanoparticles (AgNPs) is lacking, but is needed to re-evaluate the sources of AgNPs in soils, which are commonly considered to derive from anthropogenic inputs. Here we demonstrate that POM reduces silver ions to AgNPs under solar irradiation, by producing superoxide radicals from phenol-like groups. The contribution of POM to the naturally occurring AgNPs is estimated to be 11–31%. By providing fresh insight into the sources of AgNPs in soils, our study facilitates unbiased assessments of the fate and impacts of anthropogenic AgNPs. Moreover, the reducing role of POM is likely widespread within surface environments and is expected to significantly influence the biogeochemical cycling of Ag and other contaminants that are reactive towards phenol-like groups.

Extraction Method Development for Quantitative Detection of Silver Nanoparticles in Environmental Soils and Sediments by Single Particle Inductively Coupled Plasma Mass Spectrometry.

For understanding the environmental behavior and toxicity of Ag nanoparticles (Ag-NPs), a quantitative method for characterizing the AgNPs in soils and sediments is urgently needed. In this study, we validated a previously developed extraction method by optimizing the extraction of silver nanoparticles from soil and sediment samples to which engineered AgNPs had been added. The samples were analyzed by single particle inductively coupled plasma mass spectrometry (SP-ICP-MS). Initially, different extraction conditions were evaluated to validate the optimal extraction procedure. Then the optimal extraction procedure was applied to environmental soil and sediment samples spiked with AgNPs. The extraction data for Ag-NPs with sizes below 30 nm was not shown due to the particle size detection limit of the SP-ICP-MS method (∼20 nm). The number concentrations of Ag particles extracted from different environmental soils and sediments matrices were in the range of (12 ± 1-23 ± 1) × 107 particles/g soil. Similarly, 53.4-100.0% of the particulate Ag mass was recovered. For the relatively low Ag mass recovery of Guiyu agricultural soil, the Ag mass recovery shows great improvement (from 53.4 to 105.8%) by the soil dilution using SiO2. The optimal method was validated to be feasible for extracting Ag-NPs from environmental soils and sediments, except for the soil with high soil organic matter (SOM) content. The SiO2 dilution of soil provides a promising way to promote the extraction of Ag-NPs in soil (or sediment) with high SOM content, which could further promote the study on the environmental behavior and toxicity of Ag-NPs in soil and sediment environment.

Retention of silver nanoparticles and silver ion to natural soils: effects of soil physicochemical properties

The mass production and widespread use of silver nanoparticles (AgNPs) have led to their wide dissimilation in the subsurface environments (e.g., natural soils). The retention propensities of AgNPs in soils dictate their fate, transport, and transformation in the subsurface environments. The aim of this study was to explore the retention behaviors of AgNPs and Ag+ ion (as a comparison) in ten natural soils with different physicochemical properties, identifying which properties dominate their mobility in soils. Ten surface (0–20 cm) soils sampled across five geographical regions of China and AgNPs coated by polyvinylpyrrolidone (PVP) with an average transmission electron microscopy (TEM) diameter of ~ 10 nm were used in this study. Batch retention experiments of AgNPs and AgNO3 in ten soils (pass through 60-mesh sieve) were conducted in triplicate at 25 °C for 24 h. Multiple regression analyses of maximum retention capacity (Qmax for AgNPs or Ag+ ion) simulated by Langmuir retention models were performed to identify which soil physicochemical properties dominate the retention behavior of AgNPs and Ag+ ion. TEM combined with energy dispersive X-ray spectroscopy (EDS) analyses was applied to visually unravel the distribution and retention behavior of AgNPs on natural soils. The results of batch retention experiments showed that Langmuir model well-approximated the retention isotherms of AgNPs and Ag+ on ten soils and that the Qmax value of AgNPs was generally lower than that of Ag+ on soils. The results of multiple regression analyses showed that the retention capacity of AgNPs on soils was positively correlated with the iron oxide content, which is visually confirmed by TEM-EDS observations, whereas retention capacity of Ag+ ions was mainly related to soil organic matter (SOM) content. Maximum retention capacity of AgNPs and Ag+ ion in soils varied with soil physicochemical properties, and particularly, iron oxide and SOM contents are two pivotal parameters controlling Qmax. These findings advance our current understanding of the mechanisms controlling retention and transport of AgNPs in natural soils, which represents an important step toward predicting the fate, transport, and potential toxicity of AgNPs in the subsurface environment.

Retention of silver nano-particles and silver ions in calcareous soils: Influence of soil properties

The rapid production and application of silver nanoparticles (AgNPs) have led to significant release of AgNPs into the terrestrial environments. Once released into the soil, AgNPs could enter into different interactions with soil particles which play key roles in controlling the fate and transport of these nanoparticles. In spite of that, experimental studies on the retention of AgNPs in soils are very scarce. Hence, the key objective of this research was to find out the retention behavior of AgNPs and Ag(I) ions in a range of calcareous soils. A second objective was to determine the extent to which the physico-chemical properties of the soils influence the Ag retention parameters. To this end, isothermal batch experiments were used to determine the retention of Poly(vinylpyrrolidinone)-capped AgNPs (PVP-AgNPs) and Ag(I) ions by nine calcareous soils with a diversity of physico-chemical properties. The results revealed that the retention data for both PVP-AgNPs and Ag(I) ions were well described by the classical Freundlich and Langmuir isothermal equations. The retention of PVP-AgNPs and Ag(I) ions was positively correlated to clay and organic carbon (OC) contents as well as electrical conductivity (EC), pH, and cation exchange capacity (CEC) of the soils. Due to multicolinearity among the soil properties, principal component analysis (PCA) was used to group the soil properties which affect the retention of PVP-AgNPs and Ag(I) ions. Accordingly, we identified two groups of soil properties controlling retention of PVP-AgNPs and Ag(I) ions in the calcareous soils. The first group comprised soil solid phase parameters like clay, OC, and CEC, which generally control hetero-aggregation and adsorption reactions and the second group included soil solution variables such as EC and pH as well as Cl− and Ca2+ concentrations, which are supposed to mainly affect homo-aggregation and precipitation reactions.

Silver nanoparticles in soil: Aqueous extraction combined with single-particle ICP-MS for detection and characterization

Silver nanoparticles (AgNPs) are used in a growing number of applications and products. Previous studies showed AgNPs can leach from these products to the environment. As a result of AgNPs leaching, sediment, soil and sludge-treated soils may be contaminated with AgNPs. Methods to detect, quantify and characterize AgNPs in soil are urgently needed. This study describes the development and validation of a method for the extraction, quantification and particle size determination of AgNPs in soils. The final method consists of pre-wetting the sample followed by an aqueous extraction, using sonication to re-suspend adsorbed AgNPs, and analysis of the aqueous extract with single particle ICP-MS. Validation of the method showed that the recovery of AgNPs spiked to soil was 44% for sandy soil and 42% for clayey soil. Although this recovery is relatively low, the repeatability and reproducibility values of the particle concentration were within the limits of Horwitz ratio, which makes the method suitable for its purpose. Further, the method concentration detection limit, LODc., is 5μgkg−1 soil. The developed method can be applied in eco-toxicological and risk-assessments studies for AgNP in the soil environment.

Silver nanoparticles in soil–plant systems

Silver nanoparticles (AgNPs) have broad spectrum antimicrobial/biocidal properties against all classes of microorganisms and possess numerous distinctive physico-chemical properties compared to bulk Ag. Hence, AgNPs are among the most widely used engineered NPs in a wide range of consumer products and are expected to enter natural ecosystems including soil via diverse pathways. However, despite: (i) soil has been considered as a critical pathway for NPs environmental fate, (ii) plants (essential base component of all ecosystems) have been strongly recommended to be included for the development of a comprehensive toxicity profile for rapidly mounting NPs in varied environmental compartments, and (iii) the occurrence of an intricate relationship between “soil–plant systems” where any change in soil chemical/biological properties is bound to have impact on plant system, the knowledge about AgNPs in soils and investigations on AgNPs–plants interaction is still rare and in its rudimentary stage. To this end, the current paper: (a) overviews sources, status, fate, and chemistry of AgNPs in soils, AgNPs-impact on soil biota, (b) critically discusses terrestrial plant responses to AgNPs exposure, and (c) illustrates the knowledge-gaps in the current perspective. Based on the available literature critically appraised herein, a multidisciplinary integrated approach is strongly recommended for future research in the current direction aimed at unveiling the rapidly mounting AgNPs-fate, transformation, accumulation, and toxicity potential in “soil–plant systems,” and their cumulative impact on environmental and human health.

Soil components mitigate the antimicrobial effects of silver nanoparticles towards a beneficial soil bacterium, Pseudomonas chlororaphis O6

Silver nanoparticles (Ag NPs) are widely used for their antimicrobial activity and consequently the particles will become environmental contaminants. This study evaluated in sand and soil matrices the toxicity of 10nm spherical Ag NPs (1 and 3mg Ag/L) toward a beneficial soil bacterium, Pseudomonas chlororaphis O6. In sand, both NP doses resulted in loss in bacterial culturability whereas in a loam soil, no cell death was observed. Amendments of sand with clays (30% v/v kaolinite or bentonite) did not protect the bacterium when challenged with Ag NPs. However, culturability of the bacterium was maintained when the Ag NP-amended sand was mixed with soil pore water or humic acid. Imaging by atomic force microscopy revealed aggregation of single nanoparticles in water, and their embedding into background material when suspended in pore water and humic acids. Zeta potential measurements supported aggregation and surface charge modifications with pore water and humic acids. Measurement of soluble Ag in the microcosms and geochemical modeling to deduce the free ion concentration revealed bacterial culturability was governed by the predicted free Ag ion concentrations. Our study confirmed the importance of Ag NPs as a source of ions and illustrated that processes accounting for protection in soil against Ag NPs involved distinct NP- and ion-effects. Processes affecting NP bioactivity involved surface charge changes due to sorption of Ca2+ from the pore water leading to agglomeration and coating of the NPs with humic acid and other organic materials. Removal of bioactive ions included the formation of soluble Ag complexes with dissolved organic carbon and precipitation of Ag ions with chloride in pore water. We conclude that mitigation of toxicity of Ag NPs in soils towards a soil bacterium resides in several interactions that differentially involve protection from the Ag NPs or the ions they produce.

Sulfidation Processes of PVP-Coated Silver Nanoparticles in Aqueous Solution: Impact on Dissolution Rate

Despite the increasing use of silver nanoparticles (Ag-NPs) in nanotechnology and their toxicity to invertebrates, the transformations and fate of Ag-NPs in the environment are poorly understood. This work focuses on the sulfidation processes of PVP-coated Ag-NPs, one of the most likely corrosion phenomena that may happen in the environment. The sulfur to Ag-NPs ratio was varied in order to control the extent of Ag-NPs transformation to silver sulfide (Ag₂S). A combination of synchrotron-based X-ray Diffraction (XRD) and Extended X-ray Absorption Fine Structure spectroscopy shows the increasing formation of Ag₂S with an increasing sulfur to Ag-NPs ratio. TEM observations show that Ag₂S forms nanobridges between the Ag-NPs leading to chain-like structures. In addition, sulfidation strongly affects surface properties of the Ag-NPs in terms of surface charge and dissolution rate. Both may affect the reactivity, transport, and toxicity of Ag-NPs in soils. In particular, the decrease of dissolution rate as a function of sulfide exposure may strongly limit Ag-NPs toxicity since released Ag⁺ ions are known to be a major factor in the toxicity of Ag-NPs.