Effects of silver nanoparticles (NM-300K) on Lumbricus rubellus earthworms and particle characterization in relevant test matrices including soil

Reproductive toxicity perspectives of nanoparticles: an update

INTRODUCTION

The rapid development of nanotechnologies with their widespread prosperities has advanced concerns regarding potential health hazards of the Nanoparticles.

RESULTS

Nanoparticles are currently present in several consumer products, including medications, food, textiles, sports equipment, and electrical components. Despite the advantages of Nanoparticles, their potential toxicity has negative impact on human health, particularly on reproductive health.

CONCLUSIONS

The impact of various NPs on reproductive system function is yet to be determined. Additional research is required to study the potential toxicity of various Nanoparticles on reproductive health. The primary objective of this review is to unravel the toxic effects of different Nanoparticles on the human reproductive functions and recent investigations on the reproductive toxicity of Nanoparticles both in vitro and in vivo.

Environmental behaviors and toxic mechanisms of engineered nanomaterials in soil

Engineered nanomaterials (ENMs) are inevitably released into the environment with the exponential application of nanotechnology. Parts of ENMs eventually accumulate in the soil environment leading to potential adverse effects on soil ecology, crop production, and human health. Therefore, the safety application of ENMs on soil has been widely discussed in recent years. More detailed safety information and potential soil environmental risks are urgently needed. However, most of the studies on the environmental effects of metal-based ENMs have been limited to single-species experiments, ecosystem processes, or abiotic processes. The present review formulated the source and the behaviors of the ENMs in soil, and the potential effects of single and co-exposure ENMs on soil microorganisms, soil fauna, and plants were introduced. The toxicity mechanism of ENMs to soil organisms was also reviewed including oxidative stress, the release of toxic metal ions, and physical contact. Soil properties affect the transport, transformation, and toxicity of ENMs. Toxic mechanisms of ENMs include oxidative stress, ion release, and physical contact. Joint toxic effects occur through adsorption, photodegradation, and loading. Besides, future research should focus on the toxic effects of ENMs at the food chain levels, the effects of ENMs on plant whole-lifecycle, and the co-exposure and long-term toxicity effects. A fast and accurate toxicity evaluation system and model method are urgently needed to solve the current difficulties. It is of great significance for the sustainable development of ENMs to provide the theoretical basis for the ecological risk assessment and environmental management of ENMs.

Multigenerational exposure of Ag materials (nano and salt) in soil - environmental hazards in Enchytraeus crypticus (Oligochaeta)

Because of its properties, silver is among the most used metals both as salt and as nanomaterials (NMs), hence reaching the environment. Multigenerational (MG) exposure testing is scarce, and especially so for NMs and soil invertebrates. In this study the MG effects of Ag NMs (Ag NM300K) and Ag salt (AgNO3) were assessed, using Enchytraeus crypticus in LUFA 2.2 soil. Survival, reproduction and internal Ag concentration in the animals were measured throughout 7 generations (5 generations (F0-F4) in spiked soil plus 2 (F5-F6) in clean soil) exposed to sublethal concentrations corresponding to the reproduction EC10 and EC50 obtained in standard toxicity tests (45 and 60 mg Ag per kg soil DW for AgNO3; 20 and 60 mg Ag per kg soil DW for Ag NM300K). MG exposure caused a dose-related decrease in reproduction for both Ag forms. Ag uptake peaked in the F1 (64 days) for AgNO3 and F2 (96 days) for Ag NM300K, after which it decreased. In agreement with toxicokinetic studies, a maximum body Ag concentration was reached (20 mg Ag per kg body DW (AgNO3) and 70 mg Ag per kg body DW (Ag NM300K)) and after which detoxification mechanisms seem to be activated with elimination of Ag accompanied by a decrease in reproduction. Transfer to clean soil allowed Ag to be (fully) eliminated from the animals. This MG study confirmed the effects determined in standard reproduction toxicity tests but further allowed to monitor the dynamics between exposure and effects of the Ag materials, and how the animals seem to cope with Ag for 7 generations by compensating between detoxification and reproductive output.

Environmental effects and interaction of nanoparticles on beneficial soil and aquatic microorganisms

A steadily increasing production volume of nanoparticles reflects their numerous industrial and domestic applications. These economic successes come with the potential adverse effects on natural systems that are associated with their presence in the environment. Biological activities and effects of nanoparticles are affected by their entry method together with their specificities like their size, shape, charge, area, and chemical composition. Particles can be classified as safe or dangerous depending on their specific properties. As both aquatic and terrestrial systems suffer from organic and inorganic contamination, nanoparticles remain a sink for these contaminants. Researching the sources, synthesis, fate, and toxicity of nanoparticles has advanced significantly during the last ten years. We summarise nanoparticle pathways throughout the ecosystem and their interactions with beneficial microorganisms in this research. The prevalence of nanoparticles in the ecosystem causes beneficial microorganisms to become hazardous to their cells, which prevents the synthesis of bioactive molecules from undergoing molecular modifications and diminishes the microbe population. Recently, observed concentrations in the field could support predictions of ambient concentrations based on modeling methodologies. The aim is to illustrate the beneficial and negative effects that nanoparticles have on aqueous and terrestrial ecosystems, as well as the methods utilized to reduce their toxicity.

Management and Mitigation of Vibriosis in Aquaculture: Nanoparticles as Promising Alternatives

Vibriosis is one of the most common diseases in marine aquaculture, caused by bacteria belonging to the genus Vibrio, that has been affecting many species of economically significant aquatic organisms around the world. The prevention of vibriosis in aquaculture is difficult, and the various treatments for vibriosis have their limitations. Therefore, there is an imperative need to find new alternatives. This review is based on the studies on vibriosis, specifically on the various treatments and their limitations, as well as the application of nanoparticles in aquaculture. One of the promising nanoparticles is graphene oxide (GO), which has been used in various applications, particularly in biological applications such as biosensors, drug delivery, and potential treatment for infectious diseases. GO has been shown to have anti-bacterial properties against both Gram-positive and Gram-negative bacteria, but no research has been published that emphasizes its impact on Vibrio spp. The review aims to explore the potential use of GO for treatment against vibriosis.

Toxicokinetics and toxicodynamics of Ag nanomaterials (NM300K) in the soil environment-impact on Enchytraeus crypticus (Oligochaeta)

Silver (Ag) is one of the most used elements in the nanomaterials (NMs) form, which upon release to the environment can be harmful to organisms. We compared the toxicokinetics (TK) and toxicodynamics (TD) of Ag from AgNO₃ (0, 15, 45, 135, 405 mg Ag/kg soil) and AgNM300K (0, 75, 150, 300, 600, 1200 mg Ag/kg soil) in the model organism Enchytraeus crypticus. Organisms were exposed in LUFA 2.2 soil, and besides body Ag concentrations, survival and reproduction were determined, in a time series (for 21 days). In the soil, the available (CaCl₂ extractable) Ag fraction from Ag NM300K increased from 0 to 21 days but did not consistently change for AgNO₃. Internal concentrations reached equilibrium in most exposures to both Ag forms. The organisms were able to internalize and eliminate Ag, but less when exposed to Ag NM300K. The overall uptake rate constants for Ag from AgNO₃ and Ag NM300K exposures were 0.05 and 0.06 kg soil/kg organism/day, respectively, the elimination rate constants 0.2 and 0.1 day^-1, respectively. For AgNO₃ the median lethal concentrations decreased steadily with time, while for Ag NM300K they remained constant during the first 10 days of exposure followed by a 2-fold decline in the last 7 days. The 21-d LC50s for both Ag forms were similar but the LC50_inter (based on internal concentrations) were 63 and 121 mg Ag/kg body DW (Dry Weight) for AgNO₃ and Ag NM300K, respectively, showing higher toxicity of AgNO₃. These results show the importance of assessing time to toxicity, a relevant factor in toxicity assessment, especially for NMs.

Evaluation of the Toxic Effect of Bauhinia purpurea Mediated Synthesized Silver Nanoparticles against In-vitro and In-vivo Models

Metal nanoparticles, such as gold nanoparticles, silver nanoparticles, etc., have many benefits and have been in use for a very long time. Nevertheless, a number of concerns have been raised about the environmental impact and the possibility of exposure to various living systems at the moment. Thus, in this study, silver nanoparticles were synthesized by using plant gum from Bauhinia purpurea and characterization was done using UV-Visible Spectroscopy, Scanning Electron Microscopy, X-ray Diffraction, etc. To determine the accumulation and toxic effects caused by the nanoparticles, Eudrilus eugeniae, Danio rerio, and their embryos were exposed to the synthesized silver nanoparticles and evaluated using microscopic observation, histology, and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES).

A review on the toxicity of silver nanoparticles against different biosystems

Despite significant progress made in the past two decades, silver nanoparticles (AgNPs) have not yet made it to the clinical trials. In addition, they showed both positive and negative effects in their toxicity from unicellular organism to well-developed multi-organ system, for example, rat. Although it is generally accepted that capped (bio)molecules have synergistic bioactivities and diminish the toxicity of metallic Ag core, convincing evidence is completely lacking. Therefore, in this review, we first highlight the recent in vivo toxicity studies of chemically manufactured AgNPs, biologically synthesized AgNPs and reference AgNPs of European Commission. Then, their toxic effects are compared with each other and the overlooked factors leading to the potential conflict of obtained toxicity results are discussed. Finally, suggestions are given to better design and conduct the future toxicity studies and to fast-track the successful clinical translation of AgNPs as well.

Commonwealth of Soil Health: How Do Earthworms Modify the Soil Microbial Responses to CeO2 Nanoparticles?

Soil ecotoxicological assays on nanoparticles (NPs) have mainly investigated single components (e.g., plants, fauna, and microbes) within the ecosystem, neglecting possible effects resulting from the disturbance of the interactions between these components. Here, we investigated soil microbial responses to CeO₂ NPs in the presence and absence of earthworms from the perspectives of microbial functions (i.e., enzyme activities), the community structure, and soil metabolite profiles. Exposure to CeO₂ NPs (50, 500 mg/kg) alone decreased the activities of enzymes (i.e., acid protease and acid phosphatase) participating in soil N and P cycles, while the presence of earthworms ameliorated these inhibitory effects. After the CeO₂ NP exposure, the earthworms significantly altered the relative abundance of some microbes associated with the soil N and P cycles (Flavobacterium, Pedobacter, Streptomyces, Bacillus, Bacteroidota, Actinobacteria, and Firmicutes). This was consistent with the pattern found in the significantly changed metabolites which were also involved in the microbial N and P metabolism. Both CeO₂ NPs and earthworms changed the soil bacterial community and soil metabolite profiles. Larger alterations of soil bacteria and metabolites were found under CeO₂ NP exposure with earthworms. Overall, our study indicates that the top-down control of earthworms can drastically modify the microbial responses to CeO₂ NPs from all studied biological aspects. This clearly shows the importance of the holistic consideration of all soil ecological components to assess the environmental risks of NPs to soil health.

A critical review of the environmental impacts of manufactured nano-objects on earthworm species

The presence of manufactured nano-objects (MNOs) in various consumer or their (future large-scale) use as nanoagrochemical have increased with the rapid development of nanotechnology and therefore, concerns associated with its possible ecotoxicological effects are also arising. MNOs are releasing along the product life cycle, consequently accumulating in soils and other environmental matrices, and potentially leading to adverse effects on soil biota and their associated processes. Earthworms, of the group of Oligochaetes, are an ecologically significant group of organisms and play an important role in soil remediation, as well as acting as a potential vector for trophic transfer of MNOs through the food chain. This review presents a comprehensive and critical overview of toxic effects of MNOs on earthworms in soil system. We reviewed pathways of MNOs in agriculture soil environment with its expected production, release, and bioaccumulation. Furthermore, we thoroughly examined scientific literature from last ten years and critically evaluated the potential ecotoxicity of 16 different metal oxide or carbon-based MNO types. Various adverse effects on the different earthworm life stages have been reported, including reduction in growth rate, changes in biochemical and molecular markers, reproduction and survival rate. Importantly, this literature review reveals the scarcity of long-term toxicological data needed to actually characterize MNOs risks, as well as an understanding of mechanisms causing toxicity to earthworm species. This review sheds light on this knowledge gap as investigating bio-nano interplay in soil environment improves our major understanding for safer applications of MNOs in the agriculture environment.

Microplastic fibers influence Ag toxicity and bioaccumulation in Eisenia andrei but not in Enchytraeus crypticus

Microplastic fibers (MF) are released from synthetic textiles during washing and end up in the wastewater. Similarly, silver nanoparticles (AgNP), incorporated in textiles as antimicrobial agents, are released in washing machines, also reaching the wastewater treatment plants. Therefore, both MF and AgNP co-exist in the environment and enter the soil compartment mainly via the application of biosolids. Yet, the combined effect of MF and AgNP has not been studied. Here, we assessed the effects of polyester MF on the toxicity of AgNP and AgNO₃ to the earthworm Eisenia andrei and the enchytraeid Enchytraeus crypticus. The organisms were exposed to a range of concentration of AgNP (32, 100, 320, 1000, 3200 mg Ag/kg) and AgNO₃ (12.8, 32, 80, 200, 500 mg Ag/kg) in LUFA 2.2 soil in the absence or presence of MF (0.01% DW). Reproduction tests were conducted and the toxicity outcomes compared between soils with and without MF. The exposure to MF caused a decrease in the number of juveniles and changed the biochemical composition of earthworms. Moreover, the presence of MF increased the toxicity of AgNP to earthworm reproduction (EC50 = 165 mg Ag/kg) when compared to AgNP exposure alone (EC50 = 450 mg Ag/kg), but did not alter the toxicity of AgNO₃ (EC50 = 40 mg Ag/kg). For enchytraeids, no significant difference in Ag toxicity could be detected when MF was added to the soil for both AgNP and AgNO₃. Overall, Ag bioaccumulation was not affected by MF, except for a decrease in earthworm body concentration at the highest Ag soil concentration (3200 mg Ag/kg). Our results suggest that the presence of MF in the soil compartment may be a cause of concern, and that the joint exposure to Ag may be deleterious depending on the Ag form, organism, and endpoint. The present work provides the first evidence that a realistic MF concentration in soil lowers AgNP concentration necessary to provoke reproductive impairment in earthworms. The influence of MF on the risk assessment of AgNP should be considered.

Impact of multigenerational exposure to AgNO3 or NM300K Ag NPs on antioxidant defense and oxidative stress in Caenorhabditis elegans

Adaptation of the nematode Caenorhabditis elegans towards NM300K silver nanoparticles (Ag NPs) has previously been demonstrated. In the current study, the sensitivity to a range of secondary stressors (CeO2 NP, Ce3+, Cu2+, Cd2+, and Paraquat) following the multigenerational exposure to silver nanoparticles (Ag NPs NM300K) or AgNO3 was investigated. This revealed improved tolerance to the ROS inducer Paraquat with higher fecundity after pre-exposure to Ag NP, indicating an involvement of reactive oxygen species (ROS) metabolism in the adaptive response to NM300K. The potential contribution of the antioxidant defenses related to adaptive responses was investigated across six generations of exposure using the sod-1::GFP reporter (GA508), and the Grx1-roGFP2 (GRX) biosensor strains. Results showed an increase in sod-1 expression by the F3 generation, accompanied by a reduction of GSSG/GSH ratios, from both AgNO3 and Ag NP exposures. Continuous exposure to AgNO3 and Ag NP until the F6 generation resulted in a decreased sod-1 expression, with a concomitant increase in GSSG/GSH ratios. The results thus show that despite an initial enhancement, the continuous exposure to Ag caused a severe impairment of the antioxidant defense capacity in C. elegans.

Embryotoxicity of silver nanomaterials (Ag NM300k) in the soil invertebrate Enchytraeus crypticus - Functional assay detects Ca channels shutdown

Despite that silver (Ag) is among the most studied nanomaterials (NM) in environmental species and Ag's embryotoxicity is well known, there are no studies on Ag NMs embryotoxicity in soil invertebrates. Previous Full Life Cycle (FLC) studies in Enchytraeus crypticus, a standard soil invertebrate, showed that Ag materials decreased hatching success, which was confirmed to be a hatching delay effect for silver nitrate (AgNO₃) and mortality for Ag NM300K. In the present study, we aimed to investigate if the impact of Ag takes place during the embryonic development, using histology and immunohistochemistry. E. crypticus cocoons were exposed to a range of concentrations of Ag NM300K (0-10-20-60-115 mg Ag/kg) and AgNO₃ (0-20-45-60-96 mg Ag/kg) in LUFA 2.2 soil, in an embryotoxicity test, being sampled at days 1, 2, 3 and 6 (3, 4, 5 and 7 days after cocoon laying). Measured endpoints included the number of embryonic structures, expression of transferrin receptor (TfR) and L type calcium channels (LTCC) through histological and immunohistochemistry analysis, respectively. Results confirmed that Ag materials affected the embryonic development, specifically at the blastula stage (day 3). The expression and localization of TfR in E. crypticus was shown in the teloblasts cells, although this transcytosis mechanism was not activated. Ag affected calcium (Ca) metabolism during embryonic development: for AgNO_3, LTCC was initially activated, compensating the impact, for Ag NM300K, LTCC was not activated, hence no Ca balance, with irreversible consequences, i.e. terminated embryonic development. An Adverse Outcome Pathway was drafted, integrating the mechanisms here discovered with previous knowledge.

Nanomaterials and Annelid Immunity: A Comparative Survey to Reveal the Common Stress and Defense Responses of Two Sentinel Species to Nanomaterials in the Environment

Simple Summary

Nanotechnology is a dynamically developing field producing large amounts of nanocompounds that are applied in industry, daily life, and health care. During production, use, and waste these materials could end up in water or soil. Large scale contaminations of our environment are a threat to public health. Pollution can have harmful effects on the immune system, as revealed by numerous studies in humans and other vertebrates. The relative simplicity of invertebrate immune functions offers potentially sensitive and accessible means of monitoring the effects and complex interactions of nanoparticles which ultimately affect host resistance. Among terrestrial and freshwater invertebrates, earthworms and leeches are the “keystone” species to evaluate the health of our ecosystems. In this review we compare the conserved stress and immune responses of these invertebrate model organisms toward nanoparticles. The obtained knowledge provides exciting insights into the conserved molecular and cellular mechanisms of nanomaterial-related toxicity in invertebrates and vertebrates. Understanding the unique characteristics of engineered nanoproducts and their interactions with biological systems in our environment is essential to the safe realization of these materials in novel biomedical applications.

Abstract

Earthworms and leeches are sentinel animals that represent the annelid phylum within terrestrial and freshwater ecosystems, respectively. One early stress signal in these organisms is related to innate immunity, but how nanomaterials affect it is poorly characterized. In this survey, we compare the latest literature on earthworm and leeches with examples of their molecular/cellular responses to inorganic (silver nanoparticles) and organic (carbon nanotubes) nanomaterials. A special focus is placed on the role of annelid immunocytes in the evolutionarily conserved antioxidant and immune mechanisms and protein corona formation and probable endocytosis pathways involved in nanomaterial uptake. Our summary helps to realize why these environmental sentinels are beneficial to study the potential detrimental effects of nanomaterials.

Green Synthesis of Gold and Silver Nanoparticles from Plant Extracts and Their Possible Applications as Antimicrobial Agents in the Agricultural Area

Currently, metal nanoparticles have varied uses for different medical, pharmaceutical, and agricultural applications. Nanobiotechnology, combined with green chemistry, has great potential for the development of novel and necessary products that benefit human health, environment, and industries. Green chemistry has an important role due to its contribution to unconventional synthesis methods of gold and silver nanoparticles from plant extracts, which have exhibited antimicrobial potential, among other outstanding properties. Biodiversity-rich countries need to collect and convert knowledge from biological resources into processes, compounds, methods, and tools, which need to be achieved along with sustainable use and exploitation of biological diversity. Therefore, this paper describes the relevant reported green synthesis of gold and silver nanoparticles from plant extracts and their capacity as antimicrobial agents within the agricultural field for fighting against bacterial and fungal pathogens that can cause plant, waterborne, and foodborne diseases. Moreover, this work makes a brief review of nanoparticles' contribution to water treatment and the development of "environmentally-friendly" nanofertilizers, nanopesticides, and nanoherbicides, as well as presenting the harmful effects of nanoparticles accumulation in plants and soils.

Novel understanding of toxicity in a life cycle perspective - The mechanisms that lead to population effect - The case of Ag (nano)materials

Silver (Ag) is amongst the most well studied nanomaterials (NMs), although most studies have only dealt with a single AgNM at a time and one biological endpoint. We here integrate the results of various testing-tools (endpoints) using a terrestrial worm, the standard ecotoxicological model organism Enchytraeus crypticus. Exposure spanned both water and soil exposure, it covered all life stages (cocoons, juveniles and adults), varying exposure durations (1-2-3-4-5-21 days), and covered 5 biological endpoints: hatching success, survival, reproduction, avoidance and gene expression (qPCR target genes GABA and Acetyl cholinesterase). We tested 4 Ag materials: PVP coated (PVP-AgNM), non-coated (NC-AgNM), the JRC reference Ag NM300K and AgNO₃. Results showed that short-term exposure via water to assess impact on cocoons' hatching predicted longer term effects such as survival and reproduction. Moreover, if we extended the exposure from 11 to 17 day this allowed discrimination between hatch delay and impairment. Exposure of juveniles and adults via water showed that juveniles were most sensitive with survival affected. Across materials the following toxic ranking was observed: AgNO₃ ≥ Ag NM300K ≫ NC-AgNM ≥ PVP-AgNM. E. crypticus avoided AgNO₃ in a dose-response manner, avoiding most during the first 24 h. Avoidance of Ag NM300K and NC-AgNM only occurred during the first 24 h and the PVP coated AgNM were not avoided at all. The up-regulation of the GABA triggering anesthetic effects, indicated the high ecological impact of Ag materials in soil: Ag affects the GABAergic system hence organisms were not able to efficiently avoid and became intoxicated, this caused impacts in terms of survival and reproduction.

In vivo assessment of silver nanoparticle induced reactive oxygen species reveals tissue specific effects on cellular redox status in the nematode Caenorhabditis elegans

The current study provides an in vivo analysis of the production of reactive oxygen species (ROS) and oxidative stress in the nematode Caenorhabditis elegans following exposure to EU reference silver nanoparticles NM300K and AgNO₃. Induction of antioxidant defenses was measured through the application of a SOD-1 reporter, and the HyPer and GRX biosensor strains to monitor changes in the cellular redox state. Both forms of Ag resulted in an increase in sod-1 expression, elevated H₂O₂ levels and an imbalance in the cellular GSSG/GSH redox status. Microscopy analysis of the strains revealed that AgNO₃ induced ROS-related effects in multiple tissues, including the pharynx, intestinal cells and muscle tissues. In contrast, NM300K resulted in localized ROS production and oxidative stress, specifically in tissues surrounding the intestinal lumen. This indicates that Ag from AgNO₃ exposure was readily transported across the whole body, while Ag or ROS from NM300K exposure was predominantly confined within the luminal tissues. Concentrations resulting in an increase in ROS production and changes in GSSG/GSH ratio were in line with the levels associated with observed physiological toxic effects. However, sod-1 was not induced at the lowest Ag concentrations, although reprotoxicity was seen at these levels. While both forms of Ag caused oxidative stress, impaired development, and reprotoxicity, the results suggest different involvement of ROS production to the toxic effects of AgNO₃versus NM300K.

Silver nanoparticles: Toxicity in model organisms as an overview of its hazard for human health and the environment

Silver nanoparticles (AgNPs) have attracted remarkable attention due to their powerful antimicrobial action as well as their particular physicochemical properties. This has led to their application in a wide variety of products with promising results. However, their interaction with the environment and toxicity in live terrestrial or aquatic organisms is still a matter of intense debate. More detailed knowledge is still required about the toxicity of AgNPs, their possible uptake mechanisms and their adverse effects in live organisms. Several studies have reported the interactions and potential negative effects of AgNPs in different organisms. In this review, we report and discuss the current state of the art and perspectives for the impact of AgNPs on different organisms present in the environment. Recent progress in interpreting uptake, translocation and accumulation mechanisms in different organisms and/or living animals are discussed, as well as the toxicity of AgNPs and possible tolerance mechanisms in live organisms to cope with their deleterious effects. Finally, we discuss the challenges of accurate physicochemical characterization of AgNPs and their ecotoxicity in environmentally realistic conditions such as soil and water media.

Exposure to nickel oxide nanoparticles insinuates physiological, ultrastructural and oxidative damage: A life cycle study on Eisenia fetida

Although, health and environmental hazards of Ni are ironclad; however, that of Nickle oxide nanoparticles (NiO-NPs) are still obscure. Therefore, impact of NiO-NPs exposure (0, 5, 50, 200, 500 and 1000 mg kg^-1 soil) on the earthworm (Eisenia fetida) survival (at 28th day), reproduction (at 56th day), histopathology, ultrastructures, antioxidant enzymes and oxidative DNA damage was appraised in full life cycle study. Lower concentrations of NiO-NPs (5, 50 and 200) did not influence the survival, reproduction and growth rate of adult worms significantly. However, reproduction reduced by 40-50% with 500 and 1000 mg kg^-1 exposure, which also induced oxidative stress leading to DNA damage in earthworms. Ultrastructural observation and histology of earthworms exposed to higher NiO-NPs concentrations revealed abnormalities in epithelium layer, microvilli and mitochondria with underlying pathologies of epidermis and muscles, as well as adverse effects on the gut barrier. To the best of our knowledge, this is the first study unveiling the adverse effects of NiO-NPs on a soil invertebrate (Eisenia fetida). Our findings clue towards looking extensively into the risks of NiO-NPs on soil organisms bearing agricultural and environmental significance.

A new test system for unraveling the effects of soil components on the uptake and toxicity of silver nanoparticles (NM-300K) in simulated pore water

Fate, bioavailability and toxicity of silver nanoparticles (AgNP) are largely affected by soil properties. Here we focused on how these processes are connected in simulated soil pore water. OECD soil components (sand, kaolin clay, peat) were covered with NM-300K-, AgNO₃- and NM-300K dispersant-contaminated water, and Folsomia candida were exposed on the water surface. After 14 days the majority of AgNP was in nano form in sand pore water where also silver uptake was highest. Multilayered cross sections from X-ray micrographs of Collembola exposed to AgNP showed that silver was located in animal areas of direct contact to the contaminated pore water and was ingested. In contrast, in simulated peat pore water only a small fraction of silver was bioavailable. AgNO₃ was only bioavailable at the start of the test and not anymore at test end. AgNP and AgNO₃ caused immobilization in sand and kaolin pore water while no toxicity was found with peat and OECD soil. A strong correlation (correlation coefficient = 0.901) existed between the concentration of nano silver and immobilization; for ionic silver this was not the case. The dispersant of AgNP was toxic on its own in sand and kaolin pore water. As there are analytical limitations of quantifying AgNP in complex matrices this test system enables a mechanistic view of exposure and uptake of AgNP (and other substances) by F. candida from soil pore water.

TiO2 nanoparticles in irrigation water mitigate impacts of aged Ag nanoparticles on soil microorganisms, Arabidopsis thaliana plants, and Eisenia fetida earthworms

Treated wastewater is reclaimed to irrigate crops in a growing number of arid and semi-arid areas. In order to study the impacts of metallic nanoparticles (NPs) present in treated wastewater on soil ecosystems, a soil micro-ecosystem containing Arabidopsis thaliana plants, soil microorganisms, and Eisenia fetida earthworms was developed. The soil was irrigated with deionized water containing environmentally relevant concentrations of 70 µg/L of TiO₂ NPs; or 20 µg/L of an Ag mixture, which included 90% (w/w) Ag₂S NPs, 7.5% (w/w) Ag⁰ NPs, and 2.5% (w/w) Ag⁺ to represent speciation of aged Ag NPs in treated wastewater; or a combination of the TiO₂ NPs and the Ag mixture to reflect the frequent presence of both types of materials in treated wastewater. It was found that TiO₂ NPs alone were not toxic to the soil micro-ecosystem. Irrigation water containing 20 µg/L of the Ag mixture significantly reduced the soil microbial biomass, and inhibited the growth of plants and earthworms; however, a combination of 70 µg/L of TiO₂ and 20 µg/L of Ag did not show toxic impact on organism growth compared to the Control of deionized water irrigation. Taken together, these results indicate the importance of investigating the effects of different nanomaterials in combination as they are introduced to the environment-with environmentally relevant concentrations and speciation-instead of only selecting a single NP type or residual ion. Moreover, the results of this study support the safe application of reclaimed water from wastewater treatment plants for use in agricultural lands in regard to limited concentrations of aged NPs (i.e., TiO₂ and Ag) if present in combination.

Gold and silver nanoparticles effects to the earthworm Eisenia fetida - the importance of tissue over soil concentrations

To address and to compare the respective impact of gold and silver nanoparticles (Au and Ag NPs) in soil invertebrate, the earthworm Eisenia fetida was exposed to soil containing 2, 10, and 50 mg/kg of Au and Ag in both nanoparticulate and ionic forms for 10 days. Both metal NPs were 2-15 times less bioavailable than their ionic forms, and displayed similar transfer coefficients from soil to earthworm tissues. Both metal NPs triggered the onset of an oxidative stress as illustrated by increased glutathione S-transferase levels, decreased catalase levels, and increased malondialdehyde concentrations. Protein carbonylation distinguished the nanoparticular from the ionic forms as its increase was observed only after exposure to the highest concentration of both metal NPs. Au and Ag NPs triggered DNA modifications even at the lowest concentration, and both repressed the expression of genes involved in the general defense and stress response at high concentrations as did their ionic counterparts. Despite the fact that both metal NPs were less bioavailable than their ionic forms, at equivalent concentrations accumulated within earthworms tissues they exerted equal or higher toxic potential than their ionic counterparts.Capsule: At equivalent concentrations accumulated within earthworm tissues Au and Ag NPs exert equal or higher toxic potential than their ionic forms.

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.

Copper accumulation and toxicity in earthworms exposed to CuO nanomaterials: Effects of particle coating and soil ageing

Engineered nanomaterials (ENMs) may be functionalised with a surface coating to enhance their properties, but the ecotoxicity of the coatings and how hazard changes with ageing in soil is poorly understood. This study determined the toxic effect of CuO ENMs with different chemical coatings on the earthworm (Eisenia fetida) in fresh soil, and then after one year in aged soil. In both experiments, earthworms were exposed for 14 days to the CuO materials at nominal concentrations of 200 and 1000 mg Cu kg^-1 dry weight and compared to CuSO₄. In the fresh soil experiment, CuO-COOH was found to be the most acutely toxic of the nanomaterials (survival, 20 ± 50%), with tenfold increase of total Cu in the earthworms compared to controls. Sodium pump activity was reduced in most CuO ENM treatments, although not in the CuSO₄ control. There was no evidence of glutathione depletion or the induction of superoxide dismutase (SOD) activity in any treatment. Histology showed a mild hypoplasia of mucous cells in the epidermis with some nanomaterials. In the aged soil, the CuO-NH₄⁺ was the most acutely toxic ENM (survival 45 ± 3%) and Cu accumulation was lower in the earthworms than in the fresh soil study. Depletion of tissue Mn and Zn concentrations were seen in earthworms in aged soil, while no significant effects on sodium pump or total glutathione were observed. Overall, the study showed some coating-dependent differences in ENM toxicity to earthworms which also changed after a year of ageing the soil.

Characterizing the behavior, uptake, and toxicity of NM300K silver nanoparticles in Caenorhabditis elegans

Using Caenorhabditis elegans as a model organism, we addressed the potential linkage among toxicity of NM300K Ag nanoparticles (AgNPs), their particle size distribution, and the presence of dissolved Ag in the test media. Of the 3 endpoints assessed (growth, fertility, and reproduction), reproduction was the most sensitive, with the 50% effect concentration (EC50) ranging from 0.26 to 0.84 mg Ag L^-1 and 0.08 to 0.11 mg Ag L^-1 for NM300K and AgNO₃ , respectively. Silver uptake by C. elegans was similar for both forms of Ag, whereas bioaccumulation was higher in AgNO₃ exposure. The observed differences in toxicity between NM300K and AgNO₃ did not correlate with bioaccumulated Ag, which suggests that toxicity is a function of the type of exposing agent (AgNPs vs AgNO₃ ) and its mode of action. Before addition of the food source (Escherichia coli), size fractionation revealed that dissolved Ag comprised 13 to 90% and 4 to 8% of total Ag in the AgNO₃ and NM300K treatments, respectively. No dissolved Ag was detectable in the actual test media due to immediate Ag adsorption to bacteria. The results of the present study indicate that information on behavior and characterization of exposure conditions is essential for nanotoxicity studies. Environ Toxicol Chem 2018;37:1799-1810. © 2018 SETAC.

Is a Water Content of 60% Maximum Water Holding Capacity Suitable for Folsomia candida Reproduction Tests? A Study with Silver Nanoparticles and AgNO₃

Silver nanoparticles (AgNP) are increasingly emitted to the environment due to a rise in application in various products; therefore, assessment of their potential risks for biota is important. In this study the effects of AgNP at environmentally relevant concentrations (0.6–375 µg kg⁻¹ soil) on the soil invertebrate Folsomia candida in OECD (Organisation for Economic Co-operation and Development) soil was examined at different soil water contents. Animals were retrieved by heat extraction, which had an efficiency of about 90% compared with the floatation method. The tested water content range is set by OECD Guideline 232 (40–60% of the maximum water holding capacity, WHC), and we detected significant differences in toxicity due to these. With AgNO₃, used as an ionic control, the number of juveniles significantly decreased only at 40% WHC, which might be due to dilution of the toxicant at higher soil water content. In turn, at 60% WHC, the reproduction of F. candida significantly increased in the presence of AgNP compared with in the control. However, at this water content, the required number of juveniles in the control treatment was not reached in three independent tests. The fact that the OECD validity criterion is not met indicates that the soil conditions are not suitable for reproduction at 60% WHC.

The effect of soil properties on the toxicity and bioaccumulation of Ag nanoparticles and Ag ions in Enchytraeus crypticus

Standard natural Lufa soils (2.2, 2.3 and 5M) with different organic carbon contents (0.67-1.61%) and pH_CaCl2 (5.5-7.3) were spiked with ionic Ag (AgNO₃) and polyvinyl pyrrolidone (AgNP-PVP) and citrate (AgNP-Cit) coated Ag nanoparticles (NPs). Enchytraeus crypticus were exposed for 21 days to assess effects on survival and reproduction. Soil, pore water and animals were analyzed for Ag. AgNP-Cit had a strong increasing effect on soil pH, leading to high enchytraeid mortality at concentrations higher than 60-100mg Ag/kg dry soil which made it impossible to determine the influence of soil properties on its toxicity. LC50s were lower for AgNO₃ than for AgNP-PVP (92-112 and 335-425mg Ag/kg dry soil, respectively) and were not affected by soil properties. AgNO₃ and AgNP-PVP had comparable reproductive toxicity with EC50s of 26.9-75.2 and 28.2-92.3mg Ag/kg dry soil, respectively; toxicity linearly increased with decreasing organic carbon content of the soils but did not show a clear effect of soil pH. Ag uptake in the enchytraeids was higher at higher organic carbon content, but could not explain differences in toxicity between soils. This study indicates that the bioavailability of both ionic and nanoparticulate Ag is mainly affected by soil organic carbon, with little effect of soil pH.

The toxicity of silver to soil organisms exposed to silver nanoparticles and silver nitrate in biosolids-amended field soil

The use of engineered silver nanoparticles (AgNPs) is widespread, with expected release to the terrestrial environment through the application of biosolids onto agricultural lands. The toxicity of AgNPs and silver nitrate (AgNO₃ ; as ionic Ag⁺ ) to plant (Elymus lanceolatus and Trifolium pratense) and soil invertebrate (Eisenia andrei and Folsomia candida) species was assessed using Ag-amended biosolids applied to a natural sandy loam soil. Bioavailable Ag⁺ in soil samples was estimated using an ion-exchange technique applied to KNO₃ soil extracts, whereas exposure to dispersible AgNPs was verified by single-particle inductively coupled plasma-mass spectrometry and transmission electron microscopy-energy dispersive X-ray spectroscopy analysis. Greater toxicity to plant growth and earthworm reproduction was observed in AgNP exposures relative to those of AgNO₃ , whereas no difference in toxicity was observed for F. candida reproduction. Transformation products in the AgNP-biosolids exposures resulted in larger pools of extractable Ag⁺ than those from AgNO₃ -biosolids exposures, at similar total Ag soil concentrations. The results of the present study reveal intrinsic differences in the behavior and bioavailability of the 2 different forms of Ag within the biosolids-soils pathway. The present study demonstrates how analytical methods that target biologically relevant fractions can be used to advance the understanding of AgNP behavior and toxicity in terrestrial environments. Environ Toxicol Chem 2017;36:2756-2765. © 2017 Crown in the Right of Canada. Published Wiley Periodicals Inc., on behalf of SETAC.

Integrative assessment of the effects produced by Ag nanoparticles at different levels of biological complexity in Eisenia fetida maintained in two standard soils (OECD and LUFA 2.3)

There is a potential risk to increase the release of silver nanoparticles (Ag NPs) into the environment: For instance. in soils receiving sludge models estimate 0.007 mg Ag NPs kg^-1 that will annually increase due to sludge or sludge incineration residues land-disposal. Thus, the concern about the hazards of nanosilver to soils and soil invertebrates is growing. Studies performed up to now have been focused in traditional endpoints, used limit range concentrations and employed different soil types that differ in physico-chemical characteristics. Presently, effects of Ag NPs have been measured at different levels of biological complexity in Eisenia fetida, exposed for 3 and 14 d to high but sublethal (50 mg Ag NPs kg^-1) and close to modeled environmental concentrations (0.05 mg Ag NPs kg^-1). Since characteristics of the exposure matrix may limit the response of the organisms to these concentrations, experiments were carried out in OECD and LUFA soils, the most used standard soils. High concentrations of Ag NPs increased catalase activity and DNA damage in OECD soils after 14 d while in LUFA 2.3 soils produced earlier effects (weight loss, decrease in cell viability and increase in catalase activity at day 3). At day 14, LUFA 2.3 (low clay and organic matter-OM-) could have provoked starvation of earthworms, masking Ag NPs toxicity. The concentration close to modeled environmental concentrations produced effects uniquely in LUFA 2.3 soil. Accurate physico-chemical characteristics of the standard soils are crucial to assess the toxicity exerted by Ag NPs in E. fetida since low clay and OM contents can be considered toxicity enhancers.

Nanoparticle silver coexposure reduces the accumulation of weathered persistent pesticides by earthworms

Although the use of engineered nanomaterials continues to increase, how these materials interact with coexisting contaminants in the environment is largely unknown. The effect of silver (Ag) in bulk, ionic, and nanoparticle (NP; bare and polyvinyl pyrrolidone-coated) forms at 3 concentrations (0 mg/kg, 500 mg/kg, 1000 mg/kg, 2000 mg/kg; ion at 69 mg/kg, 138 mg/kg, 276 mg/kg) on the accumulation of field-weathered chlordane and dichlorodiphenyldichloroethylene + metabolites (DDX) by Eisenia fetida (earthworm) was investigated. Earthworm biomass and survival were unaffected by treatment. At the 500 mg/kg and 1000 mg/kg exposure levels, NP-exposed earthworms contained significantly greater Ag (194-245%) than did the bulk exposed organisms; NP size or coating had no impact on element content. Generally, exposure to Ag of any type or at any concentration significantly reduced pesticide accumulation, although reductions for DDX (35.1%; 8.9-47.0%) were more modest than those for chlordane (79.0%; 17.4-92.9%). For DDX, the reduction in pesticide accumulation was not significantly affected by Ag type or concentration. For chlordane, the 3 NP exposures suppressed chlordane accumulation significantly more than did bulk exposure; earthworms exposed to bulk Ag contained 1170 ng/g chlordane, but levels in the NP-exposed earthworms were 279 ng/g. At the 500 mg/kg exposure, the smallest coated NPs exerted the greatest suppression in chlordane accumulation; at the 2 higher concentrations, chlordane uptake was unaffected by NP size or coating. The findings show that in exposed earthworms Ag particle size does significantly impact accumulation of the element itself, as well as that of coexisting weathered pesticides. The implications of these findings with regard to NP exposure and risk are unknown but are the topic of current investigation. Environ Toxicol Chem 2017;36:1864-1871. © 2016 SETAC.

Effects of silver nanoparticles on survival, biomass change and avoidance behaviour of the endogeic earthworm Allolobophora chlorotica

Increasing commercial application of silver nanoparticles (Ag NP) and subsequent presence in wastewater and sewage sludge has raised concerns regarding their effects in the aquatic and terrestrial environment. Several studies have employed standardised acute and chronic earthworm-based tests to establish the toxicological effects of Ag NP within soil. These studies have relied heavily on the use of epigiec earthworm species which may have limited ecological relevance in mineral soil. This study assessed the influence of Ag NP (uncoated 80nm powder) and AgNO₃ on survival, change in biomass and avoidance behaviour in a soil dwelling (endogiec) species, Allolobophora chlorotica. Earthworms were exposed for 14 days to soils spiked with Ag NP or AgNO₃ at 0, 12.5, 25, 50 and 100mgkg^-1 either separately for survival and biomass measurement, or combined within a linear gradient to assess avoidance. Avoidance behaviour was shown to provide the most sensitive endpoint with an observable effect at an Ag NP/AgNO₃ concentration of 12.5mgkg^-1 compared with 50mgkg^-1 for biomass change and 100mgkg^-1 for survival. Greater mortality was observed in AgNO₃ (66.7%) compared with Ag NP-spiked soils (12.5%) at 100mgkg^-1, attributed to increased presence of silver ions. Although comparison of results with studies employing Eisenia fetida and Eisenia andrei suggest that the A. chlorotica response to Ag NP is more sensitive, further research employing both epigeic and endogeic earthworms under similar experimental conditions is required to confirm this observation.

Effects of silver nanowire length and exposure route on cytotoxicity to earthworms

To accurately evaluate the environmental toxicity of silver nanowires (AgNWs), it is necessary to characterize how the cytotoxicity of these nanomaterials is affected by the route of exposure. However, few studies have addressed the exposure route or mechanism of toxicity of nanomaterials, particularly of nanowires, in living organisms. In this study, we therefore analyzed the main exposure route of AgNWs in vitro, using earthworms (Eisenia andrei) as a model system, via flow cytometry. We subsequently examined the in vivo toxicity of AgNWs to earthworms in soil. These tests revealed that intracellular esterase activity was correlated with adsorption of the nanowires to the surfaces of coelomocytes in vitro, and that in vivo cytotoxicity resulted mainly from oral, rather than dermal, exposure to the nanowires. Overall, shorter AgNWs (10 μm) were more toxic than longer AgNWs (20 μm). To our knowledge, this study is the first report regarding the ecotoxicity of nanowires to earthworms in soil. Our findings provide important information to help assess the risk of toxic AgNW contamination of soil ecosystems.

Effect of silver nano-particles on soil microbial growth, activity and community diversity in a sandy loam soil

Silver nano-particles (AgNPs) are widely used in a range of consumer products as a result of their antimicrobial properties. Given the broad spectrum of uses, AgNPs have the potential for being released to the environment. As a result, environmental risks associated with AgNPs need to be assessed to aid in the development of regulatory guidelines. Research was performed to assess the effects of AgNPs on soil microbial activity and diversity in a sandy loam soil with an emphasis on using a battery of microbial tests involving multiple endpoints. The test soil was spiked with PVP coated (0.3%) AgNPs at the following concentrations of 49, 124, 287, 723 and 1815 mg Ag kg^-1 dry soil. Test controls included an un-amended soil; soil amended with PVP equivalent to the highest PVP concentration of the coated AgNP; and soil amended with humic acid, as 1.8% humic acid was used as a suspension agent for the AgNPs. The impact on soil microbial community was assessed using an array of tests including heterotrophic plate counting, microbial respiration, organic matter decomposition, soil enzyme activity, biological nitrification, community level physiological profiling (CLPP), Ion Torrent™ DNA sequencing and denaturing gradient gel electrophoresis (DGGE). An impact on microbial growth, activity and community diversity was evident from 49 to 1815 mg kg^-1 with the median inhibitory concentrations (IC50) as low as 20-31 mg kg^-1 depending on the test. AgNP showed a notable impact on microbial functional and genomic diversity. Emergence of a silver tolerant bacterium was observed at AgNP concentrations of 49-287 mg kg^-1 after 14-28 days of incubation, but not detectable at 723 and 1815 mg kg^-1. The bacterium was identified as Rhodanobacter sp. The study highlighted the effectiveness of using multiple microbial endpoints for inclusion to the environmental risk assessment of nanomaterials.

Effects of a silver nanomaterial on cellular organelles and time course of oxidative stress in a fish cell line (PLHC-1)

Among the nanomaterials currently in commercial products, those based on silver are the most used, and so there is a high probability that silver nanoparticles (AgNPs) will be released into aquatic environments where they could adversely affect aquatic organisms, including fish. Taking this into account, the aim of the present work was to characterize in depth the mechanisms underlying the toxic action of AgNPs using fish cell lines, determining specifically the contribution of alterations in cellular structures and oxidative stress time course to the cytotoxicity of AgNPs. Since liver plays a key role in detoxification, the hepatoma cell line PLHC-1 was used. Exposure to AgNPs (NM-300K, obtained from the Joint Research Centre Repository) caused alterations at the lysosomal and mitochondrial levels at lower concentrations than those that disrupted plasma membrane (evaluated by means of neutral red, alamarBlue, and 5-carboxyfluorescein diacetate, acetoxymethyl ester assays respectively). AgNO₃, used as a control Ag⁺ ion source, produced similar cytotoxic effects but at lower concentrations than AgNPs. Both silver forms caused oxidative disruption but the initial response was delayed in AgNPs until 6h of exposure. Transmission electron microscopy analysis also evidenced the disruption of mitochondrial structures in cells exposed to cytotoxic concentrations of both forms of silver. At non-cytotoxic concentrations, AgNPs were detected inside the nucleoli and mitochondria, thereby pointing to long-term effects. The present work evidences the mutual interaction between the induction of oxidative stress and the alterations of cellular structures, particularly mitochondria, as cytotoxicity mechanisms not exclusively associated to NPs.

Effects of Ag nanomaterials (NM300K) and Ag salt (AgNO3) can be discriminated in a full life cycle long term test with Enchytraeus crypticus

Information on effects of silver nanoparticles on soil invertebrates, especially using long-term exposures, is scarce. In this study we investigated the effects of the reference Ag (NM300K) (compared to AgNO3) using the full life cycle test (FLCt) of the soil invertebrate Enchytraeus crypticus. Results showed that effects were higher compared to the standard reproduction test, which is shorter and does not cover the FLC. Both Ag forms caused a reduction on hatching success, juvenile and adult survival and reproduction with similar ECx. Differences between AgNO3 and Ag NM300K could be discriminated using the FLCt: AgNO3 decreased hatching success was shown to be a delay in the process, whereas Ag NM300K caused irreversible effects during the same time frame. These effects may have occurred during the embryo development, hatching (inhibition) or survival of hatched juveniles. Ag NM300K caused non-monotonic concentration-response effect as observed by the high effect of the lowest concentration (20mgkg-1). It is known that dispersion is higher at lower concentrations - this could explain the increased effect at low concentration. Non monotonic responses are well described in the literature, where effects of high cannot predict for low concentrations, hence special attention should be given for NMs low concentration effects.

Properties of silver nanoparticles influencing their uptake in and toxicity to the earthworm Lumbricus rubellus following exposure in soil

Physicochemical properties of nanoparticles influence their environmental fate and toxicity, and studies investigating this are vital for a holistic approach towards a comprehensive and adequate environmental risk assessment. In this study, we investigated the effects of size, surface coating (charge) of silver nanoparticles (AgNPs) - a most commonly-used nanoparticle-type, on the bioaccumulation in, and toxicity (survival, growth, cocoon production) to the earthworm Lumbricus rubellus. AgNPs were synthesized in three sizes: 20, 35 and 50 nm. Surface-coating with bovine serum albumin (AgNP_BSA), chitosan (AgNP_Chit), or polyvinylpyrrolidone (AgNP_PVP) produced negative, positive and neutral particles respectively. In a 28-day sub-chronic reproduction toxicity test, earthworms were exposed to these AgNPs in soil (0-250 mg Ag/kg soil DW). Earthworms were also exposed to AgNO₃ at concentrations below known EC₅₀. Total Ag tissue concentration indicated uptake by earthworms was generally highest for the AgNP_BSA especially at the lower exposure concentration ranges, and seems to reach a plateau level between 50 and 100 mg Ag/kg soil DW. Reproduction was impaired at high concentrations of all AgNPs tested, with AgNP_BSA particles being the most toxic. The EC₅₀ for the 20 nm AgNP_BSA was 66.8 mg Ag/kg soil, with exposure to <60 mg Ag/kg soil already showing a decrease in the cocoon production. Thus, based on reproductive toxicity, the particles ranked: AgNP_BSA (negative) > AgNP_PVP (neutral) > Chitosan (positive). Size had an influence on uptake and toxicity of the AgNP_PVP, but not for AgNP_BSA nor AgNP_Chit. This study provides essential information on the role of physicochemical properties of AgNPs in influencing uptake by a terrestrial organism L. rubellus under environmentally relevant conditions. It also provides evidence of the influence of surface coating (charge) and the limited effect of size in the range of 20-50 nm, in driving uptake and toxicity of the AgNPs tested.

Silver Nanoparticles, Ions, and Shape Governing Soil Microbial Functional Diversity: Nano Shapes Micro

Silver nanoparticles (AgNPs) affect microbial metabolic processes at single cell level or lab-culture strains. However, the impact of different AgNPs properties such as the particle, ion release, and shape on functional responses of natural soil microbial communities remain poorly understood. Therefore, we assessed the relative importance of particles and ions of AgNPs in bacterial toxicity and how the functional diversity of soil microbial communities were impacted by AgNPs shapes (i.e., plates, spheres, and rods) in laboratory incubations. Our results showed that the relative contribution of AgNPs_(particle) increased with increasing exposure concentrations (accounted for about 60–68% of the total toxicity at the highest exposure level). In addition, the functional composition of the microbial community differed significantly according to different AgNPs shapes. The various properties of AgNPs thus can significantly and differentially affect the functional composition of microbial communities and associated ecosystem processes depending on the level of environmental exposure.

Ecotoxicity of titanium silicon oxide (TiSiO4) nanomaterial for terrestrial plants and soil invertebrate species

The huge evolution of nanotechnology and the commercialization of nanomaterials (NMs) positively contributed for innovation in several industrial sectors. Facing this rapid development and the emergence of NMs in the market, the release of this nanometric sized materials in the environment and the possible impact on different ecosystem components attracted the attention of researchers in the last few years. In our study we aimed to assess the impact of titanium silicon oxide nanomaterial (nano-TiSiO4) on soil biota to estimate a risk limit for this material. In the present research a battery of standardized ecotoxicological assays aimed at evaluating a wide range of endpoints (avoidance and reproduction of earthworms and collembolans, emergence/growth of four selected terrestrial plants) were carried out, using OECD artificial soil as test substrate spiked with aqueous suspension of different concentrations of nano-TiSiO4. The results showed a maximum avoidance percentage of 40% for earthworms (Esenia andrei) at the highest concentration tested (1000mgkg(-1) soildw of nano-TiSiO4). No significant effect on the reproductive function of both invertebrate species was recorded. Nevertheless, significant phytotoxic data was registered at least for the growth of dicotyledonous plant species (Lactuca sativa and Lycopersicon lycopersicum) with EC20 values ranging between 236 and 414 mg kg(-1) soildw of nano-TiSiO4 for L. sativa dry mass and fresh mass, respectively. Further, the characterization of nano-TiSiO4 in suspensions used to spike the soil, performed by Dynamic Light Scattering, showed the formation of aggregates with important average size diameter, thus demonstrating that the toxic effects observed were likely not size dependent. A deterministic PNEC (predicted no effect concentration) for this NM of 10.02mg kg(-1) soildw of nano-TiSiO4, is suggested, while no more ecotoxicological information exists.

Surface Structure of Silver Nanoparticles as a Model for Understanding the Oxidative Dissolution of Silver Ions

The toxicity of silver nanoparticles (AgNPs) has been related to the release of ionic silver. This process is influenced by a large variety of factors and is poorly understood. The key to understanding Ag(+) release by AgNPs is its subvalency. This is a fundamental property of Ag that can be elucidated by analyzing the crystal structures of a specific class of Ag materials as well as MO/DFT (molecular orbital/density functional theory)-optimized Ag13(OH)4 clusters, being precursors of AgNPs. Semimetallic silver at the (111) faces of AgNPs has a subvalency of +(1)/3 v.u., forming ≡Ag3OH(0) surface groups with a maximum site density of 4.7 sites/nm(2). Oxidative dissolution may remove these groups with the simultaneous formation of oxygen radicals that may further interact with the surface via different pathways. Reactive oxygen species (ROS) can create a circular process with the dissolution of ≡Ag3OH(0), exposure of new metallic sites at the underlying lattice, and subsequent oxidation to ≡Ag3OH(0). This regeneration process is interrupted by the penetration of O(•) radicals into the lattice, forming highly stable Ag6O octahedra with subvalent silver that protects the AgNP from further oxidation. A thermodynamic model has been developed that quantitatively describes the equilibrium condition between ≡Ag3OH(0) and ≡Ag6O(0) and explains a large variety of collectively observed phenomena.

Toxicokinetics and toxicodynamics of differently coated silver nanoparticles and silver nitrate in Enchytraeus crypticus upon aqueous exposure in an inert sand medium

The aim of the present study was to evaluate the effect of silver nanoparticles (AgNPs) on Enchytraeus crypticus, applying a combined toxicokinetics and toxicodynamics approach to understand the relationship between survival and the development of internal Ag concentrations in the animals over time. Toxicity tests were conducted in medium composed of well-defined aqueous solutions added to inert quartz sand to avoid the complexity of soil conditions. Citrate-coated AgNPs (AgNP-Cit) and polyvinylpyrrolidone-coated AgNPs (AgNP-PVP) were tested and compared with silver nitrate (AgNO3), which was used as a positive control for Ag ion effects. The median lethal concentration (LC50) values based on Ag concentrations in the solution phase of the test medium decreased over time and reached steady state after 7 d, with AgNO3 and AgNP-PVP being more toxic than AgNP-Cit. Slow dissolution may explain the low uptake kinetics and lower toxicity of AgNP-Cit compared with the other 2 Ag forms. The LC50 values based on internal Ag concentrations in the animals were almost stable over time, highlighting the importance of integrating toxicokinetics and toxicodynamics and relating survival with internal Ag concentrations. Neither survival-based elimination rates nor internal LC50s in the organisms showed any significant evidence of nano-specific effects for both AgNPs, although they suggested some uptake of particulate Ag for AgNP-Cit. The authors conclude that the toxicity of both types of AgNP probably is mainly attributable to the release of Ag ions.

Ag Nanoparticles (Ag NM300K) in the Terrestrial Environment: Effects at Population and Cellular Level in Folsomia candida (Collembola)

The effects of nanomaterials have been primarily assessed based on standard ecotoxicity guidelines. However, by adapting alternative measures the information gained could be enhanced considerably, e.g., studies should focus on more mechanistic approaches. Here, the environmental risk posed by the presence of silver nanoparticles (Ag NM300K) in soil was investigated, anchoring population and cellular level effects, i.e., survival, reproduction (28 days) and oxidative stress markers (0, 2, 4, 6, 10 days). The standard species Folsomia candida was used. Measured markers included catalase (CAT), glutathione reductase (GR), glutathione S-transferase (GST), total glutathione (TG), metallothionein (MT) and lipid peroxidation (LPO). Results showed that AgNO₃ was more toxic than AgNPs at the population level: reproduction EC₂₀ and EC₅₀ was ca. 2 and 4 times lower, respectively. At the cellular level Correspondence Analysis showed a clear separation between AgNO₃ and AgNP throughout time. Results showed differences in the mechanisms, indicating a combined effect of released Ag⁺ (MT and GST) and of AgNPs (CAT, GR, TG, LPO). Hence, clear advantages from mechanistic approaches are shown, but also that time is of importance when measuring such responses.

Oxidative Stress Mechanisms Caused by Ag Nanoparticles (NM300K) are Different from Those of AgNO3: Effects in the Soil Invertebrate Enchytraeus Crypticus

The mechanisms of toxicity of Ag nanoparticles (NPs) are unclear, in particular in the terrestrial environment. In this study the effects of AgNP (AgNM300K) were assessed in terms of oxidative stress in the soil worm Enchytraeus crypticus, using a range of biochemical markers [catalase (CAT), glutathione peroxidase (GPx), glutathione S-transferase (GST), glutathione reductase (GR), total glutathione (TG), metallothionein (MT), lipid peroxidation (LPO)]. E. crypticus were exposed during 3 and 7 days (d) to the reproduction EC₂₀, EC₅₀ and EC₈₀ levels of both AgNP and AgNO₃. AgNO₃ induced oxidative stress earlier (3 d) than AgNP (7 d), both leading to LPO despite the activation of the anti-redox system. MT increased only for AgNP. The Correspondence Analysis showed a clear separation between AgNO₃ and AgNP, with e.g., CAT being the main descriptor for AgNP for 7 d. LPO, GST and GPx were for both 3 and 7 d associated with AgNO₃, whereas MT and TG were associated with AgNP. These results may reflect a delay in the effects of AgNP compared to AgNO₃ due to the slower release of Ag⁺ ions from the AgNP, although this does not fully explain the observed differences, i.e., we can conclude that there is a nanoparticle effect.

Establishment of toxicity thresholds in subpopulations of coelomocytes (amoebocytes vs. eleocytes) of Eisenia fetida exposed in vitro to a variety of metals: implications for biomarker measurements

Coelomocytes comprise the immune system of earthworms and due to their sensitivity responding to a wide range of pollutants have been widely used as target cells in soil ecotoxicology. Recently, in vitro assays with primary cultures of coelomocytes based in the neutral red uptake (NRU) assay have been developed as promising tools for toxicity assessment chemical in a reproducible and cost-effective manner. However, NRU showed a bimodal dose-response curve previously described after in vivo and in vitro exposure of earthworm coelomocytes to pollutants. This response could be related with alterations in the relative proportion of coelomocyte subpopulations, amoebocytes and eleocytes. Thus, the aims of the present work were, first, to establish the toxicity thresholds that could be governed by different cell-specific sensitivities of coelomocytes subpopulations against a series of metals (Cu, Cd, Pb, Ni), and second to understand the implication that coelomocyte population dynamics (eleocytes vs. amoebocytes) after exposure to pollutants can have on the viability of coelomocytes (measured by NRU assay) as biomarker of general stress in soil health assessment. Complementarily flow cytometric analyses were applied to obtain correlative information about single cells (amoebocytes and eleocytes) in terms of size and complexity, changes in their relative proportion and mortality rates. The results indicated a clear difference in sensitivity of eleocytes and amoebocytes against metal exposure, being eleocytes more sensitive. The bimodal dose-response curve of NRU after in vitro exposure of primary cultures of coelomocytes to metals revealed an initial mortality of eleocytes (decreased NRU), followed by an increased complexity of amoebocytes (enhanced phagocytosis) and massive mortality of eleocytes (increased NRU), to give raise to a massive mortality of amoebocytes (decrease NRU). A synergistic effect on NRU was exerted by the exposure to high Cu concentrations and acidic pH (elicited by the metal itself), whereas the effects on NRU produced after exposure to Cd, Ni and Pb were due solely to the presence of metals, being the acidification of culture medium meaningless.

Nanosilver pathophysiology in earthworms: Transcriptional profiling of secretory proteins and the implication for the protein corona

Previously we have identified lysenin as a key protein constituent of the secretome from Eisenia fetida coelomocytes and revealed its critical importance in priming interactions between the cells and the protein corona around nanosilver. As alterations of the protein environment can directly affect the corona composition, the extent to which nanoparticles influence the cells' protein secretion profile is of remarkable interest that has rarely acquired attention. Here, we have probed transcriptional responses of E. fetida coelomocytes to the representative nanosilver NM-300K (15 nm) in a time-dependent manner (2, 4, 8 and 24 h at a low-cytotoxic concentration), and examined the implication of the temporal changes in transcriptional profiles of secretory proteins with a particular reference to that of lysenin. NM-300K was accumulated in/at the cells and lysenin was, after transient induction, gradually suppressed over time indicating a negative feedback cycle. This may limit further enrichment of lysenin in the corona and thereby decrease the lysenin-assisted uptake of the nanoparticles. Other differentially expressed genes were those involved in metal stress (likewise in AgNO3-stressed cells) and in Toll-like receptor (TLR) signaling. This offers an intriguing perspective of the nanosilver pathophysiology in earthworms, in which the conserved pattern recognition receptor TLRs may play an effector role.