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

Multidimensional applications and potential health implications of nanocomposites

This study reviews the concept, classifications, and techniques involved in the synthesis of nanocomposites. The environmental and health implications of nanoparticles and composite materials were detailed, as well as the applications of nanocomposites in water remediation, antibacterial application, and printed circuit boards. The study gave insights into the challenges of water pollution treatment and provided a broad list of nanocomposites that have been explored for water remediation. Moreover, the emergence of multi-drug resistance to many antibiotics has made current antibiotics inadequate in the treatment of disease. This has engineered the development of alternative strategies in the drug industries for the production of effective therapeutic agents, comprising nanocomposites with antibacterial agents. The new therapeutic agents known as nanoantibiotics are more efficient and have paved the way to handle the challenges of antibiotic resistance. In printed circuit boards, nanocomposites have shown promising applications because of their distinct mechanical, thermal, and electrical characteristics. The uniqueness of the write-up is that it provides a broad explanation of the concept, synthesis, application, toxicity, and harmful effects of nanocomposites. Thus, it will provide all-inclusive awareness to readers to identify research gaps and motivate researchers to synthesize novel nanocomposites for use in various fields.

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.

The effect of polystyrene microplastic and biosolid application on the toxicity and bioaccumulation of cadmium for Enchytraeus crypticus

Plastics smaller than 5 mm that end up in a soil environment are known as microplastics (MPs). Microplastics have become a common contaminant in agricultural areas in addition to metals. However, the effect of cadmium (Cd) on soil organisms has not been clearly defined in the presence of MPs. In addition to MPs, biosolid application as a soil amendment in agricultural lands is also leading to shifts in soil conditions, such as the concentrations of nutrients and organic matter. Therefore, the aim of this study is to investigate the toxicity and bioaccumulation of Cd for Enchytraeus crypticus in the presence of polystyrene (PS)-MPs and biosolids to provide insight into their possible interactions. The lethal toxic concentration (LC50) for Cd was higher than 650 mg Cd/kg dry soil for all conditions. The presence of PS-MPs increased the toxicity of Cd for which EC50 was 102 and 38 mg Cd/kg dry soil without and with Cd, respectively, which may be the result of an increased exposure rate through adsorption of Cd on PS-MPs. On the contrary, the presence of biosolids decreased the toxicity of Cd where EC50 was 193 and 473 mg Cd/kg dry soil for the sets applied with 0.6 and 0.9 g biosolids, respectively. Coexistence of biosolids and PS-MPs decreased the reproduction toxicity of Cd, which is similar to the biosolid effect (EC50 is 305 mg Cd/kg dry soil). Bioaccumulation of Cd only positively correlated with its initial concentration in soil and was not affected by the presence of PS-MPs or biosolids. Integr Environ Assess Manag 2023;19:489-500. © 2022 SETAC.

The effect of sulfidation and soil type on the uptake of silver nanoparticles in annelid Enchytraeus crypticus

Hazard assessment of silver nanoparticles is crucial as their presence in agricultural land is increasing through sewage sludge application. This study compared the uptake and elimination kinetics in the annelid Enchytraeus crypticus of AgNPs with different core sizes and coatings in Lufa 2.2 soil, and of Ag₂S NPs (simulating aged AgNPs) in three different soils. For both experiments, AgNO₃ was used as ionic control. E. crypticus was exposed to soil spiked at 10 μg Ag g^-1 dry soil for 14 days and then transferred to clean soil for a 14-day elimination phase. The uptake rate constants were similar for 3-8 nm and 60 nm AgNPs and AgNO₃, but significantly different between 3 and 8 nm and 50 nm AgNPs. The uptake kinetics of Ag from Ag₂S NPs did not significantly differ compared to pristine AgNPs. Therefore, Ag bioavailability was influenced by AgNP form and characteristics. Uptake and elimination rate constants of both Ag forms (AgNO₃ and Ag₂S NPs) significantly differed between different test soils (Lufa 2.2, Dorset, and Woburn). For AgNO₃, significantly higher uptake and elimination rate constants were found in the Dorset soil compared to the other soils, while for Ag₂S NPs this soil showed the lowest uptake and elimination rate constants. Therefore, not only the form and characteristics but also soil properties affect the bioavailability and uptake of Ag nanoparticles.

Effects of microplastics from disposable medical masks on terrestrial invertebrates

This study investigated impacts of microplastics from disposable polypropylene medical masks on woodlice Porcellio scaber, mealworm larvae Tenebrio molitor and enchytraeids Enchytraeus crypticus. Effects of microplastics on survival, reproduction, immune parameters and energy-related traits were assessed after 21 days exposure in soil. Microplastics obtained from each medical mask layer separately differed in size and shape (inner frontal layer: 45.1 ± 21.5 µm, fibers; middle filtering layer: 55.6 ± 28.5 µm, fragments; outer layer: 42.0 ± 17.8 µm, fibers) and composition of additives. Overall, the concentrations of metals and organic chemicals were too low to cause effects on soil invertebrates. The microplastics from disposable medical masks at 0.06%, 0.5%, 1.5%, w/w did not induce severe adverse effects on survival or reproduction (for enchytraeids). A transient immune response of woodlice and a change in energy-related traits in mealworms were observed, which was most clearly seen for the microplastics from the outer layer. This was reflected in increased electron transfer system activity of mealworms and different immune response dynamics of woodlice. In conclusion, the tested soil invertebrates respond to microplastics from disposable medical masks, but it remains unclear what these changes mean for their fitness on the long term.

The impact of engineered nanomaterials on the environment: Release mechanism, toxicity, transformation, and remediation

The presence and longevity of nanomaterials in the ecosystem, as well as their properties, account for environmental toxicity. When nanomaterials in terrestrial and aquatic systems are exposed to the prevailing environmental conditions, they undergo various transformations such as dissociation, dissolution, and aggregation, which affects the food chain. The toxicity of nanomaterials is influenced by a variety of factors, including environmental factors and its physico-chemical characteristics. Bioaccumulation, biotransformation, and biomagnification are the mechanisms that have been identified for determining the fate of nanomaterials. The route taken by nanomaterials to reach living cells provides us with information about their toxicity profile. This review discusses the recent advances in the transport, transformation, and fate of nanomaterials after they are released into the environment. The review also discusses how nanoparticles affect lower trophic organisms through direct contact, the impact of nanoparticles on higher trophic organisms, and the possible options for remediation.

Ecotoxicity of as-synthesised copper nanoparticles on soil bacteria

Release of metallic nanoparticles in soil poses a serious threat to the ecosystem as they can affect the soil properties and impose toxicity on soil microbes that are involved in the biogeochemical cycling. In this work, in vitro ecotoxicity of as‐synthesised copper nanoparticles (CuNPs) on Bacillus subtilis (MTCC No. 441) and Pseudomonas fluorescens (MTCC No. 1749), which are commonly present in soil was investigated. Three sets of colloidal CuNPs with identical physical properties were synthesised by chemical reduction method with per batch yield of 0.2, 0.3 and 0.4 gm. Toxicity of CuNPs against these soil bacteria was investigated by MIC (minimum inhibitory concentration), MBC (minimum bactericidal concentration), cytoplasmic leakage and ROS (reactive oxygen species) assay. MIC of CuNPs were in the range of 35–60 µg/ml and 35–55 µg/ml for B. subtilis and P. fluorescens respectively, while their MBC ranged from 40–70 µg/ml and 40–60 µg/ml respectively. MIC and MBC tests reveal that Gram‐negative P. fluorescens was more sensitive to CuNPs as compared to Gram positive B. subtilis mainly due to the differences in their cell wall structure and composition. CuNPs with smaller hydrodynamic size (11.34 nm) were highly toxic as revealed by MIC, MBC tests, cytoplasmic leakage and ROS assays, which may be due to the higher active surface area of CuNPs and greater membrane penetration. Leakage of cytoplasmic components and generation of extra‐cellular oxidative stress by reactive oxygen species (ROS) causes cell death. The present study realizes in gauging the negative impact of inadvertent release of nanoparticles in the environment, however, in situ experiments to know its overall impact on soil health and soil microflora can help in finding solution to combat ecotoxicity of nanoparticles.

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.

Toxicokinetics of silver nanoparticles in the mealworm Tenebrio molitor exposed via soil or food

Silver nanoparticles (AgNPs) may reach the soil compartment via sewage sludge or nanoagrochemical applications. Understanding how NPs interact with biological systems is crucial for an accurate hazard assessment. Therefore, this study aimed at determining the Ag toxicokinetics in the mealworm Tenebrio molitor, exposed via Lufa 2.2 soil or via food to different Ag forms (uncoated 50 nm AgNPs, paraffin coated 3-8 nm and PVP-stabilised 60 nm, Ag₂S NPs 20 nm, and ionic Ag). Mealworms were exposed for 21 days followed by a 21-day elimination phase (clean soil/food). A one-compartment kinetics model with inert fraction (simulating a storage compartment, where detoxified forms are located) was used to describe Ag accumulation. Fully understanding the uptake route in mealworms is difficult. For that reason several approaches were used, showing that food, soil and pore water all are valid uptake routes, but with different importance. Silver taken up from soil pore water or from soil showed to be related to Ag dissolution in soil pore water. In general, the uptake and elimination rate constants were similar for 3-8 nm and 60 nm AgNPs and for AgNO₃, but significantly different for the uncoated 50 nm AgNPs. Upon food exposure, uptake rate constants were similar for 50 nm AgNPs and AgNO₃, while those for 60 nm and 3-8 nm AgNPs and for Ag₂S NPs also grouped together. NP exposure in soil appeared more difficult to characterize, with different patterns obtained for the different NPs. But it was evident that upon soil or food exposure, particle characteristics highly affected Ag bioavailability and bioaccumulation. Although Ag₂S NPs were taken up, their elimination was faster than for other Ag forms, showing the lowest inert fraction. The significantly different elimination rate constants suggest that the mechanism of elimination may not be the same for different AgNPs either.

Ecotoxicity of arsenic contamination toward the soil enchytraeid Enchytraeus crypticus at different biological levels: Laboratory studies

The ecotoxicity of arsenic (As) contamination toward small soil fauna living in soil pore water such as soil enchytraeids has rarely been studied but is important in the assessment of soil pollution. Here, the endpoints of As ecotoxicity to Enchytraeus crypticus were studied at three biological levels, i.e., individual (morphology and body tissue As concentrations), population (survival, reproduction and growth) and cell biochemistry (antioxidant enzymes CAT, POD and SOD and peroxidation malondialdehyde MDA). Contact filter paper tests without soil and single species tests with OECD artificial and field soils were conducted. Arsenic contamination resulted in severe morphological pathologies in E. crypticus and the symptoms and degree of damage increased gradually with increasing As concentration and exposure time up to 48 h. The abnormal morphological effects occurred before the impairment of fecundity. The population endpoints responded to the As concentration and the EC50 values increased in the following sequence: reproduction, juvenile body weight, adult body weight, juvenile length and adult length. Changes in biochemistry parameters were induced rapidly and changed with increasing As concentration and exposure time. The activity peak values of enzymes were 3-5 times higher and the activity maximum values of MDA were 1-3 time higher than their controls. The sensitivity of enzyme activities was generally much higher than that of MDA and CAT generally showed the highest enzyme activity. The results indicate that As contamination can be very harmful to soil enchytraeids and the endpoints of the ecotoxicity tests of soil enchytraeids can be used to complement existing soil As assessment systems or may be used alone for the assessment of soil As pollution.

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.

Soil Pollution from Micro- and Nanoplastic Debris: A Hidden and Unknown Biohazard

The fate, properties and determination of microplastics (MPs) and nanoplastics (NPs) in soil are poorly known. In fact, most of the 300 million tons of plastics produced each year ends up in the environment and the soil acts as a log-term sink for these plastic debris. Therefore, the aim of this review is to discuss MP and NP pollution in soil as well as highlighting the knowledge gaps that are mainly related to the complexity of the soil ecosystem. The fate of MPs and NPs in soil is strongly determined by physical properties of plastics, whereas negligible effect is exerted by their chemical structures. The degradative processes of plastic, termed ageing, besides generating micro-and nano-size debris, can induce marked changes in their chemical and physical properties with relevant effects on their reactivity. Further, these processes could cause the release of toxic oligomeric and monomeric constituents from plastics, as well as toxic additives, which may enter in the food chain, representing a possible hazard to human health and potentially affecting the fauna and flora in the environment. In relation to their persistence in soil, the list of soil-inhabiting, plastic-eating bacteria, fungi and insect is increasing daily. One of the main ecological functions attributable to MPs is related to their function as vectors for microorganisms through the soil. However, the main ecological effect of NPs (limited to the fraction size < than 50 nm) is their capacity to pass through the membrane of both prokaryotic and eukaryotic cells. Soil biota, particularly earthworms and collembola, can be both MPs and NPs carriers through soil profile. The use of molecular techniques, especially omics approaches, can gain insights into the effects of MPs and NPs on composition and activity of microbial communities inhabiting the soil and into those living on MPs surface and in the gut of the soil plastic-ingesting fauna.

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.

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.

Protective effect of N-acetylcysteine on the toxicity of silver nanoparticles: Bioavailability and toxicokinetics in Enchytraeus crypticus

We previously demonstrated that N-acetylcysteine (NAC) could reduce the toxicity of silver (Ag) materials (nanoparticles (NPs) and Ag nitrate) to the soil invertebrate Enchytraeus crypticus (Oligochaeta). It remains however, unclear whether the antitoxic mechanism of NAC was caused by NAC-Ag binding in the soil or inside the organisms. This study aimed at determining the bioavailability of Ag in the soil in a 21-day toxicity test as well as the Ag uptake and elimination kinetics in E. crypticus exposed to AgNPs in LUFA 2.2 standard soil amended with low (100 mg/kg dry soil) and high (600 mg/kg dry soil) NAC concentrations. The addition of NAC to the soil alleviated the toxicity of AgNPs by decreasing the internal Ag concentration of E. crypticus in a dose-dependent manner. Indeed, NAC reduced the binding of Ag to the soil, which probably was due to the formation of soluble but biologically unavailable Ag-cysteine complexes. The reduced Ag uptake in the enchytraeids was explained from an increased elimination at high NAC levels. These findings reinforce the view that metal complexing-compounds like NAC play a key role in the modulation of AgNP toxicity and bioavailability in terrestrial environments. Further, it may inform on the potential of NAC as a remediation solution for Ag or other metal-contaminated soils.

Do combined nanoscale polystyrene and tetracycline impact on the incidence of resistance genes and microbial community disturbance in Enchytraeus crypticus?

It has been proved that nanoplastics can effectively adsorb pollutants and thus influence their behavior and availability. The combined toxic effects of nanoplastic and its adsorbed pollutant on the soil fauna are still not well known. We used high-throughput quantitative PCR to explore the effects of oral nanoscale polystyrene and tetracycline exposure on antibiotic resistance genes in the soil invertebrate Enchytraeus crypticus, and used bacterial 16S rRNA gene amplification sequencing to examine the response of the microbiome of E. crypticus. After 14 days of tetracycline and nanoscale polystyrene exposure, we terminated exposure and monitored the restoration of ARGs and microbiome in the E. crypticus. Results showed that the number of ARGs, especially macrolide-lincosamide-streptogramin B (MLSB), tetracycline ARGs, as well as multidrug ARGs, increased with exposure to nanoscale polystyrene and tetracycline. The abundance of Aminoglycoside and Beta_Lactamase ARGs in E. crypticus also significantly increased. The exposure significantly perturbed the abundance of families Microbacteriaceae, Streptococcaceae, Enterobacteriaceae, Rhodocyclaceae and Sphinomonadaceae. After terminating exposure for 14 days, the diversity and abundance of ARGs were not completely restored, while the microbiome was not permanently changed but reversibly impacted.

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.

Effects of single and combined exposure to nano and bulk zinc-oxide and propiconazole on Enchytraeus albidus

Organisms in soil are often exposed to different mixtures of contaminants. These contaminants may interact with each other and, consequently, may have a different effect on organisms than each of them alone. We wanted to investigate possible effects of ZnO mixtures in bulk and nano form and fungicide propiconazole (PCZ) on biochemical parameters and reproduction in Enchytreus albidus. These compounds were applied separately and in binary mixture. In the single exposure experiment the EC₅₀ values for the number of juveniles were calculated: nano ZnO (641.21 ± 88.82 mg kg^-1), bulk ZnO (445.78 ± 148.4 mg kg^-1) and PCZ (3.63 ± 1.68 mg kg-1), respectively. These concentrations were subsequently used in the binary exposure experiment. Calculated combination indices (CI), that allow quantitative determination of chemical interactions at different concentration and effect level, indicated additive or antagonistic interactions (CI ≥ 1) of applied mixture ratios. The only ratio that showed synergistic interaction (CI < 1) was 75% EC₅₀ nZnO/25% EC₅₀ PCZ. Both ZnO forms caused acetylcholinesterase (AChE) activity increase of up to 40% of control level, as well as increased catalase (CAT) and glutathione S-transferase (GST) activities and malondialdehyde (MDA) level. PCZ did not affect AChE and CAT activities, yet it increased GST activity and MDA level. Induced levels of measured biomarkers indicate an oxidative stress after binary exposure, as well. These effects were not enhanced after binary exposure but reflected the effects on biomarkers that corresponding concentrations of these compounds generated in a single exposure experiment.

Exposure to tetracycline perturbs the microbiome of soil oligochaete Enchytraeus crypticus

Microbial symbiosis is essential for the normal development and growth of hosts. Past attention has mostly been paid to its effects on plants and vertebrates. The effects of environmental pressures such as antibiotics on the microbiome of soil fauna remain largely elusive. We used bacterial 16S rRNA gene high-throughput sequencing to examine the response of microbiome of soil invertebrate Enchytraeus crypticus to oral tetracycline exposure. After two-week exposure, tetracycline-free oat was used as food to monitor the restoration of E. crypticus microbiome. The results showed that Proteobacteria, Actinobacteria and Planctomycetes were the three dominant phyla in all samples, Rhizobiaceae and Kaistia were the most abundant family and genus in all samples, respectively. After 14 days tetracycline exposure, Planctomycetes declined dramatically from 33.05% to 3.28% (P = 0.016), but Actinobacteria elevated substantially from 2.47% to 23.65% (P = 0.004). The alpha-diversity of microbial community increased significantly after tetracycline exposure compared to the control (P = 0.014). Terminating tetracycline exposure led to the recovery of E. crypticus microbiome back to the background level within 14 days. Our results suggest that while tetracycline can disturb the microbiome in E. crypticus significantly, the effects of the antibiotic on E. crypticus microbiome may not be permanent but reversibly diminish after stopping exposure for a period of time. The results may contribute to extending our understanding of the effect of antibiotics on microbiome of soil invertebrates. CAPSULE: The microbiome of E. crypticus exposed to tetracycline is perturbed and reversibly restored after terminating the exposure.

The nanotechnology among US: are metal and metal oxides nanoparticles a nano or mega risk for soil microbial communities?

Metal nanoparticles and metal oxides nanoparticles (MNPs/MONPs) have been widely included in a great diversity of products and industrial applications and they are already a part of our everyday life. According to estimation studies, their production is expected to increase exponentially in the next few years. Consequently, soil has been suggested as the main sink of MNPs/MONPs once they are deliberately or accidentally released into the environment. The potential negative perturbations that may result on soil microbial communities and ecological processes are resulting in concerns. Several nano-toxicological studies of MNPs/MONPs, reported so far, have focused on aquatic organisms, animals, and soil invertebrates. However, during recent years, the studies have been oriented to understand the effects of MNPs/MONPs on microbial communities and their interaction with soil components. The studies have suggested that MNPs/MONPs are one of the most toxic type to soil biota, amongst different types of nanomaterials. This may threaten soil health and fertility, since microbial communities are known to support important biological processes and ecosystem services such as the nutrient cycling, whereby their protection against the environmental pollution is imperative. Therefore, in this review we summarize the actual knowledge available from the last five years (2013-2018) and gaps about the potential negative, positive or neutral effects produced on soil by different classes of MNPs/MONPs. A particular emphasis has been placed on the associated soil microorganisms and biological processes. Finally, perspectives about future research are discussed.

Exposure to nanoplastics disturbs the gut microbiome in the soil oligochaete Enchytraeus crypticus

Microplastics are emerging pollutants that have recently aroused considerable concern but most toxicological studies have focused on marine biota, with little investigation of the influence of microplastics on terrestrial ecosystems. Here, we fed the soil oligochaete Enchytraeus crypticus with oatmeal containing 0, 0.025, 0.5, and 10% (dry weight basis) nano-polystyrene (0.05-0.1 μm particle size) to elucidate the impact of microplastics on the growth and gut microbiome of Enchytraeus crypticus. We observed a significant reduction of weight in the animals fed 10% polystyrene and an increase in the reproduction of those fed 0.025%. More importantly, using 16S rRNA amplification and high-throughput sequencing we found a significant shift in the microbiome of those fed 10% microplastics with significant decreases in the relative abundance of the families Rhizobiaceae, Xanthobacteraceae and Isosphaeraceae. These families contain key microbes that contribute to nitrogen cycling and organic matter decomposition.

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.

Nanoparticles in the environment: where do we come from, where do we go to?

Nanoparticles serve various industrial and domestic purposes which is reflected in their steadily increasing production volume. This economic success comes along with their presence in the environment and the risk of potentially adverse effects in natural systems. Over the last decade, substantial progress regarding the understanding of sources, fate, and effects of nanoparticles has been made. Predictions of environmental concentrations based on modelling approaches could recently be confirmed by measured concentrations in the field. Nonetheless, analytical techniques are, as covered elsewhere, still under development to more efficiently and reliably characterize and quantify nanoparticles, as well as to detect them in complex environmental matrixes. Simultaneously, the effects of nanoparticles on aquatic and terrestrial systems have received increasing attention. While the debate on the relevance of nanoparticle-released metal ions for their toxicity is still ongoing, it is a re-occurring phenomenon that inert nanoparticles are able to interact with biota through physical pathways such as biological surface coating. This among others interferes with the growth and behaviour of exposed organisms. Moreover, co-occurring contaminants interact with nanoparticles. There is multiple evidence suggesting nanoparticles as a sink for organic and inorganic co-contaminants. On the other hand, in the presence of nanoparticles, repeatedly an elevated effect on the test species induced by the co-contaminants has been reported. In this paper, we highlight recent achievements in the field of nano-ecotoxicology in both aquatic and terrestrial systems but also refer to substantial gaps that require further attention in the future.