Soil pH effects on the comparative toxicity of dissolved zinc, non-nano and nano ZnO to the earthworm Eisenia fetida

To determine how soil properties influence nanoparticle (NP) fate, bioavailability and toxicity, this study compared the toxicity of nano zinc oxide (ZnO NPs), non-nano ZnO and ionic ZnCl2 to the earthworm Eisenia fetida in a natural soil at three pH levels. NP characterisation indicated that reaction with the soil media greatly controls ZnO properties. Three main conclusions were drawn. First that Zn toxicity, especially for reproduction, was influenced by pH for all Zn forms. This can be linked to the influence of pH on Zn dissolution. Secondly, that ZnO fate, toxicity and bioaccumulation were similar (including relationships with pH) for both ZnO forms, indicating the absence of NP-specific effects. Finally, earthworm Zn concentrations were higher in worms exposed to ZnO compared to ZnCl2, despite the greater toxicity of the ionic form. This observation suggests the importance of considering the relationship between uptake and toxicity in nanotoxicology studies

Mixed messages from benthic microbial communities exposed to nanoparticulate and ionic silver: 3D structure picks up nano-specific effects, while EPS and traditional endpoints indicate a concentration-dependent impact of silver ions

Silver nanoparticles (AgNP) are currently defined as emerging pollutants in surface water ecosystems. Whether the toxic effects of AgNP towards freshwater organisms are fully explainable by the release of ionic silver (Ag+) has not been conclusively elucidated. Long-term effects to benthic microbial communities (periphyton) that provide essential functions in stream ecosystems are unknown. The effects of exposure of periphyton to 2 and 20 μg/L Ag+ (AgNO3) and AgNP (polyvinylpyrrolidone stabilised) were investigated in artificial indoor streams. The extracellular polymeric substances (EPS) and 3D biofilm structure, biomass, algae species, Ag concentrations in the water phase and bioassociated Ag were analysed. A strong decrease in total Ag was observed within 4 days. Bioassociated Ag was proportional to dissolved Ag indicating a rate limitation by diffusion across the diffusive boundary layer. Two micrograms per liter of AgNO3 or AgNP did not induce significant effects despite detectable bioassociation of Ag. The 20-μg/L AgNO3 affected green algae and diatom communities, biomass and the ratio of polysaccharides to proteins in EPS. The 20-μg/L AgNO3 and AgNP decreased biofilm volume to about 50 %, while the decrease of biomass was lower in 20 μg/L AgNP samples than the 20-μg/L AgNO3 indicating a compaction of the NP-exposed biofilms. Roughness coefficients were lower in 20 μg/L AgNP-treated samples. The more traditional endpoints (biomass and diversity) indicated silver ion concentration-dependent effects, while the newly introduced parameters (3D structure and EPS) indicated both silver ion concentration-dependent effects and effects related to the silver species applied

Toxicokinetics of Ag in the terrestrial isopod Porcellionides pruinosus exposed to Ag NPs and AgNO3 via soil and food

Silver nanoparticles (Ag NPs) have been used in numerous consumer products and may enter the soil through the land application of biosolids. However, little is known about the relationship between Ag NP exposure and their bioavailability for soil organisms. This study aims at comparing the uptake and elimination kinetics of Ag upon exposures to different Ag forms (NPs and ionic Ag (as AgNO3)) in the isopod Porcellionides pruinosus. Isopods were exposed to contaminated Lufa 2.2 soil or alder leaves as food. Uptake and elimination rate constants for soil exposure did not significantly differ between Ag NPs and ionic Ag at 30 and 60 mg Ag/kg. For dietary exposure, the uptake rate constant was up to 5 times higher for Ag NPs than for AgNO3, but this was related to feeding activity and exposure concentrations, while no difference in the elimination rate constants was found. When comparing both routes, dietary exposure resulted in lower Ag uptake rate constants but elimination rate constants did not differ. A fast Ag uptake was observed from both routes and most of the Ag taken up seemed not to be eliminated. Synchrotron X-ray fluorescence showed Ag in the S-cells of the hepatopancreas, thus supporting the observations from the kinetic experiment (i.e. low elimination). In addition, our results show that isopods have an extremely high Ag accumulation capacity, suggesting the presence of an efficient Ag storage compartment

Uptake routes and toxicokinetics of silver nanoparticles and silver ions in the earthworm Lumbricus rubellus

Current bioavailability models, such as the free ion activity model and biotic ligand model, explicitly consider that metal exposure will be mainly to the dissolved metal in ionic form. With the rise of nanotechnology products and the increasing release of metal-based nanoparticles (NPs) to the environment, such models may increasingly be applied to support risk assessment. It is not immediately clear, however, whether the assumption of metal ion exposure will be relevant for NPs. Using an established approach of oral gluing, a toxicokinetics study was conducted to investigate the routes of silver nanoparticles (AgNPs) and Ag+ ion uptake in the soil-dwelling earthworm Lumbricus rubellus. The results indicated that a significant part of the Ag uptake in the earthworms is through oral/gut uptake for both Ag+ ions and NPs. Thus, sealing the mouth reduced Ag uptake by between 40% and 75%. An X-ray analysis of the internal distribution of Ag in transverse sections confirmed the presence of increased Ag concentrations in exposed earthworm tissues. For the AgNPs but not the Ag+ ions, high concentrations were associated with the gut wall, liver-like chloragogenous tissue, and nephridia, which suggest a pathway for AgNP uptake, detoxification, and excretion via these organs. Overall, the results indicate that Ag in the ionic and NP forms is assimilated and internally distributed in earthworms and that this uptake occurs predominantly via the gut epithelium and less so via the body wall. The importance of oral exposure questions the application of current metal bioavailability models, which implicitly consider that the dominant route of exposure is via the soil solution, for bioavailability assessment and modeling of metal-based NPs

Nanoparticle tracking analysis of gold nanoparticles in aqueous media through an inter-laboratory comparison

In the field of nanotechnology, analytical characterization plays a vital role in understanding the behavior and toxicity of nanomaterials (NMs). Characterization needs to be thorough and the technique chosen should be well-suited to the property to be determined, the material being analyzed and the medium in which it is present. Furthermore, the instrument operation and methodology need to be well-developed and clearly understood by the user to avoid data collection errors. Any discrepancies in the applied method or procedure can lead to differences and poor reproducibility of obtained data. This paper aims to clarify the method to measure the hydrodynamic diameter of gold nanoparticles by means of Nanoparticle Tracking Analysis (NTA). This study was carried out as an inter-laboratory comparison (ILC) amongst seven different laboratories to validate the standard operating procedure’s performance and reproducibility. The results obtained from this ILC study reveal the importance and benefits of detailed standard operating procedures (SOPs), best practice updates, user knowledge, and measurement automation

Metal transfer to sediments, invertebrates and fish following waterborne exposure to silver nitrate or silver sulfide nanoparticles in an indoor stream mesocosm

The fate of engineered nanomaterials in ecosystems is unclear. An aquatic stream mesocosm explored the fate and bioaccumulation of silver sulfide nanoparticles (AgS NPs) compared to silver nitrate (AgNO). The aims were to determine the total Ag in water, sediment and biota, and to evaluate the bioavailable fractions of silver in the sediment using a serial extraction method. The total Ag in the water column from a nominal daily dose of 10 μg L of Ag for the AgNO or AgS NP treatments reached a plateau of around 13 and 12 μg L, respectively, by the end of the study. Similarly, the sediment of both Ag-treatments reached ~380 μg Ag kg, and with most of it being acid-extractable/labile. The biota accumulated 4–59 μg Ag g dw, depending on the type of Ag-treatment and organism. The oligochaete worm, Lumbriculus variegatus, accumulated Ag from the AgS exposure over time, which was similar to the AgNO treatment by the end of the experiment. The planarian, Girardia tigrina, and the chironomid larva, Chironomus riparius, showed much higher Ag concentrations than the oligochaete worms; and with a clearer time-dependent statistically significant Ag accumulation relative to the untreated controls. For the pulmonate snail, Physa acuta, bioaccumulation of Ag from AgNO and AgS NP exposures was observed, but was lower from the nano treatment. The AgNO exposure caused appreciable Ag accumulation in the water flea, Daphnia magna, but accumulation was higher in the AgS NP treatment (reaching 59 μg g dw). In the rainbow trout, Oncorhynchus mykiss, AgNO, but not AgS NPs, caused total Ag concentrations to increase in the tissues. Overall, the study showed transfer of total Ag from the water column to the sediment, and Ag bioaccumulation in the biota, with Ag from AgS NP exposure generally being less bioavailable than that from AgNO.This work was supported by the project NanoFASE (Nanomaterial Fate and Speciation in the Environment), financed by the European Union's Horizon 2020 research and innovation programme under grant agreement no 646002. RDH was partly supported by NanoHarmony under grant agreement 885931 in Horizon 2020 while redrafting the main text. PVS was awarded with a PhD grant (SFRH/BD/51571/2014) by FCT – Fundação para a Ciência e a Tecnologia. SL and PVS received additional financial support from FCT/MCTES, through national funds, to CESAM (UIDP/50017/2020+UIDB/50017/2020+ LA/P/0094/2020)

Effects of silver nanoparticles on freshwater microbial communities

Nanoparticles (NPs) display special chemical properties because of their size, shape, composition and electronic structure. These properties lend NPs their functionality, but may also lead to toxic effects. Due to their widespread use in consumer products an exposure of the aquatic environment to NPs is anticipated and already proven in first analytical surveys. Especially metal/metaloxide NPs are widely used, of which silver nanoparticles (AgNPs) have gained considerable attention due to their broad microbiocidal properties. This implies a specific hazard for exposed aquatic primary producers (algae) and bacteria. In a case study with AgNPs, the toxicity to natural freshwater microbial communities was determined. The microbial communities were exposed to AgNPs of different sizes (10, 20, 40 and 50 nm) as well as different coatings (non-coated, citrate coated) in concentrations from 0.1 - 5000 nmol/L expcept for one silver nanoparticle type (50 nm, uncoated) which was tested in a range from 100 - 10 000 nmol/L. The selected silver nanoparticles were all purchased from commercial producers and distributers (Amepox, British Biocell, NanoTrade, Tedpella). To distinguish between particle related effects and effects caused by free silver ions silver nitrate was tested as a reference in corresponding total silver concentrations. The effects on the algal parts of the community was studied through pigment profile analysis with HPLC. The bacterial community composition was analysed by metabolic profiling on so called ecologplates[TRADEMARK] containing different carbon sources with a redox dye responding to respiration with colour change. The metabolic activity i.e. the colour change was detected as absorbance and was measured over time in several intervals for a total time period of 96 hours. Inhibition of growth detected as decrease in total biomass was seen in both bacterial and algal communities. All experiments were backed up by analytical measurements, measuring the total silver content, dissolved Ag+ (ultrafiltration) and particle size distribution (Nanosight)

Effects of selected silver nanoparticles on freshwater microbial communities

Due to their widespread use in consumer products an exposure of the aquatic environment to nanoparticles (NPs) is most likely. Especially metal/metaloxide NPs are widely used, of which silver nanoparticles (AgNPs) have gained considerable attention due to their broad microbiocidal properties implying a specific hazard for exposed aquatic algae and bacteria.In a case study with selected AgNPs (different sizes (10, 20 and 40 nm), and different coatings (citrate coated, non-coated)), the toxicity to natural freshwater microbial communities was determined. To distinguish between particle related effects and effects caused by free silver ions silver nitrate (AgNO3) was tested as a reference. The effects on the algal part of the community was studied through pigment profiling with HPLC. The bacterial community composition was analysed by metabolic profiling (ecologplates™). Inhibition of growth detected as a decrease in total biomass was seen in both bacterial and algal communities, for some cases in the range of environmentally realistic concentrations. Differences in toxicity could be determined for the different particles with AgNO3 being for almost all cases the most toxic compound with one excpetion. All experiments were backed up by analytical measurements (total silver content, dissolved silver (ultrafiltration), particle size distribution (Nanosight))

Toxicity of differently sized and coated silver nanoparticles to the bacterium Pseudomonas putida: risks for the aquatic environment?

Aim of this study was to describe the toxicity of a set of different commercially available silver nanoparticles (AgNPs) to the gram-negative bacterium Pseudomonas putida (growth inhibition assay, ISO 10712) in order to contribute to their environmental hazard and risk assessment. Different AgNP sizes and coatings were selected in order to analyze whether those characteristics are determinants of nanoparticle toxicity. Silver nitrate was tested for comparison. In general Pseudomonas putida reacted very sensitive towards the exposure to silver, with an EC05 value of 0.043 μg L−1 for AgNO3 and between 0.13 and 3.41 μg L−1 for the different AgNPs (EC50 values 0.16 μg L−1 for AgNO3, resp. between 0.25 and 13.4 μg L−1 for AgNPs). As the ionic form of silver is clearly the most toxic, an environmental hazard assessment for microorganisms based on total silver concentration and the assumption that AgNPs dissolve is sufficiently protective. Neither specific coatings nor certain sizes could be linked to increasing or decreasing toxicity. The characterization of particle behavior as well as the total and dissolved silver content in the medium during the exposures was not possible due to the high sensitivity of Pseudomonas (test concentrations were below detection limits), indicating the need for further development in the analytical domain. Monitored silver concentrations in the aquatic environment span six orders of magnitude (0.1–120,000 ng L−1), which falls into the span of observed EC05 values and might hence indicate a risk to environmental bacteria