Multigenerational exposure to silver ions and silver nanoparticles reveals heightened sensitivity and epigenetic memory in Caenorhabditis elegans

The effects from multigenerational exposures to engineered nanoparticles (ENPs) in their pristine and transformed states are currently unknown despite such exposures being an increasingly common scenario in natural environments. Here, we examine how exposure over 10 generations affects the sensitivity of the nematode Caenorhabditis elegans to pristine and sulfidized Ag ENPs and AgNO3. We also include populations that were initially exposed over six generations but kept unexposed for subsequent four generations to allow recovery from exposure. Toxicity of the different silver forms decreased in the order AgNO3, Ag ENPs and Ag2S ENPs. Continuous exposure to Ag ENPs and AgNO3 caused pronounced sensitization (approx. 10-fold) in the F2 generation, which was sustained until F10. This sensitization was less pronounced for Ag2S ENP exposures, indicating different toxicity mechanisms. Subtle changes in size and lifespan were also measured. In the recovery populations, the sensitivity to Ag ENPs and AgNO3 resulting from the initial multigenerational exposure persisted. Their response sensitivity for all endpoints was most closely related to the last ancestral exposed generation (F5), rather than unexposed controls. The mechanisms of transgenerational transfer of sensitivity are probably organized through the epigenome, and we encourage others to investigate such effects as a priority for mechanistic toxicology

Influence of soil porewater properties on the fate and toxicity of silver nanoparticles to Caenorhabditis elegans

Engineered nanoparticles (NPs) entering the environment are subject to various transformations that in turn influence how particles are presented to, and taken up by, organisms. To understand the effect of soil properties on the toxicity of nanosilver to Caenorhabditis elegans, toxicity assays were performed in porewater extracts from natural soils with varying organic matter content and pH using 3–8 nm unfunctionalized silver (Ag 3–8Unf), 52‐nm polyvinylpyrrolidone (PVP)‐coated Ag NPs (Ag 52PVP), and AgNO3 as ionic Ag. Effects on NP agglomeration and stability were investigated using ultraviolet‐visible (UV‐vis) spectroscopy and asymmetric flow field‐flow fractionation (AF4); Ag+ showed greater overall toxicity than nanosilver, with little difference between the NP types. Increasing soil organic matter content significantly decreased the toxicity of Ag 3–8Unf, whereas it increased that of AgNO3. The toxicity of all Ag treatments significantly decreased with increasing porewater pH. Dissolution of both NPs in the porewater extracts was too low to have contributed to their observed toxic effects. The UV‐vis spectroscopy revealed low levels of agglomeration/aggregation independent of soil properties for Ag 3–8Unf, whereas higher organic matter as well as low pH appeared to stabilize Ag 52PVP. Overall, both soil organic matter content and pH affected NP fate as well as toxicity to C. elegans; however, there appears to be no clear connection between the measured particle characteristics and their effect

Aging reduces the toxicity of pristine but not sulphidised silver nanoparticles to soil bacteria

In the environment engineered nanoparticles (ENPs) are subject to chemical and physical transformation processes. Thus, to understand their impact, it is important to consider how bioavailability and toxicity are influenced by these “aging” transformations with relation to environmental conditions and ENP properties. Here, two soil bacteria were exposed to Ag ENPs in ISO media (± fulvic acid) and soil pore water extracts with pH 6 and pH 8. The ENPs tested were 49 nm unfunctionalised, citrate stabilised (Ag-citr), 58 nm PVP-coated (Ag-PVP) and 36 nm sulphidised (Ag2S-PVP); AgNO3 was used as a positive control. Exposures were carried out using pristine (unaged) and 24 h aged ENPs, and the 24 h soluble fraction. Overall, toxicity was ranked AgNO3 > Ag-PVP ≥ Ag-citr ≫ Ag2S. Aging of AgNO3, Ag-PVP and Ag-citr in the ISO medium caused little change from unaged exposures and growth inhibition was mainly caused by soluble silver. Added fulvic acid decreased silver toxicity after aging and reduced the contribution of dissolution; as was the case in the soil pore waters where toxicity could not be attributed to ionic silver. Ag2S toxicity to A. globiformis in both ISO variants increased after aging, yet followed the same patterns as the metallic ENPs in the pore waters. For all ENPs pH effects were species dependent. Together this data showed that aging reduced toxicity in media with organic matter and despite soluble silver being the main driver of pristine ENP toxicity in the standard ISO medium, dissolution did not fully explain toxicity in the presence of organic matter

Versailles project on advanced materials and standards (VAMAS) interlaboratory study on measuring the number concentration of colloidal gold nanoparticles

We describe the outcome of a large international interlaboratory study of the measurement of particle number concentration of colloidal nanoparticles, project 10 of the technical working area 34, "Nanoparticle Populations" of the Versailles Project on Advanced Materials and Standards (VAMAS). A total of 50 laboratories delivered results for the number concentration of 30 nm gold colloidal nanoparticles measured using particle tracking analysis (PTA), single particle inductively coupled plasma mass spectrometry (spICP-MS), ultraviolet-visible (UV-Vis) light spectroscopy, centrifugal liquid sedimentation (CLS) and small angle X-ray scattering (SAXS). The study provides quantitative data to evaluate the repeatability of these methods and their reproducibility in the measurement of number concentration of model nanoparticle systems following a common measurement protocol. We find that the population-averaging methods of SAXS, CLS and UV-Vis have high measurement repeatability and reproducibility, with between-labs variability of 2.6%, 11% and 1.4% respectively. However, results may be significantly biased for reasons including inaccurate material properties whose values are used to compute the number concentration. Particle-counting method results are less reproducibile than population-averaging methods, with measured between-labs variability of 68% and 46% for PTA and spICP-MS respectively. This study provides the stakeholder community with important comparative data to underpin measurement reproducibility and method validation for number concentration of nanoparticles

Versailles project on advanced materials and standards (VAMAS) interlaboratory study on measuring the number concentration of colloidal gold nanoparticles

We describe the outcome of a large international interlaboratory study of the measurement of particle number concentration of colloidal nanoparticles, project 10 of the technical working area 34, "Nanoparticle Populations" of the Versailles Project on Advanced Materials and Standards (VAMAS). A total of 50 laboratories delivered results for the number concentration of 30 nm gold colloidal nanoparticles measured using particle tracking analysis (PTA), single particle inductively coupled plasma mass spectrometry (spICP-MS), ultraviolet-visible (UV-Vis) light spectroscopy, centrifugal liquid sedimentation (CLS) and small angle X-ray scattering (SAXS). The study provides quantitative data to evaluate the repeatability of these methods and their reproducibility in the measurement of number concentration of model nanoparticle systems following a common measurement protocol. We find that the population-averaging methods of SAXS, CLS and UV-Vis have high measurement repeatability and reproducibility, with between-labs variability of 2.6%, 11% and 1.4% respectively. However, results may be significantly biased for reasons including inaccurate material properties whose values are used to compute the number concentration. Particle-counting method results are less reproducibile than population-averaging methods, with measured between-labs variability of 68% and 46% for PTA and spICP-MS respectively. This study provides the stakeholder community with important comparative data to underpin measurement reproducibility and method validation for number concentration of nanoparticles

Versailles project on advanced materials and standards (VAMAS) interlaboratory study on measuring the number concentration of colloidal gold nanoparticles

We describe the outcome of a large international interlaboratory study of the measurement of particle number concentration of colloidal nanoparticles, project 10 of the technical working area 34, "Nanoparticle Populations" of the Versailles Project on Advanced Materials and Standards (VAMAS). A total of 50 laboratories delivered results for the number concentration of 30 nm gold colloidal nanoparticles measured using particle tracking analysis (PTA), single particle inductively coupled plasma mass spectrometry (spICP-MS), ultraviolet-visible (UV-Vis) light spectroscopy, centrifugal liquid sedimentation (CLS) and small angle X-ray scattering (SAXS). The study provides quantitative data to evaluate the repeatability of these methods and their reproducibility in the measurement of number concentration of model nanoparticle systems following a common measurement protocol. We find that the population-averaging methods of SAXS, CLS and UV-Vis have high measurement repeatability and reproducibility, with between-labs variability of 2.6%, 11% and 1.4% respectively. However, results may be significantly biased for reasons including inaccurate material properties whose values are used to compute the number concentration. Particle-counting method results are less reproducibile than population-averaging methods, with measured between-labs variability of 68% and 46% for PTA and spICP-MS respectively. This study provides the stakeholder community with important comparative data to underpin measurement reproducibility and method validation for number concentration of nanoparticles

What is on the outside matters — surface charge and dissolve organic matter association affect the toxicity and physiological mode of action of polystyrene nanoplastics to C. elegans

To better understand nanoplastic effects, the potential for surface functionalization and dissolve organic matter eco-corona formation to modify the mechanisms of action and toxicity of different nanoplastics needs to be established. Here, we assess how different surface charges modifying functionalization (postive (+ve) aminated; neutral unfunctionalized; negative (−ve) carboxylated) altered the toxicity of 50 and 60 nm polystyrene nanoplastics to the nematode Caenorhabditis elegans. The potency for effects on survival, growth, and reproduction reduced in the order +ve aminated > neutral unfunctionalized ≫ −ve carboxylated with toxicity >60-fold higher for the +ve than −ve charged forms. Toxicokinetic–toxicodynamic modeling (DEBtox) showed that the charge-related potency was primarily linked to differences in effect thresholds and dose-associated damage parameters, rather than to toxicokinetic parameters. This suggests that surface functionalization may change the nature of nanoplastic interactions with membrane and organelles leading to variations in toxicity. Eco-corona formation reduced the toxicity of all nanoplastics indicating that organic molecule associations may passivate surfaces. Between particles, eco-corona interactions resulting in more equivalent effects; however, even despite these changes, the order of potency of the charged forms was retained. These results have important implications for the development of future grouping approaches

Chemical transformation and surface functionalisation affect the potential to group nanoparticles for risk assessment

A major challenge in nanomaterial environmental risk assessment is to identify whether different manufactured materials need to be assessed individually or if they can be grouped for assessments based on selected properties. To date, NPs are grouped on the basis that they are manufactured (e.g., pristine materials), but these are rarely present in the environment as many nanomaterials transform before and after entry into the environment. To assess how transformations change relative hazard and, therefore, the potential for grouping, we assessed the toxicity of silver nanoparticles (NPs) of varying sizes (20, 50 nm) and surface functionalisation (PVP, citrate) in their metallic and sulphidised forms to Caenorhabditis elegans in a standard medium lacking organic matter and in extracted soil pore water. The metallic Ag NPs showed only small variations in toxicity, with citrate functionalisation reducing potency and small citrate NPs being least toxic. The toxicity of sulphidised particles was lower than for the pristine forms in all cases, however relative differences among the transformed materials were greater than for the metallic forms. Exposure in soil pore water further reduced toxicity of the citrate, but not PVP functionalised NPs. Overall, transformation reduced citrate functionalised NP toxicity in a size dependent manner, whereas PVP coating preserved similarities across sizes and transformations. Thus despite similar toxicity of the pristine materials, grouping of NPs with a similar coating independent of size appeared only possible for materials with the more persistent PVP surface coating and then only when transformations were first considered

Genomic mutations after multigenerational exposure of Caenorhabditis elegans to pristine and sulfidized silver nanoparticles

Our previous study showed heritable reproductive toxicity in the nematode Caenorhabditis elegans after multigenerational exposure to AgNO3 and silver nanoparticles (Ag-NPs). The aim of this study was to determine whether such inheritable effects are correlated with induced germline mutations in C. elegans. Individual C. elegans lineages were exposed for 10 generations to equitoxic concentrations at EC30 of AgNO3, Ag-NPs, and sulfidized Ag-NPs (sAg-NPs), a predominant environmentally transformed product of pristine Ag-NPs. The mutations were detected via whole genome DNA sequencing approach by comparing F0 and F10 generations. An increase in the total number of variants, though not statistically significant, was observed for all Ag treatments and the variants were mainly contributed by single nucleotide polymorphisms (SNPs). This potentially contributed towards reproductive as well as growth toxicity shown previously after ten generations of exposure in every Ag treatment. However, despite Ag-NPs and AgNO3 inducing stronger reproductive toxicity than sAg-NPs, exposure to sAg-NPs resulted in higher mutation accumulation with significant increase in the number of transversions. Thus our results suggest that other mechanisms of inheritance, such as epigenetics, may be at play in Ag-NP- and AgNO3-induced multigenerational and transgenerational reproductive toxicity