Background: Silver nanoparticles (AgNPs) are widely used in many fields of application and consumer products due to their antibacterial properties. The aim of this study was to prepare a hazard assessment for one specific AgNP in soil, incorporated via sewage sludge (the sewage sludge pathway). The effects of pristine AgNPs on microorganisms, plants and earthworms were first determined in screening tests. Long-term tests over 140 days were then conducted with AgNPs added to soil via sewage sludge. AgNPs were incorporated into the sludge through a simulated sewage treatment plant (STP) over 10 days to allow transformation to occur and also by manual spiking over 2 h. The results of the most sensitive organism from the long-term tests, the soil microorganisms, are presented.

Abstract-The widespread use of silver nanoparticles (Ag-NPs), for example, in textiles and cleaning products, means that they are likely to reach the environment via biosolids or the effluent from wastewater treatment plants. The aim of the present study was to determine the ecotoxicity of Ag-NPs in the earthworm reproduction test using Eisenia andrei. In addition to the usual endpoints, the authors also investigated the uptake and accumulation of Ag by adult earthworms and the concentration of free Ag þ in soil pore water. Silver nanoparticles and Ag nitrate showed similar toxicities in the earthworm reproduction test. The uptake of Ag from Ag-NPs in the earthworm was slightly higher than the uptake of Ag from Ag nitrate. Spiked soils showed a concentration-dependent effect on reproduction, but there was no concentration-dependent increase in the amount of Ag in earthworm tissues. The authors noted a concentration-dependent increase in the levels of free Ag þ in the soil pore water regardless of the Ag source. The number of juveniles is a more suitable endpoint than biomass or mortality. The uptake of Ag does not appear to inhibit reproduction. Instead, inhibition seems to reflect Ag þ released into the soil pore water, which affects cocoons and juveniles in the soil. Analysis of transformed Ag-NPs after purification in wastewater treatment plants would provide additional information. Environ. Toxicol. Chem. 2013;32:181-188. # 2012 SETAC

We investigated the effects of silver nanomaterials (AgNMs) on five well-characterized soils with distinct physicochemical properties using two standardized test systems. The carbon transformation test (OECD217) showed minimal sensitivity whereas the ammonia oxidizing bacteria test (ISO 15685) showed extreme sensitivity over 28 days of exposure. AgNM toxicity was compared with the physicochemical properties of the soils, revealing that toxicity declined with increasing clay content and increasing pH. AgNM toxicity did not appear to be affected by the organic carbon content of the soil. Our results showed that AgNM toxicity cannot be attributed to any single soil property but depends on the same parameters that determine the toxicity of conventional chemicals. Recommendations in the test guidelines for soil ecotoxicity studies are therefore applicable to AgNMs as well as conventional chemicals.

-Fordsmand (2016) Regulatory ecotoxicity testing of nanomaterials -proposed modifications of OECD test guidelines based on laboratory experience with silver and titanium dioxide nanoparticles, Nanotoxicology, 10:10, 1442-1447, DOI: 10.1080/17435390.2016

Manufactured nanomaterials (NMs) are being developed in many different variations such as size, shape, crystalline structure and surface modifications. To avoid the testing of each single nanomaterial variation, grouping and read-across strategies for nanomaterials similar to classical chemicals are discussed. Grouping and read-across aim to identify NM groups with analogous sets of properties or properties that enable reasonable predictions of a NM hazard without additional testing. This will contribute to save costs and time in the risk assessment. So far the knowledge is still limited how modifications of NMs and their properties affect ecotoxicity. This study was initiated to support the discussions on grouping regarding aquatic ecotoxicological effects and for the identification of relevant properties as well as the development of a grouping concept addressing aquatic ecotoxicity. A comprehensive and homogenous data set based on fourteen nanomaterials was established. The selected NMs were modifications of five chemical species (Ag, ZnO, TiO2, CeO2, Cu). As the focus was on the applicability for regulatory purposes, for ecotoxicity the OECD test guidelines 201 (algae), 202 (daphnids) and 236 (fish embryo) were considered. The physico-chemical properties of the chosen NMs were determined in deionized water and the test media applied for the ecotoxicological tests. Reactivity, ion release, morphology and ecotoxicity of the chemical composition (information from the bulk material) were identified as the most relevant grouping properties regarding nanomaterial's ecotoxicity. A grouping scheme and procedure was proposed considering these properties. The scheme was validated with a set of additional nanomaterials (TiO2, SiO2, Fe2O3). A rough, but reliable grouping of NMs with different chemical composition was possible. The separation of NMs with the same chemical composition, into different groups was only feasible, if the NMs show major differences in one of the relevant properties (e.g. different shape). Based on the available data set it is unknown whether either further physico-chemical properties have to be considered or whether the impact of the selected variations on ecotoxicity is too minor to result in significant ecotoxicological differences. In order to further advance the grouping concept for regulatory testing, future developments should include the specification of threshold values with regard to the properties solubility and reactivity as well as for the characterization of the morphology. Additionally, test methods addressing the sorption tendency of NMs to algae could contribute to an improvement of the ecotox-scheme with regard to the consideration of physical effects by shading resulting in limited growth

The use of silver nanoparticles (AgNPs) in consumer products such as textiles leads to their discharge into wastewater and consequently to a transfer of the AgNPs to soil ecosystems via biosolids used as fertilizer. In urban wastewater systems (e.g., sewer, wastewater treatment plant [WWTP], anaerobic digesters) AgNPs are efficiently converted into sparingly soluble silver sulfides (Ag 2 S), mitigating the toxicity of the AgNPs. However, long-term studies on the bioavailability and effects of sulfidized AgNPs on soil microorganisms are lacking. Thus we investigated the bioavailability and long-term effects of AgNPs (spiked in a laboratory WWTP) on soil microorganisms. Before mixing the biosolids into soil, the sludges were either anaerobically digested or directly dewatered. The effects on the ammonium oxidation process were investigated over 140 d. Transmission electron microscopy (TEM) suggested an almost complete sulfidation of the AgNPs analyzed in all biosolid samples and in soil, with Ag 2 S predominantly detected in long-term incubation experiments. However, despite the sulfidation of the AgNPs, soil ammonium oxidation was significantly inhibited, and the degree of inhibition was independent of the sludge treatment. The results revealed that AgNPs sulfidized under environmentally relevant conditions were still bioavailable to soil microorganisms. Consequently, Ag 2 S may exhibit toxic effects over the long term rather than the short term. Environ Toxicol Chem 2017;36:3305-3313.

Sewage sludge is repeatedly applied as fertilizer on farmland due to its high nutrient content. This may lead to a significant increase of silver nanomaterials (AgNM) in soil over years. Therefore, our aim was to investigate the ecotoxicity and fate of AgNM under environmentally relevant conditions in outdoor lysimeters over 25 months. Two AgNM concentrations (1.7 and 8.0 mg/kg dry matter soil) were applied via sewage sludge into soil. In subsamples of the soil, incubated under laboratory conditions for 180 days, the comparability of outdoor and laboratory results regarding ecotoxicity was determined. The results from our long term lysimeter experiments show no detectable horizontal displacement in combination with very low remobilization to the percolate water. Thus, indicate that the sludge applied AgNM remains nearly immobile in the pathway between soils and leachate. However, Ag uptake to the roots of wheat and canola suggests that the chemical conditions in the rhizosphere induce AgNM remobilization from the incorporated sewage sludge even after two harvesting cycles. At the higher AgNM concentration a steady inhibition of the soil microflora was observed over 25 month in the lysimeter study, while there was no effect at the lower AgNM concentration. The results of the laboratory experiment reflect the findings of the lysimeter study and indicate that a risk assessment for AgNM based on data from laboratory tests is acceptable.

Nanoenabled products (NEPs) have numerous outdoor uses in construction, transportation or consumer scenarios, and there is evidence that their fragments are released in the environment at low rates. We hypothesized that the lower surface availability of NEPs fragment reduced their environmental effects with respect to pristine nanomaterials. This hypothesis was explored by testing fragments generated by intentional micronisation ("the SUN approach"; Nowack et al. Meeting the Needs for Released Nanomaterials Required for Further Testing: The SUN Approach. Environmental Science & Technology, 2016 (50), 2747). The NEPs were composed of four matrices (epoxy, polyolefin, polyoxymethylene, and cement) with up to 5% content of three nanomaterials (carbon nanotubes, iron oxide, and organic pigment). Regardless of the type of nanomaterial or matrix used, it was observed that nanomaterials were only partially exposed at the NEP fragment surface, indicating that mostly the intrinsic and extrinsic properties of the matrix drove the NEP fragment toxicity. Ecotoxicity in multiple assays was done covering relevant media from terrestrial to aquatic, including sewage treatment plant (biological activity), soil worms (Enchytraeus crypticus), and fish (zebrafish embryo and larvae and trout cell lines). We designed the studies to explore the possible modulation of ecotoxicity by nanomaterial additives in plastics/polymer/cement, finding none. The results support NEPs grouping by the matrix material regarding ecotoxicological effect during the use phase. Furthermore, control results on nanomaterial-free polymer fragments representing microplastic had no significant adverse effects up to the highest concentration tested.