Grouping concept for metal and metal oxide nanomaterials with regard to their ecotoxicological effects on algae, daphnids and fish embryos

Abstract

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

Grouping of nanomaterials to read-across hazard endpoints: a review

“…Regarding the selected endpoints for read-across, none of the case studies available in Table 3 consider REACH-relevant endpoints 5 . A case study recently published by Hund-Rinke et al (2018) where metal and metal oxide NMs are grouped for aquatic toxicity according to ion release, morphology, and reactivity, takes finally into consideration a REACH-relevant endpoint. This aspect conflicts with the grouping frameworks study reported in Tables 1 and 2, where hazard data are related to animal studies and to apical endpoints.…”

“…A different approach for ecotoxicity was proposed by Hund-Rinke et al (2018) where metal and metal oxide NMs are grouped according to three properties that were considered relevant: ion release, morphology, and reactivity. PC characterisation of NMs is provided in the paper (surface chemistry, surface area, crystalline structure, morphology, primary particle size, hydrodynamic diameter, zeta potential, isoelectric point, and solubility rate).…”

Hazard grouping of nanomaterials for daphnia and algae toxicity: lessons learned from scientific projects for regulatory applicability

“…The physical chemical characteristics of the nanoforms, preparation of suspensions, the performance of characterisation, and ecotoxicological tests with algae and daphnids as well as the investigation of the attachment of nanoforms to the green algae R. subcapitata are described in [8,9]. In addition, for ionic silver and nanosilver data on the ecotoxicity on D. subspicatus were included as data for these forms were not generated with algae in the underlying projects [14].…”

“…All data generated or analysed during this study are included in the published articles [8][9][10]14] and their additional information files.…”

“…Data used for this publication were already published in Hund-Rinke et al [8] regarding the development of a grouping scheme for ecotoxicity. Physical-chemical properties relevant for ecotoxicity were identified.…”