Prioritising nano- and microparticles: identification of physicochemical properties relevant for toxicity to Raphidocelis subcapitata and Daphnia magna

Abstract

Background Advanced/innovative materials are an undefined group of nano- and micro-particles encompassing diverse material compositions, structures and combinations. Due to their unique properties that enable specific functions during applications, there are concerns about unexpected hazards to humans and the environment. In this study, we provide ecotoxicity data for 36 nano- and microparticles of various inorganic species (single constituents and complex compositions; materials releasing toxic ions and others), morphologies (spheroidal, cubic, flaky, elongated/fibrous) and sizes (10 nm–38 µm). By applying Raphidocelis subcapitata algae growth inhibition and Daphnia magna immobilisation tests according to OECD test guidelines 201 and 202, and extensive material characterisation, we aimed to identify indicators of concern. This would allow better predictions of the hazardous properties of these materials in the future. Results The chemical identity (toxic ion-releasing materials vs. other materials) and agglomeration behaviour, which is affected by size (nm vs. µm) and morphology (fibres vs. others), were obvious drivers of ecotoxicity on R. subcapitata. Differences in morphology had an impact on agglomeration behaviour. Fibres formed agglomerates of varying sizes with entrapped and attached algae. Small compact (e.g. spheroidal) particles attached to algae. A high coverage resulted in high ecotoxicity, while less toxic materials attached to a much lesser extent. No agglomeration of algae and particles was observed for particles with a µm size. Small toxic components of large hybrid materials did not affect ecotoxicity. For D. magna, despite uptake of all materials studied into the gut, the sole indication of toxicity was the release of toxic ions. This is in line with previous observations on nanomaterials. Based on the identified criteria, charts were developed to indicate the expected toxicity of advanced/innovative materials toward algae and daphnia. Conclusion Indicators for the toxicities of advanced materials differ for algae and daphnia. Thus, different materials give rise to concerns for the two aquatic organisms. For D. magna, only the toxic ion-releasing materials are relevant, but for R. subcapitata, more complex interactions between particular materials and cells must be considered. Graphical Abstract

Influence of Silver Fiber Morphology on the Dose–Response Relationship and Enrichment in Daphnia magna Studied by Elemental Imaging with LA-ICP-TOF-MS

“…As this material was not supplied by a professional producer it cannot ensured that all relevant parameters (e.g., surfactants, surface structure, and ion release) remained unchanged. 22 Compared to the silver fibers from the previous studies, the EC 50 values for the 5 silver fibers in this study are roughly 3 orders of magnitude higher, and hence the two silver fibers Ag − 1340 and SRM110525 show a higher toxicity.…”

“…Here, the shorter length by retaining the same diameter led to a reduction in toxicity. As this material was not supplied by a professional producer it cannot ensured that all relevant parameters (e.g., surfactants, surface structure, and ion release) remained unchanged …”

“…23 The fiber dimensions as given by the suppliers were re-evaluated by electron microscopy in a previous study 23 and are shown in Table 1. All materials were delivered as suspensions in an aqueous medium containing an undisclosed 22 quantity of PVP as a dispersant. In the case of Ag_Rod_3170, the suspension had a very high viscosity.…”

“… a RAS fibers used in previous research are shown for comparison. All fibers were supplied in an aqueous dispersion with PVP dispersant. b Data from Hund-Rinke et al c Previously published in Hund-Rinke et al …”

“…magna (Crustacea, Branchiopoda, Cladocera) was based on OECD TG 202 . Deviating from the OECD guideline, daphnids were exposed in a miniaturized assay in 24-well microplates (TPP, Switzerland), allowing the use of lower volumes of fiber dispersions. , Each treatment and control consisted of 4 replicates with 5 daphnids per well (20 animals per test concentration in total), exposed in a total volume of 1.5 mL of ADaM. Neonates were not older than 24 h, and no offspring of adults’ first brood were used.…”