In vitro safety evaluation of rare earth-lean alloys for permanent magnets manufacturing.

Due to their exceptional physico-chemical and magnetic characteristics, rare earth (RE) permanent magnets are applied in multiple critical technologies. However, several environmental and economic difficulties arising from obtaining RE elements have prompted the search of alternatives with acceptable magnetic properties but containing a lower percentage of these elements in their composition. The aim of this work was to perform a preliminary toxicological evaluation of three forms of newly developed RE-lean alloys (one NdFeTi and two NdFeSi alloys) applying different in vitro assays, using as a benchmark a commercial NdFeB alloy. Thus, the effects of the direct exposure to powder suspensions and to their derived leachates were analysed in two model organisms (the A549 human cell line and the yeast Saccharomyces cerevisiae) applying both viability and oxidative stress assays. Moreover, the impact of the alloy leachates on the bioluminescence of Vibrio fischeri was also investigated. The obtained data showed that only the direct interaction of the alloys particulates with the applied organisms resulted in harmful effects, having all the alloys a comparable toxicological potential to that presented by the reference material in the conditions tested. Altogether, this study provides new insights about the safety of NdFeTi and NdFeSi alloys.

Toxicological assessment of commercial monolayer tungsten disulfide nanomaterials aqueous suspensions using human A549 cells and the model fungus Saccharomyces cerevisiae.

The utilization of tungsten disulfide (WS2) nanomaterials in distinct applications is raising due to their unique physico-chemical properties, such as low friction coefficient and high strength, which highlights the necessity to study their potential toxicological effects, due to the potential increase of environmental and human exposure. The aim of this work was to analyze commercially available aqueous dispersions of monolayer tungsten disulfide (2D WS2) nanomaterials with distinct lateral size employing a portfolio of physico-chemical and toxicological evaluations. The structure and stoichiometry of monolayer tungsten disulfide (WS2-ACS-M) and nano size monolayer tungsten disulfide (WS2-ACS-N) was analyzed by Raman spectroscopy, whereas a more quantitative approach to study the nature of formed oxidized species was undertaken employing X-ray photoelectron spectroscopy. Adenocarcinomic human alveolar basal epithelial cells (A549 cells) and the ecotoxicology model Saccharomyces cerevisiae were selected as unicellular eukaryotic systems to assess the cytotoxicity of the nanomaterials. Cell viability and reactive oxygen species (ROS) determinations demonstrated different toxicity levels depending on the cellular model used. While both 2D WS2 suspensions showed very low toxicity towards the A549 cells, a comparable concentration (160 mg L-1) reduced the viability of yeast cells. The toxicity of a nano size 2D WS2 commercialized in dry form from the same provider was also assessed, showing ability to reduce yeast cells viability as well. Overall, the presented data reveal the physico-chemical properties and the potential toxicity of commercial 2D WS2 aqueous suspensions when interacting with distinct eukaryotic organisms, showing differences in function of the biological system exposed.