Case studies putting the decision-making framework for the grouping and testing of nanomaterials (DF4nanoGrouping) into practice

Abstract

Case studies covering carbonaceous nanomaterials, metal oxide and metal sulphate nanomaterials, amorphous silica and organic pigments were performed to assess the Decision-making framework for the grouping and testing of nanomaterials (DF4nanoGrouping). The usefulness of the DF4nanoGrouping for nanomaterial hazard assessment was confirmed. In two tiers that rely exclusively on non-animal test methods followed by a third tier, if necessary, in which data from rat short-term inhalation studies are evaluated, nanomaterials are assigned to one of four main groups (MGs). The DF4nanoGrouping proved efficient in sorting out nanomaterials that could undergo hazard assessment without further testing. These are soluble nanomaterials (MG1) whose further hazard assessment should rely on read-across to the dissolved materials, high aspect-ratio nanomaterials (MG2) which could be assessed according to their potential fibre toxicity and passive nanomaterials (MG3) that only elicit effects under pulmonary overload conditions. Thereby, the DF4nanoGrouping allows identifying active nanomaterials (MG4) that merit in-depth investigations, and it provides a solid rationale for their sub-grouping to specify the further information needs. Finally, the evaluated case study materials may be used as source nanomaterials in future read-across applications. Overall, the DF4nanoGrouping is a hazard assessment strategy that strictly uses animals as a last resort.

Surface reactivity measurements as required for grouping and read-across: An advanced FRAS protocol

“…Carbonylated proteins were analyzed on 1D and 2D immunoblots and identified by matrix assisted laser desorption time-of-flight mass spectrometry. [3] We found overall an excellent match of ESR vs. in vitro carbonylation.…”

“…We note that ZnO NM110 is used as benchmark "dissolving ENM" in the ECETOC grouping scheme. [3] All this is very plausible, and any further interpretation is beyond the scope of the present protocol-centered contribution.…”

“…Thus, single-dose screenings can group materials by properties of concern (here: surface reactivity), which we currently define as "sBOD more than 10% of Mn2O3 reactivity". [3] Additionally, the doseresponse relationship may point to differences of oxidative stress mechanisms, such as the contributions by dissolved ions, and serve to substantiate read-across.…”

“…For most of these materials, in vivo inhalation and macrophage assay results are available for benchmarking the proposed groupings/screenings. [3,12,13] Based on the outcome of this study we currently develop a comprehensive testing strategy for assessing the oxidative stress potential of ENMs, which combines acellular methods (ESR, FRAS) and fast in vitro screening approaches, as well as a more involved detailed redox proteomics approach. This allows for screening and prioritization in a tier of "system-depending properties" and, if required, also for unraveling mechanistic details down to compromised signaling pathways.…”

“…[2] Oxidative stress is a widely accepted paradigm associated with different adverse outcomes of ENMs. It has frequently been identified in in vitro and in vivo studies [2,3] and different assays have been developed for this purpose. [4][5][6][7][8][9][10][11] Previously, we have investigated a representative panel of 32 ENMs including functionalized amorphous silica (6 nanoforms), zirconium dioxide (4), silver (4), titanium dioxide (3), zinc oxide (2), multiwalled carbon nanotubes (3), barium sulfate and AlOOH.…”