Table 5.

Evaluation of suitability of genotoxicity assays for SbD hazard testing.

	Simple Cell Models		More Complex Cell Models
Performance Criteria	Gene Mutations in Cell Lines (OECD TGs 476 and 490)	Chromosome Damage in Cell Lines (OECD TGs 487 MN Assay)	Gene Mutations in Advanced Models	Chromosome Damage in Advanced Models (OECD TG 487)
Simplicity and cost	Time consuming, requiring long culture times (e.g., 10–14 days before counting colony formation). Relatively cheap.	Simple and relatively cheap. Analyses can be sped up using automatic image analysis systems and flow-cytometry.	Not used up to now, would necessitate 3D model dissociation before cell plating, i.e., simplicity reduced as compared to simple models.	Relatively simple and cheap for advanced models. Would be more time consuming and expensive than 2D models [260].
Predictivity (Sensitivity and Specificity)	Conventional chemicals: adequate (62.9%) [224,229]. NMs: no conclusions can be reached [236,259].	Conventional chemicals: adequate (67.8%) [224,229] NMs: no conclusions can be reached [236,259].	Not used up to now, no conclusion can be reached.	Co-culture systems may allow the evaluation of the involved genotoxicity mechanisms of action [246,247]. They may be more predictive of an in vivo-like response [260]. 3D models do not seem to be appropriate for applying this assay due to the lack of cell proliferation [242,243]. When the 3D model involves proliferating cells, it is more sensitive than 2D models, due to higher metabolic activity [260].
Robustness	No inter-laboratory comparisons available for NMs. Ongoing comparisons within the EU H2020 RiskGone project.	Relatively reproducible results in some cases, but material- and cell line-specific [244]. Future inter-laboratory comparisons under the OECD project 4.95.	Not used up to now, no conclusion can be reached.	Not enough studies available yet to allow reaching conclusions.
Compatibility	Too low number of studies to reach conclusions [236].	Suitable for different NMs (no interferences reported). No information about adequacy for complex materials.	No conclusion can be reached. Still, for NMs could prove unsuitable since only the cells at the periphery of the spheroid/organoid would be exposed to NMs.	Suitable for different NMs (no interferences reported). No information about adequacy for complex materials.
Readiness	No NM-specific standardized protocol available.	No NM-specific standardized protocol available.	No NM-specific standardized protocol available.	No NM-specific standardized protocol available.