Table 4 Recommendations for designing genotoxicity studies of nanomaterials with regulatory relevance

• A full set of physico-chemical characteristics should be reported in the same publication with the genotoxicity results

• The test system characteristics should be well understood, described, and selection justified

• Concurrent cytotoxicity measurements should be conducted using the parameters recommended by the latest version of the OECD test guidelines (TGs)

• In addition to the current OECD TGs, nano-specific requirements already adopted by the regulatory agencies should be checked and followed; e.g., the use of a delayed Cytochalasin-B treatment or the need of one cell cycle length treatment with nanomaterials with the in vitro micronucleus assay

• Following the OECD guideline with the inclusion of additional wash steps is recommended for the Hprt gene mutation test

• A justification of an in vivo treatment schedule should rely on evidence which confirms the presence of the test material in the target organ at a given time point and take into account the transient nature of the measured phenomenon

• Harmonized names of the assays and ways of reporting results should be used when entering genotoxicity data into the databases

• Non yet validated assays, performed with complex and realistic experimental models, that can provide information on the genotoxicity mechanisms of action of nanomaterials are urgently needed