At the request of the European Commission, EFSA have been asked to provide advice on the interpretation of some aspects related to genotoxicity assessment. The following have been addressed:

1. the suitability of the UDS in vivo assay to follow-up positive results in in vitro gene mutation tests;
2. the adequacy to demonstrate target tissue exposure in in vivo studies, particularly in the Mammalian Erythrocyte Micronucleus test;
3. the use of data in a weight of evidence approach to conclude on the genotoxic potential of substances and the consequent setting of health-based guidance values.

The following conclusions were drawn:

1. it is recommended to no longer perform the UDS test. For re-assessments, in cases with negative results, other more reliable tests such as Transgenic Rodent assay or in vivo comet assay would be needed to complete the gene mutation assessment;
2. toxicity to the bone marrow in itself provides sufficient evidence to allow concluding on the validity of a negative outcome of a study. All other direct (e.g. ADME data) or indirect (e.g. systemic toxicity) lines of evidence of target tissue exposure should be assessed within a weight-of-evidence approach;
3. available data that may assist in reducing the uncertainty in the assessment of the genotoxic potential of a substance should be taken into consideration. If the overall evaluation leaves no concerns for genotoxicity, health-based guidance values may be established. However, if concerns for genotoxicity remain, establishing health-based guidance values is not considered appropriate and additional information would be needed to complete the assessment.

The finalised EFSA Scientific Opinion genotoxicity assessment can also be found on the EFSA website: http://onlinelibrary.wiley.com/doi/10.2903/j.efsa.2017.5113/epdf

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