How many mutagens are missed under REACH due to limited low tonnage information requirements?

For industrial substances registered under REACH at 1-10 tonnes per registrant/year, only the Ames test is required to address mutagenicity. When a substance tests positive in the Ames test, further testing is needed, but when the test result is negative, additional mutagenicity testing is only mandatory at a higher tonnage level. It is correspondingly known that some mutagens produced up to 10 tonnes per year/registrant are not identified. Based on battery (Q)SAR modelling, relying on agreement from both in vitro and in vivo models, advisory self-classifications (ASC) for mutagenicity are offered by the Danish EPA. In this present study, substances with ASC for mutagenicity are compared to the identified mutagens in low tonnage REACH registrations. We conclude that for only about a quarter of the low-tonnage substances with an Muta. 2 ASC, a positive experimental Ames result is available, leading to follow-up under REACH. We recommend improving the identification of mutagenic substances at the 1-10 tonnage band by including the in vitro micronucleus test to supplement the Ames test. Concerningly, the few low tonnage REACH dossiers that do provide in vivo data, mostly report negative micronucleus test results that are not conclusive due to missing information on bone marrow exposure.