Read-across based on structural or substructural similarity is one of the strategies that could be used to group PMT/vPvM substances, which relies on the idea that substances with similar structures have similar properties. Commonly retained moieties from transformation reactions could also be a grouping strategy for PMT/vPvM substances. Substances that are structurally similar to PMT/vPvM according to read-across, or form persistent, mobile TPs could be flagged for subsequent assessment and/or regulatory actions.