Issues that were discussed concerned the usefulness and acceptability of precaution-
based NRVs as a substitute for health-based occupational exposure limits (OELs) and
derived no-effect levels (DNELs) for manufactured nanoparticles (NPs). Topics concerned the
metrics for measuring NPs, the combined exposure to manufactured nanomaterials (MNMs)
and process-generated NPs, the use of the precautionary principle, the lack of information
about the presence of nanomaterials, and the appropriateness of soft regulation for exposure
control. The workshop concluded that the NRV, as an 8-h time-weighted average, is a comprehensible
and useful instrument for risk management of professional use of MNMs with a
dispersible character. The question remains whether NRVs, as advised for risk management by
the Dutch employers’ organization and trade unions, should be under soft regulation or that a
more binding regulation is preferable.