This article summarizes the outcome of the discussions at the international workshop on nano
reference values (NRVs), which was organized by the Dutch trade unions and employers’
organizations and hosted by the Social Economic Council in The Hague in September 2011. It
reflects the discussions of 80 international participants representing small- and medium-size
enterprises (SMEs), large companies, trade unions, governmental authorities, research institutions,
and non-governmental organizations (NGOs) from many European countries, USA,
India, and Brazil. 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.