There is no internationally harmonised definition of “nanomaterial” that would fulfill the requirements for use in legislation, either at European or international level. For this reason, the authors of a Report recently published by the JRC, IHCP ("Considerations on a definition of nanomaterial for regulatory purposes") recommend using size as the only defining property. To focus the definition on materials of potential regulatory relevance, it should concern only “particulate nanomaterials” since some of these materials currently raise health and environmental concerns.
A lower limit of 1 nm for the size range of interest (the "nanoscale") is considered as a reasonable figure. The upper limit of the nanoscale should be equal to or greater than 100 nm in order to include a wide range of currently used nanomaterials of regulatory concern. Other specific physico-chemical properties and attributes (e.g. state of agglomeration, biopersistance, or whether intentionally manufactured) may be relevant in the scope of particular legislation. Therefore it may be necessary to adapt the general definition to the needs of a specific implementation.