Scientific Basis for the Definition of the Term “nanomaterial”

With the expected increase in the applications of nanotechnology, there is an urgent need to identify what can be considered as a nanomaterial by clear unequivocal descriptions. This need to identify a nanomaterial comes from the uncertainty regarding safety evaluation and the risk assessment of nanomaterials. As a result, the SCENIHR was invited to provide advice on the essential scientific elements of an overarching working definition for the term “nanomaterial” for regulatory purposes. The scientific opinion concluded that: Whereas physical and chemical properties of materials may change with size, there is no scientific justification for a single upper and lower size limit associated with these changes that can be applied to adequately define all nanomaterials. There is scientific evidence that no single methodology (or group of tests) can be applied to all nanomaterials. Size is universally applicable to define all nanomaterials and is the most suitable measurand. Moreover, an understanding of the size distribution of a nanomaterial is essential and the number size distribution is the most relevant consideration. In order to define an enforceable definition of “nanomaterial” for regulatory use it is proposed to set an upper limit for nanomaterial size and to add to the proposed limit additional guidance (requirements) specific for the intended regulation. Crucial in the guidance that needs to be provided is the extended description of relevant criteria to characterise the nanoscale. Merely defining single upper and lower cut-off limits is not sufficient in view of the size distributions occurring in manufactured nanomaterials. Alternatively, a tiered approach may be required depending on the amount of information known for any specifically manufactured nanomaterial and its proposed use. The scientific opinion recognises however that specific circumstances regarding risk assessment for regulatory purposes for certain areas and applications may require the adaptation of any overarching definition. It should be stressed that 'nanomaterial' is a categorization of a material by the size of its constituent parts. It neither implies a specific risk, nor does it necessarily mean that this material actually has new hazard properties compared to its constituent parts or larger sized counterparts.