Size should form the scientific basis for defining nanomaterials, says EU panel
This article was originally published in RAJ Devices
The European Commission's Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) believes that the size of a material or its constituent parts – and not its physical or chemical properties – should form the scientific basis for deciding whether it qualifies as a nanomaterial1.
Also, the committee thinks there is no scientific justification for preferring any specific size limit to any other in the range from 1 to 1,000 nanometers.
SCENIHR issued this opinion in response to a request by the commission, which had sought its advice on the essential elements of a science-based, overarching working definition of the term nanomaterials2. More specifically, SCENIHR was asked to identify the types of physical and chemical properties particular to nanomaterials and the thresholds at which nanomaterial-specific properties could be expected to occur3.
As physical and chemical properties of materials may change with size, the committee concluded that there can be no scientific justification for establishing a single upper or lower size limit associated with these changes that can be applied to adequately define all nanomaterials.
As part of its mandate, SCENIHR evaluated a list of physico-chemical properties – such as crystalline phase, photocatalytic activity, zeta potential, redox potential, radical formation potential, water solubility and the octanol-water partition coefficient – as possible discriminators for the identification of a nanomaterial. The committee found that while all of these properties are very useful for risk assessment, "none of them appear to be universally applicable as a criterion within a definition for all nanomaterials".
The committee found sufficient evidence to indicate that there can be a change in some physico-chemical properties of a material when it or its constituent parts are at the nanoscale, but concluded that it is currently not possible to identify a specific size at which a specific property would change or appear, or a specific property that is introduced or changed with size.
The committee also concluded that there is no scientific evidence for a single methodology (or group of tests) that can be applied to all nanomaterials.
Size universally applicable
SCENIHR believes that size (and its distribution) is universally applicable to all nanomaterials and is the "most suitable measurand". A defined size range, it says, would facilitate a uniform interpretation.
While the committee proposes a size of 1 nm as the lower limit for the definition of nanomaterials, it found no scientific evidence in favour of a single upper limit. Although an upper limit of 100 nm is commonly used, SCENIHR believes there is no scientific evidence to qualify the appropriateness of this value.
SCENIHR believes that the use of a single upper threshold value might be too limiting for the classification of nanomaterials and a differentiated approach might be more appropriate. This approach, it suggests, could be based on a relatively high upper threshold for which it is assumed that the size distribution at the lower end will most likely be above the lower, more critical threshold.
As there is no scientific evidence to qualify the appropriateness of the 100 nm cut-off, the committee believes it is important to consider the whole nanoscale metric (1-999 nm). This could be enabled by applying a tiered approach using intermediate thresholds.
References
1. European Commission, SCENIHR: Scientific Basis for the Definition of the Term "nanomaterial", 8 December 2010, http://ec.europa.eu/health/scientific_committees/emerging/docs/scenihr_o_032.pdf
2. EU a step closer to defining nanomaterials, Regulatory Affairs Medtech, 14 July 2010
3. Commission needs nanomaterials definition from SCENIHR by May, Regulatory Affairs Medtech, 3 March 2010