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EC Scientific Committee recommends a high upper Threshold for a tiered Definition of the Term
Published: Tuesday 13 July 2010
Only two weeks after the official publication of the European Commission’s JRC Reference Report on the ‘Considerations on a Definition of Nanomaterial for Regulatory Purposes’ (EUR 24403 EN), another policy-informing body of the European Commission, the Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) has published an opinion paper that, similar to the JRC Reference Report, aims to provided ‘advice on the essential scientific elements of a working definition for the term “nanomaterial” for regulatory purposes.’
Entitled ‘Scientific Basis for the Definition of the Term ‘Nanomaterial’’, the SCENIHR Opinion reviews and discusses existing definitions formulated by various governing bodies, given special emphasis to the ‘enforceability’ of a definition of the term ‘nanomaterial’.
In contrast to the JRC Reference Paper, however, the SCENIHR Opinion makes the following recommendations:
- Within a regulatory context, it seems useful to specify an upper and lower limit to facilitate a uniform interpretation.
- [...] there seems to be a need for validated standardised methods to determine size and its corresponding distribution as these would ensure comparability of results.
- [...] the definition should aim to be over-arching to also include next-generation nanomaterials to avoid quickly becoming obsolete.
- The size distribution should not be ignored and should be taken into account when defining and describing a nanomaterial. [...] any material is a nanomaterial when >0.15% of the material, based on number concentration, has a size below the upper limit.[1]
- The volume specific surface area can be considered as an additional criterion that could be used to identify dry solid powders as nanomaterial. However, for inclusion in a general definition a limitation is that not all nanomaterials are amenable to VSSA determination.
- [...] each combination of a nanomaterial with a coating has to be considered as an individual case for safety evaluation.
- [...] none of the [16 physico-chemical characteristics identified by the OECD WPMN] appears to meet the criterion of universal applicability required for a definition.
- The inclusion of “internal structure” as an element of the definition is needed to include nanocomposites into the definition of nanomaterials.
- [...] a general definition should cover all these three types [natural, man-induced, manufactured] of nanoscale materials, the distinction being provided by the use of the terms natural, man-induced, and/or manufactured.
The Committee specifically pints out that, ‘[a]t the moment, no scientific data are available to indicate that a specific size associated with special properties due to the nanoscale can be identified for nanomaterials in general. There is no scientific evidence in favour of a single upper limit.’ This statement stands in contrast to the JRC Reference Report, which highlighted that ‘there are intrinsic nanoscale properties which result from the confinement of atoms and electrons within boundaries of a few nanometres. These effects are most dominant at sizes below a few tens of nanometres (less than about 30 nm). They can considerably change fundamental physical material characteristics like the optical, electrical, and magnetic properties of the nanomaterial.’
The SCENIHR Opinion concludes that ‘[a]n upper limit of 100 nm is commonly used by general consensus but there is no scientific evidence to qualify the appropriateness of this value. The use of a single upper limit value might be too limiting for the classification of nanomaterials and a differentiated approach might be more appropriate.’ It subsequently proposes a tiered approach ‘based on a relatively high upper threshold for materials for which further information is missing. In this case it is assumed that the size distribution at the lower end will always be above the lower, more critical upper threshold. The low upper threshold would be the critical threshold for which extensive nano-specific information has to be provided in order to perform case-by-case risk assessment.
An example is presented [...] using 500 nm as high upper threshold and 100 nm as low upper threshold [...].
- Category 1 median size >500 nm for materials for which further information is missing: If the median size of the material is above 500 nm it is assumed that the size distribution at the lower end will always be above the designated lower threshold of 100 nm. Thus, no further information regarding possible nanospecific properties may be needed and classical risk assessment can be performed taking into consideration the particulate nature of the material.
- Category 2 median size <500 nm: When the median size is <500 nm a material is considered to be a nanomaterial 5 and a more detailed nanospecific risk assessment is necessary taking into consideration possible nanospecific characteristics of the material. When the size is <500 nm but >100 nm the nanospecific risk assessment may be waived when additional information is provided that the number size distribution demonstrates that the material has <0.15% (or any specified percentage) of the number size distribution <100 nm. For dry materials, the VSSA (<60 m2/cm3) may be used as an additional qualifier. In these cases a classical risk assessment can be performed taking into consideration the particulate nature of the material.
- Category 3 median size <100 nm and >1 nm: The material is considered to be a nanomaterial and nanospecific risk assessment has to be performed when >0.15% (or a specified percentage) of the number size distribution is <100 nm. For dry materials, the VSSA (>60 m2/cm3) may be used as an additional qualifier.’
The SCENIHR Opinion is open for public consultation; all interested parties are invited to submit comments via the online public consultation form by Wednesday, 15 September 2010.
Follow these links to find out more about the EC’s SCENIHR Committee, download the press release on the publication of the SCENIHR Opinion, to download the full SCENIHR Opinion, or to access the consultation website.
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