A document has been published by the Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) at the request of the Commission, which highlights the essential scientific elements such a definition will need to have.
Comments on this document are now requested and the dialogue will remain open until 15 September 2010.
Evidence for the 100nm limit?
According to the SCENIHR, a number of different definitions have been proposed by various international and national organisations that usually have a typical upper limit of about 100nm - one or more dimension under 100nm and the material is nano.
Although it is now generally accepted that something in the nanoscale has a size somewhere between 1 and 100nm, there is no scientific evidence to qualify the appropriateness of the 100nm value as an upper limit, the committee claims.
In addition, it highlights other problems with the definition including the differing sizes of particles in a nanomaterial and their distribution, and whether the definition should include internal as well as external dimensions.
Not all particles within a material are the same size, some may fall in the nano range and some may not, so a definition would have to include a cut off point for the amount of the material that is allowed to be in the nanoscale without it being classed as a nanomaterial.
Furthermore, if the definition includes only external dimensions then aggregates or agglomerates of nanomaterials will not be covered; however, if both internal and external is used exclusion criteria would have to be written in as it could lead to the classing of non-nanomaterials as nano.
SCENIHR’s report also highlighted the need for adequate, validated methodologies that can measure size in the nanoscale.
According to the report, these methods do exist but they are not always comparable, so any size measurement would have to include both particle size, size distribution and the details of the methodologies used for assessment.
Two upper limits proposed
The Opinion, published earlier this week by SCENIHR proposes a definition that has two upper limits as the use of a single upper value (in this case 100nm) might be too limited. SCENIHR’s example of how this could be organised is as follows:
Category 1 – material with a median particle size of above 500nm. In this case it is assumed that even taking into account the distribution of the particles, the smallest particles will still be above 100nm. For a category 1 material, no extra risk assessment or nano specific information would be required.
Category 2 – material with a median size of smaller than 500nm. It is assumed that some of the particles will fall below 100nm so a nanospecific risk assessment would be required. If it can be proved that particle size is smaller than 500nm but larger than 100nm this nanospecific information could be waived.
Category 3 – material with a median particle size of under a 100nm. It is assumed that this is a nanomaterial and nanospecific information is needed.