Size is the best way to define a nanomaterial but one upper limit is not sufficient, a European Commission scientific committee has concluded.
An acceptable definition of a nanomaterial is needed for regulatory purposes, and earlier this year the European Commission asked the Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) for advice on what such a definition might look like.
The SCENIHR published its first report, which was opened for public comment, back in July and has now announced its official position.
While the SCENIHR recognised the 94 comments that were made regarding the original document, and has said many have been taken into account, its final conclusions remain relatively similar to those published in July.
The SCENIHR’s report proposes a three category approach for defining nanomaterials that would take into account the distribution of particles across a size range in a material, focused on a threshold of 100nm.
Category 1: size above 500nm
If the mean or median size of the material is above 500nm it is assumed that the size distribution at the lower end is likely to be above the lower threshold of 100nm. Therefore, the need for further evaluation regarding nano specific properties is of a lower priority.
Category 2: size between 100nm and 500nm
When the median size of the material is below 500nm it can be assumed that some of the particles will be smaller than 100nm. In this case, a percentage cut off should be used to determine whether enough of the particles fall below this limit to warrant a nano specific risk assessment.
Category 3: size under 100nm
Here it is assumed that a nano specific risk assessment is needed.
However, the opinion does recognise that for specific areas and applications, some modifications of any overarching definition may be needed.
Although the SCENIHR has used the 100nm cutoff in its definition suggestions, it does recognise the somewhat arbitrary nature of this value by stating there is no scientific evidence to quality the appropriateness of the 100nm value as an upper limit.
It 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.