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Nanomaterial definitions

2018-05-09

Nanomaterial definitions

The most detailed basis for regulatory “nano” definitions has been developed, and is constantly revised, by the International Organisation for Standards (ISO). The ISO TS 80004 (part two of 13) defines a “nano-object” as a material with one, two or three external dimensions in the nanoscale and also distinguishes different types, like nanotubes or nanoparticles. For the European Union, a recommendation for a definition has been given by the European Commission (EC). It was updated in 2011 and is relatively broad, and while it is not legally binding in itself will be adapted for relevant product or sector specific legislation.

The main criterion is the size of the particles that a material is composed of. To be considered a nanomaterial, this has to be 1-100 nm in at least one external dimension, and this should apply to at least 50% (based on number) of all the particles constituting the material. If adequate, the threshold may even be lowered to 1%, in case of special environmental or health safety considerations, for example. Due to their large volume specific surface area (VSSA), most nanomaterials tend to form (loose) agglomerates or (inseparable) aggregates. Nevertheless, those are also considered nanomaterials if the constituent particles fall into the scope of the definition.

In addition, the VSSA is given as a criterion, but one which is only applicable for a positive decision (if greater than or equal to 60 m2/cm3) if the particle size distribution does not lie in the defined range. Furthermore, fullerenes, carbon nanotubes and graphene flakes are explicitly included though not covered by the size range given (all, two or one dimension(s) below 1 nm, the other(s) above 100 nm). This definition applies to intentionally or unintentionally manufactured materials as well as naturally occurring ones.

Though easy to understand, this definition has become subject to many discussions. On the one hand, it only refers to particulate materials, thus embedded nanomaterials, most nanostructured materials or colloids are not covered. On the other hand, the definition applies for a very wide range of materials, including many powders which unintentionally contain a relevant number of nanosized particles due to the production process. Also materials, which have been on the market for decades, may now be considered nanomaterials. An amendment of the recommended definition was planned by December 2014, but the process is still ongoing.

Some specific EU legislations have implemented their own (legally binding) nano definition, namely the biocidal product Regulation, the cosmetics Regulation and the Regulation on food information for consumers (FIC), adapting parts of the recommendation and/or adding new criteria, respectively. Important additional criteria, not mentioned in the recommendation, are the occurrence of new physico-chemical properties, which are not present for the bulk form (FIC), as well as the restriction of intentionally manufactured materials (FIC, cosmetics Regulation). The cosmetics Regulation, furthermore, restricts the materials of interest to biopersistent, insoluble particles, but includes nanostructured materials.

For some legislations, there are proposed amendments not yet implemented, such as fo the novel food Regulation: to adapt the definition given in the FIC Regulation, or for the medical devices Directive: to adapt the recommendation, but leaving the possibility of setting the particle-size distribution threshold below 50%. Without giving an explicit nano definition, the Regulation on plastic materials demands a case-by-case decision on nanomaterials, and only those listed in Annex 1 are allowed for the exact use specified (for example, titanium nitride nanoparticles for the use in PET bottles).

There are other relevant sectors, where nanomaterials are not (yet) mentioned explicitly, such as the Regulation on food contact materials or the chemicals regulations REACH and CLP. According to CLP, hazardous substances should be notified with Echa specifying the exact form they are put on the market (such as a nanomaterial), regardless of their production volume. Echa published guidance on nanomaterials for REACH registrants in 2013. It does not provide an overall definition, but proposes rather a case-by-case assessment, based on the registrants’ expert judgement on “the most appropriate metric” to be considered. According to the Second Regulatory Review on Nanomaterials, amendments of the REACH Annexes are planned.