Definition of a MNM. A clear definition to discriminate MNMs from other materials is a prerequisite to include provisions for MNMs in legislation. In October 2011, the European Commission published the ‘Recommendation on the definition of a MNM’. The European Commission based its recommended definition mainly on a reference report by the European Commission Joint Research Centre (JRC) (Lövestam et al., 2010) and a scientific opinion by the SCENIHR (XXXXXXX, 2010). Inevitably, the final wording, and especially the thresholds, comprise political compromises as well. In its Recommendation (EU, 2011) the European Commission states that: ‘MNM’ means a natural, incidental or manufactured material containing particles, in an unbound state or as an aggregate or as an agglomerate and where, for 50% or more of the particles in the number size distribution, one or more external dimensions is in the size range 1 nm–100 nm. In specific cases and where warranted by concerns for the environment, health, safety or competitiveness the number size distribution threshold of 50% may be replaced by a threshold between 1% and 50%. Alternatively, it is stated that a material should be considered as falling under the definition where the specific surface area by volume of the material is greater than 60 m2/cm3. The Recommendation also includes definitions for ‘particle’, ‘agglomerate’ and ‘aggregate’. The Commission foresees a review of the definition, particularly focusing on the appropriateness of the 50% limit. The recommendation contains a rather broad description of the term MNM. It potentially includes all kinds of MNMs/nanoparticles irrespective of their origin. The definition thus also covers natural nanoparticles, such as volcanic ashes, as well as incidental MNMs like nanoparticles originating from human activity such as exhaust of combustion processes, and the intentionally manufactured MNMs/nanoparticles by industry, which may be used in various industrial processes and consumer products. With the definition the Commission solely aims to identify substances within a specific size range and explicitly does not aim to classify MNMs as intrinsically hazardous. For this purpose it is appropriate to use a broad description, especially since no distinction can be made on the origin of the particle when only size is measured. However, as with other materials, distinctions between natural, incidental or manufactured materials need to be made in the specific areas of legislation since the need for...
