Discussion about the use of the volume-specific surface area (VSSA) as criteria to identify nanomaterials according to the EU definition

In the EU regulation, a material containing particles is considered as nano if, for 50 % or more of the particles in the number size distribution, one or more external dimensions is in the size range 1–100 nm. Due to the difficulty to measure in a reliable way the number particle size distribution, it is suggested to use the volume-specific surface area (VSSA) >60 m2/cm3 as simple screening criterion to identify nanomaterials. This threshold corresponds to monodispersed spherical particles with a size of 100 nm. In this paper, a theoretical study is carried out to identify the effect of the particle shape, polydispersity, agglomeration and aggregation on the VSSA threshold. It appears that the VSSA approach is overprotective because a lot of samples are identified as nanomaterials even if less than 50 % of the particles have a size lower than 100 nm, this 50 % in number criterion being the main identification criterion in the EU definition. Even if the VSSA is leading to many false positive results, it can be used to identify non-nanomaterials as soon as its value is lower than the threshold at the condition to take into account the shape of the particles and their external surface area. This conclusion is true for monomodal distributions of particles but is subject to some restrictions for bimodal distributions.