Redefining environmental nanomaterial flows: consequences of the regulatory nanomaterial definition on the results of environmental exposure models†
All nanomaterial exposure estimates require fundamental knowledge about the production volumes of the nanomaterials. Published values of production volume can vary by orders of magnitude, mainly caused by ambiguities in the definition of what a nanomaterial actually is. The recommendation for a definition of “nanomaterials” by the European Commission has to some extent clarified this issue. In the meantime, first data are available for registered production volumes of nanomaterials in France based on a mandatory registration scheme. We have compared the tonnages of registered production and import of substances in nanoform in France with the estimated total market volumes of these substances, which include both non-nanoforms (bulk) and nanoforms. These substances comprised CaCO3, carbon black, TiO2, SiO2, ZnO, AZO-based and diketo-pyrrolo-pyrrole-based (DPP) pigments as well as carbon nanotubes. The results show that some materials such as SiO2 and DPP have a good match between reported nanoform and total production volumes, whereas for other materials such as TiO2 and ZnO the reported nanoform production volumes are only a fraction of the total production volumes. This means that for SiO2 and DPP the “conventional form” and the nanoform are identical, while TiO2 and ZnO have been used as bulk materials in several applications. With this knowledge that for SiO2 the global production of “conventional” silica is in fact all nano-silica, we can apply the information on the uses of conventional silica to refine the material flow model for nano-silica. The results of this updated modeling show an input mass flow of (nano)silica to environmental compartments that is four to five times larger than previously modelled. The flows to natural and urban soils even increased by a factor of 13, because not only the production but also single specific applications (such as the use in tires) may have a considerable impact on the environmental exposure. Future environmental risk assessments ought to prioritize both by production volume and/or by the probability of direct environmental releases, considering that data on conventional substances may often represent forms of the substances that are nanomaterials in terms of the definition that is recommended by the European Commission.