This Opinion deals with the recent developments in the risk assessment of nanomaterials for both man and the environment. The in-depth characterisation of a manufactured nanomaterial on the basis of its physical-chemical characteristics is essential. Due to the
size and material specific temporal evolution of some nanomaterials, potentially hazardous nanomaterials need to be characterised both ‘as manufactured’ and in the various possible forms ‘as delivered’ in biological systems, or to a human in a specific application, or to a particular ecosystem of concern. The characterisation ‘as manufactured’ provides information for the material safety data sheet of the product
itself. The characterisation ‘as used’ in biological systems is needed as properties of nanomaterials may change considerably, notably the size distribution due to
agglomeration/aggregation of the particles. An issue of specific importance is the properties of the nanomaterial as it is actually used in products and to which consumers
may be exposed. For the risk assessment the latter characterisation is of highest relevance.