ABSTRACT
Nanotechnology produces nanoobjects and nanostructured materials with new or at least improved properties. Nanomaterial is defined as material with external or internal dimensions at the nanoscale [5, 6]. Most important building blocks are nanoobjects with one or more external dimension at the nanoscale. These are spherical nanoparticles, nanofibers or nanoplates. Often they occur as assembled nanomaterials, as a subgroup of nanostructured material with internal or surface structure at the nanoscale in form of loosely connected agglomerates and strongly connected aggregates. Both together, since they are man-made, are called engineered nanoparticles (ENPs). Besides shape and structure differences ENPs may also differ with respect to the composition and their surface properties. All properties may also change during lifetime, because of different stress situations. After synthesis in the solid, liquid or gaseous phase they may be introduced into other gaseous, liquid or solid matrix material. We can differentiate between several forms of nanostructured materials: aerosols, powders, suspensions and composites. Coatings can be considered to be a thin layered form of composites on a substrate. It is assumed that there is a release risk for ENPs from synthesis processes and the different material forms leading to an exposure risk and followed eventually by a hazard risk. Up to now there does not exist any study, which considers all these steps for one nanostructured material [4]. Instead exposure and hazard are treated independently. The exposure studies are justified mainly based on arguments such as the following: • Any material consisting of or containing ENPs is a potential
source for ENP release-a tremendous amount of different materials has to be investigated • Any treatment or stress of ENPs or nanostructured materials
may cause ENP release-a tremendous amount of different treatment and stress processes under different conditions has to be investigated
• Often only a few ENPs are occurring in exposure situations; we cannot detect them because their small contribution disappears in a large background. The result is a big measurement effort for eventually not hazard relevant ENPs The greatest interest of industrial hygienists and toxicologists is
in the release of synthesized ENPs during production (synthesis),
handling or application (treatment) of nanostructured materials containing ENPs and use, recycling and littering (treatment) of products containing ENPs into the environment. The case of ENP release during synthesis is best described by an emission factor (EF), which is defined as number, surface area and/or mass (volume) per unit of time released to the environment. One can also consider relating the amount of ENP release to the amount of nanostructured material produced. The ENP release per unit of mass of produced or treated nanostructured material is best described by a release factor (RF), defined as number, surface area and/or mass (volume) per unit of mass of nanostructured material. This is depending on properties of the nanostructured materials and the amount and kind of energy input during the different kinds of treatment of the material. The ENP emission and release factors can be considered to be important process and material properties, since with no emission and release there is no exposure and therefore no risk.
