Dose metrics

In the risk assessment for regular (i.e. non-nano material) substances, inhalation exposure is usually expressed on the basis of the inhaled mass. The safety of the use of the substance is assessed by comparing mass-based exposure estimates to levels of inhaled mass that are believed not to lead to adverse health effects.

For nanomaterials, it has been shown that similar mass doses of particles with different geometry may induce very different levels of effect in test animals. Therefore, mass does not seem to be an appropriate metric to base the risk characterisation on.

Different alternative dose measures have been suggested in literature, but consensus on a common metric, or whether such a metric is feasible at all, has not been achieved.

ConsExpo nano expresses the alveolar load in different, potentially relevant dose metrics.

The following dose metrics are included:

• the number of nanoparticles 
• the total surface area of nanoparticles (mm_­²)
• the total mass of nanoparticles (mg)
• the total volume of the nanoparticles (mm³)
• the number of aerosol particles
• the total surface area of aerosol particles (mm²)
• the total volume of the aerosol particles (mm³)

These dose metrics are calculated  from the particle properties provided by the model’s user, assuming that nanoparticles are adequately represented by simple geometric shapes (e.g. spheres, cylinders).