Unattached Fraction of Radon Progeny as an Experimental Tool in the Assessment of the Risk of Nanoparticles* - Aerosols: Measurement, Dosimetry, and Health Effects - page 420

According to EPA (1996) of the United States, “in epidemiological studies, an index of exposure
from personal or stationary monitors of selected pollutants is analyzed for associations with health
outcomes, such as morbidity or mortality. However, it is a basic tenet of toxicology that the dose
delivered to the target site, not the external exposure, is the proximal cause of a response. Therefore,
there is increased emphasis on understanding the exposure-dose-response relationship. Exposure
is what gets measured in the typical study and what gets regulated; dose is the causative factor.”
16.1.4 a irborne n anoParticle c oncentration M easureMent
Let us consider every step in our dosimetric nanoaerosols road map from the point of view of
available approach, methods and measurement technique. We begin with the branch which describes
the study of airborne nanoparticles.
Manufacturing and handling processes for nano-sized materials are widely variable. For
example the materials may be fabricated in a luidic system closed to the environment (e.g., colloidal
suspension of metallic crystals formed in a liquid reaction vessel), or in an open-air system where
they may directly mix with ambient air (e.g., manufacture of carbon black using combustion
techniques). For each nanotechnology the potential for fugitive emissions leading to an airborne
concentration can be different. Information on the release of the nanomaterial to the air for the
manufacture of different nanomaterials is very scarce.
It should be noticed that the problem of metric in nanoaerosol concentration is complicated.
First, nanoaerosols often exist in practice as a structure not as a single particle with the size at
least in one dimension in the range from 1 to 100 in diameter. So, generally speaking, it is not always
possible to use diameter itself as a characteristic of the particle.
Second, from the point of view of the dose to the lung the aerosol mass concentration as a
characteristic also has many disadvantages:
1. In the nanometer range when mass concentration is very small, but the number concentra-
tion, particle density at the lung tissue, and correspondingly dose can be very high.
2. By the same mass concentration particle size distribution can be different, so will be
different the local particle deposition inside the lung and correspondingly the dose and
biological effect.
3. In the case of aerosols for the dose assessment, the important role is played by only the
“respirable” particles, that is, particles with a diameter less than 5-7 μm. Unfortunately,
this limit is uncertain (Martonen et al., 1992).
According to the majority of the studies of ultraine and nano-sized aerosols, it is not the mass
concentration, but the particle number and surface area concentrations that should be used for the
assessment of dose because they appear to be better predictors of health effects (Aitken et al., 2004;
Hankin et al., 2008; Oberdörster et al., 2005; Royal Society, 2004).
As we already mentioned the use of mass concentration data alone is insuficient for the expression
of dose, and the number concentration and/or surface area need to be included.
Unfortunately there is a lack of information on measurement of nanoaerosols particles, and
especially the size distribution and surface area concentration in the working environment.
A review of the literature on environmental health in the new rapidly developing nanotechnology
industry shows that the problem of exposure has not been adequately assessed (Oberdörster
et al., 2005). Worker health and safety is of initial concern as occupational groups are likely to be
among the irst to be exposed to elevated concentrations of nanomaterials. A gap exists between
the existing particle measurement methods and those truly appropriate for nanoaerosol exposure
assessment. Until now, the primary tools available for measurement of nano-sized aerosols have
been Condensation Particle Counters (CPCs), and Differential Mobility Analyzers (DMAs).