Unattached Fraction of Radon Progeny as an Experimental Tool in the Assessment of the Risk of Nanoparticles* - Aerosols: Measurement, Dosimetry, and Health Effects - page 427

where
a represents proportionality coeficient
v represents the volumetric breathing rate
k represents the lung deposition coeficient
q b and q c represent the concentrations of the 214 Pb (RaB) and 214 Bi (RaC) correspondingly

Based on (16.1) these results yield values for the product vk, which has been termed “Filtration
Ability of Lungs” (FAL) (Ruzer and Harley, 2004), where

A
aq

γ

(16.2)

FAL vk = =

where q = q b + q c .
FAL is an important breathing parameter relecting the gross particle removing behavior of the
respiratory system. It is a “bridge” between the quantity of aerosols in the air and in the lung for
different physical activities.
Measurements were performed without disturbing the working conditions for three occupational
groups: drillers, auxiliary drillers, and inspection personnel, totaling approximately 100 workers.
The average, standard error, and the median values for a total of 297 air samples and 391 lung
measurements are shown in Ruzer et al. (1995).
The measurements were also carried out in a non-uranium mine in Tajikistan (former USSR)
with a special instrument having two probes (Antipin et al., 1978), one for lung gamma-activity
measurement and the other for air alpha-activity measurement.
As we mentioned before, these experiments, conducted in speciic underground conditions with
a high gamma-background, were provided with simple, portable instrumentation. Therefore, it was
dificult to study the detailed distribution of activity in the lung. The successful measurements made
in this study under rugged mining conditions illustrate the possibilities for using radon progeny as
a tracer in the study of aerosol distribution in the lung. This method would be particularly suited for
use in the nanometer range, under laboratory conditions, where the background is low, and instru-
mentation is much more sensitive, similar to the studies conducted at PSI. This approach could be
used to map aerosol dose to the lung because it can provide graphic information on where these
particles of different sizes are deposited in the respiratory system.
Thus, the approach is to use radon progeny as a marker at safe doses in the study of deposition
of nonradioactive nanoaerosols in the human body. The proposed radiation dose during a human
experiment will be negligible in comparison with the natural background exposure over time. This
is consistent with the use of radiological tracers for other medical research. For human experiments
we propose using a generator of unattached fraction of radon progeny. This could be a small
environmental chamber such as used in the Swiss research (Butterweck et al., 2001), or using a
respirator mask exposure apparatus attached to a small chamber. Both radon and monodisperse
aerosols of known size and morphology will be injected into the chamber under controlled
conditions.
In terms of radioactive safety, when properly handled, the gamma-activity of radium is negligible.
Through radioactive decay, radium produces radon ( 222 Rn), which in turn will produce atoms of
218 Po. Once it is released into the air, about 10-12 molecules of air constituents naturally diffuse
onto and surround the 218 Po atom. These clusters are about 1 nm in diameter and have a diffusion
coeficient of ∼0.06 cm 2 /s. They are called unattached activity of radon progeny. Again through
natural diffusion processes, these Rn progenies deposit on particles coexisting in the air ranging in
size from nanometers to micrometers.
Controlled experiments where nanometer (or larger)-sized aerosols of known diameter are
radiolabeled through natural attachment to unattached activity (e.g., becoming “attached activity”)