Radioactive Aerosols - Aerosols: Measurement, Dosimetry, and Health Effects - page 393

As a result of this nonuniformity in dose, the variability in lung sickness and lung cancer mortal-
ity among nonuranium miners in Tadjikistan was established.
This aspect of nonuniformity both for dosimetric and epidemiological data is very important. In
previous epidemiological studies, a uniformity approach to dosimetry was used and this can lead to
a substantial error in risk determination.
The nonuniformity problem together with other aspects mentioned in the following suggests that
there is good cause for reevaluating the previous epidemiological data.

15.9 AEROSOL CONCENTRATION MEASUREMENT

15.9.1 r adon and i ts c ontribution to a bsorbed d ose
In a real atmospheric environment, we have a combination of radon (inert gas) and its decay products
(natural radioactive aerosols). For the assessment of the biological effect of the inhalation of radon
and its decay products, it is important to estimate the contribution to the dose of radon itself and its
decay products separately. Such an assessment is important because of different physicochemical
properties of radon and radon progeny, and subsequently their different behaviors in the lung.

15.9.1.1 Experimental Study on Animals
In Leites and Ruzer (1959), the results of the experiments on white rats inhaling radon with its decay
products in the small chamber (“emanatorium”) are presented. Doses were determined separately
for radon and radon progeny. Besides dosimetry, pathology—anatomical study and weighting were
provided.
The animals inhaled radon for 2 h every day with radon concentrations of 4.83 × 10 8 Bq/m 3 (irst
series), 5.03 × 10 7 Bq/m 3 (second series), and 1.33 × 10 6 Bq/m 3 (third series).
As there were no available methods for the measurement of the concentration of radon decay
products for the time of this study, especially for the small-volume chamber, the simpliied variant
of the method proposed in Ruzer (1960a,b) was used.
From these data, it is clear that the general absorbed energy due to the decay of radon in the
organism is much smaller than that due to the decay of radon progeny. The main reason for this
is that the deposition of radon decay products in the lung is very high and at the same time bio-
logical clearance of the inert gas radon from the organism is high. In other words, the behavior of
decay products in the organism is determined completely by radioactive decay in the lungs with no
observed trace of the clearance. At the same time, radon, due to its chemical nature, does not deposit
in the organism for a long period and therefore does not produce a substantial amount of decay
products and a subsequently absorbed dose. A difference in terms of absorbed dose will be much
more substantial if we take into account the mass of irradiation tissue—lungs for decay products
and whole body for radon—because with some approximations we can assume that the distribution
of radon in the body is uniform. According to our calculations, the absorbed dose to the lung from
decay products of radon is two to three times higher in magnitude than from radon itself.
In the irst series of experiments, animals beginning from the second week of exposure were
inert and sluggish, with decreasing appetite and decreasing weight in comparison with the control
group. They died after the completion of the irradiation within 7-72 days in the irst series of experi-
ments and within 69-94 days in the second series. The main macro- and microscopic changes took
place in the lungs, especially in the front and median parts of it. In the third series, no changes in
the weight and behavior of animals were detected during the period of exposure and even 10 months
later.
These biological results show that in this case typical radiation sickness of the lung took place,
which was in agreement with the dosimetric data.
For directly checking the fact that the biological effect in this case was determined mainly by the
radon decay products, and not from radon itself, animals took a bath in radon water in such a way