Environmental Engineering Reference
In-Depth Information
Upper air radon—all data
100,000
10,000
1,000
100
10
1
0
10
20
30
Sampling altitude (km)
FIGURE 21.3
Radon measurements in the troposphere and stratosphere made over Alaska, the Canal Zone,
and southwest United States by WB-57 high-lying aircraft. (From Fisenne, I.M., Machta, L., and Harley, N.H.
Stratospheric radon measurements in three North American locations, in Radioactivity in the Environment,
McLaughlin, J.P., Simopolis, S.E., and Steinhausler, F. Eds. The Natural Radiation Environment, Rhodes,
Greece, 2002, Elsevier, pp. 715-721, 2005.)
concentrations in the atmosphere. An effective vertical transport rate was calculated at six different
altitudes to determine an average of 0.5 ± 0.1 cm s
−1
.
These data were supported by similar tropospheric concentrations reported by Machta and Lucas
(1962) for air samples collected over Hawaii and later by measurements of Moore et al. (1973).
The entire data set of 54 samples is shown in Figure 21.3.
21.7 RADON IN DRINKING WATER
The major determinant of internal dose and, thus, risk from radon in drinking water is not from the
ingestion of water but the lung (bronchial) dose from radon decay products in air following release
of radon from the water during use (NAS/NRC, 1999a,b). An internal dose to the stomach was
calculated, but is very small compared with the lung dose from inhaled decay products. For a given
radon concentration in drinking water, the risk ratio from both pathways (stomach cancer versus
lung cancer) is calculated to be from 1% (Harley and Robbins, 1994) to 11% (NAS/NRC, 1999a,b),
and depends upon the model used to transport the gas through the stomach wall to the cells identi-
ied as targets for stomach cancer.
Radon released from water during showering and other use combines with and is indistin-
guishable from normal residential sources. The best estimate for the transfer factor from water
to air is 10,000/1, and is based on an analysis of all published data (NAS/NRC, 1999a,b). That is,
10,000 Bq m
−3
of
222
Rn in water will, on average, add 1 Bq m
−3
of
222
Rn to the indoor air. Hess et al.
(1987) measured
222
Rn concentrations of 3.7 × 10
4
Bq L
−1
(10
6
pCi L
−1
) in the state of Maine. Surface
water (i.e., from reservoirs) is very low in
222
Rn concentration because the gas is readily removed
by surface agitation.
EPA has suggested a value for water of 11 Bq L
−1
222
Rn (300 pCi L
−1
). This value can be techni-
cally dificult to obtain. A multimedia approach suggested by EPA is to obtain an equivalent risk
by reducing the water concentration to a value that will yield upon release the standard outdoor
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