Environmental Engineering Reference
In-Depth Information
21 Radon and Thoron in
the Environment
Concentrations and
Lung Cancer Risk
Naomi H. Harley
CONTENTS
21.1 Introduction ........................................................................................................................ 539
21.2 Sources of Residential and Occupational Radon Exposure ............................................... 540
21.3 Units for Radon Exposure .................................................................................................. 540
21.4 Indoor Concentrations ........................................................................................................ 541
21.5 Outdoor Concentrations ..................................................................................................... 541
21.6 Stratospheric Concentrations.............................................................................................. 542
21.7 Radon in Drinking Water................................................................................................... 543
21.8 Occupational Radon Exposure in Underground Mines .....................................................544
21.9 Bronchial Lung Dose ......................................................................................................... 544
21.10 Dose to Other Organs......................................................................................................... 547
21.10.1 Dose to the Fetus from Radon in Drinking Water .............................................. 547
21.10.2 Radon and Childhood Leukemia......................................................................... 547
21.11 220 Rn (Thoron) Contribution to 222 Rn (Radon) Measurements .......................................... 548
21.12 Lung Cancer Risk Projections............................................................................................ 548
21.13 Guidelines for Indoor 222 Rn................................................................................................ 549
21.14 Summary ............................................................................................................................ 549
References...................................................................................................................................... 551
21.1  INTRODUCTION
Our planet is mainly rock and metal and its rock is remarkably radioactive. The sun supplies most
of our energy but the measured radioactivity in the earth contributes up to 25% of the total heat
balance of the earth (Araki et al., 2005). The primordial decay series beginning with 238 U (4.5 × 10 9
year half-life), present in all terrestrial materials, supports a chain of 13 alpha-, beta-, and gamma-
emitting radionuclides that includes the gas radon ( 222 Rn, 3.8 day half-life). The primordial decay
series beginning with 232 Th (1.4 × 10 10 year half-life) is also present in all basic earth materials, and
supports a chain of 11 radionuclides that includes another isotope of radon—common name thoron
( 220 Rn, 55 second half-life). Both radon isotopes are produced in all soil or rock from their parent
radium isotopes ( 226 Ra or 224 Ra). A fraction of both gases is released from all terrestrial substances
and can be measured in any dwelling, outdoors, and in the case of 222 Rn, even at stratospheric alti-
tudes. Thoron, however, should not exist in the stratosphere because of its short half-life and the
time required for transit to altitude.
539
 
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