Physical Characteristics
- Can’t see it
- Can’t smell it
- Can’t taste it
- Can’t hear it
- Can’t feel it
What is it? Radioactive
More about radon-222:
- Chemically inert, uncharged noble gas
- Produced from decay of uranium-238
- Seeps out of rocks and soil
- Builds up indoors and in mines
- T1/2 is 3.8 days
Decays by alpha particle emission
- Produces short-lived solid alpha-emitters - Polonium 218 and 214
Biological Effects of Radon
- Radon-222 gas does not cause health effects
- Solid charged radon progeny attach to airborne particulates (dust)
- Dust particles are inhaled and can adhere to lung lining
- Deposited progeny decay by alpha emission
- Alpha particles impact bronchial epithelium
- Alpha particles can damage nuclear DNA
- Damaged DNA can lead to lung cancer
Ionizing Radiation (IR) Review
- Radioactive atoms are unstable
- Spontaneous atomic decay produces IR
- IR breaks chemical bonds and strips electrons
- IR can damage molecules and living cells
- IR damage is related to mass, energy and dose
Animal Studies
US DOE - lung cancer, pulmonary fibrosis, COPD
NAS - resp. tumor rate increased with exposure
NAS - tumor rate increases above 20 WLM
DOE - lifetime lung tumor risk coefficients similar in animals and humans
Radium and NORM’s
Radium-226 Health Effects
Soluble solid in Uranium-238 decay chain
Decays by alpha emission (T 1/2 1,620 years) to Radon-222
Radium watch dial painters - 1920’s
US Radium Corp - “Radium Girls”
8-40 years later - Jaw-bone cancer (radium necrosis)
NORM’s ( naturally occurring radioactive materials)
Mining, coal ash, phosphate, uranium, oil and gas
Uranium, Thorium, Radium, Radon, Carbon, Potassium
Health effects poorly understood
Miners
Underground Miners Studies
20+ epidemiological studies in US, Canada, China, Europe and Australia
Consistent exposure-response relationship
Similar excess RR / WLM estimates
Low exposures over long time periods produce greater lung cancer risk
Increased lung cancer rates observed at low cumulative exposures (20 - 90 WLM)
Increased risk observed after controlling for smoking, silica, diesel, metal dust …
Underground Miners Studies
Population WLM RRC%/WLM N
Czech Uranium 313 1.92 9,403
Ontario Uranium 40-90 1.4 15,984
New Mex Uranium 111.4 1.8 3,469
Swedish Iron 81.4 1.4 1,415
Colorado Uranium 834 0.6 44,127
Eldorado Uranium 20.2 2.6 8,487
Newfoundland 382.2 0.9 1,772
WLM - “Working Level Month” = exposure to radon progeny concentration of 100 pCi / L for 170 hours
RRC% - “relative risk coefficient” = the fractional increase above the baseline lung cancer incidence
Population Health Effects - Residential
Residential Studies - Case Control
New Jersey - 480 / 442, RR increased 3.4% / WLM
Sweden - 210 / 400, borderline increase > 4 pCi/ L
Finland - 291 / 495, no statistical difference
China - 308 / 356, no statistical difference
Case Control Study Limitations
- Small sample size
- Low and variable exposure levels
- Selection bias
Exposure-Response Assessment Model
Human data - underground miners
Similar exposure levels - mines & residential
Mine studies down to radon doses of 20 - 70 WLM
Average cumulative residential dose of 18 WLM
4 pCi / L lifetime cumulative dose of 57 WLMs
Linear dose-response relationship
No evidence for a lower limit risk threshold
Radon and smoking have a multiplicative efffect
Causality Criteria - Radon and Lung Cancer
1. Consistent association -animal, occupational, residential
2. Strong association - linear exposure - response curve
3. Specific association - radon and lung cancer
4. Time Relationships -
5. Congruence - consistent with known radiation effects
6. Sensitivity -
7. Biological Mechanism - alpha particle biological effects
8. Plausibility - not contradicted by other information
9. Research / Experiments - consistent animal data
10. Analogy - radium necrosis
