Transcript Environmental Physics - Robert Morris University

Field Methods
Rado
Copyright © 2012 by DBS
Contents
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What is radon?
Health effects
Radon risks
Testing and Remediation
What is Radon?
Natural Radioactivity
222
86Rn
Invisible, odorless, colorless,
tasteless
Only gas in 238U decay chain
220Rn
from 232Th has 55s t1/2
What is Radon?
Radon
Gas
50 minutes
26.8m
Source: http://energy.cr.usgs.gov/radon/DDS-9.html
What is Radon?
Natural Radioactivity
What is Radon?
Stanley Watras
• Limerick Nuclear Power
Plant, Christmas 1984
• Set off radiation alarm bells
• Home basement Rn ~
100 000 Bq m-3
• Risk equivalent smoking 135
packs of cigarettes per day
Designed to detect radiation
on workers leaving…Watras
was entering!
What is Radon?
1988 EPA orders every
home tested
What is Radon?
What is Radon?
Radon
Radium
1,600 years
Uranium
4.5 billion years
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Radon is a gas
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It is naturally occurring
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You cannot see or smell it
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It enters buildings from
the soil via diffusion
(concentration gradient)
Question
Radon is said to be a daughter of radium-226, polonium-218 is a
daughter of radon. Why are these not called sons?
Radon decay products (RDP’s) continue to decay giving
birth to new daughters (progeny).
Indeed these RDP are the real culprits in the radon story!
What is Radon?
Stack Effect
• Warm air rises and
escapes home
• Pressure difference
inside-outside
• Replacement air drawn
in from below
• Increases with wind
speed
Stack effect enhances Rn movement
http://www.cornwallradon.co.uk/page21.html
What is Radon?
Spatial Distribution
• Radon enters from beneath
foundation and travels
upward
• Diluted with outdoor air
infiltrating building
<5
5-6
10
Health Effects
Radon Gas
Progenies (‘daughters’) build up
in confined space –are breathed
in, stick to surface of airways
and emit α-particles
Radon-222
4 day
α,γ
Polonium-218
3 min
α,γ
Lead-214
27 min
β, γ
Bismuth-214
20 min
β, γ
Polonium-214
α,γ
0.2 ms
Lead-210
22 yrs
218Po
and 214Po deliver the
radiologically significant
dose to the respiratory
epithelium
β, γ
Bismuth-210
5 day
Radon Progeny
β, γ
Polonium-210
138 day
α,γ
Lead-206
Stable
Health Effects
Alpha  Decay
4He
+
+
Nucleus Ejected from
222Rn Nucleus
+
+
+
+
+2
+
+
+
Radon - 222
4He
+ 218Po
alpha
particle
Highly energetic α, β particles
rip through tissue causing
cellular and genetic damage
Health Effects
Interaction with DNA
• Highly radioactive
particles adhere to
lung tissue, where
they can irradiate
sensitive cells
• Radiation can alter the
cells, increasing the
potential for cancer
Double Strand Breaks
+ ionize water to produce
free radicals
NCRP 93 (1987)
Natural
Radon
Cosmic
Terrestrial:
-external
-internal
(mrem)
200
27
Artificial
-Diag. X-rays
-Nuc. Med.
-Consumer Pro.
-Other
TOTAL
(mrem)
39
14
10
~1
~360
Radon delivers > 50% radiation dose
28
39
Radon Risks
Radon Levels
Outdoor?
GW > Soil >
Indoor Air >
Outdoor Air
http://energy.cr.usgs.gov/radon/georadon/2.html
Radon Risks
• Average Rn concentration inside a home 1 pCi L-1
• Roughly 2 decays per minute
• 1 Working Level (WL) = 100 pCi L-1
(defined for no ventilation or walls)
• Effect of removal can be taken into account by x2 WL = 200 pCi
L-1, thus 1 WL = 200 pCi L-1 at home
WL = qRn / 200
e.g. 1 pCi L-1 = 0.005 WL
Question
Convert pCi L-1 to dpm L-1
1 Ci = 3.7 x 1010 dps
60 secs in 1 minute
1 pCi = 0.037 dps x 60
= 2.22 dpm
Health Effects
Group A Carcinogen
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Radon is ranked as a Group A carcinogen
– Highest ranking for cancer potential
– Known to cause lung cancer in humans
– Tobacco smoke and tobacco products in same category
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Long-term exposure increases chances
– Risk of lung cancer in normal life = 1-2 % (10-20 in 1000)
– Risk of lung cancer at 1 pCi = + 0.3-1.3% (3-13 in 1000)
Health Effects
Epidemiology
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15,000 – 22,000 deaths a year
Epidemiology confirmed by NAS, WHO, NCRP
Combined effects of Rn and smoking particuarly dangerous
2nd hand
smoke!
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ALA, AMA and Surgeon General all
recommend reducing indoor Rn
Health Effects
Human Studies
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How do we know radon is
a carcinogen?
NCI study examined
68,000 uranium miners
Miners die at a rate 5 x
general population
Adverse Health Effects
Atomic
Bomb
Survivors
Observed Effects
Underground Miners
Medical Patients
Linear
Dose (rem)
No
threshold
Health Effects
U.S. Lung Cancer Deaths/yr
Biological Effects of Ionizing Radiation (BEIR) VI (1999)
20000
18000
16000
14000
12000
10000
8000
6000
4000
2000
0
Smokers
Non-Smokers
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Risk estimates based primarily
on radon-exposed miners
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Est. 15,000 – 22,000 lung
cancer deaths each year in the
U.S. from residential exposure
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10-15% of all lung cancer
deaths in US (150,000)
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Confirms 2nd leading cause
Health Effects
Comparing Radon Related Cancer
Annual U.S. Cancer Deaths
Lung Cancer (radon)
20000
18000
16000
14000
12000
10000
8000
6000
4000
2000
0
Liver Cancer
Brain Cancer
Stomach Cancer
Melanoma
Oral Cancer
Gallbladder Cancer
Bone Cancer
Health Effects
How Radon Compares To Other Causes Of Death
Upper
estimate
25,000
15,000
10,000
Lower estimate
Deaths per year
20,000
5,000
0
Drunk
Driving
Radon
Drownings
Fires/Burns
Air
Transportation
Source: U.S. EPA’s Home Buyer’s and Seller’s Guide (Radon: National Academy of
Sciences, Non-radon: National Safety Council)
Health Effects
Radon and Smoking
Darby et al., 2004
Question
Convert pCi L-1 to Bq m-3
1 pCi L-1 x 1000 L m-3 = 1000 pCi m-3
1000 pCi m-3 x 3.7 x 1010 Bq / Ci
= 1 x 10-9 Ci m-3 x 3.7 x 1010 Bq / Ci
= 37 Bq m-3
Health Effects
Radon Risks
Comparing Rn
cancer rates to
rates for
smokers
20x
Turko, 2002
Basement level
Zone 1: > 4 pCi/L (red)
Zone 2: 2-4 pCi/L (orange)
Radon-222
Zone 3: < 2 pCi/L (yellow)
Based on indoor measurements, geology, aerial radioactivity, soil
parameters and foundation type
End
• Review
Testing and Remediation
Frequencies of 222Rn in US Homes
Radon levels depend on:
• Radon strength in soil
• Soil porosity
• Building to soil pressure difference
• Building ventilation rate
• Openings into the soil
Testing and Remediation
Frequencies of 222Rn in US Homes
8 million homes
Types of Measurement
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Continuous
Integrated long and short term
Multiple
Single 1-7 day – ‘screening’
All rely on measurement of
emitted radiation
Testing and Remediation
Testing
Charcoal
Alpha Track
Photovoltaic Alpha-track Sensor
Testing and Remediation
Testing
Alpha-tracks are plastics - microscopic
radiation tracks after chemical treatment
Alpha Track
Magnified only 100 times
3 months at EPA Action Level of 4 pCi/L
These are pits in CR-39 plastic made by alpha
particles. If they can make these pits in plastic,
imagine what they can do to your DNA
Testing and Remediation
Testing
Sun-Nuclear
Photo-diode – EPA verified continuous
monitor
Detects radon’s α-particle with 5.590 MeV
energy. Works by measuring the voltage
change across an P-N semiconductor
bridge.
Factors Affecting the Emission of Radon
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Frost, rain, asphalt caps soil –
stack effect exerted on larger
area
Wind
Factors Affecting the Emission of Radon
What interpretation can you provide for the data in Fig. 1?
Factors Affecting the Emission of Radon
• Concentration varies
continuously
• High in winter
• Low in summer
Testing and Remediation
Radon Mitigation
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Active Soil
Depressurization
(ASD)
– Creates a
vacuum
beneath the
foundation
Caulking and
sealing
Ventilation
http://www.radon-services.com/animations/animation.htm
Testing and Remediation
Passive System
Junction Boxes
(to power fan and warning
device, if needed)
Vent pipe running between
sub-slab gravel and roof
Sealing and caulking
Polyethylene soil-gas retarder
between slab and gravel
Large gravel beneath slab
Key Findings
• Studies of uranium miners implicated radon as a
known cause of lung cancer in humans
• Recent residential studies have provided direct
evidence of increased lung cancer risk due to radon
• Suggest radon may play a role in 10% of all lung
cancer deaths
• Nearly ¾ of radon-associated deaths occur among
smokers
• Radon is an avoidable risk
Rebuked
• http://www.seered.co.uk/radon_newsci.htm
• http://removeradon.com/articles.htm
Further Reading
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Cothern (1999) Indoor Air Radon. Environmental Geochemistry and Health, Vol. 21, No. 1, pp. 83-90.
Darby S., Whitley E., Silcocks T., Thakrara B., Green B.M.R., Lomas P.R., Miles J.C.H., Reeves G.,
Searn T. and Doll R., (1998) Risk of lung cancer associated with residential radon exposure in South West England: A case-controlled study. British Journal of Cancer, Vol. 78, No. 3, pp. 394-408.
Hess C.T., Weiffenbach, C.V., and Northon, S.A. (1983) Environmental radon and cancer correlations
in Maine. Health Physics, Vol. 45, No. 2, pp. 339-348
Krafthefer B. (1984) Measurements of radon decay products in residential environments, Ashrae
Journal - American Society of Heating, Refrigeration and Air-Conditioning Engineers, Vol. 26, No. 5,
pp. 55.
Harley N.H. (1984) Radon and lung cancer in mines and homes, New England Journal of Medicine,
Vol. 310, No. 23, pp. 1525-1527.
Joyce C., Kenward M. and Pearce F. (1986) Perils in the all-American home, New Scientist, Vol. 110,
No. 1511, pp. 22-23.
Pearce F. (1987) A deadly gas under the floorboards, New Scientist, Vol. 113 (1546), pp. 33-35.
Oge M. (1994) The US environmental agency`s strategy to reduce risks of radon, Radiation Protection
Dosimetry, Vol. 56, No. 4, pp. 343-354.
Phillips P.S. and Denman A.R. (1997) Radon: a human carcinogen. Science Progress, Vol. 80, No. 4,
pp. 317-336.
Phillips P.S., Denman A.R., and Barker S. (1997) Silent, but deadly. Chemistry in Britain, Vol. 33, No.
1, pp. 35-38.
Books
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Brookins, D.G. (1990) The Indoor Radon Problem. Columbia University
Press.
Cole, L.A. (1994) Element of Risk: The Politics of Radon. Oxford
University Press.
Cothern, C.R., and Smith, J.E Jr. (1987) Environmental Radon.
Springer.
Durrani, S.A., and Radomir, I. (1997) Radon Measurements by Etched
Track Detectors : Applications in Radiation Protection, Earth Sciences
and the Environment. World Scientific Publishing Company.
National Research Council (1989) Health Effects of Exposure to
Radon. BEIR IV. National Research Council.
Nazaroff, W. and Nero, Jr., A. (1988) Radon and its Decay Products in
Indoor Air. Wiley, New York.
Modeling Radon Exposure
Box Model
V
Source
Q
Sink
S
q
L
Q=Sτ
Q = quantity
q = concentartion
q = Q / V = Sτ / V
Modeling Radon Exposure
Sources and Sinks
Sources,
SRn = 0.01 – 10, mean = 0.5 pCi L-1 h-1
Background concentration,
q0Rn = 0.2 pCi L-1
Residence time of air in the home, τv
Background gas ventilation rate (per unit voume),
Sv = Q0 = q0Rn
V
V τv
τv
Sinks,
Ventilation loss rate,
Decay loss rate,
Lv = qRn / τv
Ld = qRn / τRn
Steady-state:
(qRn = Rn concentration inside)
(τRn = half-life = 91 hrs)
SRn + Sv = Lv + Ld
Question
SRn + Sv = Lv + Ld
SRn + q0Rn / τv = qRn / τv + qRn / τRn
Rearrange to find qRn
qRn = q0Rn + τv SRn
1 + τv / τRn
Modeling Radon Exposure
Radon Concentration
SRn + Sv = Lv + Ld
SRn + q0Rn / τv = qRn / τv + qRn / τRn
qRn = q0Rn + τv SRn
1 + τv / τRn
Usually simplified:
Since:
qRn ≈ q0Rn + τv SRn (denominator = 1)
q0Rn = 0.2 pCi L-1, SRn = 0.01 - 10, mean = 0.5 pCi L-1 h-1 and τv = 1 hr
qRn = 0.7 pCi L-1
Rn concentrations are clearly dependent on source and ventilation!
Modeling Radon Exposure
Radon Concentration
qRn ~ q0Rn + τv SRn
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With fast ventilation τv = 0, qRn ≈ q0Rn
With no ventilation τv = ∞, qRn ≈ τRn SRn
(depends on outside air conc.)
(depends on source and t1/2)