Field Methods

Rado

Copyright © 2012 by DBS

Contents

• What is radon?

• Health effects

• Radon risks

• Testing and Remediation

What is Radon?Natural Radioactivity

22286Rn

Invisible, odorless, colorless, tasteless

Only gas in 238U decay chain

220Rn from 232Th has 55s t1/2

What is Radon?Radon Gas50 minutes

26.8m

What is Radon?Natural Radioactivity

Source: http://energy.cr.usgs.gov/radon/DDS-9.html

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 is a gas

• It is naturally occurring

• You cannot see or smell it

• It enters buildings from the soil via diffusion (concentration gradient)

Uranium

Radium

Radon

1,600 years

4.5 billion years

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

http://www.cornwallradon.co.uk/page21.html

Stack effect enhances Rn movement

What is Radon?Spatial Distribution

• Radon enters from beneath foundation and travels upward

• Diluted with outdoor air infiltrating building

10

< 5

5-6

Health EffectsRadon Gas

Progenies (‘daughters’) build up in confined space –are breathed in, stick to surface of airways and emit α-particles

Radon Progeny

218Po and 214Po deliver the radiologically significant dose to the respiratory epithelium

Lead-210

Polonium-214

Bismuth-214

Lead-214

Polonium-218

Radon-222

ββ, , γγ

αα,,γγ

αα,,γγ

αα,,γγ

ββ, , γγ

Lead-206

Polonium-210

Bismuth-210

ββ, , γγ

ββ, , γγ

22 yrs22 yrs

4 day

3 min

27 min

20 min

0.2 ms

5 day

138 day

Stable

αα,,γγ

Health Effects Alpha Decay

4He Nucleus Ejected from 222Rn Nucleus

+2+2

4He + He + 218PoPo

+

+

+

+

+

+

+

+

+

Radon - 222Radon - 222

alpha alpha particleparticle

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 (mrem)Radon 200Cosmic 27Terrestrial: -external 28 -internal 39

Artificial (mrem)-Diag. X-rays 39-Nuc. Med. 14-Consumer Pro. 10-Other ~1TOTAL ~360

Radon delivers > 50% radiation dose

Radon Risks Radon Levels

http://energy.cr.usgs.gov/radon/georadon/2.html

GW > Soil > Indoor Air > Outdoor Air

Outdoor?

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

• 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

• 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 EffectsEpidemiology

• ALA, AMA and Surgeon General all recommend reducing indoor Rn

• 15,000 – 22,000 deaths a year• Epidemiology confirmed by NAS, WHO, NCRP• Combined effects of Rn and smoking particuarly dangerous

2nd hand smoke!

Health Effects Human Studies

• How do we know radon is a carcinogen?

• NCI study examined 68,000 uranium miners

• Miners die at a rate 5 x general population

Dose (rem)

Ad

vers

e H

ea

lth E

ffect

s

Atomic Bomb Survivors

Medical Patients

Observed EffectsObserved EffectsObserved EffectsObserved Effects

? ?

?

Underground MinersUnderground Miners

Linear

No threshold

Health EffectsBiological Effects of Ionizing Radiation (BEIR) VI (1999)

• Risk estimates based primarily on radon-exposed miners

• Est. 15,000 – 22,000 lung cancer deaths each year in the U.S. from residential exposure

• 10-15% of all lung cancer deaths in US (150,000)

• Confirms 2nd leading cause

02000400060008000100001200014000160001800020000

U.S

. L

un

g C

ance

r D

eath

s/yr

Smokers Non-Smokers

Health Effects Comparing Radon Related Cancer

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

An

nu

al U

.S.

Can

cer

Dea

ths

Lung Cancer (radon)

Liver Cancer

Brain Cancer

Stomach Cancer

Melanoma

Oral Cancer

Gallbladder Cancer

Bone Cancer

Health Effects How Radon Compares To Other Causes Of Death

0

5,000

10,000

15,000

20,000

25,000

Dea

ths

per y

ear

Low

er e

stim

ate

Drunk Driving

Drownings Fires/Burns Air Transportation

Radon

Upp

er

estim

ate

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

Radon-222Zone 1: > 4 pCi/L (red)

Zone 2: 2-4 pCi/L (orange)

Zone 3: < 2 pCi/L (yellow)

Based on indoor measurements, geology, aerial radioactivity, soil parameters and foundation type

End

• Review

Testing and RemediationFrequencies 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 RemediationFrequencies of 222Rn in US Homes

8 million homes

Types of Measurement

• Continuous• Integrated long and short term• Multiple• Single 1-7 day – ‘screening’

All rely on measurement of emitted radiation

Testing and RemediationTesting

Alpha Track

Photovoltaic Alpha-track Sensor

Charcoal

Testing and RemediationTesting

Alpha Track

Alpha-tracks are plastics - microscopic radiation tracks after chemical treatment

Magnified only 100 times3 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 RemediationTesting

Sun-NuclearPhoto-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

• 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 RemediationRadon Mitigation

• Active Soil Depressurization (ASD)

– Creates a vacuum beneath the foundation

• Caulking and sealing

• Ventilation

http://www.radon-services.com/animations/animation.htm

Testing and RemediationPassive System

Large gravel beneath slab

Polyethylene soil-gas retarderbetween slab and gravel

Sealing and caulking

Vent pipe running betweensub-slab gravel and roof

Junction Boxes(to power fan and warning device, if needed)

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• 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

• 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 ExposureBox Model

Q = S τ

q = Q / V = Sτ / V

Source

S

Sink

L

V

Q

q

Q = quantity

q = concentartion

Modeling Radon ExposureSources 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, τvBackground gas ventilation rate (per unit voume),

Sv = Q0 = q0Rn

V V τv τvSinks,

Ventilation loss rate, Lv = qRn / τv (qRn = Rn concentration inside)

Decay loss rate, Ld = qRn / τRn (τRn = half-life = 91 hrs)

Steady-state: 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 ExposureRadon Concentration

SRn + Sv = Lv + Ld

SRn + q0Rn / τv = qRn / τv + qRn / τRn

qRn = q0Rn + τv SRn

1 + τv / τRn

Usually simplified: qRn ≈ q0Rn + τv SRn (denominator = 1)

Since: 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 ExposureRadon Concentration

qRn ~ q0Rn + τv SRn

• With fast ventilation τv = 0, qRn ≈ q0Rn (depends on outside air

conc.)

• With no ventilation τv = ∞, qRn ≈ τRn SRn (depends on source and t1/2)