Radon -222


Characteristics of Radon-222

Fate and Transport

Monitoring in the Environment

Measurement

Measurement Methods

Control and Prevention

Harmful Effects

Absorption, Distribution and Organic Sites of Toxicity

Radon Dose

Radon Biomarkers

Risk Assessment

Molecular Action and Genetic Effects


Radon for Skeptics

Radon for Children

Methods of Measuring Human Exposure to Radon-222:


EXPOSURE ROUTE

- inhalation- virtually all human exposure occurs through the respiratory system
- ingestion - minimal exposure
- dermal - no significant exposure
- delivered human dose from radon exposure cannot be measured directly
- radon exposure assessment is modeled beginning with measured air concentration


RADON CONCENTRATION IN AIR

1) Radon-222 gas:
- is measured by its activity or rate of decay in units called "curies"
- One curie equals 3.7 x 10(7) radioactive disintegrations per second
- One pico curie (pCi) equals 3.7 x 10(-2) radioactive disintegrations per sec
2) Solid radon-222 decay products (primarily polonium 218 and 214)
- ratio of solid radon-222 progeny to radon-222 gas in air is 0.2 - 0.8
- solid radon-222 progeny deliver the actual radiation dose to lung tissue
- radiation dose of radon-222 decay products is expressed as "working levels" (WL's)
- one WL equals a combination of radon decay products which releases 1.3 x 10(5) MeV of potential alpha energy (equivalent to the decay of 100 pCi/L of radon-222)
- cumulative exposure is expressed in WLM_s (working level
months) for exposure to one WL for one working month (170 hours)


RECOMMENDED EXPOSURE LIMITS FOR RADON-222

1) Miners Safety and Health Act (underground miners)
- No worker exposure to air containing 1.0 WL (100 pCi/L) of radon progeny
- Annual exposure limited to no more than 4.0 WLM per year
2) Occupational Safety and Health Administration (all other covered workers)
- exposure limited to 30 pCi/L or or 0.33 WL based on
continuous workplace exposure of 40 hours per week and 52 weeks per year
3) Environmental Protection Agency (residential recommendations)
- year-long average radon exposure of less than 4.0 pCi/L
(0.04 WL) in any livable area of a home


POTENTIAL DOSE OF RADON-222 DECAY PRODUCTS

- potential dose = radon concentration in air times intake rate of media (air) and duration of exposure
- potential dose is affected by respiratory rate, lung tidal volume and bronchial morphology as well as aerosol characteristics
- a high percent of airborne radon decay products attach to ambient aerosols
- quantity, size and density of airborne particles affect deposition in respiratory tract
- intake rate of media (air) is approximately 0.5 L/Min or 20 m(3)/day


INTERNAL (ABSORBED) DOSE OF RADON-222 DECAY PRODUCTS

- absorbed dose = potential dose x absorbtion factor
- absorbtion factor is affected by mucous thickness and clearance rate
- radiation absorbed dose is defined as energy deposited per unit mass of tissue
- radiation absorbed dose is expressed in "rads" or "greys" (Gy)
- 1 rad = 100 ergs/gram, 1 Gy = 100 rads
- absorbed dose is modified by a qualitative factor related to linear energy transfer
- modified absorbed dose is measured in "rems" (roentgen equivalent man)
- the average effective dose equivalent exposure of ionizing radiation from all sources to the US population is estimated at 300 mrem / year
- radon decay products account for 200 mrem / year of this total (NCRP Report #94)


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