other risks of lung cancer, such as smoking, but risk is modified by time since exposure.

To express lifetime risk after a single exposure, it is necessary to sum the risk over the number of years of life after exposure, taken as age of exposure to age 85. The lifetime risk, TR, posed by continuous exposure was expressed as the sum of lifetime risk for a single year's exposure over the total exposure interval considered.

When the model was developed, there was not enough information on the risk associated with smoking and 222Rn exposure combined to separate an additional effect from this carcinogen. It was stated that the risk coefficient, C, could be modified when sufficient data were available.

Numerical values of lifetime risk for different models are shown in table 5.5.

Table 5.5

Lung Cancer Risk for Continuous Whole-Life Exposure to 4 pCi/L (148 Bq m-3 or 0.56 WLM/ yr at Indoor Conditions) as Predicted by Various Models of Domestic Exposurea

Model

Lifetime Risk, %

Model Type

Comment

NCRP (1984a)

0.50

Modified Absolute Risk. Two parameter model

Risk decreases with time since exposure

ICRP (1987)

0.90

Constant Relative Risk

 

ICRP (1987)

0.62

Constant Additive Risk

 

ICRP (1993b)

0.56

Single Value Risk per WLM

Adopted Lifetime Risk per WLM exposure

BEIR IV (National Research Council 1988)

1.1

Modified Relative Risk. Two time windows. Two parameter model

Risk decreases with time since exposure and decreases with very high exposures

NIH (Lubin and others 1994

1.8

Modified Relative Risk. Three time windows, age and exposure rate. Three parameter model

Risk decreases with time since exposure and decreases with very high exposures

1.8

 

 

 

BEIR VI (National Research Council 1999)

2.0

Modified Relative Risk. Three time windows, age and exposure rate. Three parameter model.

Risk decreases with time since exposure and decreases with very high exposures.

Meta-analysis 8 domestic case-control (Lubin and Boice 1997)

0.7

Observed mortality

Linear regression fit to data from 8 domestic studies

a Exposure assumes a home concentration of 148 Bq m-3 (4 pCi L-1 or 0.56 WLM), calculated with 40% decay product equilibrium, and actual exposure is 70% of the home exposure.



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