particles, and ICRP59 risk factors for low-LET radiation, Eatough and Henshaw (1995) have estimated that about 1–10% of nonmelanoma skin cancers in the UK can be theoretically associated with domestic radon, including possible interaction with UV radiation. Calculated doses from thoron, available only for lung and bone marrow, tend to be lower than those from radon (Table 4-2).

Doses to red marrow from radon are substantially lower but nevertheless lead, by conventional risk estimation, to expectations of contributions to the natural incidence of leukemia. Richardson and others (1991) suggested that about 6–12% of myeloid leukemia in the U.K. could be from radon. Similarly, Simmonds and others (1995) have applied age-dependent radon doses and risks to a national study population of children in Seascale, U.K. From their evaluations, it can be deduced that some 34% of the expected natural childhood-leukemia incidence is attributable to natural radiation, made up of about 20% from natural low-LET radiation and about 14% from natural high-LET radiation (Simmonds and others 1995; COMARE 1996). About 3% of the 14% is due to radon and thoron. James (1992) has estimated from ICRP (1991) risk factors that 1.25% of the additional cancers caused by indoor radon and thoron are expected to be leukemia; the vast majority (98%) of the additional cancers are expected to be in the lung. However, no excess leukemia has been observed in the studies of the mining cohorts.

NONMALIGNANT RESPIRATORY DISEASES

In addition to radon, potential causes of nonmalignant respiratory diseases in the underground miners include silica (well documented as causing silicosis) γ, blasting fumes, and, in some mines, diesel exhaust. Persons with silicosis are at

TABLE 4-2 Estimated doses to adult tissues from thoron and its short-lived decay products for typical domestic thoron concentration corresponding to 212Pb-progeny concentration of 0.3 Bqm-3 (0.008 pCiL-1)

Tissue

Annual dose (μGy y-1)

Reference

Lung

34

Simmonds and others 1995

Red marrow

1.5

Stather and others 1986

 

0.5

James 1992a

Bone surface

22

Simmonds and others 1995

 

3.0

James 1992a

Liver

1.7

James 1992a

Kidney

10

James 1992a

a The doses presented here are one third of those tabulated in James (1992), so as to correspond to a typical PAEC for indoor thoron progeny of 21 nJM-3 (1 mWL) (Nero and others 1990) and 212Pb concentration of 0.3 Bqm-3 (0.008 pCiL-1) (James, personal communication).



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