A survey on radon (222Rn), thoron (220Rn) and its decay products (220RnD) was conducted in Chinese traditional residential dwellings constructed with loam bricks or soil wall. The activity concentrations in 164 dwellings under investigation were 72.4+/-59.2 (arithmetic mean, AM) and 57.5+/-2.0 Bq m-3 (geometric mean, GM) for 222Rn, and 318+/-368 and 162+/-3.7 Bq m-3 for 220Rn, respectively. For 220RnD, 67 dwellings were studied. The AM of the 220RnD equilibrium equivalent concentration was 3.8+/-3.3 Bq m-3 with a maximum value of 15.8 Bq m-3. On the basis of these results, the average annual effective doses to the local residents due to radon and thoron exposure were 1.44-4.62 mSv. Thoron contributes 12.9-56.6% to the total doses. Preliminary results show that there is a relation between 220RnD in air and 232Th in soil. The correlation factors of outdoor and indoor were 0.88 and 0.40. The 232Th activity content of Chinese soil is estimated to be about two times the world average. The traditional residential dwellings with soil construction are still common in China. Further investigations on the 220Rn level in these dwelling with the aim of dose reduction are proposed.
Incomplete combustion of coal in homes has been linked with lung cancer in China. We report on a lung cancer case-control study in a rural area of China, where many residents live in underground dwellings and burn coal and unprocessed biomass (crop residues, wood, sticks, and twigs) for heating and cooking. We interviewed 846 patients with lung cancer (626 men, 220 women; aged 30 to 75 years) diagnosed between 1994 and 1998, and 1740 population-based controls. The odds ratio for lung cancer associated with coal use compared with that for biomass in the house of longest residence was 1.29 (95% confidence interval, 1.03 to 1.61), adjusted for smoking and socioeconomic status. The risk for lung cancer increased relative to the percentage of time that coal was used over the past 30 years (P = 0.02). Our findings suggest that coal may contribute to the risk of lung cancer in this rural area of China.
Our recent study in Gansu Province, China reported an increasing risk of lung cancer with increasing residential radon concentration that was consistent with previous pooled analyses and with meta-analyses of other residential studies (Wang et al., Am. J. Epidemiol. 155, 554-564, 2002). Dosimetry used current radon measurements (1-year track-etch detectors) in homes to characterize concentrations for the previous 30 years, resulting in uncertainties in exposure and possibly reduced estimates of disease risk. We conducted a 3-year substudy in 55 houses to model the temporal and spatial variability in radon levels and to adjust estimates of radon risk. Temporal variation represented the single largest source of uncertainty, suggesting the usefulness of multi-year measurements to assess this variation; however, substantial residual variation remained unexplained. The uncertainty adjustment increased estimates of the excess odds ratio by 50-100%, suggesting that residential radon studies using similar dosimetry may also underestimate radon effects. These results have important implications for risk assessment.
222Rn concentrations in drinking water samples from Beijing City, China, were determined based on a simple method for the continuous monitoring of radon using a radon-in-air monitor coupled to an air-water exchanger. A total of 89 water samples were sampled and analyzed for their 222Rn content. The observed radon levels ranged from detection limit up to 49 Bq/L. The calculated arithmetic and geometric means of radon concentrations in all measured samples were equal to 5.87 and 4.63 Bq/L, respectively. The average annual effective dose from ingestion of radon in drinking water was 2.78 μSv, and that of inhalation of water-borne radon was 28.5 μSv. It is concluded that it is not the ingestion of waterborne radon, but inhalation of the radon escaping from water that is a substantial part of the radiological hazard. Radon in water is a big concern for public health, especially for consumers who directly use well water with very high radon concentration.
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