Contribution of Waterborne Radon to Indoor Radon Concentration and Dose Evaluation in the Shikaka Area, Fukuoka

We described the relationship between the radon concentration in household water and the airborne radon concentration for houses at Shikaka area in Fukuoka Prefecture. The radon concentration in household water ranged from 36 to 130 Bq/L. Of these, the arithmetic mean of radon concentration of tap water from a small scale public water supply was 43 Bq/L, that of private well water was 100 Bq/L. For all samples, radon concentrations were between the MCL and the AMCL (USEPA proposed regulation now) . Indoor radon concentrations ranged from 4.5 to 46 Bq/m3 (arithmetic mean : 14 Bq/m3), were not found to exceed of action guideline of USEPA. While outdoor radon concentrations ranged from 2 to 7.5 Bq/m3 (arithmetic mean : 4 Bq/m3) . The radon concentration in the atmosphere was not so different from the nationwide mean concentration in Japan. The incremental airborne radon concentration volatiled from the water was estimated to be from 3.6 to 13 Bq/m3. Although radon concentration in bathrooms seemed to be elevated by water use, there was little influence to other rooms. The annual effective dose equivalent to the population for radon was calculated with the dose conversion factor from the UNSCEAR 2000 report. It was estimated to be 0.44 mSv/y. It could be concluded that the average radon levels in the household water at Shikaka area do not contribute to any additional radiological risk to the population.