Radon (222Rn) concentration in indoor air near the coal mining area of Nui Beo, North of Vietnam

Abstract

Concentrations of radioactive radon gas (222Rn) were measured using passive monitors based on LR115 solid state track detectors during June–July 2010 in indoor air of dwellings in the Nui Beo coal mining area, mostly in Cam Pha and Ha Long coastal towns, Quang Ninh province, in the North of Vietnam. Global results of 222Rn concentrations indoors varied from ≤6 to 145 Bq m−3 averaging 46 ± 26 Bq m−3 (n = 37), with a median value of 47 Bq m−3. This was similar to outdoor 222Rn concentrations in the region, averaging 43 ± 19 Bq m−3 (n = 10), with a median value of 44 Bq m−3. Indoor 222Rn concentrations in the coastal town dwellings only were in average lower although not significantly different from indoor 222Rn concentrations measured at the coal storage field near the harbor, 67 ± 4 Bq m−3 (n = 3). Furthermore, there was no significant difference in the average 222Rn concentration in indoor air measured in the coastal towns region and those at the touristic Tuan Chau Island located about 45 km south of the coal mine, in the Ha Long Bay. The indoor 222Rn concentration in a floating house at the Bai Tu Long Bay, and assumed as the best estimate of the baseline 222Rn in surface air, was 27 ± 3 Bq m−3 (n = 3). Indoor average concentration of 222Rn in dwellings at the Ha Noi city, inland and outside the coal mining area, was determined at 30 Bq m−3. These results suggest that 222Rn exhalation from the ground at the Nui Beo coal mining area may have contributed to generally increase 222Rn concentration in the surface air of that region up to 1.7 times above the baseline value measured at the Bai Tu Long Bay and Ha Noi. The average indoor concentration of 222Rn in Cam Pha–Ha Long area is about one-third of the value of the so-called Action Level set up by the US EPA of 148 Bq m−3. Results suggest that there is no significant public health risk from 222Rn exposure in the study region.