Radon and Thoron levels in Dwellings of Bangalore City, India: A Review

Aims: 222Rn, a radioactive inert gas is a large component of the natural radiation that humans are exposed to, can pose a threat to the public health when it accumulates in poorly ventilated residential and occupational settings. About half of the total radiation effective dose to the general public is due to the irradiation of the lungs by alpha particles following the inhalation of 222Rn decay products. In this outlook, a comprehensive estimate of the natural inhalation dose requires both 222Rn and 220Rn levels in the indoor atmosphere.
Place and Duration of Study: Quite a large number of measurements have been carried out during the period 2007 to 2011. About 300 dwellings of different types of construction in ten different locations of Bangalore city, India were chosen on the basis of construction, age of the building, nature of walls, floorings, rooms and different volume of dwellings for the present study to see the effective dose rates due to indoor 222Rn, 220Rn and their progeny levels during different seasons of the year.
Methodology: The concentration of gamma active radio nuclides viz., 226Ra, 232Th and 40K in soil samples were determined by gamma spectrometry method by employing an HPGe spectrometer. The activity of radon in water samples were determined using emanometry method. The emanometry setup is calibrated at BARC, Mumbai. Solid State Nuclear Track Detector based dosimeters were used for the measurement of 222Rn and 220Rn and this is a good technique to study the long-term measurements.
Results: The estimated concentration of 222Rn and 220Rn for the environment of Bangalore, India varied from 17.2 ± 1.2 to 85.8 ± 2.3 Bqm–3 and 8.3 ± 1.2 to 38.3 ± 5.4 Bqm-3 with a mean of 32.2 ± 1.6 and 21.4 ± 1.0 Bqm-3, respectively. It is alarming that the dwellers of lower volume and granite floorings receive relatively a higher dose rate and the result shows significant radiological risk. Volumetric variations of indoor 222Rn, 220Rn and their progeny levels reveals higher concentrations in lower volume room compared to higher volume room at all the monitored locations.
Conclusion: The investigation shows no significant radiological risks for the inhabitants and is well within the limits prescribed by UNSCEAR. Further, it is recommended that the lower volume houses should have good ventilation and the dwellings should be granite free flooring, to reduce the effective dose rate. More detailed studies on the evaluation of public exposure from the natural radiation; particularly the exposure from 220Rn and their progeny should be planned and performed in this region and in the country.