Determination of the risk associated with the natural and anthropogenic radionuclides from the soil of Skardu in Central Karakoram.

The radioactivity levels were determined in 39 soil samples from six towns of Skardu using gamma-ray spectrometry. The samples were collected at an average altitude of 2293 m above sea level in Central Karakoram. The activity concentration data were analysed by principal component analysis for outlier detection and data structure elucidation and for frequency distributions. The median activity concentrations of (226)Ra, (232)Th, (40)K and (137)Cs were found to be 49.8 ± 12.6, 80.9 ± 18.7, 977 ± 91 and 4.37 ± 4.08 Bq kg(-1), respectively. An uncertainty analysis showed that the main contribution to uncertainty budget was from the counting statistics and uncertainty in the reference activity of standard. The activity concentration data showed a positive significant correlation between (226)Ra and (232)Th. Three hazard indices named the radium equivalent activity, external hazard index and internal hazard index were calculated. In the total activity concentration, (40)K accounted for the most (87.5 %), whilst in the radium equivalent activity, (232)Th contributed the most (48.5 %). In the Skardu samples, the air-absorbed dose rate was found to be 112 ± 17 nGy h(-1), annual effective dose rate from terrestrial to be 243 ± 38 μSv y(-1), effective dose rate due to the deposition of (137)Cs on soil to be 1.1 ± 2.4 μSv y(-1) and dose rate from the cosmic radiations to be 1371 ± 107 μSv y(-1). The ratio of mass fractions of Th/U was 4.8 ± 0.6.The results were compared with the similar measurements made in other parts of the world. A comparison with the other cities of Pakistan revealed that the soil in Skardu presented the highest external exposure rate.