Geospatial assessment of natural radionuclides in urban soil of Chennai Metropolitan City.

This study evaluates the distribution of terrestrial radionuclides and their associated radiological indices in urban topsoil samples from Chennai. Two hundred one (201) urban topsoil samples were collected across the Chennai metropolitan area, and gamma-emitting radionuclides were measured using NaI (TI) gamma-ray spectrometers. The activity concentrations of 238U varied from 12 ± 1.53 to 118 ± 9.63 with an average of 21 (stdev ± 16.14) Bq/kg. dry, 232Th varied from 24 ± 4.23 to 268 ± 17.83 with an average of 96 (stdev ± 45.88) Bq/kg. dry, and 40K varied from 126 ± 11.56 to 918 ± 32.52 with an average of 431 (stdev ± 88.69) Bq/kg. dry. These results indicate that the abundance of terrestrial radionuclides in urban topsoil follows 40K > 232Th > 238U. The study found that the activity concentration of 238U is within the recommended limits, while 232Th and 40K exceed the national limits by 1.58 and 1.11 times, respectively, and the international limits by 3.2 and 1.05 times, respectively. Radiological indices and dose parameters were calculated and described in detail, including Radium Equivalent Activity, Dose Rate, Annual Effective Dose Equivalent, Activity Utilization Index, Internal Hazard Index, External Hazard Index, Alpha Index, and Gamma Index. The activity utilization index (AUI) values ranged from 0.4 to 3.7, with a mean value of 1.4. The radionuclide activity concentration data suggest that geo-genic sources and industrial activities influence the topsoil in Chennai. This reflects the presence of heavy minerals, urban industrialization, and the characteristics of the study area.