Potential impact of bituminous coal-based subcritical thermal power plant on the soil resources of Barapukuria area, Dinajpur, Bangladesh

Abstract

Coal-fly-ash is one of the major byproducts of coal-based power-plant in which 238U, 226Ra, 232 Th and 40K radionuclides are drastically enriched compared to those of feed coals. To determine the level of radioactivity concentrations and to estimate the associated radiological risk, coal, combustion residuals (CCRs) and soils from the Barapukuria coal-based thermal power-plant surroundings were analyzed by gamma-ray spectrometer with high-purity germanium (HPGe) detector. Along with the radioactivity concentrations, soil minerals were also studied by X-ray diffractometer to assess the mineralogical source of radionuclides. The results reveal that the mean radioactivity concentrations (Bq.kg1) in feed coal samples are 66.5 ±24.2, 41.7 ± 18.2, 62.5 ± 26.3 and 232.4 ± 227.2 for 238U, 226Ra, 232Th and 40K, respectively while in CCRs they are 206.3 ± 72.4, 140.5±28.4, 201.7 ± 44.7 and 232.5 ± 43.8, respectively. The mean values of the radiological hazard indices in the coal and their associated residuals are 153.1 and 446.8 Bq kg"1 for radium equivalent activity; 0.41 and 1.21 for the external hazard index; 70 and 200.1 nGy.h"1 for the absorbed gamma dose rate; 0.09 and 0.25 mSv.y1 for the annual effective dose rate; and 3.0×10+ and 8.6×104 Sy1 for the excess lifetime cancer risk, respectively, most of which exceed the UNSCEAR recommended respective threshold limits. Mean radioactivity concentrations (in Bq kg1) in soil samples for 238U, 226Ra, 232Th and 40K are 102.9 ± 41.4, 63.6 ± 7.4, 103.4 ± 13.9 and 494.2±107.5, respectively which are comparatively higher than the typical world mean value. Elevated levels of radioactivity are likely due to the presence of illite, kaolinite, monazite, rutile and zircon minerals in the soil sample rather than technogenic contributions from the power-plant. Furthermore, mean soil contamination factor (CF) are close to unity and mean pollution load index (PLI) is below unity while the average radium equivalent activity (Raq in Bq kg1), external hazard index (Hex), absorbed gamma dose rate (D in nGy.h1), annual effective dose rate (E in mSv.y1) and excess lifetime cancer risk (ELCR) are 249.5 ± 21.7, 0.67 ± 0.06, 114.2 ± 9.4, 0.20±0.02, 4.9×10± 0.4×10+, respectively, which are within the permissible limit. Thus, in terms of radioactivity concentrations and associated environmental and radiological indices, the effect of the power- plant on soil is insignificant.