| dc.description.abstract | The study was performed around the Morupule-B Coal Power Station in the central district of Botswana. A total of 99 water, soil, coal, bottom ash as well as fly ash samples were collected from the study area. Coal, bottom ash, soil and fly ash activity concentrations for natural radionuclides were measured through gamma spectrometry while ICP-MS was used to measure the concentrations of heavy toxic metals in water, soil, coal, bottom ash and fly ash samples. The mean activity concentrations of ²³²Th, ²³⁸U and ⁴⁰K in soil samples in this study were 19.101 ± 2.140 Bq/kg, 14.149 ± 1.762 Bq/kg and 196.115 ± 4.392 Bq/kg respectively. For coal, bottom ash and fly ash samples, the mean ²³⁸U activity concentrations were found to be 54.771 ± 4.460 Bq/kg, 97.311 ± 6.151 Bq/kg and 150.444 ± 9.595 Bq/kg respectively. The mean activity concentrations of ²³²Th in coal, bottom ash and fly ash were found to be 27.319 ± 0.714 Bq/kg, 81.702 ± 1.030 Bq/kg and 116.674 ± 1.457 Bq/kg respectively. The mean ⁴⁰K activity concentrations for coal, bottom ash and fly ash samples were found to be 17.117 ± 3.831 Bq/kg, 37.265 ± 3.849 Bq/kg and 66.847 ± 10.107 Bq/kg respectively. The average fly ash activity concentration values for ²³⁸U and ⁴⁰K from this study were generally lower than those from average world activity concentrations, while those of ²³²Th were greater than the average world values by a factor of close to two. The average coal activity concentration values for ²³⁸U and ²³²Th from this study were generally higher than those from average world activity concentrations, while those of ⁴⁰K were lower than the average world values. From the current study results, it was observed that the activity concentrations of ²³⁸U and ²³²Th increased in ascending order from soil, coal, bottom ash to fly ash samples. Radiological hazards assessment for soil, coal, bottom ash and fly ash samples were performed in this study. The estimated absorbed dose rate (D) for soil samples was 25.549 ± 9.026 nGy/h, which was lower than the worldwide absorbed dose rate of 57 nGy/h for soil. The estimated annual effective dose equivalent (AEDE) from soil samples was 31.333 ± 11.070 μSv/y, which was lower than the recommended worldwide value of 70 μSv/y for soils. The radium equivalent activity (Raeq) for soil was 54.435 ± 19.464 Bq/kg. The external hazard index (Hₑₓₜ) for soil was 0.147 ± 0.053. The estimated absorbed dose rate (D) in coal was 42.519 ± 5.288 nGy/h. The estimated annual effective dose equivalent (AEDE) for coal was 52.146 ± 6.480 μSv/y, which was lower than the worldwide value of 406 μSv/y. The radium equivalent activity (Raeq) in coal samples was 95.156 ± 11.482 Bq/kg. The external hazard index (Hₑₓₜ) for coal was 0.257 ± 0.031. The estimated absorbed dose rate (D) for bottom ash samples was 95.859 ± 20.357 nGy/h, which was slightly higher than the worldwide absorbed dose rate of 60 nGy/h. The estimated annual effective dose equivalent (AEDE) for bottom ash was 117.563 ± 24.967 μSv/y, which was lower the recommended worldwide value of 460 μSv/y. The radium equivalent activity (Raeq) for bottom ash was 217.015 ± 46.052 Bq/kg. The external hazard index (Hₑₓₜ) for bottom ash 0.586 ± 0.124. The estimated absorbed dose rate (D) for fly ash was 142.763 ± 46.278 nGy/h. The estimated annual effective dose equivalent (AEDE) for fly ash was 175.086 ± 56.756 μSv/y. The radium equivalent activity (Raeq) value for fly ash samples was 322.435 ± 104.923 Bq/kg. The mean Raeq values for soil, bottom ash, coal and fly ash were all below the worldwide accepted value of 370 Bq/kg. The external hazard index (Hₑₓₜ) for fly ash was 0.871 ± 0.283. The average Hₑₓₜ value for soil, coal, bottom ash and fly ash were all below the worldwide recommended value of one. Based on these findings, materials from the area under study can safely be used for building and construction. The total carcinogenic risk from soil and water samples was found to be 1.04 such that soil samples contributed the most to the total cancer risk. RESRAD-OFFSITE computer code estimated the cancer risk from natural radionuclides ²³⁸U, ²³²Th and ⁴⁰K over a duration of 130 years to residents and other public members in the vicinity of the power station such that the maximum cancer risk with all pathways summed was found to be 3 x 10⁻³ from year 25, also depicting that the total cancer risks from year 0 to year 130 were higher than the acceptable South African and USEPA risk limits of 5 × 10⁻⁶ and 1 × 10⁻⁶ to 1 × 10⁻⁴ respectively. | en_US |
