Measurement of Environmental Radioactivity and Assessment of Doses to the General Public in Rechna Doab, Pakistan

Abstract

A systematic study in Rechna Doab, Pakistan was carried out to establish background radiation data and to assess the radiological environmental pollution and its impact on the humans and the environment. The study was carried out through the measurement of gamma and beta emitting radionuclides in different environmental media e.g. soil, surface water, vegetation and staple food. The concentration levels of primordial radionuclides 226 Ra, 232 Th and 40 K and anthropogenic radioisotopes 137 Cs and 90 Sr were determined. As the study area was quite large, having different lithological components so it was divided into three parts as northern, mid and southern. Gamma ray spectroscopy technique was used to study the gamma emitting radionuclides in different environmental media. Mean radioactivity levels in soil of northern parts of the study area came out to be 45.0±1.3 Bq kg -1 , 232 -1 Th, 59.6 ±2.8 Bq kg , 40 K, 613.8 ±20.0 Bq kg -1 and 137 226 Ra, Cs, 4.0±0.2 Bq kg -1 . The concentration levels of radioisotopes in soil of mid Rechna Doab were 226 Ra, 49.0±1.6 Bq kg -1 232 -1 Th, 62.4 ±3.2 Bq kg , 40 -1 K, 670.6 ±33.9 Bq kg and 137 Cs, -1 3.5±0.4 Bq kg . The levels of concerned radionuclides in soil of southern parts were 226 Ra, 50.6±1.7 Bq kg -1 , 232 -1 Th, 62.3 ±3.2 Bq kg , 40 -1 K, 662.2 ±32.1 Bq kg and 137 Cs, 3.1±0.3 Bq kg -1 . The radioactivity levels in surface water collected from the study area were 226 Ra, 0.9±0.2 Bq l -1 and radionuclides in vegetation were 40 K, 2.5±1.6 Bq l -1 while the levels of the concerned 226 Ra, 2.7±0.4 Bq kg -1 232 -1 Th, 2.2 ±0.1 Bq kg and 40 K, -1 172.7 ±4.0 Bq kg . Potassium-40 was the only radionuclide found in the staple food consumed by the general public of the study area, having concentration levels 174.3±2.7 Bq kg -1 (wheat) and 27.6±1.4 Bq kg -1 (rice). The radioactivity levels of 40 K were found to be slightly higher than that of 232 Th and 226 Ra at all the places of the study area. These raised levels of 40 K is an indication of the fact that most of the area under xxiiistudy is fertile and fertilizers are being used copiously in large quantities to get good crops. The average values of soil to plant transfer factors in the vegetation samples collected from the Rechna Doab were 0.06, 0.26 and 0.04 for 226 Ra, 40 K and 232 Th respectively. In most of the collected vegetation samples, the transfer factors for different radionuclides were in the order: 40 K> 232 Th> 226 Ra. Average 40 K daily intake through the staple food consumed by the humans residing in the study area was 64.6 Bq day -1 . The levels found in staple food of the study area were on lower side than the ICRP values and other global values. Liquid scintillation counting system was used to determine the radioactivity levels of beta emitting radionuclide, 90 Sr. Mean radioactivity levels of beta emitting anthropogenic radionuclide 90 Sr in soil samples of the study area were 3.0 Bq kg -1 while it was 1.4 Bq kg -1 in vegetation samples. The levels of 90 Sr in soil and vegetation have been compared with the same determinations in some European countries, USA and Ukraine and found less than these countries. Annual internal dose through ingestion of staple food was found to be 146 μSv y -1 . The results of ingestion doses obtained were comparable with other countries of the world. Radium equivalent activity levels in three parts of the study area in north, mid and south were found to be 177.6, 189.9 and 190.8 Bq kg -1 while the absorbed dose rates in air were came out to be 85.09, 70.1 and 69.8 nGy h -1 respectively. Indoor radiation hazard index was determined as 0.60, 0.65 and 0.65 and out door radiation hazard index was 0.48, 0.51 and 0.52 while a nnual effective dose was 0.52, 0.43 and 0.43 mSv y -1 . Fatal cancer risk assessment was made on the basis of total external dose received to the population through soil and vegetation and internal dose received through ingestion of staple food. Fatal cancer risk to the population was found to be comparable in all parts of the study area. Health risks to the population of the Rechna Doab, Pakistan due to external and internal radiation doses were much smaller than the risks associated with other activities of daily life. On the basis of the present study, it is concluded that annual radiation doses received by population of the study area neither pose any significant radiological impact on human health nor contribute towards fatal cancer risk to the population.