Effect of the natural radioactivity concentrations and 226Ra/238U disequilibrium on cancer diseases in Penang, Malaysia

Abstract

Natural radioactivity measurements and assessment of radiological hazards in soil and sand samples obtained from Penang, Malaysia were carried out using the Exploranium GR-135 Plus “Identifier” Radioisotope Identification Device and high-resolution High Purity Germanium (HPGe) detector system. The activity concentrations of 238U, 226Ra, 232Th, and 40K were found to be 184±11, 396±22, 165±14, and 835±28Bqkg−1 respectively, and the external gamma dose rate is 315±44nGyh−1 for soil samples. For sand samples, the activity concentrations of 238U, 226Ra, 232Th and 40K were 31±8, 62±16, 36±6, and 369±17Bqkg−1, respectively, and the external gamma dose rate is 66±12nGyh−1. To assess the radiological hazard of radioactivity present in the samples, the radium equivalent activity, annual effective dose, annual gonadal dose equivalent, external hazard, and internal indices were calculated.The Raeq values of soil samples were higher than the limit of 370Bqkg−1, which is equivalent to a gamma dose of 1.5mSvyr−1, whereas the Raeq for sand samples was lower than 370Bqkg−1. The calculated concentrations by HPGe spectroscopy were compared with the measured concentrations detected by a GR-135 spectrometer. The calculated and measured gamma dose rates had an ideal correlation coefficient R of 0.72. The gamma dose rates in Penang increased with the average annual age-standardized rates (ASR) for all cancers between 1994 and 2010. The effects of the pH value of soil and sand samples on natural radionuclides concentrations were investigated. The high concentration of 226Ra/238U ratio disequilibrium (226Ra/238U of 1.76–2.33) was observed in the sampling sites. Moreover, a portable continuous radon monitor (SNC, model 1029, Sun Nuclear Corporation) was used to measure the radon concentration of the soil surface. The radon concentrations were found to vary from 7 to 50Bqm−3. A positive correlation was observed between the radon and radium concentrations in samples measured by the SNC continuous radon monitor and HPGe detector.