RESUMO
PURPOSE: The purpose of this paper is to evaluate the morbidity excess cancer risk (ECR) due to internal and external exposure to three category levels of natural radionuclides in soil like 238U, 232Th and 40K. Although the exposure rate in soil is low but effect this radiation over time can lead to cancer risk and this risk can be calculated. MATERIALS AND METHODS: Natural activity concentration levels of 40K, 238U and 232Th in soil were selected from last reports in three concentration categories including: low, medium and high levels. The excess cancer risks of three concentration levels were calculated by means of RESidual-RADioactivity (RESRAD) code. RESULTS AND CONCLUSIONS: The calculated average morbidity ECR from 40K, 238U and 232Th in three concentration categories levels in soil were 1.40 × 10-4, 8.56 × 10-4 and 1.35 × 10-3, respectively. This calculation shows that the excess cancer risk value is the highest value in 100 years' time in all categories. Overall ECR from 40K radionuclide was maximal and the highest exposure pathways was through plant pathway; however, these pathway changes over 60 years to the drinking water pathway. The results of this study may be useful to risk assessment and for decision making for public health protection against high-level radiation.
