Using the RESRAD Code to Assess Human Exposure Risk to 226Ra, 232Th, and 40K in Soil

This article evaluates the health risk raised by exposure to naturally occurring radionuclides in soil around Khak-Sefid, Ramsar, Iran, which is an area of high natural background radiation. A high purity germanium detector was used to determine levels of radionuclides in soil samples and the cancer morbidity risk for a hypothetical resident farmer was evaluated using the RESidual RADioactivity (RESRAD) code. The average activity concentrations of Ra-226, Th-232, and K-40 were found to be 13,201 +/- 391, 27.9 +/- 2.4, and 415.5 +/- 16 Bq/kg, respectively. The maximum assessed cancer morbidity risks were calculated from external and internal exposure pathways as 4.73 x 10(-2) and 3.40 x 10(-2) for Ra-226, 1.41 x 10(-4) and 7.88 x 10(-5) for Th-232, and 1.3 x 10(-4) and 4.233 x 10(-4) for K-40. The RESRAD calculations also showed total cancer morbidity risks from external gamma and plant ingestion pathways were more important than from other exposure pathways. A sensitivity analysis was also performed to determine the input parameter values in the risk assessment process. In general, due to the high calculated risk of Ra-226 compared with Th-232 and K-40 it can be the major source of concern for human heath in the study area.