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

ABSTRACT

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 ²²⁶Ra, ²³²Th, and ⁴⁰K 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 × 10⁻² and 3.40 × 10⁻² for ²²⁶Ra, 1.41 × 10⁻⁴ and 7.88 × 10⁻⁵ for ²³²Th, and 1.3 × 10⁻⁴ and 4.233 × 10⁻⁴ for ⁴⁰K. 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 ²²⁶Ra compared with ²³²Th and ⁴⁰K it can be the major source of concern for human heath in the study area.

Key Words:

• risk assessment
• human health
• natural radionuclides
• cancer morbidity
• RESRAD.

ACKNOWLEDGMENT

The author cordially appreciates the extensive and constructive comments made by Dr. Ken Nicholson at Nicholson Environmental, UK.