Radiological hazard assessment and excess lifetime cancer risk evaluation in surface soil samples collected from Ban Chang and Nikhom Phatthana districts in Rayong province, Thailand

Specific activity of natural (⁴⁰K, ²²⁶Ra and ²³²Th) and anthropogenic (¹³⁷Cs) radionuclides have been measured and analyzed in 27 surface soil samples in Rayong province in the eastern region of Thailand where is the home of the Southeast Asia industrial estate and one of the largest petrochemical plants in the world. Such high activity concentrations might be associated with the increase in cancerous patients who live in the studied area. All surface soil samples were collected from Ban Chang (12 samples) and Nikhom Phatthana (15 samples) districts in Rayong province. The average specific activities were analyzed and estimated by employing hyper-pure germanium (HPGe) detector and gamma-ray spectrometry analysis system. It was found that the frequency distribution of specific activities of ⁴⁰K, ²²⁶Ra, ²³²Th and ¹³⁷Cs for the investigated area were asymmetrical distribution with the skewness of 1.09, 1.54, 0.39 and 0.42, respectively. The median values of specific activities of ⁴⁰K, ²²⁶Ra, ²³²Th and ¹³⁷Cs in Bq/kg were 423.75 ± 11.30, 96.65 ± 2.16, 36.73 ± 1.06 and 1.32 ± 0.24 Bq/kg, respectively. In addition, four radiological hazard indices which are gamma-absorbed dose rate (D), radium equivalent activity (Ra_eq), external hazard index (H_ex) and annual external effective dose rate (AED_out) were also studied and assessed by using the measured (median) values of specific activities. Furthermore, the excess lifetime cancer risk (ELCR(outdoor)) could be evaluated by using the AED_out value. The results were also compared with the Office of Atoms for Peace (OAP) annual report data, Thailand and global radioactivity measurement and calculations. Moreover, the radioactive contour maps of the investigated area were also created and presented in this paper. From this study, value for D was higher than the worldwide average value (84.98 ± 2.12 nGy/h). The AED_out and ELCR(outdoor) values were equal to 0.10 ± 0.003 mSv/y and (0.39 ± 0.01)×10^-3, respectively and lower than the worldwide average. Further studies and evaluations need to assess the real risks and effects to people health. (paper)