Investigation of natural radioactivity in soil of selected hospitals in Imo State, Nigeria

Abstract

We measured the terrestrial activity contents, radiation doses; hazard indices and excessive lifetime cancer risk (ELCR) from primordial radionuclides (²²⁶Ra, ²³²Th and ⁴⁰K) in 50 soil samples collected from the five selected hospitals within Imo State, Nigeria. Radioactivity measurements were carried out by the method of gamma-ray spectrometry with thallium doped sodium iodide [NaI(Tl)] detector. The mean activity values obtained for the radionuclides ²²⁶Ra, ²³²Th and ⁴⁰K (respectively) in Federal Medical Centre, Owerri (FMC); General Hospital, Umuguma, Owerri West, (GHW); Neuroscience Hospital, Ohaji Egbema (NHO); St. Joseph Hospital, Okigwe (SJH); Imo State University Teaching Hospital, Orlu (IMSUTH) are: 20.56±4.73, 14.96±3.42 and 105.65±31.40 Bqkg^-1; 11.77±3.03, 17.45±4.20 and 63.67±18.44 Bqkg^-1; 17.97±4.65,10.02±2.18 and 190.43±42.83 Bqkg^-1; 11.36±3.71, 17.39±4.46 and 76.29±25.08 Bqkg^-1; and 11.84±3.64, 4.89±2.25 and 165.18±58.41 Bqkg^-1 respectively. These values were below the worldwide average values: 32 Bqkg^-1 for ²²⁶Ra, 45 Bqkg^-1 for ²³²Th, and 412 Bqkg^-1 for ⁴⁰K as documented by UNSCEAR (2000). ⁴⁰K recorded the highest mean activity compared to ²²⁶Ra and ²³²Th in the studied soil samples. Radium equivalent activity (Ra_eq), absorbed gamma dose rate (D_r), annual effective dose equivalent (AEDE), external hazard index (H_ex), gamma representative index (Ι_ϒr) and annual gonadal dose equivalent (AGDE), were calculated to quantify the radiation risk to the public from exposure to ²²⁶Ra, ²³²Th and ⁴⁰K in the studied samples. In addition, excess lifetime cancer risk (ELCR) was also accessed. The mean computed values of the excess lifetime cancer risk for FMC, GHW, NHO, SJH and IMSUTH are 0.08±0.03, 0.09±0.15, 0.10±0.2, 0.10±0.03 and 0.07±0.02 respectively. The mean values of these hazard parameters were within the acceptable safety limits provided for human safety and environmental protection.