Radiological risk evaluation of primordial radionuclides in roadside soils from trunk B road in southwest Nigeria

Abstract

Pedestrians, commuters and street hawkers along busy roadways are exposed not only to organic and inorganic airborne contaminants, but also to radionuclide-laden, road-associated materials. Thus, it is imperative to investigate the radioactivity concentrations in road-associated soil so as to appraise the prospective radiological risks to the surroundings and the public. To achieve this aim, fifteen (15) composite surface roadside soil samples were collected along Trunk B roadway (Ayegun-University of Ibadan road) characterized by three surface conditions (tarred (TP), untarred (UTP) and potholes (PTH)) during December, 2023. Activity concentrations of 40 K, 232 Th as well as 226 Ra were determined by employing gamma ray spectrometry equipped with NaI (Tl) detector and later employed to estimate the associated radiological risks due to exposed soils on the investigated roadway. The mean activity concentrations (AC) ranged from 11.99 ± 1.74 (in PTH) to 38.09 ± 12.47 Bqkg − 1 (in UTP) for 226 Ra; 67.79 ± 12.64 (in UTP) to 128.17 ± 11.38 Bqkg − 1 (in PTH) for 232 Th and 139.05 ± 23.16 (in UTP) to 288.06 ± 18.15 Bqkg − 1 (in TP) for 40 K. The mean ACs of 232 Th in roadside soils from the investigated road conditions exceeded the world average value of 45 Bqkg − 1 whereas that of 40 K were below the world average of 420 Bqkg − 1 specified by UNSCEAR. The average values for radium equivalent, and both internal and external hazard indices from the three road conditions were less than acceptable international reference values. However, absorbed dose rates (88.96 & 92.05 nGyh − 1 ), outdoor annual effective date equivalent (109.10 &112.89 µSvy − 1 ) and excess lifetime cancer risk (0.38 × 10 − 3 and 0.40 × 10 − 3 Sv − 1 ) for both TP and PTH roadside soils, respectively were above the allowable limits which can be attributed to the activity level of radionuclides in the study area.