Assessment of Outdoor Gamma Exposure Level of Some Swampy Agricultural Soils of Nasarawa West, Nigeria

Abstract

In this study, assessment of outdoor background exposure levels in some selected swampy agricultural soil in Nasarawa West, Nigeria has been conducted. An in-situ measurement of outdoor background exposure rate (in mRhr-1) for a total of fifty farms (ten each from Keffi (KF), Kokona (KK), Karu (KR), Toto (TT), and Nasarawa (NS))  were  done  using  a  well  calibrated  portable  halogen-quenched  Geiger  Muller  (GM)  detector (Inspector alert Nuclear radiation monitor SN:3544). A geographical positioning system (GPS) was used at an elevation of 1.0 m above ground level to obtain the geographical location.  The radiological hazard parameters were evaluated using the measured outdoor background exposure rates.  The values obtained were compared with recommended permissible limits to ascertain the radiological hazard status of the swampy agricultural farms.  The  mean  values  of  the  outdoor  background  exposure  levels (0.23, 0.038, 0.028, 0.022, and 0.039 mRh-1), absorbed dose rates (458.49, 334.95, 188.79, 194.01,  and 343.65 nGyh-1) and excess lifetime cancer risk (1.968, 1438, 0.810, 0.832, and 1.475)  each for KF, KK, KR, TT, and NS respectively, are higher than the  recommended  safe  limits  of  0.013  mRh-1,  84.0  nGyh-1,  0.00029 respectively  as  recommended by UNSCEAR and ICRP. On the other hand, the mean annual effective dose equivalent (AEDE) values (0.563, 0.410, 0.232, 0.238, and 0.421 mSvy-1 for KF, KK, KR, TT, and NS respectively) are below the recommended permissible limits of 1.00 mSvy-1 for general public exposure. Generally, the study revealed that swampy agricultural soils in Nasarawa west are radiologically safe with little contamination which could be attributed to the geological formation and partly due to human activity in the area.