Outdoor Gamma Dose Rates and Excess Lifetime Cancer Risks Due to Exposure Rates at Salt Water Lakes, Ebonyi State, Nigeria

Abstract

Exposure rates, gamma dose rates and excess lifetime cancer risk around saltwater lakes in Okposi Okwu and Uburu town, Ebonyi State, Nigeria were carried out, in situ, using two nuclear radiation meters (Radalert – 100 and Digilert – 50) and geographical position system (GPS). Measurements were taking randomly (at about 5 cm to 20 cm away from each lake) in thirty one (31) sampling locations each around the saltwater lakes at the standard level of one meter (1 m) above the ground to determine the exposure rates (in mRh-1). Outdoor absorbed dose rate (DOut), outdoor annual effective dose (AEDOut ) and the excess lifetime cancer risk (ELCR) were evaluated and compared with similar reports in other countries and standards. Comparatively, the exposure rates, DOut, AEDOut  and ELCR values obtained for Uburu were similar to that of Okposi Okwu salt lake traceable to bluish black shale, with minor sandstone and silt lithology of the study locations. The mean results recorded for the two salt lakes exceeded the suggested safety limit of 0.013 mRh-1, 60 nGy h-1, 0.07 mSv y-1 , and 0.290 x 10-3 for general public respectively. In general, the results showed that terrestrial background ionizing radiation due to radionuclides in soil within the salt lakes is relatively higher and chance of developing cancer by immediate populace is very significant. Baseline study has been provided in the locations. Length of time spent within the salt lakes either at nearby farmlands and residential buildings should be minimized. Food crop cultivated near the salt lakes should be investigated for radioactivity concentrations.