Estimation of Annual Effective Dose and Excess Lifetime Cancer Risk from Background Ionizing Radiation Levels Within and Around Quarry Site in Okpoto-Ezillo, Ebonyi State, Nigeria

Abstract

A study to estimate the annual effective dose equivalent (AEDE) and excess lifetime cancer risk (ELCR) due to background ionizing radiation (BIR) within and around Okpoto quarry site has been carried out, using a portable GQ GMC-320 Plus Geiger Counter nuclear radiation detector. An in-situ measurement of absorbed dose rate (ADR) in air at 1.0 meter above ground level was carried out at twenty different locations each for within and around the quarry site. ADR values of 0.15 µSv/hr to 0.22 µSv/hr with mean value of 0.19±0.02 µSv/hr were recorded within the quarry site and values of 0.11 µSv/hr to 0.18 µSv/hr with mean of 0.14±0.02 µSv/hr were recorded for around the quarry site. These values are observed to be slightly lower than 0.274 µSv/hr global average value. Mean values of 0.32±0.04 mSvy-1 and 0.24±0.03 mSvy-1 for the AEDE were observed respectively for within and around the quarry site. Similarly, mean values of 1.115×10-3 and 0.847×10-3 for ELCR were reported for within and around the quarry site respectively. The AEDE values are within the permissible limits as recommended by the international bodies. The ELCR values exceed the average standard value of 0.29×10-3. The implication of the AEDE and ELCR values is that the quarry site is radiation safe for any immediate radiological health burdens that might arise due to absorbed dose from BIR, but the probability of one developing cancer over a life time exposure in the quarry environment is very high. It is however recommended that periodic BIR monitoring and evaluation and radioactivity concentration of radionuclides in soil and rocks of the area be carried out by local authority, management of the quarry company and interested researchers to ascertain the absorbed dose level by workers and people living within the area from time to time. In the same vein, the time spent by workers in the excavation and quarry/crushing section of the quarry site, buyers of the quarry products, and other persons who visit the site regularly for commercial activities and sightseeing should be minimized. Keywords: Background ionizing radiation (BIR), absorbed dose, Annual effective dose equivalent (AEDE), Okpoto quarry site.