Radiation Organ Doses and Excess Lifetime Cancer Risk Due to Exposure to Gamma Radiation from Two Cement Industries in Nigeria

Abstract

A study of background ionizing radiation (BIR) levels to estimate organ dose rates and excess lifetime cancer risk in Unicem cement producing company, Calabar, Cross River state and Bua cement producing company, Okpella in Edo state have been carried out using Digilert 100 and Radalert-200 nuclear radiation monitor and a geographical positioning system (GPS) for GIS mapping of the area. The in-situ measurement of the exposure rate was between May, 2018 and June, 2019 at regular intervals. The average exposure rate of 0.023 mRh-1 was measured at Unicem, Calabar and 0.027 mRh-1 at Bua cement area, Okpella. The mean equivalent doses of 1.92 mSvy-1 and 2.29 mSvy-1 was recorded in Unicem and Bua Okpella respectively. The estimated mean outdoor absorbed dose rate value of 196.74 nGyh-1 in Unicem and its environment while in Bua cement industry, Okpella, the value of 234.9 nGyh-1 was obtained. The mean annual effective dose calculated was 0.24 and 0.29 mSvy-1 for Unicem and Bua Okpella respectively. The mean excess life time cancer risk recorded in the areas 0.72 x10-3 in Unicem area and 1.01 x10-3 in Bua cement environment. The calculated dose to organs showed that the testes have the highest organ dose of 0.74 mSvy-1 and 0.83 mSvy-1 for Unicem and Bua Okpella areas respectively while the liver has the lowest organ dose of 0.08 mSvy-1 and 0.11 mSvy-1 for Unicem and Bua Okpella respectively. This study revealed that the exposure rate and all the radiological risk parameters exceeded their recommended safe values. The area of study is radiologically polluted and may be detrimental to human health for long term exposure.