Preliminary assessment of excess life time cancer risk due to radon exposure in small scale Tanzanite mines in Tanzania

This study focused on assessing the excess life time cancer risk (ELCR) due to radon exposure in small scale Tanzanite mines in Northern Tanzania. Radon concentrations were measured using the solid state nuclear track detectors (SSNTD) type CR-39. Three to six CR-39 detectors were placed in the underground working environment of each mine for a period of four months then removed and sent to Niton laboratory in Italy for processing and determination of radon concentrations. The obtained radon concentrations were used to estimate exposure to radon progenies, Excess Relative Risk (ERR) of developing lung cancer, Total Lung Cancer Risk (TCR) and Excess Lifetime Risk (ELCR) using standard equations. It showed that radon levels in 58% of the assessed mines were below the action level of 300 Bqm -3 recommended by the International Commission on Radiological Protection (ICRP) while 42% were above this limit. The estimated mean exposure to radon and its progenies ranged from 0.08 to 1.18 WLM corresponding to annual effective doses of 0.8 and 11.8 mSvy -1 , for the minimum and maximum values respectively. These values are below the annual limit of 20 mSv for occupational exposure recommended by the ICRP. The ELCR estimated using simplified linear model from BEIR IV report ranged from 0.0% to 0.03% which is below the U.S. EPA action level of 1.3% due to radon exposure of 148 Bqm -3 . The ELCR due to exposure to radon in the assessed mines is negligible. However, follow up studies are recommended as the depths of the mines increase especially in the mines were radon concentrations exceeded the action level.