In Situ Gamma Dose Rates and Radiological Risk Indices at Artisanal Mining Sites in Kauru, Kaduna State, Nigeria

Abstract

Artisanal and small-scale mining is widespread across the Precambrian Basement Complex of Northern Nigeria, a geological setting known to host elevated concentrations of naturally occurring radioactive materials (NORM). This cross-sectional study measured ambient gamma radiation dose rates once, during the dry season, at thirty (30) locations (coded K1–K30) selected by combined systematic and purposive sampling within mining areas of Kauru Local Government Area (LGA), Kaduna State, Nigeria, using a portable scintillation survey meter (Thermo Fisher Scientific RadEye PRD) held 1 m above ground level, following UNSCEAR protocol. The absorbed dose rates in air were used to derive indoor and outdoor annual effective dose (AED) and excess lifetime cancer risk (ELCR) with standard UNSCEAR/ICRP conventions; indoor AED and ELCR were modelled from the outdoor readings using occupancy factors and were not measured indoors, and ELCR is a model-derived screening index, not an observed cancer outcome. Dose rates ranged from 20 to 400 nGy h⁻¹, with a mean of 139.2 ± 105.4 nGy h⁻¹ (median 117.5 nGy h⁻¹), about 2.4 times the UNSCEAR world average of 59 nGy h⁻¹; 19 of the 30 locations exceeded this value, one (K30) equalled it and ten fell below it. The mean indoor and outdoor AED were 0.683 mSv y⁻¹ (0.098–1.962) and 0.171 mSv y⁻¹ (0.025–0.491), respectively; eight locations (26.7%) exceeded 1 mSv y⁻¹ indoors, and the mean total AED of 0.854 mSv y⁻¹ was about 1.8 times the UNSCEAR world average of 0.48 mSv y⁻¹ for terrestrial gamma exposure.