Multivariate Statistical Evaluation and Comparative Risk Ranking of Natural Radionuclides in Nigerian Solid Minerals

Abstract

Natural radionuclides in solid minerals contribute to terrestrial radiation exposure, particularly where mining, processing, and industrial use increase human contact with naturally occurring radioactive materials. This study presents a multivariate statistical evaluation and comparative radiological risk ranking of K-40, U-238, and Th-232 in fifty selected solid mineral samples from Nigeria. Activity concentrations and radiological hazard parameters determined by gamma-ray spectrometry were evaluated using descriptive statistics, Pearson correlation, principal component analysis (PCA), hierarchical clustering, composite risk scoring, and Monte Carlo uncertainty analysis. Activity concentrations ranged from 108.36–223.37 Bq kg⁻¹ for K-40, 9.07–16.72 Bq kg⁻¹ for U-238, and 2.00–7.33 Bq kg⁻¹ for Th-232. Positive correlations (r > 0.996) among the radionuclides indicate common geochemical controls and co-occurrence within mineral matrices. PCA revealed that a single component accounted for nearly all standardized variance, demonstrating that radiological behaviour is predominantly governed by a unified radioelement loading factor. Comparative risk ranking identified zircon sand, columbite, tin concentrate, phosphate, monazite, tantalite, zircon, granite, and wolframite as priority materials for monitoring. However, all radium equivalent activity values remained well below the 370 Bq kg⁻¹ UNSCEAR limit, while external and internal hazard indices were below unity. Monte Carlo analysis showed narrow distributions for zircon sand, columbite, tin concentrate, phosphate, monazite, and tantalite, with mean values of approximately 41.4–44.4 Bq kg⁻¹ and low standard deviations (σ ≈ 0.2–0.3). Overall, the studied minerals are radiologically acceptable under normal use, although targeted monitoring is recommended during mining and processing, particularly during crushing, concentration, handling, storage, transportation, and industrial processing operations.