Radiological health risk assessment of natural radioactivity in Pakistan clay

This study investigates the natural radioactivity levels and associated radiological risks in Pakistan clays-Kaolinite, Illite, Smectite, and Mixed types; widely used in cosmetic, construction, and industrial applications. Forty representative clay samples were analyzed for naturally occurring radionuclides (²²⁶Ra, ²³²Th, and ⁴⁰K). The mean activity concentrations were 41.11 ± 2.53 Bqkg⁻¹ for ²²⁶Ra, 53.87 ± 5.80 Bqkg⁻¹ for ²³²Th, and 689.34 ± 86.34 Bqkg⁻¹ for ⁴⁰K, exceeding corresponding global reference levels of 32 Bqkg⁻¹, 45 Bqkg⁻¹ and 420 Bqkg⁻¹ respectively. ⁴⁰K showed the highest activity and variability, particularly in Kaolinite and Illite clays. Statistical analysis revealed a strong positive correlation between ²²⁶Ra and ²³²Th, indicating a common geochemical origin, whereas ⁴⁰K exhibited distinct mineralogical behavior. This research presents the first comprehensive radiological characterization of major Pakistan clay types, integrating radionuclide distribution, mineralogical variation, and hazard assessment. Radiological hazard assessment showed that the mean absorbed dose rate (80.27 nGyh⁻¹); annual effective dose outdoor (0.10 mSv) and indoor (0.39 mSv) exceeded global average values. The estimated Excess Lifetime Cancer Risk (ELCR) with a mean value of 0.35 × 10^-3, slightly exceeding the global reference level. Although the gamma activity index ranged from 0.45 to 0.98 and exceeded the conservative screening threshold of 0.5 in several samples, the radium equivalent activity remained below the recommended safety limit of 370 Bqkg^-1, while external and internal hazard indices were below unity. The findings establish a baseline for natural radioactivity in Pakistani clays and provide essential data for radiological risk assessment, regulatory planning, and the safe utilization of clay-based materials.