Marble and granite as natural radiation sources: Risk assessment and their impact on health and the environment

Driven by growing public health concerns and limited regional data, this study investigates natural radioactivity and associated radiological hazards in marble and granite widely used in Al-Jouf, Saudi Arabia. Twenty-eight marble and thirty granite samples were systematically collected and analyzed via gamma-ray spectrometry using a high-purity germanium (HPGe) detector. The mean activity concentrations (±SD) for marble were 14.82 ± 10.63 Bq/kg ( 226 Ra), 16.54 ± 8.53 Bq/kg ( 232 Th), and 78.61 ± 41.64 Bq/kg ( 40 K). For granite, the values were 28.58 ± 19.89 Bq/kg, 37.04 ± 27.35 Bq/kg, and 960.48 ± 494.08 Bq/kg, respectively. Key hazard indices showed mean values for marble of radium equivalent activity (Ra eq ) 38 ± 19.36 Bq/kg, external hazard index (H ex ) 0.10 ± 0.05, internal hazard index (H in ) 0.15 ± 0.07, and representative gamma index (I γ ) 0.27 ± 0.13. For granite, the mean values were Ra eq 151.14 ± 92.75 Bq/kg, H ex 0.41 ± 0.25, H in 0.48 ± 0.3, and I γ 1.16 ± 0.7. The mean annual indoor effective dose equivalent (AEDE) was 0.087 ± 0.042 mSv/y for marble and 0.363 ± 0.219 mSv/y for granite—both below the public exposure limit of 1 mSv/y—although some granite samples exceeded the recommended gamma index threshold due to elevated potassium content. Most marble samples were deemed radiologically safe for construction, while certain granite varieties may require additional processing or regulatory oversight. This work provides the first comprehensive radiological baseline for building stones in Al-Jouf, supporting material safety regulations and public health protection.