Radionuclides distribution and hazards of black shales: A case study in El Hommr area using gamma-ray spectrometry

This study explores the natural radioactivity and radiological risks associated with black shale in the El Hommr area of Egypt, focusing on ²³⁸U, ²³²Th, and ⁴⁰K. Analysis of 21 samples revealed that uranium, thorium, and potassium, to some extent, have high concentrations (average 97 Bq kg^-1, 117 Bq kg^-1 and 518 Bq kg^-1, respectively). These activity concentration levels are well above global averages. The poor correlation between various radio elements, excepting thorium with potassium, illustrates the presence of these elements in different minerals or their mobilization away from each other. The important radiological hazard indices, including radium equivalent activity (mean 304 Bq kg^-1), absorbed dose rate (mean 137 nGyh^-1), and annual effective dose (mean 0.78 mSvy^-1 indoors), often exceed the international recommended safety limits. The external hazard index (average 1.08) and the internal hazard index (average 0.85) also indicate that many samples exceed safe exposure thresholds. Statistical analysis shows that uranium is the main source of radiological risk, strongly influencing all hazard indices. Mineralogical studies exhibited that xenotime and zircon are the primary hosts of uranium and thorium in the rock. Generally, the results clarify significant health risks due to elevated natural radioactivity in this black shale environment, and some cautions must be taken during their use.