Integrated γ/α spectrometry of natural radioactivity and PHITS Monte Carlo dosimetric assessment of Balengou kaolin, Cameroon.

Abstract

This study investigates the radiological characteristics and potential health implications of Balengou kaolin, a clay widely mined in Western Cameroon, used as a building material and distributed nationwide for geophagy and cosmetic purposes. Fifteen kaolin samples and ten surrounding control soil samples were collected, prepared, and analysed using a NaI(Tl) γ-ray spectrometer to determine ²²⁶Ra, ²³²Th, and ⁴⁰K activity concentrations and establish an environmental baseline for earthen building materials. Complementary α-spectrometric analyses quantified uranium and thorium isotopes on six selected samples, following radiochemical separation and electrodeposition. The mean activity concentrations in Bq.kg^-1 were 118 ± 62 for ⁴⁰K, 47 ± 4 for ²²⁶Ra, and 145 ± 9 for ²³²Th, yielding mean gamma absorbed dose rates of 211.48 and 113.84 nGy h^-1, and annual effective doses of 1.04 and 0.13 mSv.y^-1 for indoor and outdoor, respectively. A voluntary survey (N = 201), conducted in major urban centres where Balengou kaolin is consumed, provided data on the ingestion and cosmetic use habits of kaolin, which served as input for PHITS Monte Carlo dose calculations. Organ and effective doses from ingestion and dermal application, estimated using PHITS and ICRP mesh-type reference computational phantoms, showed the highest doses in the colon and stomach, reaching 1.2 mSv.y^-1 for frequent female consumers, whereas external doses from cosmetic use were negligible (<1 μSv.y^-1). This integrated approach provides a comprehensive radiological assessment of Balengou kaolin across environmental, construction, and human-use contexts and establishes a reference dataset for future studies and public awareness initiatives.