Radiation hazard assessments of natural radioactivity in clay-based cosmetic products in Malaysia

Natural sources such as clays, plant extracts, and raw materials containing naturally occurring radioactive material (NORM) have been used as ingredients for medicinal and cosmetic purposes since ancient times. Nowadays, a variety of commercially available cosmetics products used clay minerals containing NORMs as the main formulation, which poses unknown radiation risks to the consumer. In this study, 11 samples of clay-based cosmetic products were used to conduct dose assessments on members of the public for various usage scenarios to evaluate the external exposure dose. Gamma-ray spectroscopy was utilised to measure the activity concentrations of 238U, 232Th, and 40K in the sample. Meanwhile, doses to skin and other organs from these cosmetic products were modelled using Geant4 Monte Carlo simulations and the MIRD5 mathematical phantom, incorporating dose conversion factors (DCFs). The results revealed that the activity concentration for 238U, 232Th, and 40K ranged from 0.1 – 1.3, 0.06–15.6, and 0.22–6.9 Bq g−1, respectively, which were lower than the reference provided by the international regulation. The analysis for heavy metals showed that sample 9 contained a high amount of Cd, which gave an immediate alert to that particular product. Furthermore, the effective doses in the skin estimated in this study with the range of 2.7–240 μSv y−1, were significantly lower than the International Commission on Radiological Protection (ICRP) reference limit of 50 mSv per year for members of the general public. Based on the few μSv of effective dose exposure, it is sufficient to conclude that the dose from these products poses no radiological risk to the user. The addition of NORMs in cosmetic products should be done with caution because higher concentrations can raise the dose.