Natural radionuclide distribution and radiological risk assessment in Brazilian building finishes: Paints, varnishes, sealers, primers, and enamels

This study investigates the natural radioactivity levels in paints, varnishes, sealers, primers, and enamels used in residential buildings in Rio de Janeiro, Brazil, addressing a gap in the existing literature on naturally occurring radioactive materials (NORM) in surface finishing materials. While the contribution of building materials to radiation exposure is well documented, limited data exists on the specific activities of ²²⁶Ra, ²³²Th, and ⁴⁰K in common surface finishes such as paints, varnishes, sealers, primers, and enamels. Thirty-three samples from leading Brazilian manufacturers were analyzed using gamma spectrometry to determine activity concentrations. Results revealed significant variations across material types, with paints exhibiting the highest levels—notably sample T9 with 40.45 Bq kg⁻¹−1 (²²⁶Ra), 36.68 Bq kg⁻¹−1 (²³²Th), and 194.56 Bq kg⁻¹ (⁴⁰K)—while sealers consistently showed the lowest. Calculated annual effective doses for all samples, including the highest at 0.4 mSv y⁻⁻¹ (T9), remained well below the international safety limit of 1 mSv y⁻⁻¹. Importantly, the activities of the majority of radionuclides in the compounds were found to be below their respective dose limits, confirming compliance with global safety standards. The calculated radiological hazard metrics, including annual effective dose and associated economic costs, highlighted the importance of minimizing overall radiation exposure by prioritizing lower radioactivity finishing materials, especially when combined with other high-activity construction materials. This research establishes the first comprehensive database of radioactivity levels in Brazilian surface finishing materials and offers practical guidance for enhancing building safety standards.