Radiological Characterization of Wood Ash and Sheep Wool: Relevance to Applications in Circular Economy

Wood ash from biomass power plants and coarse, low-grade sheep wool from farming are underutilized biowastes that are often landfilled. Their valorization could reduce waste and emissions, decrease reliance on virgin materials, and support the circular economy and European Green Deal targets. However, both materials may contain naturally occurring radionuclides, primarily 40 K, as well as trace uranium and thorium isotopes, with higher concentrations typically found in wood ash due to combustion processes. Assessing their activity concentrations and bioavailability is therefore essential to ensure regulatory compliance and protect public health. This study quantified radionuclide levels in wood ash and sheep wool samples collected in Croatia and evaluated their suitability for agricultural applications. Natural radionuclides ( 40 K, 232 Th, 238 U, 214 Pb, 214 Bi, 226 Ra, 210 Pb, 210 Po) and 137 Cs were determined using high-resolution gamma-ray and alpha spectrometry. The influence of different factors on radionuclide content was discussed, and transfer factors within the soil–hay–wool pathway were calculated to assess bioavailability. Measured activity concentrations were consistently low, and transfer factors indicated minimal radionuclide mobility. The results support the safe agricultural reuse of these materials and provide baseline data for radiological safety assessments in sustainable waste management practices.