Characterization of natural and artificial radionuclide concentrations in soil and ecological dose screening using RESRAD-BIOTA: a baseline study of El Kala National Park, Algeria

Twenty-eight composite surface soil samples collected from four ecosystem types across El Kala National Park, Algeria — a United Nations Educational, Scientific and Cultural Organization (UNESCO) Biosphere Reserve. UNESCO Biosphere Reserve — were characterized for 40K, 137Cs, 226Ra, 228Ra, and 232Th by high-purity germanium (HPGe) gamma spectrometry. Mean activity concentrations were 178.7 ± 84.4 Bq kg−1 for 40K, 12.1 ± 9.7 Bq kg−1 for 137Cs, 112.1 ± 30.3 Bq kg−1 for 226Ra, and 25.4 ± 11.8 Bq kg−1 for 232Th-series (all uncertainties reported at coverage factor k = 2). Radium-226 concentrations exceeded the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) worldwide median of ~35 Bq kg−1 by a factor of ~3, reflecting geological enrichment within Tertiary phosphatic sedimentary formations of north-eastern Algeria. Potassium-40 and 232Th concentrations were within worldwide typical ranges; 137Cs was consistent with residual global fallout from mid-twentieth century atmospheric nuclear weapons testing. In-situ absorbed dose rates (park mean 83.8 nGy h−1) include a cosmic radiation contribution of ~35 nGy h−1 that is absent from terrestrial dose rates calculated using UNSCEAR (2000) conversion coefficients applied to site-specific data (park mean 74.8 nGy h−1. Subtracting the cosmic component yields a corrected terrestrial in-situ mean of ~49 nGy h−1 — ~35% below the calculated value — consistent with systematic overestimation by the UNSCEAR semi-infinite source geometry when applied to surface-concentrated (0–15 cm) radioactivity profiles. RESRAD-BIOTA Level 1 ecological screening, applying ICRP Publication 108 protective benchmarks of 10 mGy d−1 for terrestrial animals and 1 mGy d−1 for terrestrial plants, produced sum ratio factors (SRFs) of 0.0119 and 0.146, corresponding to safety margins of 84-fold and 6.8-fold below their respective benchmarks. Both SRF values were well below unity, confirming that Level 1 screening criteria are satisfied without requiring higher-tier assessment for terrestrial animals; a Level 2 assessment is recommended for terrestrial plants given the more constrained margin. Radium-226 dominated total biota dose (53% for animals; 75% for plants). These results establish the first systematic radiological baseline for this ecologically sensitive Mediterranean protected area and demonstrate the applicability of RESidual RADioactivity — BIOlogical Transport of Activity (RESRAD‑BIOTA) graded screening in naturally enriched geological settings.