Radiological impact of the 2021 Tajogaite eruption (La Palma, Canary Islands): Evidence of 226Ra enrichment in volcanic soils.

Volcanic eruptions can redistribute natural radionuclides and modify radiological background levels in inhabited areas. This study assesses the radiological impact of the 2021 Tajogaite eruption on La Palma (Canary Islands, Spain) by characterising eruptive materials, surface soils and terrestrial gamma radiation. Activity concentrations of radionuclides from the 238U and 232Th decay series, together with 40K and 235U, were determined in lava, ash, xenopumice and soil samples using gamma and alpha spectrometry. Eruptive products showed 226Ra enrichment relative to 230Th within the 238U decay series. Lava samples had a mean 226Ra activity concentration of 48 Bq kg-1 and a mean 228Ra/226Ra ratio of 0.67, defining a radiological signature of the eruptive materials. This pattern was also identified in nearby soils, where proximal soils showed higher 226Ra activity concentrations than northern soils (48.9 vs 23.8 Bq kg-1, geometric means), while 228Ra/226Ra decreased from 1.15 in northern to 0.70 in proximal soils, consistent with the contribution of recent volcanic materials. Terrestrial outdoor gamma absorbed dose rates showed a clear post-eruptive spatial pattern, with the highest values in areas affected by the 2021 eruption. This pattern contrasted with pre-eruptive conditions and showed spatial coherence with the post-eruptive 226Ra enrichment in proximal soils. Nevertheless, the calculated doses and radiological hazard indices indicated no significant radiological concern for external gamma exposure. These findings support post-eruptive radionuclide monitoring in ocean-island basalt settings.