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 relative 226Ra enrichment within the 238U decay series, resulting in low 228Ra/226Ra activity ratios. Lava samples had a mean 226Ra activity concentration of 48.0 Bq kg-1 and a mean 228Ra/226Ra ratio of 0.67, defining a radiological fingerprint 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, indicating the contribution of recent volcanic materials. Terrestrial gamma dose rates showed a clear post-eruptive spatial pattern, with the highest values in areas affected by the 2021 eruption. This increase contrasted with pre-eruptive conditions and was consistent with the observed 226Ra enrichment in proximal soils. Nevertheless, the calculated doses and radiological hazard indices indicated no significant radiological concern for external gamma exposure. The Tajogaite eruption produced a measurable but non-hazardous radiological effect; however, the observed 226Ra enrichment suggests a potential increase in 222Rn generation, highlighting the need for indoor radon monitoring in nearby dwellings.