Radiological impact of El Hierro submarine volcano on the brown algae Lobophora variegata

Abstract

In this work, we present the radiological impact in the surroundings of the Tagoro submarine volcano several years after its eruptive analysing marine environmental samples. For this purpose, besides collecting coastal water, brown algae Lobophora variegata were collected along the coastal perimeter of El Hierro island, with the aim of using them as an environmental dosimeter due to their high accumulation power. Radionuclides analysed by alpha and gamma spectrometry were 238U, 234Th, 234U, 226Ra, 210Pb, 210Po, 235U, 228Th, and 40K. The activity concentrations, concentration factors (CF) and ratios were calculated for all the samples considering the area affected by the volcano and the unaffected area. In the latter case, L. variegata algae collected on Las Canteras beach were also analysed. Lower values of activity concentrations for 234Th and 234U were measured in La Restinga zone (1310 ± 50 Bq/Kg; 5.8 ± 0.6 Bq/Kg) than ones obtained in the other areas non affected by the volcano (1660 ± 70 Bq/Kg; 7.5 ± 0.6 Bq/Kg); however, they were higher in El Hierro (1570 ± 60 Bq/Kg; 94 ± 8 Bq/Kg) than in Las Canteras (600 ± 30 Bq/Kg; 77 ± 8 Bq/Kg). Respect to coastal water samples, activity concentrations for 210Po measured in El Hierro island were considerably higher both in volcano zone and in Las Canteras beach. The calculated CF in algae from both islands do not seem to show any noticeable difference. For the ratios among the radionuclides, those close to equilibrium were associated to conservative radionuclides (234U and 238U) and those in not equilibrium to reactive particle (234Th, 210Po and 210Pb). Finally, two-way ANOVAs tested for differences in the radionuclides’ activity concentrations and the activity concentration ratios, between the two areas (affected and nonaffected) and sites within each area were performed. Significant differences between El Hierro and Las Canteras, mainly for 40K and 234Th were found.