Radiocesium distribution in soils of Tenerife Island (Canary Islands, Spain)

Tenerife is the largest and most populated island of the Canary Islands; with a surface of 2,034 km² and 917,841 inhabitants (in January 2019), it hosts 43% of the total population of the archipelago.

Large amounts of ¹³⁷Cs, an artificial radionuclide with a half-life of 30.2 years, were released into the environment due to the nuclear weapon tests carried out from the 1950s to the 1970s and by nuclear power plant accidents, such as the Chernobyl in 1986. The most recent ¹³⁷Cs release into the environment was due to the Fukushima Daiichi Nuclear Power Plant accident, following the earthquake and tsunami of 11 March 2011. Radionuclides released by this accident were measured in air filters collected in the Canary Islands despite the tremendous distance to the source (López-Pérez et al., 2013).

In this work, we provide the concentrations of ¹³⁷Cs measured in 73 soil samples collected in 2013 in Tenerife. Besides, a second dataset of ¹³⁷Cs concentrations recorded in 103 soil samples collected in 1991 (22 years before) have been used to provide information on the spatial and temporal variability of this anthropogenic radionuclide at this site.

In both surveys, sampling sites were randomly selected on a predefined 3x3 km sampling grid covering the whole island and superficial samples were collected from uncultivated fields. Radiometric measurements were performed by gamma spectrometry with a coaxial-type germanium detector (Canberra Industries Inc., USA). The activity concentration of ¹³⁷Cs was directly measured by its gamma-ray photopeak at 661.65 KeV. The Minimum Detectable Activity was 0.08 Bq kg^-1.

¹³⁷Cs activity concentrations in the 1991 survey ranged from 0.08 to 100.90 Bq kg^-1 and from 0.08 to 88.85 Bq kg^-1 in 2013. Comparing the results of both campaigns, ¹³⁷Cs activity concentrations were found to be rather similar, despite the 22 years gap between the measurements. We believe that, in addition to the ¹³⁷Cs atmospheric fallout, there is an additional contribution to the inventory of this radionuclide in the soils of this island produced by the deposition of ¹³⁷Cs-loaded dust particles frequently transported from the Sahara Desert as dust storms (Karlsson et al, 2008).

In terms of radiological risk, in some few locations, the contribution to the outdoor gamma absorbed dose from the ¹³⁷Cs activity concentrations present in the soils were as high as 50%. Therefore, it is important to identify the various sources of this radionuclide to the studied sites in order to enhance the understanding of the radiological hazard produced by this man-made radionuclide.

References:

Karlsson L, Hernandez F, Rodríguez S, López-Pérez M, Hernandez-Armas J, Alonso-Pérez S, Cuevas, E. (2008). Using ¹³⁷Cs and ⁴⁰K to identify natural Saharan dust contributions to PM10 concentrations and air quality impairment in the Canary Islands. Atmospheric Environment, 42: 7034-7042

López-Pérez M, Ramos-López R, Perestelo NR, Duarte-Rodriguez X, Bustos JJ, Alonso-Pérez S, E. Cuevas, J. Hernández-Armas. (2013). Arrival of radionuclides released by the Fukushima accident to Tenerife (Canary Islands). Journal of Environmental Radioactivity, 116: 180-186