Soil radioactivity in the highest volcanic region of Northern Andes

Abstract

This work studied the spatial pattern of four natural radionuclides (²²⁶Ra, ²²⁸Ra, ²²⁸Th and ⁴⁰K) as well as one artificial one (¹³⁷Cs) in soils in the Chimborazo province (Ecuador), which belongs to the North Andes of South America. Soil samples were collected considering the Ecuador geological map. Statistical analyses showed that activity concentrations of ²²⁶Ra, ²²⁸Ra, ²²⁸Th do not exceed the worldwide average, while one geological unit exceeds the worldwide average for ⁴⁰K. These high activity concentrations are attributed to radionuclide accumulation in plutonic and metamorphic rocks and also in ash resulting from eruptions of the Sangay volcano. The inverse distance weighted interpolation method was used to develop corresponding radioactivity maps where the highest activity concentrations are in the central-east of the studied area. In addition, a distribution pattern of ²²⁶Ra and ⁴⁰K is observed in the geologies influenced by the presence of Chimborazo, Igualata, Tungurahua and Altar volcanoes. Spearman's nonparametric test shows positive correlations suggesting the presence of very homogeneous lithologies and that volcanic activities can influence the distribution of radionuclides in our environment. In seven of the samples, ¹³⁷Cs was detected.

Keywords: Activity concentration; Artificial (137)Cs; Natural radioactivity; Spatial pattern.