Anthropogenic and naturally occurring radionuclide content in near surface air in Cáceres (Spain).

The anthropogenic ( ¹³⁷ Cs, ⁹⁰ Sr, ^239+240 Pu and ²⁴¹ Am) and naturally occurring radionuclide ( ⁴⁰ K, ^234,238 U, ^228,230,232 Th, ²²⁶ Ra and ²¹⁰ Pb) content in near surface air present seasonal variations related to natural processes, such as soil erosion, resuspension of fine particles of soil and radon exhalation from soil ( ²¹⁰ Pb). The objective is to analyze seasonal variations of their concentrations and compare with radiological events (Fukushima fallout and wild fire) in a location without any known source of anthropogenic radionuclides. The ²¹⁰ Pb, ⁴⁰ K, and ¹³⁷ Cs presented annual variations, with maximum activity levels in summer. Solar radiation and rainfall were correlated with ²¹⁰ Pb and ⁴⁰ K. The ^234,238 U, ^228,230,232 Th, ²²⁶ Ra, ¹³⁷ Cs and ⁹⁰ Sr presented positive correlation with monthly mean values of temperature. The ratio ⁹⁰ Sr/ ¹³⁷ Cs was within the range of those reported for soils in Spain. Finally, the maximal effective dose rate was estimated to be 37 and 88 μSv/y for infants and adults, respectively, well below 1 mSv/y reference level. The main contributor to effective dose was ²¹⁰ Pb, about 92%, followed by: ²¹⁰ Pb ≫  ^228,230,232 Th >  ²²⁶ Ra, ^234,238 U >  ⁷ Be, ^239+240 Pu >  ⁴⁰ K, ⁹⁰ Sr >  ¹³⁷ Cs >  ²² Na.
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