Determination of natural radionuclides, U, Th-232, Ra-226, Ra-228, Pb-210 and K-40 in sediments from Cananéia-Iguape system, Brazil

Abstract

The Cananéia-Iguape estuarine-lagoon complex, located in the south of São Paulo State, Brazil, is a protected area recognized by UNESCO as part of the Biosphere Reserve, due to its importance as a natural ecosystem. However, along the years, the mining activities in the region affected the river basin, to such an extent that contamination was observed for As, Cu, Pb and Zn. Since the mining activities can also enhance the levels of natural radioactivity in the sediments, this study aimed to determine the activity concentration of the natural radionuclides (K-40, U, Ra-226, Pb-210, Th-232 and Ra-228) in 34 bottom sediments samples collected in the Cananéia-Iguape system. The samples were measured by gamma spectrometry, using a HPGe for the determination of K-40, Ra-226, Pb-210 and Ra-228. The concentration of U and Th-232 was determined by instrumental neutron activation analysis. The activity concentration of K-40 varied from 119 ± 17 to 522 ± 74 Bq kg-1; U-238 varied from 0.31 ± 0.05 to 5.8 ± 0.3 mg kg-1; Ra-226 varied from 3.7 ± 0.3 to 43.3 ± 1.5 Bq kg-1; Pb-210 varied from 5.8 ± 2.6 to 118 ± 12 Bq kg-1; Th-232 varied from 0.67 ± 0.02 to 16.6 ± 0.4 mg kg-1 and Ra-228 varied from 3.5 ± 0.6 to 64.9 ± 2.4 Bq kg-1. These results were compared with literature values for the region, indicating that they are the background of the region and no contamination was observed from NORM (Naturally Occurring Radioactive Material) industries.