Distribution of 137Cs, 238Pu and 239 + 240Pu in sediments of the southeastern Brazilian shelf–SW Atlantic margin

Abstract In this work levels of 137 Cs, 238 Pu and 239 + 240 Pu as well as activity ratios of anthrophogenic radionuclides in sediment samples from the southeastern Brazilian shelf are presented. Instrumental gamma spectrometry was used to determine 137 Cs and alpha spectrometry to determine 238 Pu and 239 + 240 Pu after a radiochemical procedure. The levels ranged from 0.30 to 1.79 Bq kg − 1 for 137 Cs, from 15 to 150 mBq kg − 1 for 238 Pu and, from 18 to 117 mBq kg − 1 for 239 + 240 Pu. There was a bathymetric differentiation in the radionuclides distribution. 137 Cs values were generally higher in the samples collected at water depths of less than 100 m. On the other hand, plutonium isotopes exhibit higher values at greater depths. The mean ratio of 239 + 240 Pu /  137 Cs obtained was 0.112 ± 0.072 which is in agreement with the value reported for the Atlantic from atmospheric fallout of nuclear explosions in the past. The 238 Pu /  230 + 240 Pu ratios varied widely (from 0.339 to 2.088) and showed the influence of the SNAP-9A accident in the 238 Pu levels for this area. The main goal of this work was to present unpublished anthropogenic radionuclide levels and activity ratios related to the contamination of the southeastern Brazilian shelf.