Radiological baseline, mineralogy and Fe oxides of the eastern coast of the Province of Buenos Aires

Abstract

Buenos Aires Province coastline is a populated area visited yearly by millions of tourists. However, the radioactivity baseline data of the sand has not been reported yet, and, therefore, the external dose rate received by tourists and inhabitants is also unknown. This work is a study of the natural (238U, 232Th and 40K) and anthropogenic (137Cs) radionuclides activity, an analysis of the sand mineralogy, and the correlations between activity values and sand properties, still unclear in regions belonging to no high background radiation areas. Activity values have been determined on the three Holocene geomorphological units of the region, from Punta Rasa to Santa Teresita (30 km coast). The 238U, 232Th and 40K activities vary between 9 and 16 Bq/kg, 14 and 25 Bq/kg and 497 and 647 Bq/kg, respectively. These results indicate that Buenos Aires Province coastline is not a high background radiation area, related to the sediments sources (coastal cliff, Patagonian sediments, and the Andean volcanoes), which contain relatively low concentrations of radionuclide bearing minerals. Significant and positive correlations were found between the three natural radionuclides, contrary to high background radiation areas, where 40K activity does not correlate to those of 238U and 232Th. After separating sand in two fractions by means of a permanent magnet, called black and brown fractions, the major activity of the three radionuclides were observed in the former, as well as a higher amount of feldspar, magnetite/maghemite, and ilmenite. Pearson correlation coefficient determined between magnetite plus ilmenite content and the activity of the three radionuclides seems indicate the inclusion of these radionuclides on that Fe compounds, without discarding the inclusion of 40K on feldspar. 137Cs was not detected in the sand or the deeper clayey layers, but it was found on clay samples collected from the discharge zone of the region, indicating the relevance of horizontal groundwater flow. External dose rate determined across the studied area was 38 ± 2 nGy/h, which is lower than the external dose determined for other regions of Buenos Aires Province and the mean worldwide value. From the dosimetric point of view, the seashore of Buenos Aires Province is a safe area.