Natural and artificial radioactivity in surface waters of the Ebro river basin (Northeast Spain)

A radiological characterisation of surface waters of the Ebro river basin was carried out during November 1994. For this purpose, 75 water samples were collected from points distributed throughout the Ebro river basin. Analysis included gross alpha and gross beta activities, relevant natural radionuclides (40K, 226Ra, 234,238U -uranium total-) and several artificial radionuclides (3H, 90Sr and radiocaesium). Mean gross alpha and gross beta activities in surface waters of the riverʹs main course were 0.095±0.004 and 0.213±0.012 Bq l−1, respectively. Mean activities of 40K, 226Ra and uranium (total) were 0.132±0.009, 0.0282±0.0008 and 0.053±0.006 Bq l−1, respectively. Regarding artificial radionuclides, the mean 90Sr activity was 6.6±0.3 mBq l−1, 3H was detected in 8% of the samples, and radiocaesium was not detected in any sample. It is estimated that almost 100% of gross alpha and 97% of gross beta activities of surface waters in the Ebro river came from natural sources. Furthermore, results showed that the geological setting, large cities, agricultural areas and dams strongly influence the occurrence of natural radionuclides. Contamination from nuclear power plants located along the river was not detected. Finally, we estimated that the annual dose equivalent due to the hypothetical ingestion of Ebro river waters was 7.59 μSv y−1, which represented only 0.3% of the average annual effective dose attributable to natural background radiation in the area.