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 w as carried out during November 1994. For this purpose, 75 water samples wer e collected from points distributed throughout the Ebro river basin. Analys is included gross alpha and gross beta activities, relevant natural radionu clides (K-40, Ra-226, U-234,U-238 -uranium total-) and several artificial r adionuclides (H-3, Sr-90 and radiocaesium). Mean gross alpha and gross beta activities in surface waters of the river's main course were 0.095 +/- 0.0 04 and 0.213 +/- 0.012 Bql(-1), respectively. Mean activities of K-40, Ra-2 26 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 mea n Sr-90 activity was 6.6 +/- 0.3 mBq l(-1), H-3 was detected in 8% of the s amples, and radiocaesium was not detected in any sample. It is estimated th at almost 100% of gross alpha and 97% of gross beta activities of surface w aters in the Ebro river came from natural sources. Furthermore, results sho wed that the geological setting, large cities, agricultural areas and darns 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 inge stion of Ebro river waters was 7.59 mu Sv y(-1), which represented only 0.3 % of the average annual effective dose attributable to natural background r adiation in the area. (C) 2000 Elsevier Science Ltd. All rights reserved.