Impact of 134Cs and 137Cs from the Chernobyl reactor accident on the Spanish Mediterranean marine environment

As part of a study aiming to establish the distribution and bioavailability of man-made radionuclides in the marine environment, radiocaesium levels were determined in large volume sea water samples and in the sea-grass Posidonia oceanica collected along the Spanish Mediterranean coast. Results obtained from 1987 to 1991 showed the enhancement of radiocaesium levels in the Spanish Mediterranean marine environment after the Chernobyl accident. The well-known Cs-134/Cs-137 isotopic ratio in Chernobyl fresh deposition was used to identify the weapon tests fall-out and Chernobyl deposition components. Cs-137 and Cs-134 mean concentrations in surface waters from the Spanish Mediterranean shoreline were 4.8 +/- 0.2 and 0.27 +/- 0.01 Bq m(-3), respectively. Cs-137 concentration incorporated into Mediterranean waters as a consequence of the post-Chernobyl deposition was estimated to be 1.16 +/- 0.04 Bq m(-3) which is a 33 +/- 2% increase over the previous levels. Cs-137 estimated inventory in the surface water layer (0-50 m) of the Catalan-Balearic basin was 17.4 +/- 0.5 TBq for Cs-137, of which 4.3 +/- 0.2 TBq must be attributed to post-Chernobyl deposition, and 1.00 +/- 0.04 TBq for Cs-134. Activation and fission products such as Ru-106, Ag-110m, Cs-134, Cs-137 and Ce-144, were detected in all samples of Posidonia oceanica. Mean radiocaesium levels in the bioindicator were 1.02 +/- 0.16 and 0.20 +/- 0.03 Bq kg(-1) for Cs-137 and Cs-134: respectively, corresponding to a mean isotopic ratio Cs-134/Cs-137 equal to 0.20 +/- 0.03 (1987). Cs-137 activity incorporated by Posidonia oceanica after the Chernobyl deposition over the Mediterranean Sea was estimated as 0.51 +/- 0.08 Bq kg(-1). Therefore, Cs-137 specific activity had increased 100 +/- 40% one pear after the accident. Low level radioactive liquid effluent from the nuclear power plants located on the southern Catalan shoreline did not have a significant effect on the water radioactivity levels, since they were confined to the immediate vicinity of the site. Cs-134/Cs-137 isotopic ratio in water samples from the vicinity of Vandellos NPP was found to be 0.11 +/- 0.01, which is twice the mean observed in the Spanish Mediterranean coastal waters, namely 0.057 +/- 0.003 (1988-1991), and were in good agreement with the value observed in samples of Posidonia oceanica collected from the same location, namely 0.107 +/- 0.004. (C) 1999 Elsevier Science Ltd. All rights reserved.