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 134Cs/137Cs isotopic ratio in Chernobyl fresh deposition was used to identify the weapon tests fall-out and Chernobyl deposition components. 137Cs and 134Cs mean concentrations in surface waters from the Spanish Mediterranean shoreline were 4.8±0.2 and 0.27±0.01 Bq m-3, respectively. 137Cs 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. 137Cs estimated inventory in the surface water layer (0–50 m) of the Catalan-Balearic basin was 17.4±0.5 TBq for 137Cs, of which 4.3±0.2 TBq must be attributed to post-Chernobyl deposition, and 1.00±0.04 TBq for 134Cs. Activation and fission products such as 106Ru, 110mAg, 134Cs, 137Cs and 144Ce, were detected in all samples of Posidonia oceanica. Mean radiocaesium levels in the bioindicator were 1.02±0.25 and 0.20±0.03 Bq kg-1 for 137Cs and 134Cs, respectively, corresponding to a mean isotopic ratio 134Cs/137Cs equal to 0.20±0.04 (1987). 137Cs activity incorporated by Posidonia oceanica after the Chernobyl deposition over the Mediterranean Sea was estimated as 0.51±0.08 Bq kg-1. Therefore, 137Cs specific activity had increased 100±40% one year after the accident. Low level radioactive liquid effluents 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 inmediate vicinity of the site. 134Cs/137Cs isotopic ratio in water samples from the vicinity of Vandellós 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.