VERTICAL-DISTRIBUTION OF RADIOCESIUM, PLUTONIUM AND AMERICIUM IN THE CATALAN SEA (NORTHWESTERN MEDITERRANEAN)

Caesium-137, Pu-239,Pu-240 and Am-241 concentration profiles (0-1000 m ) have been determined in unfiltered large volume water samples collec ted from the Catalan Sea (northwestern Mediterranean). Results showed that radiocaesium concentration decreases quickly through the water co lumn while the transuranic concentration increases with depth, showing a faster migration to the bottom layers. Comparing our results with t hose reported by other authors (1975-1980), radiocaesium input from Ch ernobyl releases has been identified through the profile. In addition, transuranic concentrations have decreased considerably in the differe nt layers of the profile. Integrated activities through the water colu mn were 2.6+/-0.2 kBq m(-2) for Cs-137, 23+/-3 Bq m(-2) for Pu-239,Pu- 240 and 1.5+/-0.5 Bq m(-2) for Am-241. According to the estimated inve ntory and the integrated fall-out in the Mediterranean area, about 56% of Cs-137, 27% of Pu-239,Pu-240 and 4% of Am-241 which was deposited over the Mediterranean Sea by generalized fall-out remains at present in the first 1000 m of the water column. Vertical distribution of Pu-2 39,Pu-240/Cs-137 activity ratios showed a clear separation between tra nsuranics and radiocaesium through the water profile. Am-241/Pu-239,Pu -240 activity ratio revealed faster sinking of americium relative to p lutonium.