Cs-137 and Sr-90 behavioural regularities in the southeastern part of the Baltic Sea

Variations in Cs-137 concentrations were investigated over the period 1986- 1997 in the southeastern part of the Baltic Sea, following the Chernobyl po wer plant accident. The rate of "self-cleaning" was demonstrated to be very slow, the average concentration of Cs-137 in 1996 being almost the same as that measured directly after the accident, in 1986. Measurements of both C s-137 and Sr-90 concentrations generally revealed homogeneous distributions in this region of the Baltic Sea, though patchy distributions did develop under some hydrometeorological conditions. Specifically, the Cs-137 concent ration distribution became heterogeneous with values varying in the range 6 0-92 Bq/m(3) under south-southwesterly wind conditions whilst the 90Sr conc entration distribution developed similar characteristics with values rangin g from 15 to 64 Bq/m(3) under east-southeasterly wind conditions. In additi on, in coastal waters, over extensive periods of north-northwesterly winds in 1995, Cs-137 concentrations increased to values 1.5-2 times the overall average concentration, which was registered in 1986 and 1996. These data th erefore reveal a continuing significant pollution of the waters of the Balt ic Sea resulting from the Chernobyl power plant accident, a pollution compo unded by the slow rate of radionuclide self-cleaning and significant probab ility of sudden regional concentration increase. (C) 2000 Elsevier Science Ltd. All rights reserved.