Experimental study and modelling of 137Cs sorption behaviour in the Baltic Sea and the Curonian Lagoon

Sorption-desorption behaviour of 137Cs in the Baltic Sea and the Curonian Lagoon was studied in 1997-2009 with the aim to better understand processes responsible for redistribution and sink of 137Cs in the system. Data obtained from several sampling campaigns were analyzed and short and long-term kinetic tracer experiments using natural water and bottom sediments were carried out with particles of various sizes from 0.2 to 50 μm. Samples of suspended particles and bottom sediments collected during two sampling campaigns were fractionated according to the size, and association of 137Cs with solid phase was studied using sequential extraction. The difference in 137Cs behaviour observed between expeditions in 1999 and 2001 was attributed to seasonal variations in chemical composition of suspended particles entering the system and consequent differences between the sorption (in 1999) and the desorption (in 2001) of 137Cs in sea water. Data obtained from tracer kinetic sorption experiments with 134Cs and bottom sediment fractions of different grain size were used for finding a suitable kinetic sorption model, kinetic constants and the corresponding equilibrium Kd values. It has been found that the modelled data best conform to the mechanism of ion diffusion through the so-called inert layer on the surface of the sediment particles. (author)