Abstract: The behaviours of Cs-137 and Cs-134 were comprehensively studied in a marine microhabitat in the presence of Zn-65, Co-60, Fe-59 and Mn-54 by applying artificial modelling. The results showed that after getting into sea water, Cs-137 and Cs-134 were behaving similarly in term of physiology and ecology. They were slowly adsorbed by suspensate and phytoplankton, and existed mainly in ionic form in the sea water; the concentration coefficients of the sediment were very low. The distribution of Cs-137 and Cs-134 in marine animals and some biochemical materials was studied at the same time. The critical organ of concentrating Cs-137, Cs-134 was not distinct. Both Cs-137 and Cs-134 in biochemical materials could be detected. At the end of excretion experiment, the loss of Cs-137 and Cs-134 in stomach-intestine and liver(or digestive-gland) was marked. Their residual rates were in the range of 0—30%. The gill and muscle in individual animal underwent a reabsorption of Cs-137 and Cs-134. The nuclides in the nuclear acid of Tilapia mossambica were dif icult to excret with a residual rate of 50%. The sediments had a process of deabsorption-readsorption.

Key words: Cs-137, Cs-134, Microhabitat, Concentration, Migration, Marine environmental protection