CO-60 ACCUMULATION FROM SEDIMENT AND PLANKTONIC ALGAE BY MIDGE LARVAE (CHIRONOMUS-LURIDUS)

This paper reports the results of several experiments carried out to evaluate uptake and retention by a limicolous midge larva of Co-60 retained in sediment, either adsorbed on mineral particles or bound to planktonic algae. In order to determine their relative contributions in radionuclide accumulation, the different vectors (water, algae and sediment) were first labelled individually and then simultaneously. Co-60 accumulation from water and from algae results in a maximum concentration factor of 30 and in a mean trophic transfer factor of 4.5 x 10(-3). The level of contamination of midge larvae from sediment is markedly influenced by the presence of endogenous organic matter. Thus the radionuclide transfer factor is about twice as high for larvae placed in labelled raw sediment than for larvae placed in labelled incinerated sediment, in the presence as in the absence of contaminated planktonic algae. Irrespective of the contamination conditions, Co-60 depuration from midge larvae is a very rapid phenomenon that corresponds, in all cases, to a radionuclide half-life of only a few days.