Bioindicators for monitoring radioactive pollution of the marine environment. Experiments on the feasibility of Mytilus as a bioindicator in estuarine environments - with some comparisons to Fucus

Mussels (Mytilus edulis) are globally used as bioindicators for pollution of coastal and estuarine environments by metals and radionuclides. The aim of this work has been to improve the use of Mytilus edulis as a bioindicator by gaining knowledge on its accumulation and loss of certain radionuclides (65Zn, 57Co, 54Mn, 51Cr, 59Fe and 134Cs) under different fieldcomparable environmental conditions.

A laboratory set-up in which natural concentrations of suspended phytoplankton are kept constant for weeks was evolved for the accumulation experiments with mussels. It is argued that continuous feeding at very low (natural) levels is necessary if field-comparable experiments are to be performed with suspension feeding bivalves.

Accumulation via food intake was studied by comparing experiments with different concentrations of contaminated phytoplankton (Phaeodactylum tricornutum). This comparison showed no effect of varying the phytoplankton concentration. Decreasing the salinity and increasing the temperature elevated the influx (initial rate of accumulation) of the radionuclides.

During one year excretion experiments were performed by weekly wholebody countings of laboratory contaminated mussels which had been re-introduced in their natural environment. A seasonal effeet on the biological half life was detected for 65Zn. It is concluded that mussels are useful bioindicators provided the variability due to environmental factors, e.g. season and salinity, is taken into consideration.

Brown algae, expecially Fucus vesiculosus, were used to trace the controlled liquid discharges (mainly 60Co, 58Co, 65Zn, 54Mn and 110Ag) from two Swedish nuclear power plants (Barseback and Ringhals). Fucus showed higher accumulation than Mytilus. Transfer factors between discharge and sample from a specified location are presented.

It is argued that these transfer factors may be useful in estimating the magnitude of an uncontrolled accidental release of activity and its transport to man.