INCREASED CADMIUM EXCRETION IN METAL-ADAPTED POPULATIONS OF THE MIDGECHIRONOMUS-RIPARIUS (DIPTERA)

Cadmium kinetics were studied in cadmium-adapted and nonadapted field populations of the midge Chironomus riparius. Accumulation and elimina tion experiments were carried out using first-generation laboratory-re ared animals. Differences between populations were, therefore, assumed to have a genetic basis. Larvae were dissected to analyze the guts an d the remainder of the larvae separately. First-order one-compartment models were not always successful in describing accumulation processes , probably due to acclimation. No interpopulation differences were obs erved in larval development based on dry weights, whereas some differe nces existed based on pupation rate. In most cases more than 80% of th e total amount of cadmium was found in the guts of all populations. La rvae from cadmium-adapted populations showed a decreased net accumulat ion rate as well as higher equilibrium values (15-20%) compared to non adapted populations. In addition, cadmium excretion efficiency was inc reased for cadmium-adapted larvae, which was due to an increased elimi nation rate from the guts. It was concluded that exposure to high cadm ium concentrations in the field resulted in populations of C. riparius with an increased storage capability and an increased excretion effic iency, especially regarding the guts.