CADMIUM, ZINC, LEAD AND COPPER IN CHIRONOMUS-RIPARIUS (MEIGEN) LARVAE (DIPTERA, CHIRONOMIDAE) - UPTAKE AND EFFECTS

Cadmium, Zn, Pb and Cu uptake and effects in larvae of Chironomus riparius (Meigen) were studied in an integrated laboratory investigation, in which metal analyses in different instar stages, uptake kinetics and effects on development and growth were considered in three separate experiments. In short-term experiments with fourth instar larvae, it was demonstrated that only a minor portion of metals was adsorbed on the larval exoskeletons. No conclusive evidence on tile uptake mechanism was found, but active uptake of trace metals seemed highly unlikely. In partial life cycle experiments. all four metals studied were readily accumulated in chironomid larvae. Uptake could be described satisfactorily utilizing a first-order one-compartment uptake model which incorporated growth. In all cases steady state conditions were approached and high uptake and elimination rate constants were estimated. Distinct differences between essential (Zn and Cu) and nonessential (Cd and Pb) metals were noted. Larval growth was significantly impaired upon exposure. Finally, long-term exposure experiments with low Cd concentrations (0.010 and 0.025 mg l-1) resulted initially in growth impairment and high mortality in first instar stages, but surviving larvae restored growth and adults emerged even before control adults. In similar experiments with Zn (0.1 and 1.0 mg l-1), development of larvae was significantly retarded. High Zn concentrations in larvae were noted and almost no adult midges emerged.