CADMIUM AND ZINC UPTAKE BY 2 SPECIES OF AQUATIC INVERTEBRATE PREDATORS FROM DIETARY AND AQUEOUS SOURCES

Cadmium and Zn uptake rates via food and water were determined under l aboratory conditions for two species of freshwater invertebrate predat ors, Water mites (Limnesia maculata) and caddisfly larvae (Mystacides spp.) were exposed for 4 wk to either contaminated chironomid larvae ( Chironomus riparius, 288-639-mu-g Cd.g-1 or 778-1152-mu-g Zn.g-1) or c ontaminated water (0.1 mg Cd.L-1 or 1.0 mg Zn.L-1). Cadmium was readil y accumulated in the two species from both dietary and aqueous sources . A clear difference between exposed and untreated organisms was estab lished. Zinc uptake was generally lower than that of Cd, resulting in small differences between exposed and nonexposed organisms. Cadmium up take from food and Zn uptake from water dominated in both species. It is concluded that, in addition to uptake of free metal ions from aqueo us sources, invertebrate predators can accumulate trace metals from th eir food. This is an underestimated source of contamination for freshw ater invertebrate predators. Changes in internal metal concentrations in the predators are described with a first-order one-compartment upta ke model. This model was appropriate where steady-state conditions wer e approached. When uptake continued throughout the experimental period , uptake rate constants were estimated using linear regression.