Cadmium and Zinc Uptake by Two Species of Aquatic Invertebrate Predators from Dietary and Aqueous Sources

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Abstract
Cadmium and Zn uptake rates via food and water were determined under laboratory conditions for two species of freshwater invertebrate predators. Water mites (Limnesia maculata) and caddisfly larvae (Mystacides spp.) were exposed for 4 wk to either contaminated chironomid larvae (Chironomus riparius, 288–639 μg Cd∙g−1 or 778–1152 μg Zn∙g−1) or contaminated water (0.1 mg Cd∙L−1 or 1.0 mg Zn∙L−1). Cadmium was readily accumulated in the two species from both dietary and aqueous sources. A clear difference between exposed and untreated organisms was established. Zinc uptake was generally lower than that of Cd, resulting in small differences between exposed and nonexposed organisms. Cadmium uptake from food and Zn uptake from water dominated in both species. It is concluded that, in addition to uptake of free metal ions from aqueous sources, invertebrate predators can accumulate trace metals from their food. This is an underestimated source of contamination for freshwater invertebrate predators. Changes in internal metal concentrations in the predators are described with a first-order one-compartment uptake model. This model was appropriate where steady-state conditions were approached. When uptake continued throughout the experimental period, uptake rate constants were estimated using linear regression.

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