Abstract
| - The relative importance of water and food as Cd sourcesto the predatory insect Chaoboruspunctipenniswasestablished using a three-link planktonic food chaincomposedof larvae of the insect, its crustacean prey(Ceriodaphniadubia), and the prey's algal food (Selenastrumcapricornutum). To ensure that our laboratory resultswerereliable and could be extrapolated to field conditions, weintroduced Cd at the bottom of the food chain; we used Cdconcentrations to which animals might be exposed innature; we measured Cd loss from the food to the watercompartment; and we controlled the availability andconcentrations of Cd in water and food. There was nosignificant difference between the Cd concentrations inlarvaeexposed to the metal in their food alone versus thoseexposed to Cd in both food and water, indicating that Cdbioaccumulation from water was negligible. Theseresultssuggest that, although Cd concentrations in the predatorcanbe correlated with those in lake water, direct uptake fromwater is probably unimportant; instead, the correlation islikely a consequence of Cd uptake from water by organisms at a lower level in the food chain. The importanceoffood as a Cd source suggests that models designed topredict Cd concentrations in animals will be more completeand probably more reliable if they consider metal uptakethrough the food chain.
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