A kinetic model for the relative contribution of waterborne and dietary cadmium and zinc in the common carp (Cyprinus carpio)

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Abstract
In this work, the uptake and whole-body accumulation of Cd and Zn by the common carp from water, diet, and a combination of both was studied using the radioactive tracers 109Cd and 65Zn. A three-compartment pharmacokinetic model was constructed and revealed metal- and exposure route–dependent accumulation profiles. Under the tested exposure conditions in water (0.1 μM Cd and 1 μM Zn), only 0.1 and 0.07%, respectively, of the total Cd and Zn load that passed the branchial surfaces was accumulated by the carp. In contrast, the carp accumulated 20 and 29% of the total ingested Cd and Zn load (mean concentrations in food of newly accumulated metals were 2.24 ± 0.29 and 19.91 ± 2.89 nmol/g wet weight, respectively). However, the contribution of the waterborne metals to the whole-body metal accumulation was higher than the metal uptake from food. The constructed model was used to simulate the effect of variable assimilation efficiency (AE) values on the relative importance of dietary Cd and Zn exposure to the overall metal accumulation in common carp. This simulation was performed under a realistic exposure scenario and with Cd and Zn AE values ranging from 5 to 95%. Dissolved Zn levels were higher and Cd levels lower compared to the laboratory experiments. Levels in the midge larvae were much higher. The results show that under these conditions, even at the lowest Cd and Zn AEs, almost 40% of the total body Cd and Zn concentrations originated from dietary Cd and Zn exposure. Taking into account the Cd and Zn AE of the laboratory experiments, respectively, 31 and 55%, more than 85% of the total body Cd and Zn was taken up from the food.

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