Biokinetics and modelling of pollutant accumulation in Cat fish (Clarius casonii) and Silver fish (Rasteneobola argentea) from selected aquatic ecosystems in Uganda
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Concentrations of DDT and its residues and heavy metals (Zn, Cu, Pb and Cd) were determined in Clarius casonii collected from Nakivubo and Lubigi wetlands and Rasteneobola argentea from lakes Victoria and Kyoga. Measured concentrations were as follows: Zn ranged from 7.2 × 101 to 1.342 × 103, Cu 5.12 to 1.255 × 103, Pb 8.16 to 8.83 × 101 and Cd 1.01 to 4.79 µg g-1. Total DDT ranged from 0.147 to 1.328 µg kg-1ww. The Nakivubo wetland had the most contaminated fish. The wetland was therefore used as a natural laboratory to simulate and model Zn, Cu, Pb and Cd bioaccumulation in the gills, gut, muscle and liver of C. casonii using a biokinetic model. The model, which considers both dietary and aqueous sources of metals, was first used to predict the kinetic parameters of the metals using transfer and caging studies for 70 days. The experimental data obtained was then used to test the ability of the model to predict metal bioaccumulation in organs (gills, gut, muscle and liver) of C. casonii. The model predicted mean metal concentrations (µg g-1) in the gut of C. casonii was 1257 (Zn), 379.7 (Cu) and 74.58 (Pb). Mean concentrations (µg g-1) for the muscle were 124, 114.9 and 1.75 for Zn, Cu and Pb, respectively and for the gills 1480 (Zn), 460.9 (Cu) and 94.3(Pb). The predicted mean values were about 2 times the observed, suggesting that these organs can alter the ability to take up or eliminate the metals once a threshold is exceeded. Model simulations for hepatic Zn, Cu, Pb and Cd agreed well with the observed time course of metals in the liver. The model was able to predict Cd concentrations in all the organs, indicating low Cd concentration in Nakivubo wetland. Results suggest that kinetic bioaccumulation models may better apply to some organs than others. Because metal-induced toxicity is normally organ-specific, their application in a risk assessment context should be undertaken with caution.