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Abstract As a result of industrial activities, the aquatic ecosystem has been increasingly contaminated by heavy metals. This posses great stresses to aquatic organisms in particular and to the whole ecosystem in general. Investigation of heavy metal concentrations in water, sediments and fish organs compartment of the environment are an important aspect of the control of environmental pollution to counteract the human activities which progressively increase heavy metal concentrations in aquatic ecosystem. In the present study, distribution patterns of some heavy metals (Cu, Zn, Cd, Mn, Fe and Pb) and associated pollution-induced changes in some organs (gills, kidney, liver and muscles) of three fresh water species (Bagrus bajad, Clarias gariepinus and Oreochromis niloticus) were identified in Assiut district in three sites, (Two stations on the River Nile ,Electricity station in El Walidia (ES) and Mankbad (Mank.), and an irrigation canal ,El-Malah canal (EM)). The results of this study can be summarized in the following points: 1. The general common physico-chemical characteristics of water were found lower than the permissible limits indicating the good condition of the aquatic ecosystem in the three sites studied during study period. 2. Metal concentrations in water (ppm) of Cu (0.32, 0.09, 0.3), Zn (0.211, 0.082, 0.26), Cd (0.016, 0.011, 0.013), Fe (0.57, 0.9, 0.7), Mn (0.05, 0.07, 0.02), Pb (0.05, 0.08, 0.024) in Electricity Station, El-Malah Canal and Mankbad respectively, demonstrating higher values than the international permissible ones for Cadmium, Iron and Lead only. 3. Metal concentrations in sediments (ppm) of Cu (147.7, 161.3, 262.4), Zn (259.7, 382.2, 117.8), Cd (49.3, 58.2, 47.9), Fe (532.8, 459.7, 560.3), Mn (98.6, 244.7, 72.5), Pb (77.6, 68.1, 76.7) in Electricity Station, El-Malah Canal and Mankbad respectivey, demonstrating higher value than the international permissible ones for Cadmium only. 4. Kidney and/or gills represent the primary sites of accumulation of most heavy metals in the three species under investigation followed by liver and muscles in the majority of cases. 5. Lipid peroxidation and DNA fragmentation impacts were found in association with heavy metal residues in fish organs. 6. The highest metal concentration in sediment was Fe in Mankbad (560 ppm) whereas the lowest was Cd in the same locality (47.9 ppm). 7. Cu and Pb accumulations in Clarias gariepinus were the highest in kidney followed by gills in all localities. The highest accumulation of Cu was in kidney in El-Malah Canal and Mankbad, both of them were above the permissible limits. However, Cu accumulation in muscles was under the permissible limits. 8. In Clarias gariepinus, lead accumulation had the same pattern of Copper; the highest accumulation was in kidney in El-Malah Canal. However, muscles accumulation of Pb was above the permissible limits in all studied localities (3.13,2.96 and 2.34 ppm in Electricity Station, El-Malah Canal and Mankbad respectively). 9. Zinc and iron had the same pattern of accumulation in Clarias gariepinus. Zn and Fe accumulations were the highest in liver (53.08 and 51.15 ppm in Electricity Station, 61.67 and 28.66 ppm in El-Malah Canal and 31.79 and 23.59 ppm in Mankbad respectively). However, muscles accumulation of these metals were under the permissible limits. 10. Cadmium and Manganese had the same pattern of accumulation as gills had the highest values of accumulation. Gills in Mankbad had the highest of Cd residues (0.88 ppm) which was over the permissible limits. Gills in Electricity Station had the highest accumulation of Mn (15.13 ppm) which was also above the permissible limits in Clarias gariepinus. Muscles accumulations for Cd and Mn were under these limits. 11. The highest values of lipid peroxidation and DNA fragmentation were in kidney in all studied localities in Clarias gariepinus. 12. In Oreochromis niloticus, copper, zinc, cadmium and iron accumulations were the highest in kidney in all studied localities followed by gills. 13. Gills had the highest values of Mn accumulation (9.75, 9.66 and 15.08 ppm in Electricity Station, El-Malah Canal and Mankbad respectively). whereas, lead had the highest accumulation residues in liver in the three localities. Pb accumulation in muscles of Oreochromis niloticus was above the permissible limits (2.33 and 2.58 ppm in Electricity Station and El-Malah Canal respectively); whereas, in Mankbad (1.9 ppm) still under these limits. 14. Lipid peroxidation had the highest values in kidney in the three studied localities (24.6, 24.4 and 34.7 ppm in Electricity Station, El-Malah Canal and Mankbad respectively) followed by gills. Also DNA fragmentation had the same pattern of values and it was the highest in kidney (29.53, 26.89 and 30.93 % in Electricity Station, El-Malah Canal and Mankbad respectively). • Based on discussion, the variability in heavy metal residues and associated LPO and DNA fragmentation in organs confirm the variation in different aquatic ecosystems and species. |