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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.