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Abstract
SUMMARY
It is known that river Nile and its branches are polluted with industrial, agricultural and sewage wastes. So, the current study was performed to declare the degree of pollution with heavy metals in fish and water of the river Nile at Gharbia Governorate.
Heavy metals and other trace elements have been considered as dangerous substances causing serious health hazards.
Ninety random samples of Clarias lazera, Tilapia nilotica and Bagrus bayad (30 of each) were collected after catching in Kafr El-zayat city, Gharbia Governorate. All the collected samples were equally divided to small and large sized fish (15 of each fish species) for estimation of heavy metal concentrations. Also 15 random samples from water related to the area of catching were examined for detection of heavy metals residues.
The obtained results revealed that the mean values of mercury concentrations (mg/kg) in small and large sized fresh water fish were 0.72±0.04, 0.98±0.08 mg/Kg for Clarias lazera, 0.49±0.05&0.81±0.05 mg/Kg for Tilapia nilotica and 0.28±0.03&0.44±0.03 mg/Kg for Bagrus bayad.
Further more , 40 % , 33.33 % and20 % of small sized Clarias lazera , Tilapia nilotica and Bagrus bayad were exceeded the maximum permissible limit of mercury (0.5mg/kg), respectively. While,60%,46.67% and 26.67% of large sizes of these fish species were unfit .
Concerning lead concentrations (mg/kg), small sized Clarias lazera , Tilapia nilotica and Bagrus bayad contained 0.15 ± 0.02 ; 0.11 ± 0.01 and 0.05 ± 0.01mg/kg as average levels, respectively.
However, the average concentrations of lead (mg/kg) in large sized fresh water fishes were 0.27±0.04, 0.16±0.03 and 0.09±0.01 mg/kg, respectively. Accurately , 26.67%,13.33% and 6.67% of small sized and 46.67% , 26.67% and 20% of large sized Claria lazera, Tilapia nilotica and Bagrus bayad exceeded the safe permissible limit
The mean values of cadmium concentrations in the examined samples of small and large sized fresh water fish were 0.11±0.01 & 0.20 ± 0.03mg/kg for Clarias lazera, 0.08 ± 0.01&0.12±0.02 mg/kg for Tilapia nilotica and 0.03± 0.01& 0.07±0.01mg/kg for Bagrus Bayad , respectively. Moreover , 20 % & 26.67% and 13.33 % & 20% of small and large sized Clarias lazera and Bagrus bayad were unfit for human consumption based on their contents of cadmium which exceeded the maximum permissible limits (0.1mg/kg ), respectively.
On regard to copper concentrations in small and large sized fresh water fishes, the mean values were 2.88 ± 0.32 & 4.26 ± 0.45 mg/kg for Clarias lazera, 2.16±0.20&3.51 ± 0.37 mg/Kg for Tilapia nilotica and 1.34 ±0.11&1.94±0.21mg/Kg for Bagrus bayad. However, all the examined samples of Clarias lazera, Tilapia nilotica and Bagrus bayad were accepted and not exceeded the safe permissible limit of copper.
The concentrations of these heavy metals were determined in the water from which the examined fish were caught. The average concentrations of mercury, lead, cadmium and copper in the examined samples of water were 0.26±0.03, 0.15±0.02, 0.09±0.01 and 1.01±0.13 mg/kg , respectively.
Finally, the public health significance of these serious heavy metals and the possible sources of fish contamination with such dangerous pollutants as well as some recommendations to improve the quality and hygienic conditions of fresh water fish were discussed.