الفهرس 
Chapter I : IntroductionOnly 14 pages are availabe for public view
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Abstract
The present study was carried out to analyze fish samples for determination of their contents of heavy metals (mercury and lead), oragnochlorin (aldrin) and organophosphrous (diazinon). This study were applied on 90 random samples of Clarias lazera, Tilapia niloticus and Common carp (30 of each) were collected from different fish markets represented by farm and wild ones (15 of each)
The obtained results revealed that the mean values of mercury in the examined farm Clarias lazera, Tilapia niloticus and Common carp were 0.58±0.04, 0.31±0.02 and 0.24±0.01, respectively. However, the average concentration of mercury in wild fishes were 0.83±0.06, 0.54±0.03 and 0.38±0.02 mg/ kg, respectively.
The differences associated with mercury were highly significant among fish habitat (P<0.05) and significant among species and according to Egyptian standard, the examined farm common carp were accepted. While, wild common carp and other examined fishes were unfit that exceed the permissible limit.
In regard to lead, the average concentrations in the examined farm and wild fishes of Clarias lazera, Tilapia niloticus and common carp were0.11±0.01 and 0.18±0.02, 0.09±0.01 and 0.15±0.01 and 0.04±0.01 and 0.11±0.01mg/kg, respectively.
It was revealed that there are high significant differences among species and habitat (P<0.05).Also, farmed common carp was safe for human consumption than other fishes according to Egyptian standard.
Concerning aldrin residue, it was found that the average concentration in farm and wild Clarias lazera were 137.54±8.16 and 170.57±9.01 ppb, respectively. In farm Tilapia niloticus 83.53 ± 5.29 ppb and 146.20 ± 8.72 ppb for wild Tilapia niloticus and 0.0% and 120.56 ±6.08 for farm and wild common carp, respectively.
The analysis of variance revealed that there high significant differences among fish species and habitat. The farm Tilapia niloticus and Common carp were safe and not exceed the permissible limit of aldrin stipulated by EOS (1992).
The average concentrations of diazinon in farm Clarias lazera 331.84 ±19.78 and 548.59±40.12 ppb in wild fish, respectively. In farm and wild Tilapia niltoicus they were 290.05 ±16.53 and 503.36 ±29.97 ppb, respectively. Wild common carp showed average concentration of diazinon 275.54±13.86 ppb. In contrast, all examined samples of farm common carp were free from diazinon.
High significant differences were revealed among species and habitat (P<0.05).
According to the Egyptian standard, all farm fishes were safe for aldrin residue. While, Wild Clarias lazera (13.33%) and Tilapia niloticus (6.67%) were unfit for human consumption.
Public health significance of these chemical residues and possible sources of fish contamination as well as some recommendations to control or minimize such toxic pollutants to gain access into fresh water fishes were discussed.