الفهرس 
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Abstract
Water pollution is caused basically by man, s inability to dispose of wastes in ways that do not change the water quality. The most serious pollution effects are caused by waste chemical substances entering and accumulating in ecosystems and food chains. Edku Lake is situated approximately 18 km west of Rashid branch of the River Nile, so different environmental pollutants like agricultural wastes of fertilizers, pesticides, industerial wastes and heavy metals are continually discharged to the main sources of the River water and its branches without proper treatment for these pollutants. This is essential cause of water deterioration and thus affecting its ability to be purposes used in different purposes of drinking, irrigation, industry and domestic uses.
The problem today, is not the quantity of the available water, but it is the quality and requriments to meet with the national and international standards.
For the above reasons, different samples (water, sediments, and fish) were collected from different locations of Edku Lake. The present study was made in an attempt to cover following topics:
1. Water quality measurement:
1.1. Physical parameters:
The physical parameters of water quality were determined in the selected sampling locations of Edku Lake during summer 2004 and winter 2005 and the results achieved:
* Air temperature values were ranged from 29.0 to 45.0 oC with mean value of 35.7 oC in summer and 19.0 to 20.0 oC with mean value of 19.51 oC in winter.
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* The statistical analysis showed that there was high significant difference between the air temperature values during summer and winter seasons in all sampling locations.
* Water temperature values of samples ranged between 31.3 to 34.9 oC with mean value of 32.89 oC and 19.2 to 20 oC with mean value of 19.63 oC in summer and winter, respectively.
* There was high significant difference between water temperature values of all locations during the studied seasons
* Salinity of the water may increase or decrease due to the loss or gain of water from evaporation, rainfall, freezing, melting, or other processes. The results showed that concentrations of water salinity ranged between 600 to 1900 mg/L with mean value of 1185.7mg/L and 600 to 3300 mg/L with mean value of 1800 mg/L in summer and winter, respectively. The higher values were recorded in Nehayet Canat Taher water samples in summer (1900 mg/L) and in Gezzeret El-Kotalah samples in winter (3300 mg/L), while the lowest values were recorded in Masraf Edku (600 mg/L) in each season. These levels are much
higher than that given by the WHO Standard Limit (500-1500mg/L) and Egyptian Standards ES (500-1000mg/L).
* No significant difference was recorded between the salinity values during summer and winter seasons in the sampling locations.
* Clarity is a measure of the water clarity, and we measured water clarity using a Secchi Disc. Results indicated that the clarity values of water samples in the different locations of Edku Lake ranged from 22.5 cm to 62.5 cm with mean value of 40.0 cm in summer and from 22.5 cm to 42.5cm with mean value of 33.93 cm in winter, respectively. This result indicated that there was no significant difference between clarity of the Lake either in summer or in winter in the studied Lake locations.
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* Electrical conductivity (EC) values of investigated water locations were found to be higher for Nehayet Canat Taher water samples in summer (3.67 mmohs /cm) and Gezzeret El-Kotalah in winter (6.11 mmohs /cm); while they were lowest in Masraf Edku samples (1.55 and 1.5mmohs/cm) in summer and winter, respectively. Generally, their levels for all samples were above WHO and ES permissible limits (0.5-1.0 mmohs/cm).
* There was no significant difference between the values of EC during summer and winter in the selected locations.
1.2. Chemical parameters:
The chemical parameters of water quality in the selected water sampling location were determined and the results showed that:
* pH values of the Lake waters at investigated locations were within the standard values of WHO and ES. They were generally in the neutral and slightly alkaline side being ranged between 7.76 - 8.87 with mean value of 8.55 in summer and from 7.26 to 7.8 with mean value of 7.41 in winter. This indicates moderately high alkalinity from the selected locations of the Edku Lake, and provides a natural protection against acid precipitation.
* The statistical analysis results showed that there was high significant difference between pH values among the studied seasons in all selected locations.
* Total alkalinity levels of investigated water samples ranged from 163.6 to 307 mg/L with mean value of 223.44 mg/L in summer and from 239.36 to 370.2 mg/L with mean value of 298.69 mg/L in winter. These results revealed that total alkalinity concentrations were higher in collected water samples during
winter than that during summer. The highest values (307 and 370.2 mg/L) were recorded for Nehayet Canat Taher water samples in summer and winter, respectively, while the lowest one (163.6 mg/L) was for Nehayet Bab Hassan samples in summer. These calculated levels of total alkalinity were within the MPLs of WHO (100-500 mg/L).
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* There was a significant difference between the values of total alkalinity during summer and winter seasons of all selected locations.
* Total hardness concentration values in water samples ranged between 109.21 to 196.8 mg/L with mean value of 141.38 mg/L in summer and between 114.21 to 282.68 mg/L with mean value of 185.72mg/L in winter. The maximum concentration was recorded in Nehayet Canat Taher water samples in winter (282.68 m/L), while the minimum level was found in El-Shalasheel in summer (109.21 mg/L). All water sample values were within the WHO standard limits (100-500 mg/L) and less the Egyptian Standards (ES) (300-400 mg/L CaCO3).
* There was no significant difference between the values of total hardness during summer and winter in the studied locations.
* Chloride ion concentration values for water samples were 283 and 283 mg/L and the maximum values were 992 and 1840 mg/L in summer and winter, respectively. These results revealed that the concentrations were higher in winter than in summer. These results also show that most water samples have Cl concentration levels above the ES limit (250-350 mg/L) and permissible limits of WHO (200-600 mg/L).
* There was no significant difference between the chloride values among both summer and winter in the selected locations.
* Dissolved Oxygen (DO) is an important measurement of aquatic health, since aquatic organisms must get all of their oxygen from water. Our results recorded DO concentrations ranged between 6.0 to 14.8 mg/L with mean value of 10.17 mg/L in summer and 5.2 to 26.0 mg/L with mean value of 16.46 mg/L in winter.
* There was no significant difference between the values of DO during summer and winter in the Lake locations.
* Biological/ Biochemical Oxygen Demand (BOD) measures how much oxygen is consumed by bacteria as they break down pollution and organic matter in the water. It is measured by observing how much dissolved oxygen levels
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decrease in a sealed sample over a 5-day period. The results summarized the concentration values of BOD at all investigated water sampling locations. No concentrations of BOD were detected in Gezzeret El-Kotalah, Gezzeret Deyab and El-Shalasheel water samples during the summer season. This means that these locations were less polluted than the other locations.
* No significant difference between the values of BOD during summer and winter seasons in all selected locations.
* Chemical Oxygen Demand (COD) was measured in the water samples and the average values were 74.74 and 75.2 mg/L in summer and winter, respectively.
* There was no significant difference recorded between the COD values of water samples in different selected locations during summer and winter seasons.
* It could be concluded that the overall pollutant concentrations in the studied Lake varied from location to another according to the comparison of the detected concentrations with those of the national and international standards. Any way if there is pollution even with low concentration, it will be the most suggestive essential cause of deterioration of water quality for different water supplies and then affect on its fitness for use in different purposes of drinking, domestic, irrigation and industry.
2. Monitoring of pesticides in different samples:
Organochlorine pesticides (OCPs) were analyzed in different selected sampling sites of Edku Lake using gas chromatography equipped with Ni 63 electron capture detector (GC-ECD).While OPs were analyzedby gas chromatography equipped with flame photometric detector (GC-FPD).
2.1. Monitoring of organochlorine pesticide residues in water samples:
Organochlorine pesticide residues of water samples collected from selected regions of Edku Lake during summer 2004 and winter 2005 were analyzed by GC-ECD and the results indicated that:
* The average recoveries of OCPs were ranged from 87.0 to 94.0 %, 80.0 to 89.6 % and 76.0 to 91.6 %, from water, sediment and fish samples, respectively.
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* The detection limits of OCPs ranged from 0.04 to 0.32 ng/L in water, 0.04 to 0.08 ng/kg in sediment (dry weight) and 0.04 to 0.06 ng/kg in fish
* Total DDTs (o, p´-DDT; p, p´-DDT; p, p´-DDD; and p, p´-DDE) were detected in all water samples during winter season with concentrations ranged from 0.299 to 13.3 ppb. In summer season they detected in water samples of Nehayet Bab Hassan; El-Shalasheel and Masraf Edku with levels ranged between 0.52 to 2.374 ppb, while they absent in Nehayet Canat Taher and El-Boughaz samples.
* Total HCHs (-HCH; -HCH; - HCH (lindane) and -HCH) were completely absent from all water samples of the tested locations in both summer and winter.
* The total aldrins (aldrin and dieldrin) were detected in all water sampling locations in winter season with ranges from 0.067 –0.85ppb, while, they were not detected in Masraf Edku water samples in summer season and detected in samples of the other locations with values varied from 0.225 to 0.713ppb.
* Total heptachlors (heptachlor and heptachlor-epoxide) were detected only in water samples of Nehayet Canat Taher with level of 0.468 ppb, in summer and absent from samples of the other locations in both seasons.
* Endrin was observed in the water samples of El-Shalasheel with levels of 2.16 and 0.245ppb in summer and winter, respectively while, it was detected in winter in El-Boughaz and Masraf Edku samples with concentrations of 1.098 and 0.095 ppb respectively.
* Chlordane was detected only in El-Shalasheel water samples in winter season with value of 1.204 ppb.
2.2. Monitoring of organochlorine pesticide residues in sediment samples:
OCP concentrations in all sediment samples from the selected locations of Edku Lake during summer 2004 and winter 2005 were determined and the results indicated that:
* Total DDTs were detected in all sediment samples with varied concentrations. In winter season the highest value of these pesticides was 12.56 ppb in Nehayet Canat Taher sediment samples, and the lowest value was 0.2 ppb in Masraf Edku
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samples, while in summer the highest value (15.33ppb) was detected in El-Shalasheel samples and the lowest value (0.21 ppb) was found in Masraf Edku samples.
* Total HCHs were detected in Nahayet Bab Hassan, El-Shalasheel, El-Boughaz and Masraf Edku sediment samples in summer season with level values ranged
from 40.0 to 118.0 ppb, while they were absent from samples of these locations in winter season. Total HCHs were not observed in Nehayet Canat Taher samples either in summer or in winter.
* Total aldrins were observed in Nahayet Bab Hassan and El-Boughaz sediment samples in summer season with level values of 113.0 ppb and 2.0 ppb, respectively while they were not detected in samples of the other locations in both seasons.
* Total heptachlors were observed in all sediment sample locations in summer with concentration values ranged from 0.2 to 14.33 ppb, while in winter they were completely absent from Nehayet Canat Taher, Nehayet Bab Hassan and El-Shalasheel samples and detected in El-Boughaz and Masraf Edku samples with concentration values of 2.87 and 18.13 ppb, respectively.
* Endrin was found in Nehayet Canat Taher, Nehayet Bab Hassan, El-Shalasheel and Masraf Edku sediment samples in summer with rates of 2.4, 0.24, 2.53 and 0.113 ppb, respectively while it was absent from samples of all selected locations in winter season. Chlordane was appeared in Nehayet Canat Taher and Nehayet Bab Hassan in summer with values of 3.466 and 3.4 ppb, respectively, while it was detected in El-Boughaz samples with value of 76.57 ppb in winter season.
2.3. Monitoring of organochlorine pesticide residues in fish samples:
* The results indicated that the total DDTs were detected in all analyzed fish samples from all selected locations in summer and winter seasons with rates ranged between 0.4 to 37.13 ppb, followed by total aldrins that detected in most samples (0.604 to 13.6 ppb), while absent from Nehayet Canat Taher and El-Boughaz samples in winter and summer, respectively.
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* Total HCHs were observed in Nehayet Canat Taher, El-Boughaz and Masref Edku fish samples in summer with levels of 1.33, 2.0 and 1.466 ppb, respectively and absent from samples of these sites in winter. They were found in El-Shalasheel samples in winter season (0.561 ppb) and not detected in the summer of this location. Also, they were completely absent from Nehayat Bab Hassan samples in the two seasons.
* Total heptachlors were detected in El-Boughaz fish samples with level values of 7.466 and 0.213 ppb in summer and winter, respectively and in El-Shalasheel samples with rate of 3.6 ppb in summer, while they were completely disappeared from samples of the other locations either in summer or winter.
* Endrin was appeared in Nehayet Bab Hassan fish samples with concentrations of 5.66 and 3.362 ppb in summer and winter, respectively while it was found in Nehayet Canat Taher and Masraf Edku samples with rates of 6.145 and 6.43ppb
in winter, and it was completely disappeared from samples of the other locations in both seasons.
* From these results, it could be concluded that the OCPs in all selected locations of Edku Lake were detected with varied concentrations in the different contaminated samples of the Lake during the studied seasons.
3. Monitoring of organophosphorus pesticide residues in different samples:
Organophosphorus pesticides are less persistent in water, soil, and food for animals than the organochorine pesticides; however they are relatively soluble in water and are highly toxic. They break down into nontoxic metabolites and detected with low concentrations in drinking water, surface water or groundwater
OPs were analyzed in different samples by GC-FPD and the results indicated that:
* The average recoveries of organophosphorus pesticides (OPs) were ranged between 91 to 97 % in water samples, 85.3 to 88.6 % in sediment samples and 78 to 83 % in fish samples. While the detection limits of these pesticides were 0.4 to
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1.2 ng/L, 0.6 to 1.5 ng/kg (dry weight) and 2.0 ng/kg in water, sediment and fish (dry weight), respectively.
* There was trace amounts of organophosphorus pesticide residues were detected in the different samples from all selected locations represented Edku Lake either during summer or winter season.
4. Frequency % of pesticides in different samples:
4.1. Frequency % of each pesticide in different samples:
The frequency % of each organochlorine or organophosphorus pesticide in water, sediment and fish samples was calculated. The frequency % of the contamination was found with varied percentages in relation to site and season of sampling. The results indicated that there was contamination with these pesticides in some sampling sites, while it was completely absent in some others.
In water samples:
* The following OCPs were frequently detected with 100 % : p, p´- DDE and p, p´- DDD in Nehayet Bab Hassan and El-Shalasheel samples, respectively; aldrin in each of Nehayet Canat Taher, Nehayet Bab Hassan, El-Shalasheel and El-Boughaz samples and endrin in El-Shalasheel samples.
* This indicates that there was completely contamination with these monitored pesticides in water samples of these mentioned locations.
* The following OCPs were frequently detected with 50%: o,p´-DDT in Nehayet Bab Hassan and El-Shalasheel samples ; p,p’-DDT in El-Shalasheel and Masraf Edku samples ; p,p´- DDD in Nehayet Canat Taher, El-Boughaz and Masraf Edku samples ; p,p´- DDE in Nehayet Canat Taher, El-Shalasheel and Masraf Edku samples; chlordane and dieldrin in El-Shalasheel samples; heptachlor in Nehayet Canat Taher and endrin in El-Boughaz and Masraf Edku samples.
* The contamination with total HCHs was completely disappeared from all water sampling locations.
In sediment samples:
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* Most of the OCPs were frequently observed in 50% of cases.
* The highest frequency % (100%) was noticed for p, p´- DDD in Nehayet Canat Taher and Nehayet Bab Hassan and for o, p´-DDT and heptachlor in El-Boughaz and Masraf Edku samples, respectively.
In fish samples:
* The highest frequency % of OCPs (100%) were recorded as follow: for o, p´-DDT; dieldrin and endrin in Nehayet Bab Hassan samples, for p, p´- DDD; chlordane and heptachlor in El-Boughaz fish samples, for p, p´- DDE in Nehayet Canat Taher, for aldrin in El-Shalasheel samples, and for p,p’-DDT in Masraf Edku fish samples.
* From these results it was clear that most investigated fish samples were completely contaminated with one or more of these monitored pesticides.
* In the case of organophosphorus pesticides, the data showed negligible frequency % of these pesticides at all selected locations. There was slightely high contamination with these pesticides in sediment samples if compared with those in water or fish.
* Chlorpyrifos was frequently detected with 100% in Nehayet Bab Hassan and El-Boughaz sediment samples, followed by (50%) for dimethoate in El-Shalasheel and El-Boughaz samples; malathion and chlorpyrifos-methyl in Nehayet Bab Hassan samples and at last dichlorofos in Nehayet Canat Taher sediment samples.
* In water samples the only organophosphorus pesticide profenofos was frequently detected with 50% in El-Shalasheel and Masraf Edku samples.
* In fish samples chlorpyrifos-methyl and profenofos were frequently observed with 50% in El-Boughaz and Nehayet Bab Hassan samples, respectively.
4.2. Frequency % of contaminated samples:
The frequency % of contaminated samples with either OCPs or OPs in each season was recorded. The results showed that:
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* In water samples, and in summer season the data showed that the highest frequency percentage of OCPs contaminated samples was 42.9 % and detected in El-Shalasheel samples followed by 21.4% in Nehayet Bab Hassan, and 14.3% in Nehayet Canat Taher water samples, while the lowest percentage was 7.14 % and observed in El-Boughaz and Masraf Edku water samples.
* In winter season, data recorded that the highest frequency percentage of OCPs contaminated samples was 35.7 % and detected in El-Shalasheel samples, followed by 28.6% in Masraf Edku ; 21.4 % in Nehayet Canat Taher and El-Boughaz water samples, while the lowest percentage was 14.3% and detected in Nehayet Bab Hassan water samples.
* In sediment samples, the frequency % of the contaminated samples with OCPs was higher in summer than in winter season.
* In summer season the highest frequency percentage of the samples contaminated with OCPs was 42.9% and noticed in Nehayet Bab Hassan samples, followed by 35.7% in sediment samples of the other locations.
* In winter season the highest frequency percentage of the OCPs contaminated samples was 21.4% and observed in El-Boughaz samples, followed by 14.3% in Nehayet Canat Taher and Nehayet Bab Hassan samples, while the lowest percentage was 7.14 % in El-Shalasheel and Masraf Edku sediment samples.
* In fish samples the data indicated that:
* The highest frequency percentage of the OCPs contaminated samples was 35.7 % and recorded in El-Boughaz fish samples during summer and winter, followed by 28.6 % in El-Shalasheel samples in both seasons.
* The frequency % was also 28.6% in Nehayet Canat Taher and Masraf Edku samples in summer and in Nehayet Bab Hassan samples in winter season, while, the lowest frequency % of the OCPs contaminated samples was 21.4% and observed in Nehayet Bab Hassan samples in summer and in Nehayet Canat Taher and Masraf Edku samples in winter season.
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* Also, the results showed that the frequency % of different contaminated samples (water, sediment, and fish) with organophosphorus pesticides were absent from most sampling locations in both summer and winter seasons. The contamination was slightly higher in sediment samples than that in water and fish samples.
* It was clear from these results that contamination of different samples with organochlorine pesticides was higher than those with organophosphorus pesticides in all selected locations. It may be due to the persistent and bioaccumulation of the organochlorine pesticides, while rapidly biologically and chemically degradation of the organophosphorus in the environment.
5. Monitoring of heavy metals in different samples:
The heavy metals were determined in different selected sampling locations of Edku Lake during summer 2004 and winter 2005.The analysis was conducted by Atomic Absorption Spectrometer.
5.1. Monitoring of Heavy metals in water samples:
The concentrations of heavy metals were determined in water samples and the results showed that:
* The level values of iron were higher in summer than those in winter. They ranged between 0.22 to 0.9 mg/L with mean value of 0.373 mg/L in summer and from 0.01 to 0.09 mg/L with mean value of 0.071 mg/L in winter season. The iron concentrations in water samples were within the maximum permissible levels (MPLs) of WHO and ES in summer season, while they were below these levels in winter season.
* The statistical analysis results indicated that there was high significant difference between the concentration values of iron in all water samples during summer and winter
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* The copper concentrations were higher in winter than in summer with averages values of 0.009 and 0.059 mg/L in summer and winter, respectively. The detected copper levels were below the WHO and ES recommended levels in summer season, while they were within the MPLs of WHO and below the ES levels in winter season.
* There was high significant difference between copper concentrations in the water samples among summer and winter seasons
* There was no significant difference detected between the zinc values in all water samples either in summer or in winter, where mean values recorded 0.053 and 0.059 mg/L in summer and winter, respectively. The concentration values of all water samples were below the MPLs as recorded by WHO and ES.
* The detected concentration levels of cadmium were within the MPLs of WHO and above those of ES.
* There was no significant difference were detected between the concentrations of cadmium in all water samples during the two studied seasons
* Lead concentration values were higher in summer than those in winter. They ranged between 0.92 to 1.11 mg/L with mean value of 0.984 mg/L and between 0.02 to 0.8 mg/L with mean value of 0.516mg/L in summer and winter, respectively. As shown from these results the lead levels were above the MPLs of WHO and ES.
* There was high significant difference between lead concentrations in water samples during the summer and winter.
* The concentration values of nickel in water samples were ranged from 0.21 to 0.61 mg/L with mean value of 0.386 mg/L in summer and from 0.11 to 0.45 mg/L with mean value of 0.227mg/L in winter. These nickel levels were above the MPLs of ES.
* There was significant difference between the level values of nickel in the water samples during summer and winter.
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* From these results it was noticed that the metals Fe, Pb and Ni were detected in selected water samples with levels higher than that in Cu, Zn and Cd.
5.2. Monitoring of Heavy metals in sediment samples:
* The results showed that the detected levels of iron in all sediment sampling locations were very higher in summer than those in winter.The levels ranged from 1940 to 3980 mg/kg with mean value of 3361.4 mg/kg in summer and from 458 to 897mg/kg with mean value of 604.6 mg/kg in winter.
* The statistical analysis results showed that there was high significant difference between the values of iron in sediment samples in summer and winter seasons
* The copper concentrations in sediment samples were higher in winter than those in summer. The mean values were 6.46 and 14.06 mg/kg in summer and winter, respectively.
* There was significant difference between copper concentrations in the sediment samples among summer and winter seasons.
* The highest concentration values of zinc (37.86 mg/kg) were recorded for Masraf Edku sediment samples in summer and 56.05 mg/kg for Nehayet Bab Hassan in winter. While the lowest values were 21.17 and 4.72 mg/kg for El-Boughaz samples in summer and winter, respectively.
* There was no significant difference between zinc levels in the sediment samples during the studied seasons.
* The cadmium concentrations in sediment samples of all selected locations were higher in winter with mean value of 2.77mg/kg than those detected in summer season with mean value of 0.969 mg/kg.
* There was high significant difference between the concentration values of cadmium in sediment samples during the summer and winter seasons.
* There was high significant difference was recorded between the concentration levels of lead in all sediment samples either in summer or in winter seasons. The lead concentrations were relatively higher in summer than in winter.
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* Nickel concentrations of sediment samples were ranged from 0.13 to 0.398 mg/kg with mean value of 0.271 mg/kg in summer and from 0.273 to 1.6 mg/kg with mean value of 0.583mg/kg in winter.
* No significant difference was recorded between the nickel levels in the sediment samples during the two studied seasons.
* From these results it was clear that Fe was detected with levels much higher than those of the other metals in all selected sampling locations.
* Also, it could be noticed from the results that the concentrations of all detected heavy metals were higher in Masraf Edku sediment samples than those in other locations, particularly during summer. It may be due to that Masraf Edku is considered one of three main drains discharge about 90% of the water into the
Lake included large amounts of pollutants from industries and other contamination sources.
5.3. Monitoring of Heavy metals in fish samples:
* The highest concentration of iron in fish samples (197 mg/kg) was detected in El-Shalasheel samples, and the lowest concentration (63.1 mg/kg) was in Gezzeret Deyab samples during summer season. While, in winter season the higher level (78.9 mg/kg) was observed for Masraf Edku samples, and the lowest level (64.1 mg/kg) was in Gezzeret El-Kotalah samples.
* The statistical analysis results indicated that there was significant difference between the concentration values of iron in fish samples during summer and winter seasons
* The concentration values of copper were higher in winter with mean value of 13.05 mg/kg than those in summer with mean value of 4.1 mg/kg.
* There was high significant difference detected between the concentrations of copper in fish samples in summer and winter
* The level values of zinc metal in fish samples were higher in summer with mean value of 10.51 mg/kg than those in winter with mean value of 4.22 mg/kg.
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* There was high significant difference detected between the concentrations of zinc in fish samples in summer and winter
* The results indicated that there were higher cadmium concentrations in winter than in summer. The mean values were 1.49 and 0.663 mg/kg in winter and summer, respectively.
* There was high significant difference detected between the levels of cadmium in fish samples during the studied seasons
* In summer the highest lead concentration (1.53 mg/kg) was for Gezzeret El-Kotalah samples and the lowest value (0.794 mg/kg) was for Nehayet Bab Hassan samples, while in winter the highest value (2.094 mg/kg) was found in Nehayet Bab Hassan samples and the lowest (0.807 mg/kg) was detected in Nehayet Canat Taher samples.
* No significant difference was recorded between the concentration values of lead in fish samples in summer and winter seasons
* The nickel concentrations in all sampling locations were ranged from 0.112 to 0.487mg/kg with mean value of 0.304 mg/kg in summer and from 0.093 to 0.277mg/kg with mean value of 0.195 mg/kg in winter.
* No significant difference was recorded between the concentration values of nickel in fish samples in summer and winter seasons
* From these results, it was clear that the levels of heavy metals in all sampling locations affected by locations and seasons. Some metal concentrations were higher in summer season, may be due to the high temperature which increases the solubility of metals, while some other were higher in winter season.
6. The role of certain microorganisms in pesticides degradation:
A study was conducted to evaluate the role of some isolated microorganisms in the degradation of the organochlorine pesticide dieldrin and the organophosphorus pesticide chlorpyrifos on nutrient agar medium for bacteria and PDA medium for fungai.
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6.1. Capability of microorganisms for growing and utilize pesticides as a sole carbon source:
The results indicated that:
* There are only four starins from the isolated strains could be growing without inhibition, while other strains showed different trend. These growing strains were: Bacillus subtillus (M1); Escherichia coli (M2); Aspergillus flavus (M3) and Trichoderma sp (M4).
* It was clear that these isolated strains may be the highest degradability for the pesticides than the other isolated strains.
6.2. Biodegradation of pesticides by microorganisms:
The biodegradation rate of chlorpyrifos or dieldrin by the selected microorganisms was calculated in this study and the results indicated that:
* The disappearance rate of chlorpyifos was higher than that of dieldrin, and the isolated starin B. subtillus was the greatest potential one than the other strains in the pesticides degradation .
* The calculated half-life values of chlorpyrifos were 7.66, 7.12, 9.33 and 10.47 days , while they were 9.33, 9.86, 12.49 and 22.43 days for dieldrin by B. subtillus (MI), E. coli (M2), A. flavus (M3) and T. sp. (M4), respectively.
* In control treatment, the degradation rate of tested pesticides was slower and the half-life values were 105 and 147.5 days for chlorpyrifos and dieldrin, respectively.
* The obtained results showed that bacteria and fungi play an important role in the degradation of pesticides. It may be due to the hydrolytic enzymes, which excreted by many microorganisms, and these enzymes are capable of hydrolyzing pesticides.
* The activity of isolated growing microorganisms in the pesticides degradation followed the order: B. subtillus (MI) > E. coli (M2) > A. flavus (M3) > T. sp. (M4).