1. Introduction

Water pollutants affect directly and/or indirectly consumers’ health and should not exceed international allowable limits [1]. In Egypt, the agricultural sector consumes about 67000 million m³ (about 86%) of water resources [2]. Irrigation water is provided mainly from the River Nile with fewer amounts from groundwater and rain [2]. Along with water shortages in Egypt, its quality is degraded with waste from agricultural, industrial, and municipal effluents [3]. Industrial and municipal wastewaters are considered important pollutants, especially for drinking and irrigation water [4]. Contamination of water canals by industry- and public-originated wastes is due to irresponsible or negligent practices. Such activities intensify pollution problems of water, such as impaired biological oxygen demand (BOD), suspended matter, bacteria, metals, and chemicals [5]. Also, agrochemicals including pesticides and fertilizers exert short- and long-term effects on water quality [6-8]. Persistent (POPs) and volatile (VOPs) organic pollutants and pesticides might be leached from agricultural or urban areas causing contamination of the aquatic systems [6-13].

Pesticides, including the organochlorines might accumulate in food chains; for example, DDT was found in shrimp and fish at 1,000 to 10,000-fold of its concentration in water [14-22]. Monitoring pesticides and other pollutants in agricultural irrigation streams would enlighten officials about possible intervention methods to lessen potential adverse effects and type of environmental pollutants. With a limited number of environmental screening studies about sources and types of water pollutants in Egypt, the objective of the current study was to evaluate the water quality of El-Mahmoudia stream at El-Beheira Governorate, Egypt as a main irrigation canal in Northern Egypt via the estimation of physicochemical characteristics, persistent and/or volatile organic pollutants, plasticizers, plant residues, and pesticide residues.

2. Materials and Methods

2.1 Materials

Nitric acid, MacConky broth w/Natural Red medium, sodium sulfate (anhydrous), acetonitrile, ethyl acetate, hexane, and methylene chloride were HPLC-grade and were obtained from local reputed chemical distributors. Pesticides reference standards (Table 1) were purchased from ULTRA Scientific Analytical Solutions, RI, USA.

2.2 Location of study area

El-Mahmoudia canal (77 km long) starts from the Westside of Rosetta branch and ends at Alexandria harbor. It provides irrigation water for an area of 285,714 Feddans (120,000 Hectares) and provides water for municipality and industrial activities in both Alexandria and El-Beheira Governorates. Moreover, it provides water to 67 branch canals that provide water to more than 90 villages [3].

*Numbers between brackets represent the limits of quantification (LOQ; µg L^-1)

Table 1: List of scanned for pesticides in water samples that were collected in Autumn (A), Winter (W), Spring (SP), and Summer (SU) seasons using the GC-MS.

2.3 Collection of water samples

Water samples were collected over one year starting in December 2016 to August 2017 representing Winter, Spring, Summer, and Fall of 2017. Samples of 2.5 L each were collected from a mid-point of El-Mahmoudia canal in clean Pyrex borosilicate brown glass bottles at 50 cm below the water surface. The bottles were transported to the laboratory and filtered, then analyzed for water pollutants, including plant residues (secondary metabolites), pesticide residues, and domestic and industrial effluent pollutants within 3 hrs of collection. The physicochemical, microbiological characteristics and mineral contents were estimated on water samples collected during the Autumn season due to elevated contamination levels compared to other seasons.

2.4 Gas chromatography-mass spectrometry (GC-MS) analysis of pollutants and pesticides residues extraction

A modified solid phase extraction (SPE) technique using the Empore disc technology, according to EPA 353523 was used. The disks were washed with 5 ml of a 1:1 mixture of ethyl acetate and methylene chloride (ETAC:MeCL2). Water samples were extracted under vacuum for about 10 min, then disks were rinsed with two 3 ml portions of 1:1 ETAC:MeCL2. Combined eluates were passed over sodium sulfate (anhydrous). Gently, the extract was dried over a water bath under a stream of nitrogen to a volume of 0.5 to 1 mL. The concentrated extract was injected into the GC-MS. To check the recovery of the internal standards, aliquots of the standard were added to the blank (distilled) water and is passed through the same extraction process.

2.5 Separation and estimation conditions

Water extracts and recovered samples (2 µL) were analyzed using GC-MS equipped with Varian 8200 autosampler, which was operated in splitless mode. An HP-5MS capillary column (30 m × 0.53 mm i.d. 0.25 um film thickness) was used to separate the components. Helium was used as the carrier gas. Separation conditions were as follows: initial column temperature set at 80°C for 6 min. It was increased to 215°C at 15°C min^-1 (hold for 1 min), then to 230°C at 5°C min^-1 and finally to 290°C at 5°C min^-1 (hold for 2 min). The carrier gas was at a constant flow rate of 1.1 mL min^-1. The GC-MS was controlled by a computer system, which has EI-MS libraries. The target compounds were identified by their full mass spectra scans and retention time using the total ion current as a monitor to give a total ion chromatogram (TIC). The use of the full scan mode allowed the contrast of the spectrum of obtained compounds with the EI-MS libraries. Pollutants and pesticide compounds identified on NIST 14, Willey 9, and PEST database libraries. Then individually listed compounds were re-confirmed through the online databases: AMDIS, PUBCHEM, ChemSpider, and Chinese Chemical database.

2.6 Method and machine precision

The precision of the analytical method was confirmed through the repeatability (intra-day assay) and intermediate precision (inter-day assay) [24]. The precision was expressed as coefficient of variation percentages ((mean/standard deviation) × 100). The limits of quantification (LOQs) were calculated from the signal-to-noise (S/N) ratios of the samples with the lowest concentration level of the same studied pesticides. Fortified water samples (0.1 and 1 µg L^-1 of pesticide standards) were extracted and analyzed as previously mentioned. The average recovery percentages and the percent relative standard deviation (%RSD) for recoveries were calculated. All data of pesticide residue analysis were corrected according to these obtained recovery percentage values.

2.7 Heavy metals measurements

Determination of heavy metals: copper (Cu), ferrous (Fe), manganese (Mn), potassium (K), sodium (Na), calcium (Ca), chlorine (Cl), lead (Pb), and cadmium (Cd) were done following the method of APHA [25, 26] using the Atomic Absorption Spectrophotometer (Model Thermo Scientific ICE 3000 series).

2.8 Physicochemical analyses

Temperature, pH value, electric conductivity (EC), total dissolved solids (TDS), total solids (TS), turbidity, dissolved oxygen (DO), biological oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), ammonium (NH₄), nitrate (NO₃?), chloride, carbonate, and bicarbonate were measured according to the reference methodology reported by APHA [25]. Data were expressed as mg L^-1 and compared to the listed permissible limits of APHA, FAO, and WHO [25, 27, 28].

2.9 Microbiological examination

The multiple tube fermentation technique was carried out to estimate the most portable number (MPN) of the total microbial count according to APHA [25] using MacConky broth w/natural red (HIMEDIA M007) medium. Aliquots of 1 mL of each of serial dilution of the water samples were added to each of 3 tubes containing 9 mL of McConkey broth. Cultural characteristics observed after incubation at 35-37°C for 18-24 hrs.

2.10 Statistical analysis

Data were analyzed using the Statistical Analysis System (SAS, Cary, USA, version 9.3) software. The physicochemical parameters, heavy metals, and pesticide residues were presented as mean ± SD. Significant means were compared using Tukey’s Studentized Range (HSD) post-hoc Test (P ≤ 0.05). Plant residues and plasticizers were reported in tables when the probability of a match with the reference database libraries exceeds 70% probability.

3. Results

3.1 Accuracy and precision of GC-MS method

The results of precision and repeatability (intra-day assay and inter-day assay) of the employed method were presented in Table 2. Also, the recovery percentages of standard pesticides ranged from 92 to 102 % (Table 2). Data showed that the developed method was precise as the coefficient of variation (CV%) values were less than 10% [24, 29]. These results demonstrate that the analytical method is reliable and effective.

*Inter-assay and intra-assay precision data obtained from the analysis of the concentrations of each standard pesticide in fortified laboratory blank water samples.

Table 2: Coefficients of variation (CV%) and recovery (%) percentages ± RSD for the pesticides that were extracted from spiked blank water (distilled) samples.

3.2 GC-MS analysis of water pollutants

Data in Figure 1 and Tables 3, 4, 5, and 6 showed the combined results of the GC-MS analysis of pollutants in water samples during winter, spring, summer, and autumn seasons. Various organic chemicals, pesticides, oils, fatty acids, carboxylic acids, plant metabolites, and plasticizers were identified and confirmed using NIST 14, WILEY 9, and PEST mass spectral libraries.

3.3 Pesticide residues

Results in Table 3 and Figure 1 lists the detected pesticides’ residues and limits of quantification. Out of the organochlorine insecticides (OC) screened for, only p,p-DDE, p,p-DDD, and dieldrin were detected at different concentrations at the four seasons but at lower levels than the ADI permissible limits. The first two compounds were adducts of DDT that was banned worldwide in the previous century. Also, out of the pesticides mix (insecticides, fungicides, nematicides, acaricides, and herbicides) that were studied, the organophosphate insecticide chlorpyrifos-methyl was detected only during Summer and Autumn seasons. Noticeably, levels of chlorpyrifos-methyl were greater during the Summer compared to autumn.

Figure 1: List of groups of plant metabolites, pesticides, plasticizers, saponins, surfactants, and triglycerides detected in water samples (n=4) collected on Autumn, Winter, Spring, and Summer seasons and verified in the Willey 9, NIST 14, and AMIDS 32 metabolite databases.

n=4, Means were compared using Tukey’s Studentized Range (HSD) post-hoc Test (P ≤ 0.05). Means with the same superscript letter are not significantly different.

Table 3: List of the detected pesticides in water samples that were collected from all-Mahmoudia canal in Autumn (A), Winter (W), Spring (SP), and Summer (SU) seasons using the GC-MS.

3.4 Triglycerides, plant residues, and phthalates (domestic waste)

Results in Figure 1 and Table 4 showed the presence of 2',6'-dihydroxyacetophenone, bis(trimethylsilyl) ether, 9,12-octadecadienoic acid (Z,Z)-, 2,3-bis[(trimethylsilyl) oxy]propyl ester, n-hexadecanoic acid, 2,3-bis[(trimethylsilyl) oxy]propyl (9E,12E,15E)-9,12,15-octadecatrienoate, 6,9,12,15-docosatetraenoic acid, methyl ester, cyclopropaneoctanoic acid, 2-octyl-, methyl ester, 16-octadecenoic acid, methyl ester, pentadecanoic acid, methyl ester, 9,12,15-octadecatrienoic acid, 2,3-bis[(trimethylsilyl)oxy]propyl ester, (Z,Z,Z), oleic acid, 3-(octadecyloxy)propyl ester, olean-12-ene-3,15,16,21,22,28-hexol, (3β,15α,16α,21β,22α), oleic acid, eicosyl ester as the major compounds detected mostly during Winter, Spring, and Autumn. Also, results in Figure 1 and Table 5 showed the presence of various residues of plants: hydrocarbon alkanes, flavonoids, prostaglandins, steroids, alkaloids, sterols, retinoids, amino acids, eicosenoic acids, triterpene, and terpenoids. Moreover, most of the organic pollutants detected using the GC-MS data analysis were identified as endocrine disrupting phthalate esters, fatty acids, phenolic acids, and plasticizers (Figure 1 and Table 6) including decamethylcyclopentasiloxane, 1-(2-acetoxyethyl)-3,6-diazahomoadamantan-9-one oxime, nonadecane, 2',6'-dihydroxyacetophenone, bis(trimethylsilyl) ether, 4H-1-benzopyran-4-one,2-(3,4-dimethoxyphenyl)-3,7-dimethoxy-,11,16-bis(acetyloxy)-3,20-dioxopregn-4-en-21-yl acetate, 9,12-octadecadienoic acid (Z,Z)-, 2,3-bis[(trimethylsilyl) oxy]propyl ester, m-dioxane, 5-(hexadecyloxy)-2-pentadecyl-trans-dodecamethylcyclo hexasiloxane, 2-(9-bora bicyclo[3.3.1]non-9-yloxy)-3-([2-(9-borabicyclo[3.3.1]phenylnon-9-yloxy)ethyl]sulfanyl) propyl ether.

¹Detected and ²Not detected

Table 4: List of triglycerides detected in water samples (n=4) collected from El-Mahmoudia canal on Summer (SU), Autumn (A), Winter (W), and Spring (SP) seasons and verified in the Willey 9, NIST 14, and AMIDS 32 metabolites databases.

3.5 Physicochemical characteristics of water samples

Results in Table 7 showed that the turbidity value was 84% greater than of the permissible limits of the guidelines of WHO with 9.17 NTU. Such elevated levels of turbidity correspond to increased suspended materials that reduce light penetration and restrict plant growth and hence food resources and habitat for water organisms. Also, suspended solids concentration in El-Mahmoudia stream was 51 mS cm^-1, which was within the permissible limits of Egyptian law 48/1982 (<100 mg L^-1). The pH value was found to be low compared to the reference values and that might be due to the drainage of organic matter [60-63]. The BOD was significantly increased (138% greater than the reference limits) with 23.75 mg L^-1. The mean value of COD was 24.75 mg L^-1, which was 65% greater than the standard levels (Egyptian Law 48/1982), which was <10-15 mg L^-1. All previously mentioned results significantly affected microbiological level (MPN) in El-Mahmodia stream to a level (12075 cm^-3) that exceeded the limits of Egyptian Law 48/1982 (5000 100 cm^-3).

¹Detected and ²Not detected

Table 5: List of plant residues detected in water samples (n=4) of El-Mahmoudia canal on Summer (SU), Autumn (A), Winter (W), and Spring (SP) seasons and verified in the Willey9, NIST14, and AMIDS32 metabolites databases.

¹Detected and ²Not detected

Table 6: List of saponins, plasticizers, and surfactants detected in water samples (n=4) collected from El-Mahmoudia canal on Summer (SU), Autumn (A), Winter (W), and Spring (SP) seasons and verified in the Willey 9, NIST 14, and AMIDS 32 metabolites databases.

¹EC-Electrical Conductivity; TDS-Total Dissolved Solids; TSS-Total Suspended Solids; TS-Total Solids; DO-Dissolved Oxygen; BOD-Biological Oxygen Deman; COD-Chemical Oxygen Demand; and MPN-Most Probable Number (concentration of viable microorganisms). Capital letters after each value corresponding to the referencing association: A-FAO (1985); B-Law 48/1982; C-WHO (1993); D-the guidelines of WHO (Chapman 1992); and E-APHA (1992).

Table 7: Physicochemical characteristics of water samples (n=4) of El-Mahmoudia stream that were collected during the autumn season of 2017 and compared to the reference recommended limits.

3.6 Mineral content of water samples

Mineral contents of Na, K, Ca, Mg, Fe, Mn, Cd, and Cl in water samples were less compared to the standard permissible limits with averages of 49.1, 7.99, 31.80, 56.40, 0.65, 0.09, and 0.002 mg L^-1, respectively (Table 7). The total alkalinity (HCO₃ content) in water samples of El-Mahmoudia stream was 253.3 mg L^-1. HCO₃ exceeded the permissible limits of the Egyptian Law (48/1982), which is <200 mg L^-1. Ammonia levels were elevated (NH₄; 1.42 mg L^-1) compared to the set limits (Table 8). But phosphates (PO₄) were decreased to about 0.01 mg L^-1 (10 times less than the permissible values).

4. Discussions

The results reported herein showed the presence of organic chemicals, pesticides, oils, fatty acids, carboxylic acids, plant metabolites, and plasticizers in El-Mahmoudia water stream. These results were in agreement with results of Fishbein [30], APRP [31], and Saeed and Shaker [32]. The various types of pollutants might alter the aquatic environment and affect the aquatic organisms [33, 34]. Industrial wastewater was considered as a major source of pollution of Nile. There are about 129 factories discharging wastewater into the River Nile. However, wastewater effluents are partially treated [35]. In 2000, it was estimated that the total amount of reused treated wastewater in Egypt was about 1.4 billion m³ [36]. Pesticides might leach to the water stream from irrigation water. Presence of pesticide residues, that were reported herein, were reported in other water resources in Egypt [37, 38]. About 16 OC pesticides were reported in the drains including BHC and DDT [6, 12]. Sometimes the amounts that have been detected were higher than the allowable limits for healthy water streams [39-41]. Additionally, the elevated levels of chlorpyrifos-methyl in Summer compared to autumn might be due to the application of great amounts of the insecticide to control various insects on summer crops (tomato, melons, corn, and potatoes) [42]. It was noticed that season has some effects on the levels of pesticide residues. Water samples collected in Summer had increased concentrations of pesticide residues compared to the Autumn, Spring, and Winter. These results were consistent with what was found by Azab et al. [43]. They reported that in Summer, organochlorines were significantly higher in water samples.

*Capital letters after each reference value corresponds with referencing association: A-Law 48/1982; B-WHO (1993); C-BIS (2012); D-USEPA (2001); and E-Biernbaum (1995).

Table 8: Mean ± SD values of heavy metals and mineral salts in water samples (n=4) of El-Mahmoudia canal that were collected during the autumn season of 2017 and compared to assigned reference values.

Triglycerides, plant residues, and phthalates result from domestic and industrial effluents and significantly affect the quality of water. Triglycerides such as grease, oil, and fatty acids were described as major pollutants from such effluents [37, 38, 44, 45, 46]. Kandil and Abu-Taleb [47] reported that food industry discharges had significant effects on water quality. High levels of oil and grease were reported at Assiut and El-Menia [35]. Most of the organic pollutants were identified as endocrine disrupting phthalate esters, fatty acids, phenolic acids, and plasticizers that were classified as “priority pollutants” due to their severe toxicity [48]. Perceptibly, phthalates, common plasticizers, are used to impart flexibility to plastics, e.g. polyvinylchloride (PVC). It reaches the environment through volatilization, degradation, and/or leaching from plastics and drainage of industrial wastewater. Their widespread usage and stability marked them as major environmental contaminants [49]. Bioaccumulation of such compounds causes reproductive, developmental, mutagenic, genotoxic and endocrine disrupting effects to humans, animals, and aquatic organisms [50-54]. The 2,6-dihydroxybenzoic acids, that were detected in the water samples, are key metabolites of the polyaromatic hydrocarbons during wastewater treatment [55]. Moreover, it has been added to personal care products including shampoos, skin creams, cosmetics, and deodorants [56, 57]. Benzene acetonitriles and other benzyl compounds are considered as moderate to low toxicants to aquatic animals and were classified as Group 2A carcinogen [55, 58].

The physicochemical parameters of water samples were altered due to various charges of pollutants into the water stream. It was clear that various physicochemical parameters including EC, pH, TDS, turbidity, TSS, TS, DO, BOD, COD, and MPN of viable microorganisms indicate the stream water quality [27]. pH value was found to be low compared to the reference values and that might be due to the drainage of organic matter [60-63]. Chapman [61] reported that clean and wastewater had BOD values of 2 and 10 mg L^-1, respectively. The BOD values of waters of El-Mahmoudia stream exceeded the limits of the Egyptian Law (48/1982). The COD is an indicator of oxidation of the organic and inorganic materials in water and sewage [66]. Total suspended particles were the main source of turbidity in water that interferes with the penetration of light and affects the water salinity [59]. High inorganic matter and nutrient waste discharges might decrease the DO concentrations because of the increased microbial activity (respiration) [64, 65]. In another study, levels of BOD and COD were reported to be higher than the permissible levels at El-Gharbia, Dakahleya, and Damietta, which was an indication of pollution with non-degradable chemicals [35]. The increased values oxygen-related characteristics indicate the excessive content of the biodegradable organic matter that increases de-oxygenation of water to the level that aquatic life cannot survive [67]. However, fecal coliform was reported as a major pollutant in rivers and water streams, where it originates mainly from human sources [68].

Heavy metals concentrations were reduced to less than 33% for all studied elements. Only, the Cu element was increased compared to the standard value. Its content was 10 times greater than the permissible limit of the Egyptian Law (48/1982), WHO [28], and USEPA [48]. The elevated concentration of HCO₃ might be attributed to the decomposition of the dead phytoplankton leading to the release of CO₂. It exceeded the permissible limits of the Egyptian Law (48/1982), which is <200 mg L^-1. Also, elevation levels of ammonia as a result of the agricultural practices and municipal or industrial discharges [59]. Clearly, the results reported herein showed low levels of heavy metals including Cd but not for Cu. Such low values of the heavy metals (except for Cu) might be due to their deposition with sediments (silt) on the stream’s bottom [69, 70, 71]. Also, contamination with Cu in El-Mahmoudia stream might be from the discharge of domestic wastewater, manufacturing processes, steam, electrical production, the dumping of sewage sludge, and Cu-fungicides application [72]. Also, elevated levels of nitrite and total alkalinity that exceeded the standard values were reported at El-Gharbia governorate [35], which might be a result of over-use of plant fertilizers. But phosphates (PO₄) were decreased to about 0.01 mg L^-1 (10 times less than the permissible values).

5. Conclusions

Organic and inorganic pollutants: pesticides, plasticizers, plant residues were detected. Turbidity, BOD, COD, NH₄, HCO₃, MPN, and Cu were at levels above the standard safety guidelines of the Egyptian irrigation ministry laws, WHO, and FAO. Moreover, water pollutants such as heavy metals and organic pollutants occurred due to mixing domestic and industrial wastewater with agricultural water. However, all drains of Upper Egypt flow back to the Nile and many irrigation canals are contaminated with pollutants from domestic sources. The Ministry of the Environment in Egypt is observing the enforcement of the legislation regarding the treatment of industrial and domestic wastewater. It is also advocating organic farming and limiting the use of chemical fertilizers and pesticides to reduce water pollution. Moreover, specific wastewater treatment projects were established, such as the wastewater treatment plant at El-Gabal El-Asfar and the sludge conversion plants in Nawaq and El-Minia. Yet, the current study highlights important findings that would be of great help for the planning to implement more plants of wastewater treatment along the river Nile, especially in the Northern parts of Egypt.

Significance Statements

The current study revealed that the water quality of El-Mahmoudia canal is contaminated with elevated levels of organic and inorganic pollutants: pesticides, plasticizers, plant residues compared to standard safety permissible guidelines. Apparently, mixing of domestic and industrial wastes with agricultural water causes serious pollution problems.

Conflict of Interest

The authors declare no conflict of interest

Co-authors Contributions

E.R.: proposed the research problem, conducted the physicochemical and microbiological analyses and revised the manuscript; E.E.: proposed the research problem and revised the manuscript; A.N.: conducted GC/MS analyses, run statistical analysis of results, and wrote and submitted the manuscript; Y.S.: proposed the research problem, run the elemental analysis and revised the manuscript; H.H.: proposed the research problem and revised the manuscript; K.A.A.: proposed the research problem and revised the manuscript; and N.A.H.: conducted the experiments and wrote the first draft of the manuscript.

Acknowledgments

The authors would like to thank the Pesticide Residue Analysis and Toxicity Laboratory, Faculty of Agriculture, Damanhour University for the GC-MS analysis. Also, the authors would like to express their sincere thanks for the Water Analysis Laboratory, Ministry of Water Resources and Irrigation for the analysis of minerals and the physiochemical Parameters.

References

1. Van Eck W. International Standards: The International Harmonization of Pesticide Residue Standards for Food and Drinking Water, in Denis Hamilton and Stephen Crossley. Pesticide Residues in Food and Drinking Water: Human Exposure and Risks, Chapter 10. John Wiley and Sons Ltd, ISBN: 0-471-48991-3 (2004).
2. FAO, Food and Agriculture Organization of the United Nations, Egypt (2016).
3. Moghazy HM, Saleh OK, Abd El Azim NF. Hydraulic Analysis Of El Mahmoudia Canal. WIT Transactions on Ecology and The Environment 178 (2014): 41-52.
4. Mckee JE, Wolf HW. Water quality criteria, (2^nd Edn.), State Water Resources Control Board Publication, No. 34, California (1971): 23-25.
5. Schwarzenbach RP, Egli T, Hofstetter TB, et al. Global Water Pollution and Human Health. Annu Rev Environ Resour 35 (2010): 109-136.
6. El-Kabbany S, Rashed MM, Zayed MA. Monitoring of the pesticide levels in some water supplies and agricultural land, in El-Haram, Giza (A.R.E.). J Hazard Mater 72 (2000): 11-21.
7. Mansour SA, Mahram MR, Sidky MS. Ecotoxicological studies. Monitoring of pesticides residues in the major components lake Qarun. J Egypt Acad Soc Environ Dev 2 (2001): 83-116.
8. Jadwiga P, Sebastian M, Malgorzata W, et al. Survey of Persistent Organochlorine Contaminants (PCDD, PCDF, and PCB) in Fish Collected from the Polish Baltic Fishing Areas. The Scientific World Journal (2010): 1-7. 9.       Abd-Allah AM, Ali HA. Residue levels of chlorinated hydrocarbon compounds in fish from El-Max Bay and Marut Lake, Alexandria, Egypt. Toxicol Environ Chem 42 (1994): 107-114.
9. Dogheim SM, El-Zarka M, Gad Alla S, et al. Monitoring of pesticide residues in human milk, soil, water, and food samples collected from Kafr El-Zayat Governorate. Journal of AOAC International 79 (1996): 111-116.
10. Abbassy MS, Ibrahim H, Abu El-Amayem M. Occurrence of pesticides and polychlorinated biphenyls in water of the Nile river at the estuaries of Rosetta and Damiatta branches, north of Delta, Egypt. J Environ Sci and Health Part B 34 (1999): 255-267.
11. Shukla MP, Pal Singh S, Nigam RC, et al. Monitoring of Human Diet for Organochlorine Insecticide Residues. Pesticide Research Journal 14 (2002): 302-307.
12. Osibanjo O. Persistent Organic Pollutants, Organochlorines in Nigeria and Africa. The Handbook of environmental chemistry 30 (2003): 495.
13. Public Health Service, US, Department of Health. Education and Welfare. Written Communication cited from Pesticides Monitoring Journal 10 (1974): 107.
14. FAO/WHO, Joint FAO/WHO Food Standards Programme Codex Alimentarius Commission Twelfth Session (1978): 1-74.
15. USEPA, Occurrence of pesticides in drinking water, food, and air. Washington, DC: USEPA office of drinking water (1983).
16. FDA, Food and Drug Administration, JAOAC 74 (1991): 121-141.
17. Abou-Arab AAK, Gomaa MNE, Badawy A, et al. Distribution of organochlorine pesticides in the Egyptian aquatic ecosystem. Food Chem 54 (1995): 141-146.
18. Roberts D, Dissanayake W, Sheriff MHR, et al. Refractory status epilepticus following self-poisoning with the organochlorine pesticide endosulfan. Journal of Clinical Neuroscience 11 (2004): 760-762.
19. Kelderman P, Xuedong Y, Drossaert WME. Sediment pollution with respect to heavy metals and organic micropollutants in the city canals of Delft (The Netherlands)-assessment of a database of 188 sediment stations. Hennef: European Water Association (EWA) (2005).
20. Agrawal A, Pandey RS, Sharma B, et al. Water Pollution with Special Reference to Pesticide Contamination in India. J Water Res and Prot 2 (2010): 432-448.
21. Karl H, Bladt A, Rottler H, et al. Temporal trends of PCDD, PCDF and PCB levels in muscle meat of herring from different fishing grounds of the Baltic Sea and actual data of different fish species from the Western Baltic Sea. Chemosphere 78 (2010): 106-112.
22. Tompkin S, Thomas M, Presty DF. Locking mechanism for a surgical fastening apparatus, U.S. Patent No. 5,106,008 (1992).
23. Ermer J. Performance parameters, calculations, and tests. In Ed.: Ed J Ermer, McB Miller JH. Method Validation in Pharmaceutical Analysis. A Guide to Best Practice. Weinheim: Wiley-VCH Verlag GmbH ad Co. KGaA (2005).
24. APHA-AWWA-WPCF, Standard methods for the examination of water and wastewater, (18^th Edn.) American Public Health Association, American Water Works Association and Water Pollution Control Federation, Washington, DC (1992).
25. Ediger RD. Atomic absorption analysis with the graphite furnace using matrix modification. At Absorption Newslett 14 (1975): 127-130.
26. FAO, Water quality guidelines for agriculture, surface irrigation and drainage. Food and Agriculture Organization Rev1 (1985): 29.
27. WHO, Guidelines for drinking-water quality, Second edition. Volume 1: Recommendations. World Health Organization, Geneva (1993): 188.
28. ICH, International conference on the harmonization of technical requirements for the registration of pharmaceuticals for human use. ICH harmonized tripartite guideline validation of analytical procedures: text and methodology Q2 (R1). Complementary Guideline on Methodology (2005).
29. FAO, Pesticides as water pollutants, Chapter 4 (1994).
30. APRP-Water Policy Activity Contract PCE-I-00-96-00002-00 Task order 22, Survey of Nile System Pollution Sources (2002).
31. Saeed SM, Shaker IM. Assessment of heavy metals pollution in water and sediments and their effect on Oreochromis niloticus in the northern delta lakes, Egypt. 8^th International Symposium on Tilapia in Aquaculture (2008): 475-489.
32. Oyewale AO, Musa I. Pollution assessment of the lower basin of Lakes Kainji/Jebba, Nigeria: heavy metal status of the waters, sediments and fishes. Environ Geochem Health 28 (2006): 273-281.
33. Hereher ME, Assessing the dynamics of El-Rayan lakes, Egypt, using remote sensing techniques. Arab J Geosci 8 (2014): 1931-1938.
34. Nile Basin Initiative (NBI), Nile Basin National Water Quality Monitoring Baseline Study Report for Egypt (2005).
35. Abdel-Gawad S, El-Sayed AI. The effective use of agricultural wastewater in the Nile river delta for multiple uses and livelihood needs. Final report, National Water Research Centre (2008).
36. Abdo MH. Distribution of some chemical elements in the recent sediments of Damietta brach, River Nile, Egypt. J Egypt Acad Soc Environ Dev 5 (2004): 85-104.
37. Abdel-Dayem S, Abdel-Gawad S, Fahmy H. Drainage in Egypt: a story of determination, continuity, and success. Irrig Drain 56 (2007): 101-111.
38. Ismail SS, Ramadan A. Characterization of Nile and drinking water quality by chemical and cluster analysis. Sci Total Environ 174 (1995): 69-81.
39. Mohamed MA, Osman MA, Potter TL, et al. Lead and Cadmium in Nile River Water and Finished Drinking Water in Greater Cairo, Egypt. Environ Int 24 (1998): 767-772.
40. Wahaab RA, Badawy MI. Water quality assessment of the River Nile system: an overview. Biomedical and Environmental Sciences 17 (2004): 87-100.
41. MALR, Catalog of recommended pesticides to control pathogenic-pests. Ministry of Agriculture and Land Reclamation, Cairo, Egypt (2017).
42. Azab MM, Darwish AA, Mahmoud, AH, et al. Study on the pesticides pollution Manzala Lake, Egypt. Journal of Applied Sciences 27 (2012): 105-122.
43. Abdel-Satar AM. Water quality assessment of River Nile from Idfo to Cairo. Egypt J Aquat Res 31 (2005): 182-199.
44. NAWQAM, Present status of water quality in Egypt. National Water Quality and Availability Management Project (NAWQAM), National Water Research Centre, Canadian Executive Agency, Assessment Interim Report (1998).
45. NAWQAM, Nile Research Institute data. National Water Quality and Availability Management Project (NAWQAM), National Water Research Centre. Egypt (2003).
46. Kandil H, Abu-Taleb M. Integrated Water Resources Management Plan-Ministry of Water Resources and Irrigation, Egypt. The World Bank (2005).
47. USEPA, Water quality standards (2001).
48. Saint-Laurent L, Rhainds M. Les phtalates: e´tat des connaissances sur la toxicite et l’exposition de la polulation generale. Institut national de sante publique, Quebec, Toxicologie humaine (2004).
49. Bang DY, Lee IK, Lee BM. Toxicological characterization of phthalic acid. Toxicol Res 27 (2011): 191-203.
50. Benli ACK, Erkmen B, Erkoç F. Genotoxicity of sub-lethal di-n-butyl phthalate (DBP) in Nile tilapia (Oreochromis niloticus). Arh Hig Rada Toksikol 67 (2016): 25-30.
51. Chen X, Xu S, Tan T, et al. Toxicity and Estrogenic Endocrine Disrupting Activity of Phthalates and Their Mixtures. Int J Environ Res Public Health 11 (2014): 3156-3168.
52. Zhao X, Gao Y, Qi M. Toxicity of phthalate esters exposure to carp (Cyprinus carpio) and antioxidant response by biomarker. Ecotoxicol 23 (2014): 626-632.
53. Aoki KA, Harris CA, Katsiadaki I, et al. Evidence suggesting that di-n-butyl phthalate has antiandrogenic effects in fish. Environ Toxicol Chem 30 (2011): 1338-1345.
54. Lee PY, Chen CY. Toxicity and quantitative structure-activity relationships of benzoic acids to Pseudokirchneriella subcapitata. J Hazard Mater 165 (2008): 156-161.
55. Horii Y, Kannan K. Survey of organosilicone compounds, including cyclic and linear siloxanes, in personal-care and household products. Arch Environ Contam Toxicol 55 (2008): 701-710.
56. Wang R, Moody RP, Koniecki D, et al. Low molecular weight cyclic volatile methylsiloxanes in cosmetic products sold in Canada: implication for dermal exposure. Environ Int 35 (2009): 900-904.
57. IARC, International Agency for Research on Cancer Working search on Cancer Working Group on the Evaluation of Carcinogenic Risks to Humans. IARC Monogr. Eval Carcinog Risks Hum (1991): 71.
58. Ayers RS, Westcot DW. Water quality for agriculture, in: Food and Agricultural Organization of the United Nations (FAO), irrigation and drainage paper 29 rev. 1. FAO, Rome (1985).
59. Allem AA, Samman AA. Productivity of Lake Mariut, Egypt, part I. Physical and Chemical Aspects. Int Revue Ges Hydrobiol 54 (1969): 313-355.
60. Chapman D. Water quality assessments, (1^st Edn.), Chapman and Hall, London and New York (1992).
61. El-Wakeel SK, Wahby SD. Texture and chemistry of Lake Mariut Sediments. Arch Hydrobiol 67 (1970): 173-200.
62. Murdoch T. Stream keeper’s field guide: watershed inventory and stream monitoring methods. Adopt-a-Stream Foundation, Lewiston (1991).
63. Cole GA. Textbook of limnology. Mosby, St. Louis (1979): 283.
64. El-Gamel A, Shafik Y. Monitoring of pollutants discharging to the River Nile and their effect on River Water Quality. Water Qual Bull 10 (1985): 101-106.
65. Peavy HS, Rowe DR, George T. Environmental engineering. McGraw-Hill Book, Singapore (1986).
66. El Bourie MMY. Evaluation of organic pollutants in Rosetta branch water-river Nile, M.Sc. Thesis. faculty of science, Tanta University, Egypt (2008).
67. Edberg SC, Rice EW, Karlin RJ, et al. Escherichia coli: the best biological drinking water indicator for public health protection. J Appl Microbiol Symp 88 (2000): 106-116.
68. Duffus JH. “Heavy metals” a meaningless term?. Appl Chem 74 (2002): 793-807.
69. Ikem A, Egiebor N, Nyavor K. Trace Elements In Water, Fish and Sediment from Tuskegee Lake, Southeastern Usa. Wat. Air Soil Pollut 147 (2003): 79-107.
70. Thornton JA, Rast W, Holland MM, et al. Assessment and control of nonpoint source pollution of aquatic ecosystem. Parthenon Press, Man and the Biosphere Series (MAB), UNESCO, Paris 23 (1999): 455.
71. Abdel-Moati MAR, El-Sammak AA. Man-made Impact on the Geochemistry of the Nile Delta Lakes. A Study of Metals Concentrations in Sediments. Water, Air and Soil Pollution 97 (1997): 413.