Ground water samples were taken from Algezira Islanj in from four stations (A, B, C and D) and Huraizab two stations (E and F), the depth between 13-20 m. Water samples were taken after allowing the water pumps, from wells, to run for short time to remove the first water flushes, one and a half liters were collected in clean plastic bottles and half liter were collected in clean glass bottles. The bottles were rinsed twice with water before collection, and the samples are acidified with 1.5 ml of nitric acid per liter, closed and immediately transported to laboratory for physical and chemical analysis. These samples are stored at 4°C before analysis. The samples were collected during the month of July 2020.
The pH, Electrical conductivity, and total dissolved solid were measured in the field. The pH was measured using (portable-jenway pH meter). Electrical conductivity and total dissolved solid were measured using HQ30d-HACH conductivity meter. Turbidity was measured using TL2360-HACH Turbidity meter. Total hardness of water expressed as calcium carbonate, measured by Ethylene diamine tetra acetic acid EDTA titrimetric method. Alkalinity, calcium content and chloride were determined by titration method. Magnesium was determined by subtracting the calcium hardness from total hardness as mg / L. Sodium and potassium were determined by using Flame photometric method (Flame photometer). Nitrate, ammonia, Phosphate and Silica were determined by using spectrophotometer DR HACH (5000). Iron, Zinc, Lead, Arsenic and Nickel were determined by using inductively coupled plasma mass spectrometry (ICP-MS).
Table 1 showed pH values, electrical conductivity (EC), total dissolved solid (TDS) and turbidity levels.
Table 1. pH, electrical conductivity (EC), total dissolved solid (TDS) and turbidity levels for six water samples collected from Al gezira Islanj and Huraizab areas, Omdurman Sudan.
Parameter
|
A
|
B
|
C
|
D
|
E
|
F
|
pH
|
7.20
|
7.10
|
7.00
|
7.10
|
7.10
|
7.10
|
EC
|
813
|
402
|
853
|
451
|
868
|
595
|
TDS
|
534
|
226
|
503
|
247
|
508
|
319
|
Turbidity
|
13.40
|
7.10
|
21.40
|
9.20
|
1.84
|
1.02
|
The levels of alkalinity (Table 1 supplementary materials), total dissolved solids and hardness in all samples were in the range. All the pH values, electrical conductivity (EC), total dissolved solid (TDS) fall within the acceptable level of WHO (1993) and SSMO (2002) standards (6.5-8.5).
The readings of turbidity in ground water from Algezira Islanj stations (A, B, C and D) fall above the maximum level of WHO (1993) and SSMO (2002) standards (≥ 5 NTU), while the readings of turbidity in ground water from Huraizab water stations (E and F) fall in the range. The highest value of turbidity (21.40NTU) was found in (A) sample, while the lowest value (1.02NTU) was found in (F) sample. High turbidity of water is often associated with high levels of disease causing organisms such as viruses, parasites and bacteria responsible for symptoms such as nausea, cramps and diarrhea [8].
The total hardness and alkalinity readings fall below the maximum level of WHO (1993) and SSMO (2002) standards for maximum level (500mg/L)
The highest values of concentrations of chloride, ammonia, phosphate, silica and nitrate in (mg/L) were found in station (E), (F), (D), (F), and (A) respectively (Figure 1 supplementary materials). Except ammonia all these readings fall below the maximum level of WHO (1993) and SSMO (2002) standards for maximum level (500mg/L). Ammonia content from Huraizab samples were higher than the maximum value (1.5mg/L). Presence of ammonia in ground water may be attributed to natural minerals or through pollution by application of fertilizer, sewage and industrial waste [9].
Table 2. Iron, zinc, lead, arsenic and nickel values present in six water samples collected from Al gezira Islanj and Huraizab areas, Omdurman Sudan
Parameter
|
A
|
B
|
C
|
D
|
E
|
F
|
Iron
|
0.837
|
1.352
|
0.753
|
0.947
|
0.656
|
0.616
|
Zinc
|
1.670
|
2.340
|
3.020
|
0.120
|
1.350
|
1.270
|
Lead
|
0.278
|
0.270
|
0.275
|
0.274
|
0.279
|
0.271
|
Arsenic
|
0.286
|
0.260
|
0.278
|
0.293
|
0.277
|
0.301
|
Nickel
|
0.117
|
0.122
|
0.123
|
0.119
|
0.125
|
0.116
|
From (Table 2) the highest values for iron, zinc, lead, arsenic, and nickel were found in station (B), (C), (E), (F) and(C) respectively. Except zinc, all these readings of trace elements fall above the maximum acceptable level, of WHO (1993) and SSMO (2002) standards. Lead concentration scale in all studied samples are exceeding compared WHO Standards, all water samples were shown Lead contain in levels above the maximum contaminant Level (0.01mg/L) with the maximum concentration detected being (0.279 mg/L), these results are of concern as lead has been recognized for centuries as a cumulative general metabolic poison [10]. High values may be due to the effects of discharge of industrial effluents compounds including heavy metals [11]. As well as with reduced intelligence quotient in children and with attention disorders Lead enters into environment from industry, mining, plumbing, gasoline, coal, and as a water additive [12]. The elevated levels of arsenic in the study area may be due to its evaporative environment since the climate of this region is arid which can lead to more loss of water by evaporation than its gain by rainfall. Arsenic contamination is also strongly associated with high concentrations of iron, phosphate, and ammonium ions, and anthropogenic activities such as excessive groundwater withdrawal for agricultural irrigation [13]. The major source of metal pollution in water is use of pesticides in the form of calcium arsenate, lead arsenate, sodium arsenate and arsenic acid (Figure 2 supplementary materials) [14]. Iron is the second most abundant metal in the earth’s crust. it may be released to water from natural deposits, industrial wastes, refining of Iron ores, and corrosion of Iron containing metals. The maximum allowable limit for Iron as per WHO guidelines is (0.3 -0.947 mg/L), Iron concentration levels in all studied samples are exceeding then compared WHO Standards. Nickel concentrations in groundwater depend on the soil use, pH, and depth of sampling, the primary source of nickel in drinking-water is leaching from metals in contact with drinking-water, such as pipes and fittings. However, nickel may also be present in some groundwater as a consequence of dissolution from nickel ore-bearing rocks. Acid rain increases the mobility of nickel in the soil and thus might increase nickel concentrations in groundwater [15].
Limitations
This work concluded that groundwater in the study area is chemically unsuitable for drinking use. The analysis of water samples revealed that the groundwater samples from almost all the locations is highly contaminated with some heavy metals, turbidity and ammonia. It is recommended to carry out a continuous water quality monitoring program and development of effective management practices for utilization of water resources. However due to lack of some lab facilities and more sophisticated and advanced equipment, as well as lack of funding.