2.1 Location

The study area occupied the middle part of the Nile Valley between longitudes 30^∘29^′ and 30^∘54^′ E and latitudes 27^∘37^′ and 27^∘56^′ N (Fig. 1). It is bounded by the River Nile from the east and the calcareous plateau in the west between Abu Qurqas northward and Dyer Mawas in the south. The water resources in the study area are represented by the River Nile, canals, drains, as well as groundwater (Fig. 1). The stratigraphic succession (Fig. 2) in the El-Minya area is represented by Tertiary and Quaternary sedimentary rocks (Said, 1981). The main aquifer in the study area is represented by Pleistocene sediments which are composed of sand and gravel of different sizes with some clay intercalation (Sadek, 2001). The aquifer is semi-confined in the old cultivated land (in the eastern part of the study area) and unconfined in the desert fringes (in the western part of the study area). The groundwater generally flows from the southern part to the northern part of the study area. The aquifer is recharged by Nile water, irrigation systems, drains, agricultural infiltration, and vertical upward from the deeper saline aquifers (Abdalla et al., 2009). The main sources of water for different purposes in the study area are the Nile, canals, drains, and groundwater. The study area contains many industrial zones, agricultural activities, and urban areas.

Figure 1Location map of the study area.

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Figure 2Geologic map of the study area.

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2.2 Sampling and analyses

In November 2014, 30 water samples were collected from surface water resources in the study area (Fig. 1 and Table 1). In addition, 25 groundwater samples were collected from the Quaternary aquifer (Fig. 1). Pre-rinsed polypropylene bottles were filled with the samples, acidified (pH < 2) with nitric acid to prevent precipitation and microbial activity and sorption losses to container walls, and were sealed tightly. At the lab the samples were filtered through filter paper (Whatman no. 42) and digested with nitric acid (APHA, 1995). Samples were analyzed using an atomic absorption spectrometer instrument (model: Perkin Elmer 400) in the National Research Centre Laboratories.

For health risk assessment, non-carcinogenic (HQ_nc) and carcinogenic (HQ_c) hazard quotients for each contaminant were calculated according to the following equations (Kelepertzis, 2014):

where CDI, C, IR, ED, EF, BW, AT, and RfD represent chronic daily intake (mg kg⁻¹ d⁻¹), concentration of metal in water (mg L⁻¹), average daily intake rate (2 L d⁻¹ for adults and 1.2 L d⁻¹ for children), exposure duration (15 years), exposure frequency (350 d), body weight (70 kg for adults and 28 kg for children), average time (ED*365 d for non-carcinogenic and lifetime*365 for carcinogenic risk) and toxicity reference dose. According to the USEPA (2011), the RfD for Cd and Pb are 0.0005 and 0.055 mg kg⁻¹ d⁻¹, respectively, and the slope factor (SF) is 0.38 and 0.055 mg kg⁻¹ d⁻¹, respectively. The average lifetime for an adult is 65, and 6.5 years for children.

Table 3Cd and Pb concentrations (µg L⁻¹) in the studied groundwater samples.

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3.1 Surface water

The River Nile and its tributaries (canals and drains) are the main source of water in Egypt, especially for the governorates located on the river banks and on its branches. Cd concentrations (Table 2), ranging from 1 to 48 µg L⁻¹, exceeded the permissible limit (3 µg L⁻¹) for drinking water according to the WHO (2011). Excess Cd could accumulate in the kidneys and remains for many years, causing irreversible kidney damage (Goyer, 1996). The number of kidney patients in the study area is presumed to have increased from 10 patients per million in 1974 to about 165 patients per million in 1995, and in 2005 it was 260 patients per million in El-Minya Governorate (El-Minshawy and Kamel, 2006). The highest concentration of Cd was recorded in sample number S₈, 48 µg L⁻¹, close to Abu Qurqas Sugar factory (Al-Shiekh Sharf canal). The lowest concentration was recorded in sample number S₆ (1 µg L⁻¹), which was collected from the River Nile. These results are in line with those obtained by Toufeek (2011), who recorded an average Cd concentration of 12.5 µg L⁻¹ at Aswan (southern Egypt), while Melegy et al. (2014) found that the Cd levels in the collected samples from Sohag Governorate were around 16 µg L⁻¹. Osman and Kloas (2010) mentioned that the average Cd concentration in the River Nile at Assuit was 6 µg L⁻¹.

Figure 3Spatial distribution map of Cd in the studied groundwater samples.

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Pb concentration ranged from 54 to 329 µg L⁻¹ in the studied surface water samples (Table 2). The concentration of Pb passed the permissible limit (10 µg L⁻¹) for drinking water according to the WHO (2011). Pb adsorbed by the human body disturbs many body processes and is harmful to many organs and tissues such as the heart, bones, and nervous system (Bruce et al., 2012). The highest concentration of Pb was recorded in sample number S₂₈ (329 µg L⁻¹) from Al-Nasriyah canal, while sample number S₆, which was collected from the River Nile in Abu Qurqas district, contained the lowest concentration (54 µg L⁻¹). These results are in agreement with those obtained by Toufeek (2011), who reported about 214 µg L⁻¹ Pb in the River Nile at Aswan. In addition, Osman and Kloas (2010) proved that the average Pb concentration in the River Nile at Assuit was nearly 24 µg L⁻¹.

Agricultural activities are considered the most important source of Cd and Pb, where the used super-phosphate fertilizers in the study area contain about 8.5 and 16 ppm Cd and Pb, respectively (Asmoay, 2017). In addition, vehicle exhaust, industrial activities, and urban runoff contribute to a great extent to the pollution of water with these metals (Elnazer et al., 2018).

3.2 Groundwater

Groundwater is the second important water resource in the study area, and it is used for irrigation as well as for domestic use and drinking in desert fringes and some villages which do not have access to drinking water. The groundwater samples exhibit a relatively wide range of the Cd level, varying from 2 to 49 µg L⁻¹ with a mean value of 24 µg L⁻¹ (Table 3). The groundwater Cd level decreased eastward (Fig. 3), probably due to mixing with the surface water from the River Nile and the role of the silty clay layer in the adsorption of Cd, which prevent it from reaching the aquifers (Asmoay, 2017). However, there were three hotspots of Cd identified, resulting from intensive human activities and fuel stations (Asmoay, 2017). The Cd hotspot in the northwestern part of the study area adjacent to the western desert road is vulnerable as a result of the unconfined condition of the aquifers (Asmoay, 2017).

Also, the measured Pb contents of the analyzed groundwater samples show a relatively wide range varying from 90 to 410 µg L⁻¹ with an average of 242 µg L⁻¹ (Table 3). The marked high level of Pb content implies that the anthropogenic activities (agricultural and urban runoff) are the main sources of Pb. The results are in agreement with Melegy et al. (2014), who mentioned that Cd and Pb concentrations in the groundwater of Sohag were around 21 and 383 µg L⁻¹, respectively. The Pb level in the groundwater of the study area was increased in Abu Qurqas district, resulting from the effect of the sugar factory, cesspits, and fuel stations (Asmoay, 2017) as shown in Fig. 4.

Figure 4Spatial distribution map of Pb in the studied groundwater samples.

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All the samples were unsuitable for drinking purposes where they possess Cd and Pb values above the permissible limit of 3 µg L⁻¹ for Cd and 10 µg L⁻¹ for Pb (WHO, 2011). On the other hand, surface water and groundwater were suitable for irrigation purposes according to NAS-NAE (1973), since they contain less than 10 and 5000 mg L⁻¹ of Cd and Pb, respectively.

3.3 Health risk assessment

Water from the River Nile and canals as well as groundwater are used for drinking and domestic purposes. The applied treatment techniques (flocculation and coagulation with alum) in drinking water stations (Donia, 2007) in the study area are effective for the removal of toxic metals bound to suspended solids (Fatoki and Ogunfowokan, 2002). However, it was observed that a great number of residents in rural areas use groundwater from hand pumps for drinking because they do not have access to the tap water. El-Minshawy and Kamel (2006) mentioned that the use of unsafe water for drinking contributes up to 71.8 % of the renal failure in the study area. Therefore, health risk assessments of surface water and groundwater were also carried out in this study. The results of HQ_nc and HQ_c due to metal exposure in surface water and groundwater samples are provided in Tables 4 and 5.

Table 4Statistical parameters of non-carcinogenic and carcinogenic health risks for surface water samples.

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Table 5Statistical parameters of non-carcinogenic and carcinogenic health risks for groundwater samples.

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The calculated HQ_nc average values for Cd in surface water for adults and children were 1.30 and 1.96, respectively, while HQ_nc average values for Pb were 0.11 and 0.17 (Table 4). On the other hand, the calculated HQ_nc average values for Cd in groundwater for adults and children were 1.29 and 1.94, respectively, while HQ_nc average values for Pb were 0.12 and 0.18 (Table 5). According to the USEPA (2011), Cd can cause non-carcinogenic health problems because its HQ_nc values were more than 1, while Pb presence in water had no adverse health impacts (HQ_nc < 1), although its concentration did exceed WHO (2011) guidelines.

The calculated HQ_c values for Cd in the surface water for adults ranged from $\mathrm{0.17}\times {\mathrm{10}}^{-\mathrm{4}}$ to $\mathrm{7.9}\times {\mathrm{10}}^{-\mathrm{4}}$ and for children from $\mathrm{0.1}\times {\mathrm{10}}^{-\mathrm{5}}$ to $\mathrm{4.8}\times {\mathrm{10}}^{-\mathrm{3}}$ (Table 4). The calculated HQ_c values for Pb varied from $\mathrm{6.2}\times {\mathrm{10}}^{-\mathrm{3}}$ to $\mathrm{37}\times {\mathrm{10}}^{-\mathrm{3}}$ for adults and varied from $\mathrm{3.7}\times {\mathrm{10}}^{-\mathrm{2}}$ to $\mathrm{22}\times {\mathrm{10}}^{-\mathrm{2}}$ for children (Table 4), while the calculated HQ_c values for Cd in the groundwater ranged from $\mathrm{4.8}\times {\mathrm{10}}^{-\mathrm{6}}$ to $\mathrm{1.2}\times {\mathrm{10}}^{-\mathrm{4}}$ for adults and from $\mathrm{2.9}\times {\mathrm{10}}^{-\mathrm{5}}$ to $\mathrm{7.11}\times {\mathrm{10}}^{-\mathrm{4}}$ for children (Table 5). The calculated HQ_c values for Pb varied between $\mathrm{3.13}\times {\mathrm{10}}^{-\mathrm{5}}$ and $\mathrm{14.3}\times {\mathrm{10}}^{-\mathrm{5}}$ for adults and varied from $\mathrm{1.67}\times {\mathrm{10}}^{-\mathrm{9}}$ to $\mathrm{86.1}\times {\mathrm{10}}^{-\mathrm{5}}$ for children (Table 5). According to USEPA (2011) recommended values (HQ_c < 10⁻⁶), the studied surface water and groundwater consumption could cause carcinogenic health risks in adults and children.