Appraisal of surface–groundwater anthropogenic indicators and associated human health risk in El Sharqia Governorate, Egypt

Water is an essential part of our life; however, freshwater makes up a tiny portion of only 0.01% of the entire amount of water on the earth's surface (Amini et al. 2016; Moghaddama et al. 2018) and the vast bulk of the water on the earth's surface is saline or salt water (with an average salinity of 35%). Increasing human population, rapid urbanization rate, and industrial expansion led to an increment of water necessities all over the world, especially in developing countries. Water resources can be surfaces such as lakes, canals, or groundwater that are buried under the ground surface in geological formations (aquifers). In general, two main constraining factors defining water suitability for different agricultural, domestic, and industrial purposes are water availability or quantity and quality. Relying on surface water alone is not sufficient to meet these demands because of its limitations and inadequacy in most arid and semi-arid areas of developing countries. Consequently, reliance on groundwater resources has dramatically increased in these regions (Zhou et al. 2020). However, human activities have negative impacts on groundwater quality. Several anthropogenic pollution sources were found to be responsible for deterioration of water resources in developing countries such as industrial wastewater discharges, use of fertilizers and pesticides, wastewater irrigation, and atmospheric transportation that have led to the accumulation of heavy metals in the soils worldwide, especially in developing countries. The risks to human health caused by exposure to heavy metals present should not be disregarded in light of the aforementioned issues. It is crucial to assess the level of heavy metal pollution in soil and agricultural regions as well as the potential health risks caused by these toxicants. Non-point source pollution from discharging wastewater is the greatest threat to the sustainable use of water resources (surface and groundwater) in megacities. Excess untreated wastewater from villages and rural areas in the majority of developing countries is frequently discharged directly into water pathways, while household, commercial, and industrial effluents, as well as raw, untreated sewage are frequently dumped into surface and groundwater sources. Rainstorms eventually wash the wastewater into the water bodies or it percolates there. Stagnating wastewater in open lagoons and on the sides of the road frequently serves as a mosquito-breeding ground and a haven for various germs and viruses. Additionally, harmful substances like oil and grease, insecticides, ammonia, and heavy metals are present in wastewater pools. When point source pollution is reduced in many countries (even if wastewater treatment plants (WWTPs) begin to reach their capacity limits), climate (global) change impacts could increase pollution due to urban or agricultural run-off. In recent years, groundwater investigations were paying attention to assessing and understanding the hydrochemical characteristics and water quality using several effective tools, including geochemical modeling, Geographical Information System (GIS), statistical approaches (multivariate statistical analysis), and water quality indices. Many factors control groundwater hydrochemistry including dissolution, precipitation, ion-exchange, sorption–desorption together with residence time along the flow path. A number of geochemical models were developed for tracing groundwater evolution along the flow path through inverse modeling or studying different mixing processes affecting the quality of water resources in the studied areas. The use of geochemical models is increasing in addressing groundwater quality problems involving geochemistry (Slimani et al. 2015; Berihu et al. 2017; Liu et al. 2020). Assessment of the contamination risk of water resources to human health is a useful technique for determining the potential negative consequences of environmental pollutants. This method has been used extensively to estimate the heavy metal contamination of drinking water and soils (Liu et al. 2016; Fakhri et al. 2018; Kamani et al. 2018; Keramati et al. 2018a, 2018b; Rezaei et al. 2018; Youssef et al. 2018). Recently, many studies have focused on this field (Sohrabi et al. 2016; Fakhri et al. 2018; Kamani et al. 2018; Keramati et al. 2018a, 2018b; Rezaei et al. 2018; Youssef et al. 2018) and this technique has been widely utilized to determine the level of heavy metal contamination of soils and drinking water (Liu et al. 2016, Fakhri et al. 2018). The main objectives of the present study is an integration of hydrochemical and multivariate statistical investigations to evaluate major and minor nutrients including chemical and trace elements measurements (ammonia, nitrate, phosphate, biological oxygen demand (BOD), chemical oxygen demand (COD), total organic carbon (TOC), oil, and grease) to identify anthropogenic indicators for surface and groundwater resources. There are also geochemical modeling applications, especially for mixing processes that affect the chemical composition and water quality of El Sharqia Governorate. Finally, we assess potential human health risk hazards of trace elements for different age groups of people including children and adults who probably rely on these water resources for different purposes.

As a result, clay was hydrogeologically partitioned from fluviatile deposits (river sands), fine to medium sands with thin intercalations of clay and silt, with a maximum thickness of around 30 m. This reflects the floodplain deposits of the former Damietta Branch. It symbolizes the upper, unconfined aquifer with intercalated clay. In the western regions, the ratio of sand to clay can exceed 50%, while it declines in the east and north. This series' alternation of coarse and fine particles supports the idea that these sediments date from the Late Pleistocene.

In the studied area, both anthropogenic and natural factors contributed to the contamination of the majority of the groundwater. Additional analysis, including chronic daily intake (CDI) and health risk index (HRI) calculations, should be made to determine how much human health risk exposure is there (HRI). The consumption rate of element concentrations and the kind of toxicity are the key determinants of chronic health risk indices related to water consumption.

In this formula, CPTMs stand for PTM concentrations, DIPTMs for daily water intake and bw for body weight. For adults and children, respectively, the projected daily groundwater consumption rates were 2 and 1 l/day, while the assumed average body weights were 70 and 20 kg, respectively.

RfD stands for the reference dose. Based on the estimated results, it was stated that the HRI values less than 1 revealed that there was no risk to humans posed by the ingestion of groundwater through drinking. The United States Environmental Protection Agency (USEPA 2005) defined the RfD as ‘an estimate of a daily oral exposure to the human population that is likely to be without an appreciable risk of deleterious effects during a lifetime.’ HRI levels greater than 1, however, indicate a risk to human health.

Table 1 shows the descriptive statistics of the physicochemical characteristics and trace element results of drainage and groundwater collected in El Sharqia Governorate, with minimum, maximum, and average values for all parameters in the quaternary aquifer compared with guideline values set by the Environmental Protection Agency (USEPA 2009) and WHO WHO (2017) guidelines for drinking water purposes. These results indicate the following:

• The average pH of groundwater samples was 7.58, with values ranging from 7.06 to 8.19. The pH ranged from 6.54 to 7.6, with an average value of 7.08, for drainage water samples. The results showed circumstances that ranged from being slightly acidic to slightly alkaline, which may be related to pollution issues.

• The fact that drainage water had higher EC and TDS levels than groundwater may be attributable to anthropogenic pollution inputs. With an average of 1,373 μS/cm, the EC of drainage water ranged from 872 to 2,083 μS/cm. The average EC in groundwater samples was 1,124 μS/cm, with values ranging from 363 to 2,268 μS/cm. 19% of the collected samples had TDS values above the WHO (2017) standard limits for drinking water, which varied from 214 to 1,226 mg/l. TDS concentrations in drainage water samples ranged from 422 to 1,401 mg/l, exceeding WHO (2017) guidelines for drinking purposes by 12% (Table 1). In accordance with WHO salinity classifications from 2017, about 81% of groundwater samples and 89% of drainage water were categorized as fresh water, while 19 and 11%, respectively, were classified as somewhat saline.

• The relative abundance of major cations in shallow groundwater is Na⁺ > Mg²⁺ > Ca²⁺ > K⁺ (on a molar basis) and > Cl⁻ > for anions by 43 and 38%, respectively. For drainage water samples, the predominant cations are Na⁺ > Mg²⁺ > Ca²⁺ > K⁺ (on a molar basis) and > Cl⁻ > for anions by 51 and 57%, respectively.

• However, the maximum Ca²⁺ and Mg²⁺ concentrations in groundwater samples, 180 and 83 mg/l, respectively, are greater than WHO (2004) guideline limits by 38 and 62%, respectively. With the exception of sample number 54 (Na = 230 mg/l), the maximum sodium concentaration values are 230 mg/l within the established limits. However, groundwater samples have potassium concentrations of 57 mg/l, which are 14% higher than WHO (2004) limits. The maximum salt and potassium values in drainage water are 12 and 97%, respectively, above WHO guideline limits. ions present in shallow groundwater samples may be due to the dissolution of carbonate rocks, soils, and atmospheric carbon dioxide.

• The first dominating anion in the study area is the bicarbonate ion. The lacustrine deposits present in the quaternary aquifer may be the source of the majority of Cl⁻ in the groundwater. Sedimentary rocks like gypsum (CaSO₄.2H₂O) and anhydrite (CaSO₄), which permit active dissolving, leaching, and ion-exchange processes, are the most prevalent and significant occurrences of sulfate ions in the researched area. The breakdown of organic matter in the soil and the addition of leachable sulphate in fertilizers used in intensively farmed areas are two additional sources of sulphate addition to groundwater.

Using the PHREEQC software, a geochemical model was created for potential hydrochemical reactions along the flow routes (Parkhurst & Appelo 1999). Groundwater solutes may be produced by three geochemical processes: evaporation, carbonate dissolution/precipitation, and silicate weathering (Garrels & MacKenzie 1971). Table 2 shows statistical outcomes of the saturation index of drainage and groundwater samples using PHREEQC. The findings showed that several minerals and gases, such as cerussite, smithsonite, strontianite, witherite, anhydrite, gypsum, celesite, and halite, were undersaturated in the drainage and groundwater samples of the quaternary aquifer, requiring dissolution to bring them into equilibrium. Minerals/gases like calcite, dolomite, siderite, rhodochrosite, barite, and gibbsite have a propensity to precipitate in drainage and groundwater samples.

With support for a wide range of factors, SPSS version 22.0 software was used to perform mathematical and statistical computations on the data (Matiatos et al. 2014).

A statistical method for examining the correlations between numerous variables is factor analysis. This strategy entails minimizing information loss while condensing the data from a large number of original variables into a more manageable set of uncorrelated main components (factors) (Hair et al. 1992; Abu Salem et al. 2017; El Alfy et al. 2018).

Principal component analysis (PCA) was done to determine the mechanisms controlling ion concentrations. The factor loadings of each original variable were investigated after extracting factors with eigenvalues greater than 1 (Kaiser 1960). Eight distinct components that account for the majority of the variability were identified using eigenvalues and varimax rotation. According to Table 3, the overall variance for the water samples was around 73.17%. Statistically, the first dominant factor (F1) is responsible for 20.79% of the variance in the data. Strongly positive loadings on EC, TDS, hardness, Na, SO₄, Cl, and pH are characteristics of this component. pH has a substantially negative loading. This element, which might also be called the salinity factor, reveals the impact of lithogenesis on the groundwater. The influence of sewage contamination can be seen in the second factor (F2), which accounts for 10.02% of the overall variation. It exhibits high positive loadings on Al and COD as well as moderately positive loadings on nitrate and Cr. Additionally, the third factor (F3) exhibits substantial positive loadings on Fe and TSS, indicating anthropogenic input for these elements, and it describes 9.72% of the overall variance. A strong positive loading on Na, a moderately negative loading on Co, oil, and grasses, and a moderately positive loading on NO₂ are all displayed by the fourth factor (F4), which accounts for 7.98% of the overall variation. With a substantial positive loading on Ni and Zn, the fifth factor (F5), which explains 8% of the overall variance, demonstrates anthropogenic impacts on groundwater. The final factor (F6), which contributes 7% of the overall variation, exhibits a high negative loading on Cd and a moderately positive loading on Cr (Table 3).

The clustering procedure was carried out by the Ward's linkage approach using the Euclidean distance as a measure of sample similarity, which was based on the clustering Q-technique, in which similarity associations among water samples were explored. Figure 6 shows the dendrogram's findings. Based on the dendrogram classification, four preliminary groupings were chosen. With an average value for each metric shown in Table 4, each group represents a hydrochemical facies.

The first group of water, group 1, has salinity ranging from 422 to 810 mg/l with an average value of 605 mg/l with abundance orders (meq/l) of Na⁺ > Mg²⁺ > Ca²⁺ > K⁺ and > Cl⁻ > > ⁠. This water group is classified as alkaline earth water type. This is probably derived from carbonate precipitation. For group 2, the salinity of water samples varied from 773 to 1,051 mg/l with an average value of 898 mg/l, while for group 3, the salinity ranged from 214 to 338 mg/l with an average value of 284 mg/l (freshwater). For group 4 water samples, the cationic composition was dominated by Na⁺ and Mg²⁺ followed by Ca²⁺ and K⁺ and Cl⁻ > > > and high salinity ranged from 1,088 to 1,401 mg/l with an average value of 1,224 mg/l. Applying mixing process simulation between the four principal water groups using PHREEQC software is to indicate precisely the routes of mixing sources within the quaternary aquifer in El Sharqia Governorate. The geochemical modeling results shown in Table 5 illustrate that simulation of a double-mixing process (20% Group 1:80% Group 4) leads to calcium contents similar to those of samples 24 and 36. Also, mixing of 10% Group 1:90% Group 2 leads to chloride contents similar to those of samples 25, 35, 42, 46 and 49. Mixing of 90% Group 1:10% Group 2 gives sulphate contents similar to those of samples 28 and 53.

Results of the HRI of collected water samples reveal that all samples have HRI < 1 for all trace elements except Al and Pb which have HRI > 1 for both children and adults in drainage and groundwater samples. Spatial distribution of HRI values in Figures 9 and 10 of drainage and groundwater samples revealed that drainage water has higher HRI values than groundwater samples, especially near the drains with higher values for children than adults confirming that children are more sensitive to the adverse health effects of metals that have non-carcinogenic risks (USEPA 2012), because children are most likely to have oral intake by hand and mouth (Kusin et al. 2018).

Heavy metals such as Cr, Ni and Pb can potentially enhance the risk of cancer in humans (Tani & Barrington 2005). Long-term exposure to low amounts of toxic elements could result in many types of cancer diseases. Using Cr, Ni, and Pb as carcinogens, the total exposure of the residents was calculated for groundwater samples used for drinking purposes as shown in Table 7.

For one heavy metal, an ILCR less than 1 × 10⁻⁶ is considered insignificant and the cancer risk can be neglected; while an ILCR above 1 × 10⁻⁴ is considered harmful and the cancer risk is troublesome. Results of Table 7 indicate that chromium and lead may have a chance of cancer risk, while nickel has the lowest chance for cancer risk from the contaminants to resident's people.

This study was accomplished to appraise the main factors controlling water resources evolution/pollution indicators emphasizing direct/indirect human health risks in El Sharqia Governorate, Egypt. Most of the collected groundwater samples were shallow with depths ranging from 8 to 13 m, which implies that these wells are more vulnerable to contamination. Salinity classifications show that about 81% of groundwater samples and 89% of drainage water were freshwater, while about 19 and 11% were classified as slightly saline, respectively. Groundwater quality in the study area was controlled by natural processes (involving dissolution/precipitation of minerals, cation exchange, and evaporation) or anthropogenic factors (including leaching of solid waste, overuse of agricultural fertilizers, high loads of discharged sewage water) responsible for water quality deterioration. It was found that ammonia, nitrate, BOD, phosphate, turbidity, iron, manganese, lead, and aluminum values exceeded the limit of drinking water international standards. A human health risk was identified in the case of Pb and Al with high HRI values for different age groups of people including children and adults exceeding unity. It seems that the aquifer in the study area is quite vulnerable to pollution.

An advanced sanitary drainage network must be designed; chemical and bacteriological analyses must be carried out periodically for surface and groundwater to ensure the suitability of water for different purposes, taking into consideration the different hydrological and soil parameters that affect the susceptibility of the aquifer to pollution.

It is a pleasure to acknowledge the technical support provided by the Egyptian Atomic Energy Authority (EAEA), the Egyptian Desalination Research Center of Excellence (EDRC), and the Desert Research Center (DRC).

All authors contributed to the study conception and design. Material preparation, data collection, and analysis were performed by A.H.M.E.-A., R.A.H., F.A.M., S.O., and E.O. The first draft of the manuscript was written, revised, and previous versions of the manuscript were commented. All authors read and approved the final manuscript.’

This work was supported by Institutional Links grant, ID 527426826, under the Egypt-Newton-Mosharafa Fund partnership. The grant is funded by the UK Department for Business, Energy and Industrial Strategy and Science, Technology and Innovation Funding Authority (STIFA) – project NO. 42717 (An Integrated Smart System of Ultrafiltration, Photocatalysis, Thermal Desalination for Wastewater Treatment) and delivered by the British Council.

Data cannot be made publicly available; readers should contact the corresponding author for details.

The authors declare there is no conflict.