The Tigris River is a vital resource of water for domestic use and economic activities in Iraq. The evaluation of water quality in Iraq has become a critical issue in recent years, especially due to the concern that fresh water will be a scarce resource in the future and it is always susceptible to pollution [1
The Tigris River is the second longest river in Western Asia. It is 1850 km long, originating from eastern Turkey, enters Baghdad city from the north heading toward the south as a part of the alluvial plain with an average flow rate of 540 m3
/s for the period 2005–2020. The bed comprises mainly fine sand, silt, and clay [2
]. The Tigris River runs through heavily populated areas especially in Baghdad city with nearly 8 million inhabitants [3
]. The water demand is at its highest level, nevertheless the Tigris River discharge has severely declined in the last decades; combined with the fact that the wastewater quantities are increasing and the treatment plant is experiencing deficiency [4
Contamination of the Tigris River water by the transmission of toxic pollutants as a result of anthropogenic activities such as domestic wastewater, hospitals, and industrial factories which discharge their wastewater directly into the river without any real treatments pass through Baghdad city and threaten the ecosystem for plants and living organisms [5
]. Such untreated wastewater inputs contaminate the river water with trace element contaminations and by many contaminant indicators such as COD, BOD5
, and other biological parameters [6
]. Excess intake of essential trace elements in drinking water may lead to adverse health effects [10
]. In particular, elements such as cadmium, chromium, copper, zinc, and lead have significant biological toxicity and are harmful to human health. For example, if their concentration goes above the necessary amount, they are harmful to the liver, kidney, digestive system, blood system, nervous system, and brain [10
Considering the increasing need for drinking water and the stringent concentration limits of their dissolved constituents, and due to their toxicity, non-biodegradability, and persistency, heavy metals can exert adverse effects on the environment and other ecological receptors. It is mandatory to develop and apply efficient remediation systems based on geochemical considerations [12
]. Therefore, various methods have been developed and used to decrease heavy metals concentrations in ecosystems. These technologies can be categorized in physicochemical processes such as ion exchange, reverse osmosis, membrane filtration, adsorption, precipitation, electrolytic removal, and biological processes involving activated sludge and phytoremediation [14
]. In the future it is recommended to apply the nanofiltration/reverse osmosis (NF/RO) technologies for the Tigris River water to remove dissolved ions such as divalent ions(SO42+
) from contaminated water [18
Some widely used adsorbents for the removal of metal ions include clay minerals, activated carbon, biomaterials, industrial solid wastes, and zeolites [15
]. An approach that can be used to sustain the surface water is monitoring the sources of the contaminants and trying to decrease their effects.
Wastewater discharges without any treatment in rivers, sewage effluent from domestic waste, garbage dumped into the river, or washing and/or effluent human/animal tools are a major source of fecal microorganisms, including pathogens [21
]. For example, some strains of E. coli
bacteria (Escherichia coli
), are pathogenic, which means that they can cause infection that leads to diarrhea, urinary tract infections, respiratory illness, and pneumonia; coliform bacteria are capable of invading and multiplying in the intestinal epithelial cells of the distal large bowel in humans [23
Anthropogenically derived water pollution from BOD5
and COD are another major perturbation in aquatic ecosystems that results in an increased influx of pollutants and nutrients into aquatic systems and significantly disrupts the structure and function of natural microbial assemblages, leading to reduced species diversity, increased heterotrophy, and a rise in the number of potentially harmful microbes [22
The selected area extends from Tharthar-Tigris Canal which is located in the north part of Baghdad city to Al-Azizziyah city in the south of Baghdad city near Kut government within the following geographical coordinates ranges (33°55′07″–32°54′30″ N and 44°22′16″–45°4′0″ E), (Figure 1
The chosen Tigris River course is due to the effect of high salinity from the discharging water of Tharthar-Tigris Canal on the Baghdad site, in addition to the effects of human activities (hospitals, industrial factors, domestic wastewater, and others). Furthermore, the Contamination of the Al-Rustimiyah treatment plant located on the Diyala River has an important effect on water quality and contamination that affect the Tigris River southern course that is vital for the southern governorates, Waset, Misan, and Basra. The Al-Rustimiyah treatment plant has limited capacity of wastewater treatment; hence, the overload wastewater is discharging into the river without any treatment.
The used methods in this research, are to evaluate the concentration of the contaminants along the course of the Tigris River to determine the source of the contaminants, analyzing the results, explaining the reasons behind the contamination on the hydrochemistry of Tigris River for the years 2005 to 2020 as the novelty of this research.
The aim of this study is to determine the concentration of major ions, trace metals such as: Cu, Cd, Zn, Pb, Fe, and Cr, and biological parameters analysis such as BOD5, COD, E. coli bacteria and fecal coliform bacteria, that are considered good indicators of the surface water pollution, to assess the environmental pollution of the Tigris River annually during 2005–2020 along the river from Tharthar-Tigris Canal to Al-Azizziyah city.
The geology of the Tigris River in the studied sites, started from the Tharthar-Tigris Canal which it consists of the Fat’ha Formation (Middle Miocene) that is comprised of alternating beds of anhydrite, gypsum, halite, and salt, inter-bedded with limestone, marl, and relatively fine-grained clastic, and Euphrates limestone (Middle Miocene) which is comprised of shelly dolomitized limestone. At Baghdad to the south of the Al-Azizziyah sites, the river passes through the recent and quaternary sediments [27
], (Figure 2
2. Materials and Methods
Four sites were chosen: the Tharthar-Tigris Canal, Baghdad, Diyala River conjunction with the Tigris River, and Al-Azizziyah, to determine the effect of decreasing Tigris River flow on the water quality and to identify the sources of pollution for the period (2005–2020) [26
The reason for selecting this path is that the Tharthar-Tigris Canal is connected to the Tigris River as an outlet canal feeds back from the Tharthar lake, (which is used for water storage and flood relief). The Tharthar-Tigris Canal passes through gypsiferous soil (Gypcrete) that extends from Tharthar Lake to the Tigris River, with the Tharthar Lake saline water which impacts the quality of the Tigris River at the city of Baghdad. The Baghdad site was chosen because it is the capital of Iraq and the biggest city that has many domestic wastewater, industrials factories, and hospitals, which drain the untreated water directly into the Tigris River. The Diyala River conjunction site with the Tigris River was chosen because of the existence of Al-Rustimiyah wastewater treatment plant that affects Diyala River quality by pouring the overloaded untreated municipal wastewater that exceeds its operational capacity to the Diyala River. The Al-Azizziyah site represents the final mixture of the Tigris River flow with the other three selected sites that pass to the southern provinces.
The historical data applied in this research were evaluated and tested for independence, steadiness, and homogeneity [26
]. The data include the discharge of the Tigris River, the hydrochemical analysis such as major ions and trace elements, biological parameter indicators such as BOD5
, COD, E. coli
bacteria and, the most probable number for coliform bacteria MPN/100 mL, (Tables 1–3).The Phreeqc software (version 3.7.3) was applied to assess the saturation indices to determine the dominant geochemical processes responsible for surface water quality deterioration. In addition, multivariate statistical techniques, (factor analysis) were applied using the SPSS 26.0 program to evaluate spatial variations, and to interpret measured water quality within the studied sites. The application of the factor analysis (FA) helps in the interpretation of complex data matrices better understand the water quality and ecological status of the studied systems, and allows the identification of possible factors/sources that influence water systems [28
Moreover, the Aq. QA software program was used for plotting piper and Schoeller diagrams to display the relative concentrations of the different ions (epm). The hydrochemical formula was computed as an average formula based on a water type formula which was referred according to the Ivanov 1968 method. Plotting Total Ionic Salinity (TIS) was performed as proposed by [29
]. The results of the current study were compared with the previous studies to highlights the deterioration of the Tigris River quality in recent years due to the effects of climate change, as well as the construction of dams within the riparian counties [5
The high concentrations of TDS values clearly indicate the high pollution loads that are related to the input of untreated wastewater directly into the river as well as pouring the contaminated surface drainage from irrigation, industrial, and domestic activities (Table 2
, Table 3
and Table 4
The salinity varies within the studied sites depending on nature, geographic location, and the affected factors within each site such as: soil variation, agriculture, and population density, etc. Accordingly, it was noticed that the salinity within the Tharthar-Tigris Canal site is higher than that of the Baghdad site and becomes higher in the Diyala River site where there is an input of untreated sewage water from the Rustamiya wastewater, consequently the final mean water salinity is indicated within the Azizziyah site. The major ions behave equally as the salinity. In general, it was noticed that the Diyala River has the maximum values of salinity as well as the major ions. The percentage of the major ions along the Tigris River reflected that it is in the following order SO42−
for all sites except the Baghdad site that reflect SO42−
). Such a finding may indicate the limited effect of the Tharthar-Tigris Canal on Tigris River at Baghdad site, but its water deteriorated due to the Diyala River discharge.
By comparing the results of this research with the water suitability standards for drinking, it was found that Tigris River water at the Baghdad site is suitable for drinking and deteriorated after its connection with Diyala River where it is unsuitable for drinking [37
Moreover, the comparisons of this study results with previous studies shows that most of the parameters are relatively higher than the result of previous studies and these values exceeded the standard of WHO, 2018 and IQS, 2009 for drinking water [30
], (Figure 11
). This finding may reflect the deterioration of Tigris water with time due the climate change effects, low river discharge, and relatively high contamination within the past two decades.
Applying Phreeqc software [51
], is reflected that the cation exchange, as well as the dissolution/precipitation of gypsum, anhydrite, and halite were responsible for the geochemical processes. The results show that the geological composition can affect the water quality of the Tigris River especially at the Tharthar-Tigris Canal. The mean, maximum, and minimum of the saturation index of minerals along the path of the Tigris River are presented in Table 7
. Additionally, anthropogenic activities such as untreated sewage discharge and fertilizer usage also had striking effects on the hydrochemistry of the Tigris River.
Four sites were chosen: the Tharthar-Tigris Canal, Baghdad, Diyala River conjunction with the Tigris River, and Al-Azizziyah, to determine the effect of the decreasing Tigris River flow on the water quality and to identify the sources of pollution for the period (2005–2020). The annual flow of the Tigris River decreased through time due to climatic change and dams on the Iraqi–Turkey border, in addition to the increasing water consumption due to high population growth rates. TDS values were higher at Tharthar-Tigris Canal and Diyala River, for Tharthar-Tigris Canal site, these may be attributed to an increase in the salinity of Tharthar Lake which is due to high evaporation and the passing of this canal through gypsum soil as well as the drain water which comes from agricultural lands. As for high concentrations in the Diyala River site that they are due to the effects of the untreated water from Al-Rustimiyah treatment site which are thrown directly into the river. TDS concentration of the Tigris River is within the permissible limits of WHO (2018) standards and Iraqi standards (IQS, 2009), except at the Tharthar-Tigris Canal and Diyala River sites of the Tigris River which they exceeded the standards. Temperature values for all sites of the Tigris River are within the permissible limits of IQS, 2009. Ca2+, Mg2+, and K+ concentrations in the study area are within the permissible limits of WHO (2018) standards and Iraqi standards (IQS, 2009). Na2+ and SO42− concentrations along the Tharthar-Tigris Canal and Diyala River sites have exceeded the permissible limits of WHO (2018) standards and Iraqi standards (IQS,2009). Cl− concentration of the Tigris River is within the permissible limits of WHO (2018) standards and Iraqi standards (IQS, 2009) except at Diyala River site which exceeds the standards. The high concentrations of Na+, Cl−, and SO42− maybe due to man-fabricated activities and natural resources such as lithology in the basin. HCO3− concentration of the Tigris River depends on the annual rainfall and the controlling of discharges from the reservoirs. The trace elements along the Tigris River are below permissible limits. The concentrations of coliform and fecal coliform bacteria along the Tigris River were more than the international permissible levels recommended by WHO (2018). The dominant water type of the Tigris River is classified as sodium sulphate and Magnesium sulphate (NaSO4 and MgSO4). It is noted that there is a movement in the quality of the river water toward increasing salinity in the south.
By comparing these results with the local and international water suitability standards for drinking, it was found that the Tigris River water at the Baghdad site is suitable for drinking and deteriorated after its connection with Diyala River where it is unsuitable for drinking (IQS, 2009, WHO, 2018). The Total Ionic Salinity (TIS) of the Tigris River sites (Tharthar-Tigris Canal, Baghdad, and Al-Azizziyah) ranged between (20 and 40 meq/L), whereas the Diyala River site had a relatively higher TIS above (40 meq/L). By using Phreeqc software to assess the saturation indices and determine the dominant geochemical processes source responsible for surface water quality for the Tigris River path, the dominant minerals in the Tigris River were relatively high values of SI-gypsum, SI-anhydrite, and SI-halite at Tharthar-Tigris Canal, SI-calcite and SI-dolomite at Baghdad site, and SI-anhydrite, and SI-halite at Diyala River and Al-Azizziyah sites. Selection of the correct parameters and use of them in multivariate statistical technique in water quality monitoring studies is an important to be used in environmental studies to prevent pollution. Results from the factor analysis show that Tigris River water had two factors. The first factor (F1) is with 71.272% of the total variance and was strong positive loading composed with the following variables: COD, BOD, HCO3−, fecal coliform bacteria, TDS, E. coli bacteria, Na+, Cl−, Mg2+, and SO42−. The second factor (F2) is of weak positive loading composed with the following variables: Ca, K+, Mg2+, and SO42−. The contribution to different sources can be from the nature of the studied site, anthropogenic stresses, industrial activities which carry domestic and industrial wastewater of the city in addition to deficiency of water resources due to climatic change and dam construction of the riparian countries.
Recommendations: Strict measures should be taken in order to control the levels of pollutants discharged into the Tigris River and to reduce the dissemination of the Coliform and fecal coliform bacteria to protect human health. Tigris River water needs further treatment, especially at the south of Baghdad city, for that a periodic monitoring system should be established to follow up on pollution levels and water quality for the Tigris River, by conducting seasonal surveys. In addition, the treatment of the wastewater of the Al-Rustimiyah plant must be improved by applying the conventional methods that are generally employed for water, which can be grouped into adsorption, ion exchange, coagulation/precipitation, and membrane-based technologies and construct a desalination plant. Nano filtration/reverse osmosis (NF/RO) technologies can be used for water desalination to remove dissolved ions into the water of the Tharthar-Tigris Canal. Finally, local governments can form effective policies, such as reducing industrial discharge and agricultural fertilizer in addition to wastewater discharge.