Assessment of Heavy Metal Pollution in Clay Fraction of the Euphrates River Sediments, AlQaim, Haditha Area, Western Desert Iraq

Abstract


Introduction
With population growth, rapid industrial development, and a lack of pollution control measures, soil trace metal contamination is becoming a global problem at both the private and governmental levels, particularly because soils are an important component of both rural and urban environments (USDA, 2001;Rahman et al., 2012;Tang et al., 2014).Heavy metal accumulation in river sediments exposed to mining and industrial wastes is a regular occurrence in most developing countries (Islam et al., 2015).Heavy metals in the environment are sometimes carried and sourced by sediments (Haiyan et al., 2013).Heavy metals in river sediments enter through different pathways, either from point or non-point sources (Shazili et al., 2006).Grain size distribution plays an important role regarding the content of heavy metals in sediments.Many investigations indicated that when sediments grain size decreases, metal content increases more than those formed of coarser ones (Svetlana et al., 2012).This was attributed to the fact that smaller grains, such as clay fraction sediments, have a larger surface area, which allows heavy metals to be retained in high concentrations (Wang et al., 2006).
The background level is a measure used to differentiate between the concentration with an anthropogenic influence and the concentrations of the natural occurrence in a given environmental sample (Matschullat et al., 2000;García Sánchez et al., 2010).Heavy metal concentrations in the natural soil background are determined by geological substrates in the Earth's crust and soil formation processes (Alloway, 1990;Kabata -Pendias and Pendias, 2001).Rocks have a large influence on the heavy metal content of soils, with concentrations sometimes exceeding critical values (Salonen and Korkka-Niemi, 2007).The phosphate industry is the major cause of pollution in the area because most of the waste is directly discharged into the river with preliminary treatment.Iraq's major phosphate factory, which is located 20km in the western city of AlQaim, was once used to produce fertilizer for agricultural purposes.The waste is liquid or solid and its acidic or basic throw-out from different units.The units that produce the waste material from the factory are fertilizer phosphate unit, phosphoric acid unit and fluoride salt unit.The study area is located between 34 o 22′12.33″-34o 08′3.04″N and 41 o 05′46.44″-42o 22′42.19″Eincluding the Euphrates River from AlQaim on the Iraqi Syrian borders to Haditha city for a length of about 160 km (Fig. 1).Haditha reservoir is the largest dam along the Iraqi stretch of the Euphrates River with a maximum capacity of 8.2 km3.The main fluvial units on the Euphrates River in Iraq are terraces and flood plains, which are geomorphological units and forms of the river's course.The Euphrates River defines the boundary between two tectonic zones, Al-Jazira and Western Desert zones, as it enters Iraqi territory from Syria (Fig. 1).The river flows parallel to Anah anticline in W-E trend which is the only surface anticline along the course of the river within the Iraqi territory and continues until Haditha town.Although the major part of the Euphrates River's basin is located within the Stable Shelf, but still a lot of indications exist in the basin witnessing Neotectonic activities (Sissakian et al., 2014).According to Sissakian and Al-Jiburi (2007), the exposed formations in the study area are: (1) Anah (Oligocene) which consists of very hard limestone and corals with a thickness of about 40 m; (2) Euphrates Formation (Lower Miocene) which consists of highly fossiliferous limestone, dolostone, marl, with a thickness of about 60-130 m in AlQaim city; (3) Fatha Formation (Middle Miocene) which consists of cyclic deposits of green marl, reddish brown claystone, limestone and gypsum; (4) Nfayil Formation (Middle Miocene) which consists of an alternation of green marl and limestone; and (5) Zahra Formation (Pliocene-Pleistocene) and Quaternary sediments (Pliestocene) which consists of sand, gravel, fine gypsum, and silt with a thickness of about 12-35 m.Previous studies on the area include that of Ali (1972) who determined heavy mineral provinces of recent sediments in the Euphrates and Tigris Basin;Al Jalil (2000) studied the effect of industrial water leakage from the chemical complex of phosphates in Al-Qaim on ground and surface water pollution.Al-Bassam and Al-Mukhtar (2007) who studied the heavy minerals in the 63 µm fractions of the Euphrates River sediments that showed enrichment of some heavy metals in the river sediments.Al-Paruany et al., (2017) they studied the distribution of environmental isotopes (δ 18 O, δ 2 Hand 3 H) and hydrochemistry at eight stations in the Euphrates river between Qaim-Falluja.Hussain et al., (2020) twenty-five core samples were selected from eight river bed sediment sites to study the heavy metal contamination of the Euphrates and Shatt al-Arab.The Ta, W, Ni, and Mo were clearly the most contaminated heavy metals in the current investigation.The main aims of this study are to assess of heavy metal pollution in clay fractions and to evaluate the effect of waste material from phosphate chemical complex on the pollution of Euphrates River sediments in the studied area (Fig. 1).

Samples Collection
Ten surface clay samples were collected for the current study along the Euphrates River from the bank of the river between AlQaim on the Iraqi-Syrian border and Haditha towns (Fig. 1).These samples consist of sand, silt and clay.The selected samples were placed in a clean cloth bag and kept in a polyethylene bag.The samples were fully air dried at room temperature and sieved using 80 mesh sieves.The finer fraction was used to separate the clay fraction (< 2 μm) applying Pipette analysis based on Folk (1974).Fifty grams of each sample were placed into a 500 ml glass cylinder and filled to the mark by distilled water and left one day for the large particles to settle down.The suspended part was decanted into a clean tube for the separation of the < 2μm clay fraction size without adding any chemicals.The separated clay fraction was placed in a polyethylene bag for chemical analysis.The clay samples were analyzed for Cd, Pb, Cu, Ni, Co, Cr, Zn and Sr using PYE Unicom SP9 Atomic Absorption Spectrophotometer (AAS) in chemical laboratory at Babylon University.The analysis of these heavy metals was taken place in two stages:

Extraction of heavy metals by cold acid
Include the heavy metals that present in the clay fraction from solution by adsorption and organic complex, that come from the water pollution.This method is available, rapid and not expensive.The procedure of sample preparation is simple, and the analysis consists of only three steps, which can be performed simultaneously: A prepared clay samples (1.0 g) are placed in a plastic tube (5oml), and added (20) ml of cold (0.5) N hydrochloric acid (Chester and Voutsinou, 1981).The tube closed and shacked in shaker for (16) hours.Finally, put it in a centrifuge (3000) RPM for 20 min to separate the acid from heavy metals, the solution transferred to plastic tubes (20) ml closed and kept.The heavy metals content from extracted are measured with an Atomic Absorption Spectrophotometer.

Residual heavy metals
The procedure of residual extraction includes heavy metals mostly found within the structure of minerals in a silicate matrix of sediments.This extraction is determined by chemical digestion for residual clay fraction after cold extraction.The clay fraction is rinsed with 40 ml of deionized water (DIW) to remove the hydrochloric acid and ionic exchange followed by shaking the tube.The 3000-rpm centrifuge was operated for 30 minutes to separate the water and transfer the deposit to a teflon (P.T.F.E) tube.The deposit was evaporated at 80°C to near dryness; followed by adding 6 ml of HNO3 + HCl (1:1) acid mixture to be evaporated again 80°C to near dryness.An acid mixture of HF+Br l (1:1) is added to the sample and evaporated to near dryness again, followed by adding 1 ml of hydrochloric acid for 10 minutes.The digestion was diluted by 20 ml of deionized water and separated again by centrifuge and finally transferred to a plastic bottle ready to be measured by Atomic Absorption Spectrophotometer.

Assessment of Heavy Metals
The state of heavy metal contamination in the clay fractions of the studied area was evaluated using different quantitative contamination indices.The geochemistry of sediments is an effective indicator to deduce the anthropogenic activity in stream sediments.Among various environmental indices for assessing the degree of anthropogenic induced impact are the contamination factor (CF), pollution load index (PLI), geo-accumulation index (Igeo), the metal contamination index (MCI), potential ecological risk index (RI) (Rahman et al., 2012;Jiang, 2013;Adepoju and Adekoya, 2014;Singh et al., 2017;Duncan and Nyarko, 2018;Khudhur et al., 2018;Wojciechowska et al., 2019).

Contamination Factor (CF)
CF is used to express the level of metal contamination in sediment, which is calculated as: CF = Cm Sample / Cm Background (1) Where Cm Sample is the amount of a given metal in river sediment and Cm Background is the value of metal which is equivalent to Upper Continental Crust (UCC) in the studied sediments (Taylor and McLennan, 1985;McLennan, 2001;Rudnick and Gao, 2003;Avumadi et. al., 2019) which was widely used by Harikumar et al., 2009).

Pollution Load Index (PLI)
PLI for a specific site was calculated using the approach suggested by Tomlinson et al. (1980).The PLI for various sampling areas were determined as the geometric average for all assessed CF of a sampling site (Afrifa et al., 2013) (Table 2).This parameter is expressed as: Where n is the number of metals.

Geo-Accumulation Index
The Igeo was calculated using the method of Muller (1979).Geo-accumulation index is expressed as follows: Where Cm is the measured concentration of the metal examined in the sample, and Bm is the background level of the metal.The 1.5 factor was used to correct possible variations in the background values of a particular metal in the environment.

The Element Contamination Index and the Metal Contamination Index
The ECI and the overall metal contamination index (MCI) are expressions of single metal contamination within a sample or total metal contamination for a sample in comparison to the corresponding metal's background values (Singh et al., 2015).They are expressed as: According to Aikpokpodion et al. (2010), MCI was designed to describe general trace elements contamination.

Potential Ecological Risk Index
The Erm evaluates the toxicity of trace elements in sediments and has been extensively applied to assess the comprehensive pollution status in the sediments and environmental effects (Gholizadeh et al., 2019, Liu et al., 2019).).Sediments contaminated by heavy metals can cause serious ecological risks and negatively impact human health due to various forms of interaction where highly toxic heavy metals can enter the food chain.To calculate the Er for individual metals, we used the following equation: where Er is the potential ecological risk factor/index, Tr represent the toxicity coefficient of each metal whose standard values are: Hg= 40, Cd= 30, As= 10, Co=5, Cu=5, Ni=5, Pb=5, Cr=2, and Zn=1 (Hakanson, 1980;Xu et al., 2008).CF represents the contamination factor (CF = C/B), where Cm is the measured concentration of the pollutant, and Bm is the level of geological background.To calculate the potential response rate to the toxicity of all the studied heavy metals (RI), we used the following equation: RI=∑ m i=1 Er i (7)

Results
Results of heavy metals analysis in clay fraction samples of Euphrates stream sediments are listed in The highest Zn concentration in the clay fractions has been found at Rawa and Alnahiya reached 72 ppm.Lead concentration ranged between 24 to 66 ppm with an average value reached to 35ppm.The highest content (66) ppm of Pb was found at Rawa.Copper concentrations ranged from 28 to 47 ppm with an average of 37ppm.Cobalt value varied between 22 to 31 ppm with an average of 26 ppm.The chemical analyses did not show a significant variation in the cobalt concentration content, except for a relatively slight increase in the Alnahiya, Alhasa and Rawa.The result of Cr analysis in clay fractions ranged from 28 to 53 ppm with an average of 39 ppm.In general, it has been observed that there is a relative increase in the content of the cadmium, copper, and chromium in the sites located in the downstream, below Alshallal area and the disposal of liquid industrial wastes from the phosphate chemical complex, relative to its concentration when entering the Euphrates River, the Iraqi-Syrian border at Rummana.The CF value for Cd was ranged (3 -36.78) while Ni was (5.75-19.15)especially in the Alshalal which was contaminated by Cd and Alhasa companied by Ni; other metals range from Co (2.2-3.1),Pb (1.2-3.3),Cu (1.12-1.88),Cr (0.8-1.51), Zn (0.72-1.01) and Sr (0.25-1.38) (Fig. 3).
The PLI value in the studied clay samples varied from (1.51 to 2.50) with an average of (2.00) (Table 2).The highest PLI value in the studied clay has been found at Rawa (2.50) and AlShallal (2.38).The study area can be divided into three groups according to the level of PLI values for the eight elements calculated by Tomlinson et al. (1980).The first group includes Maaidged, Alobeidi, Safra, and Rumanah where PLI values range from (93.32 to 14.6).The second group includes Alnahiya, Right Albeida (R. Albeida), Left Albeida (L.Albeida), and Alhasa where PLI values varied from (36.6 to 63.18), and the third group includes Rawa (189.8) and Alshallal (130.4) (Fig. 4).The average Igeo value in clay fractions of heavy metals varied from Igeo≤0 to 2.68.The highest Igeo average value of trace metals in the studied area has been found in Cd Igeo 2.68 and Ni (Igeo 2.49) (Table 3).
The results shown that the Igeo of Zn, Cu, Sr, and Cr within Igeo≤0, while its lead and cobalt values varied from 0< Igeo<1.The study showed that the Igeo value of nickel is relatively homogeneous within the different locations, while a relative decrease was observed in the Igeo values of lead in the locations of the Down Stream (Fig. 5).The current study compared the results of the clays analyzes of heavy metals with their average in Upper Continental Crust (UCC) to assess contamination levels of the Euphrates River areas by used Element Contamination (ECI) and the Metal Contamination Index (MCI).The highest Cd-ECI value in the studied clay samples has been found at Alshallal (35.78) and lowest at Alhasa (2.0) with an average of (10.39), while the Ni-ECI value reach to 18.15 in Alhasa and to 4.75 in Rumanah.The results also showed that the values of ECI for the other elements varied from negative values and less than <5 (Table 4).As for the MCI values varied from 11.06 to 23.52, except for Alshallal where its values increased to reach 44.32 (Fig. 6).

Assessment of Heavy Metals Contamination Indices
Heavy metals content varies in the environment depending on the geological nature of river crossing areas as well as human activities such as industrial plants, pesticides, agricultural fertilizers, fossil fuel, land construction activities and soil erosion caused by rainfall (Xiang et al., 2002;Chen et al., 2004;Higgins et al., 2007).The accumulations of metal concentrations in the clay fraction are placed in the following descending order: Sr> Zn> Cr> Ni> Co> Pb> Cu> Cd.The results of Cd analysis in the present study represent the influence of the waste water disposed from the phosphate chemical complex.Generally, Cd and other metals occur in waste water at low concentrations until below detection limit of analytical instruments (Al-Jaleel, 2000).These metals tend to accumulate in the clay fraction because it contains high clay minerals that have high adsorption potential in the sedimentation environment.The highest concentration of Cd in Alshallal and Rumanah which is attributed to the urban influence of the city of AlQaim.Drever (1997) showed that Cd has the ability to be adsorbed at the surfaces of clay minerals.Fig. 2 shows that the highest concentration of zinc in Rawa and Alnahiya reached 72 ppm; this was due to human activities and waste water from the phosphate chemical complex (Yan et al., 2018).Also, Zn is found in minerals like ilmenite and magnetite which are present mainly in the sediments of the Euphrates River; this Zn can be released to the environment during weathering processes and then deposited in light basic conditions (Benni, 2014;González-Costa et al., 2017).The difference in distribution of Zn in clay fraction may be due to the effect of organic matter, iron and manganese oxides in the river environment because of high adsorption on clay minerals and organic matter (Steenfelt, 1993;Uddin, 2017).The predominance of montmorillonite over the other clay minerals may be due to the increasing rate of Ni in these areas (Forstner and Wittman, 1981;Mu'azu et.al., 2018).The burning of fuel and the emission of water pumps used for irrigation also pollute the sediments of the Euphrates River with Pb (Chester and Voutsinous, 1981;Sekabira et al., 2010).Therefore, their weathering by river can be a source of Pb in Euphrates River.
The presence of Cu explains the effect of waste water from the phosphate chemical complex at Alshallal in addition to human activity.Co is transported to the sediments after degradation of its bearing minerals, especially pyroxene, and it tends to be adsorbed on clay minerals, mineral oxides and organic matter (Steenfelt, 1993;Baghernejad et al., 2014;Maciąg, 2019).The Co content indicates the effect of the dense population and dumping of heavy waste, manufacturers and waste water that flow directly to the river and pollutes the sediment of the Euphrates River.The increase in Sr (484 ppm) content in Rawa is due to the Sr-rich rocks such as limestone and gypsum which are dominant along the Euphrates River in the study area (Ali and Wagreich, 2017).The waste water from the phosphate chemical complex contributes to the increase of the Sr content in the sediment of the Euphrates River, where the concentration in the clay extracts reaches 185 ppm at Al-Shallal area.The waste water from the agriculture land which directly drains to the river also increases the Sr content in sediments at Albeida which reached 158 and 144 ppm on both sides of the river.Sr have a tendency for ion exchange with the clay rich in calcium because of their similar property (Wissocq et al., 2017).The increasing phosphorous content in the waste water from the phosphate chemical complex can also be considered the determining factor of the increased Cr content in the clay fraction.Dissolved phosphorous in water is a catalyst for the adoption of Cr and its concentration in sediments (Ramessur and Ramjeawon, 2002;France et al., 2013).
The results of the chemical analyses of the clay models showed that the content of the elements (Zn, Ni, Pb, Cu, Co and Cr) included in the current study in the residual fractions is relatively higher than in the extracted part, except for the cadmium, which reached 100% in the extracted part, and conversely the concentration of the strontium reached to 93% in the residual fractions.The study showed that the concentration of the nickel, copper, cobalt, and zinc in the acid extracted fractions of the clay minerals is relatively homogeneous, and ranges between (26-32) %, while its percentage of lead reached 46%, and in chromium, it reached 5.4% (Table 1).
To assess the contamination levels of the Euphrates River, we compared our observations of heavy metal concentrations in clay fractions with published values for Upper Continental Crust (UCC).Pollution indices can be a helpful tool for assessing sediment contamination and have been extensively used by numerous researchers to gauge sediment pollution (e.g., Jing-Jun et al., 2013;Shaari et al., 2015;Yalcin et al., 2016).The current study showed that heavy metal pollution and their descriptive statistical results can be assessed with respect to UCC.CF values for Cd and Ni in clay fractions represent considerable to very high contaminated (CF>6), especially in Alshalal and Rummanah.Anthropogenic input, such as leaded fuel from automobiles and car batteries, is assumed to be the main source of these elements.The first source of Cd is the Phosphate chemical complex and added fertilizers to the agricultural soil also supplies a considerable amount of Cd; the Iraqi fertilizers contain Cd as TSP (21 ppm), MAP (27 ppm), NP (11 ppm), and NPK (8 ppm) (Al-Qaraqhuli, 2005).Co, Pb, Cu and Cr were moderate contaminated (1 ≤ CF< 3; Zn and Sr in low contaminated (CF < 1) (Table 7).The phosphorite deposit in the study area contains varying amounts of Cd, some of which is transferred to fertilizer products during the manufacturing process (Alloway and Steinnes, 1999;Grant and Sheppard, 2008;Terry, 2014).The accumulation of Cd in the aquatic environment can be potentially harmful due to biological activities in sediment and health of aquatic environments (Rzetala, 2016).The high levels of Cd are due to a number of sources, including municipal runoff, atmospheric deposition, and residential and industrial effluents.(Khan, 2017).
The clay fractions of Alhasa are also very highly enriched in Ni such an average comes from significant human influence (Liu et al., 2005;Zhang et al., 2007).Co, Pb, Cu and Cr showed moderate contamination especially at Alnahiya and Rawa which have an average value of 2.62, 1.75, 1.49 and 1.12, respectively.The residual Zn (0.87) and Sr (0.55) with CF averages have low contamination effect which indicates that there was no human influence on the clay fractions by these metals.The PLI is a quick tool for comparison of pollution status in various places.The highest value of PLI has 190 at sampling sites to Rawa and Alshallal, indicating the most contaminated sites (Table 11).The sites with PLI values greater >3 are polluted sites and suggest input of an anthropogenic source of pollution due to increased human activities (Mmolawa et al., 2011).However, the lowest PLI value is observed at sampling site is 3.32 indicating decreasing pollution load index trend across the Euphrates River; this represents the dilution and dispersion of metals and random fluctuation from source areas (Chakravarty and Patigiri, 2009).
According to Muller's classification, it is evident that the Igeo values for Sr (-1.68) and Zn (-0.79) falls in class (0) (Igeo≤0) in all sampling locations, indicating that they are unpolluted by this metal in the clay fractions of Euphrates River; meanwhile Cd (2.68) and Ni(2.49) fall in class 4 (Igeo=3-4),, suggesting moderate to strong pollution.The other metals fall in class 1 (Igeo=0-1) with unpolluted to moderately polluted effects are Co (0.8), Pb (0.16) and Cu (-0.03) (Table 8).This demonstrates that the Igeo values seem to be influenced by the lithology of terrain besides possible anthropogenic contribution of Cd (industrial), Cu (irrigation water and phosphate fertilizer plant), and Co, Cu and Cr (Sewage sludge mainly from municipal wastes) (Kabata and Mukherjee, 2007;Dou et al., 2013;Jing, 2014;Issa and Qanbar, 2016).Pb is used as a tracer of motor vehicles, and the combustion of leaded gasoline in cars and trucks can be considered a Pb pollution source due to atmospheric deposition (Rashed, 2001).The increased CF, PLI and Igeo were attributed to industrial and vehicle emissions and inflows (Sekabira et al., 2010).The MCI with average of 26.95, suggested a Medium to very high contamination by heavy metals in the ecological system such as plants, soil invertebrates and/or mammalian wildlife (Bortey-Sam et al. 2015); this is especially the case in Alshalal (Table 8).
The result of Er show low to moderate risk by Ni (45) and considerable to very high risk from Cd (365), especially in Alshalal and Alnaya areas by Cd and Ni, respectively.The RI range of 219-1171 and average of 442 suggests a moderate to very high ecological risk of heavy metals by Cd and Ni in the ecological system such as industrial, plants, soil invertebrates and/or mammalian wildlife (Bortey-Sam et al., 2015), especially in Al-Shallal area.The results also showed that the existence of a gradient of decreasing RI content from entering the Euphrates River to the Iraqi-Syrian border and into the Maaidged (Table 9).

Conclusions
Geo-accumulation index, Contamination Factor, Pollution load index and Potential Ecological Risk Index were calculated to evaluate the environmental impacts of key pollutant heavy metals in the clay fraction of the Euphrates River.The study area was found to be highly contaminated with Cd and Ni, moderately contaminated with Co, Pb and Sr, and uncontaminated with Cr, Cu and Zn.100% of Cd was found in the extracted part of the clay fraction, thus it may be deduced that Cd in these clay fractions is derived from industrial activities of the phosphate chemical complex and the human activities in the studied area.In spite of the very low concentrations of heavy metals in the waste water from the phosphate complex at present, their concentration may cumulatively increase in the Euphrates sediments, such an increase was observed in the content of Cr, Zn, Cu and Cd metals in the clay fractions downstream from AlQaim which may be due to pollution by the waste water from phosphate company complex at that locality.

Fig. 1 .
Fig. 1.Location map of the Euphrates River in the study area showing the location of samples and the relevant phosphate chemical complex

Fig. 2 .
Fig. 2. Average concentrations of heavy metals in extraction, residual, and accumulation of clay fractions with the standards in the study area

Fig. 4 .
Fig. 4. PLI values of heavy metals in the study area

Fig. 5 .
Fig. 5. Igeo values of heavy metals in the study area

Fig. 6 .
Fig. 6.ECI values and MCI level of heavy metals in the study area

Fig. 7 .
Fig. 7. Er values and RI level of heavy metals in the study area The highest concentration of Ni in clay fractions at Alhasa is 383 ppm while in Rawa is 212 ppm.Strontium ranged from 88 to 484 ppm with an average of 139 ppm, and the highest concentration of Sr at Rawa is 484 ppm and Alhasa company is 389ppm as shown in Fig.2.Zinc value varied between 51 to 72 ppm with an average reached to 62 ppm.
Table1and Fig.2.The results of the Cd content showed that it ranged from 0.27-3.31ppmwith an average value of 1.09ppm.The highest concentration of Cd in Alshallal reached 3.31ppm and Rumanah 1.67ppm.Alshallal area is considered as the area where phosphate chemical complex waste water is discharged in the Euphrates River.The Ni values varied between 115-383 ppm with an average value of 180 ppm.

Table 1 .
Concentrations of specific heavy metals in ppm in the extraction and residual clay fractions of the Euphrates River sediments

Table 3 .
Igeo values of heavy metals in the study area according toMuller's classification (1979)

Table 5 .
Er and RI values of heavy metals in the study area

Table 7 .
Range and average of CF and PLI values and grade for elements in the clay fraction of the Euphrates River sediments.

Table 8 .
Range, average and grades of Igeo and MCI values for elements in the sediments of Euphrates River.

Table 9 .
Range and average of Potential Ecological Risk Indices (Er) and Potential Toxicity Response Indices (RI) of heavy metals