Environmental Geochemical Assessment of Heavy Metals in Soil and Sediment of (Shatt-Al-Hilla) Babil Governorate, Central Iraq

Heavy metals concentration in the soils and sediments has increased worldwide during the last century as a result of the rapid increase in population which combined by an increase in human activity as agriculture,  industrial and many other activities. Ten soil and three river sediment samples were collected from 10 main sampling stations at Shatt Al-Hilla River from Sada area to Dora Bridge in Babylon province. The chemical analysis of the sedimentation sample in the laboratory included pH calculation, electrical conductivity (EC) (Cation Exchange Capacity (CEC), organic matter (OM), and heavy metals as (Mn, Ni, Cr, Zn, Cu, Co, Pb, Cd, As and Fe). Indirect geochemical background (IGB) of heavy metal was calculated by the iterative 2 standard deviations (SD) method. 
The results of enrichment factor for heavy metals of the soil and sediment show that the all heavy metals in the studied samples were within Ef<2 indicate to depletion to minimal enrichment (i.e. no or minimal pollution). While Cd in the sample (5), Co in the sample (7), Cr in the sample (8) and Mn in the sample (1S) are within 2 â‰¤ EF < 5 indicate to Moderate enrichment. Contamination factor (Cf) for heavy metals of soil and sediment show that the all heavy metals in the studied samples were within Cf < 1 -Low contamination. While Sample "2" (Cd, Fe), sample "3" (Ni, Cr, Pb, and Cd), sample "4" (Mn, Fe) and sample "8" (Cr) are within 1 â‰¤ Cf < 3 moderate contamination. 
Pollution load index result of all the soil and sediment samples are less than one indicate that  "no pollution" are present, except sample 3 where the PLI value higher than 1 indicates the samples have been "polluted ". The modified degree of contamination (mCd) data indicate nil to a low degree of contamination for all of the soil and sediments samples.


INTRODUCTION
The soil is an important environmental media receiving a significant amount of pollutants from different sources with time [1]. Heavy Metals associated with soils and sediments in an urban area are of environmental significance because of their direct and indirect effects on human health. Heavy metals in soils are found naturally or generated from anthropogenic activities. Anthropogenic sources of heavy metals in the environment involve many sources as the burning of fossil fuels, municipal wastes, sewage, pesticides and fertilizers [2]. River sediment of Shatt Al-Hillah and soil from surrounding areas suffer from increased effluent especially in recent years, due to increasing population, urban expansion, dense and vast agriculture lands on both sides of the river which result in increased uses of fertilizers and pesticide. Theses aforementioned factor necessity led to increased contaminants, where the emission and deposition of wastes rich in heavy could be increased in our ecosystems, particularly soil in urban and agricultural lands which act as sinks for these metals.
Consequently, this study is designed to test the effects of anthropogenic activity on heavy metals status of the soil and river sediment in Shatt Al-Hilla area by comparing the result with the geochemical background. Assessment of Metal contamination risk index, which can be used as a tool to identify the degree of pollution in the soil, was also assessed using the enrichment factor (EF), Contamination factor (Cf), Pollution Load Index (PLI), and Modified degree of contamination (mCd). It is hoped that the current study could provide baseline data regarding the distribution and accumulation of the selected metals in the river sediment of Shatt Al-Hilla and soil of the surrounding area and would help reduce the contamination by identifying the major pollution sources.

Study Area
The study area is located in Babil Governorate, Central Iraq, between longitudes (44º 2´E) (45º 13´E), and latitudes (32 º 5´N) (33 º 8´N) as shown in Figure-1. The total area of Babil Governorate is 5119 Km 2 , representing 1.3% of the total area of Iraq. Babil Governorate consists of four districts and 12 administrative units and 674 villages. These administrative units are located directly on the Shatt Al-Hilla or on one or more of its distributors. The study area is a part of Mesopotamian Plain, one of the oldest agricultural lands in the world. The main components of sediments are old river deposits and irrigation sediment [3].

Sampling Collection and Analysis
During dry seasons ( 30/7/2018), ten soil and three river sediments samples were collected from 10 main sampling stations at Shatt Al-Hilla from Sada Area to Dora Bridge in Babylon Province (Figure-1, Table-1). The soil sample was collected at 15 cm depth around the sample area; it was first air dried, mixed and transferred into clean and labeled polythene bags and carefully preserved for required chemical analysis. .The soil and sediments samples were mix, and sieved through 2-mm-mesh sieve. The resulting fine fraction was prepared for digestion. The chemical analysis of the soil and sediment samples included pH calculation, electrical conductivity (EC), Cation Exchange Capacity (CEC), organic matter (OM), and heavy metals as Mn, Ni, Cr, Zn, Cu, Co, pb, Cd, As and Fe. The previously digested soil samples were used in determining the content of heavy metals using an atomic absorption spectrophotometer. The chemical analysis of the sedimentation sample in the laboratory included PH calculation, electrical conductivity (EC) Cation Exchange Capacity (CEC), organic matter (OM)., and heavy metals include Mn, Ni, Cr, Zn, Cu, Co, pb, Cd, As and Fe.

Geochemical background of the Soil and river sediments
The background is defined as a relative measure to distinguish between the natural element or compound concentrations and anthropologically influenced concentrations in real sample collectives which may be determined with direct, indirect, and integrated methods [4] and [5]. The statistical method is iterative 2 standard deviations (SD) method. The iterative 2 SD technique [average ± 2SD] is mainly used to define background values because it approximates the original data set to a normal distribution [6].

Assessment of Metal Contamination
To evaluate the degree of contamination in the sediments, we used four parameters: Enrichment Factor (EF), Contamination Factor (CF), Pollution Load Index (PLI) and Modified degree of contamination (mCd).

The enrichment factor (EF)
The enrichment factor of metals is a useful indicator reflecting the status and degree of environmental contamination [7].
The EF calculations compare each value with a given background level, either from the local site, using older deposits formed under similar conditions, without anthropogenic impact, or from a regional or global average composition [8]. The EF was calculated using the method proposed by [9] as follows Where (Me/Fe) sample is the metal to Fe ratio in the sample of interest; (Me/Fe) background is the natural background value of metal to Fe ratio. Indirect geochemical background obtained from the computation of statistical background methods is used as a reference background. In the current study. Iron was chosen as the element of normalization because natural sources (1.5%) vastly dominate its input [10] [11]. Increasing in EF value indicate increasing metals supply from anthropogenic activity [12]. Enrichment factor categories are listed in the Table-3. Table 3-Enrichment factor (EF) categories [13] Enrichment factor (EF) Enrichment factor (EF) Categories EF < 2 Deficiency to minimal enrichment 2 ≤ EF < 5 Moderate enrichment 5 ≤ EF < 20 Significant enrichment 20 ≤ EF < 40 Very high enrichment EF ≥ 40 Extremely high enrichment

Contamination factor (Cf)
The level of contamination of sediment by metal is expressed in terms of a contamination factor. The Cf is the ratio obtained by dividing the concentration of each metal in the river sediments and soil (C M ) by the background (C B ) value [14]. ( Where Cm is the concentration of a given metal in the river sediments and soil river sediment, and C B is the background concentration of the metal. CF values for describing the contamination level are shown in the Table-4 [15]. √ (3) Where: n = number of metals and CF = contamination factor. According to [16] the PLI value higher than 1 indicates the samples have been polluted while the PLI value less than 1 indicates no pollution occurred

Modified degree of contamination (mCd)
The degree of contamination by metals is calculated based on the method presented by Hakanson [15] using the following formula: Where ∑C f is the sum of contamination factor for all metals Furthermore, all n species must be analyzed in order to calculate the correct Cd for the range of classes defined by Hakanson [15]. Abrahim & Parker [17] presented a modified and generalized form of the Hakanson [15] equation for the calculation of the overall degree of contamination at a given sample. The modified equation for a generalized approach to calculating the degree of contamination is given as follow: Where n is the number of metals analyzed and CF is the contamination factor. According to mCd classification Table-5  Table 5-Classification of mCd [17] mCd values Sediment quality mCd<1. 5 Nil to low degree of contamination 1.5≤mCd<2 Low degree of contamination 2≤mCd<4 Moderate degree of contamination 4≤mCd<8 High degree of contamination 8≤mCd<16 Very high degree of contamination 16≤mCd<32 Extremely high degree of contamination mCd>32 Ultra-high degree of contamination

Results and Discussion
Analysis results of pH, EC, CEC, and organic matter (OM) for soil and sediment samples along the Shatt Al-Hilla course are presented in Table-6. pH value of soil and Shatt Al-Hilla sediment ranges from 7.18 to 8.09 with a mean of 7.67 and7.84 to 8.1 with a mean of 7.94 respectively ( Table-6 and Figure-2). The values within the alkaline range may be due to the sediment content of carbonate, which affects the pH values. Carbonate increases pH moderately [18] whereas the alkaline soils are primarily caused by a calcium carbonate-rich parent materials.
Electrical conductivity values of soil and Shatt Al-Hilla sediment ranged from 3.4 to 85 ds/ m with a mean 32.19 ds/m and 13.2 to 34 with mean 22.86 respectively. The values of the electrical conductivity of soil and sediment samples of the Shatt Al-Hilla were shown in (Table-6 and Figure-2). According [19] the sample 8 considered as a very slightly saline, sample 1 as a slightly saline, sample 2-3-2S as a moderately saline while samples 4-5-6-7-9-10-1S-and 3S as a strongly saline (Table 7) Cation exchange capacity (CEC) is a measure of the soil"s ability to hold positively charged ions [20]. CEC of the different types of material (modified from [81] are presented in Table- (Table-6 and Figure-2). CEC result of the studied soil is within the normal range and has the ability to retain and supply nutrients, specifically cations, Organic matter (OM) content of soil and sediment samples ranges from 0.88 to 1.63 with a mean of 1.044 % and0.78 to 0.91 with mean 0.84% respectively. The results of the organic matter analysis showed that the levels of the organic matter presented in sediment samples varied throughout the river and all sampling sites have relatively low organic matter content (Table-6      Heavy metals concentration in ppm of soil and sediments with geochemical background index and sediment quality guidelines, are presented in Table-9. Sediment contamination in (trace element) is a measure of environmental pollution. The increase in soil content from rare elements leads to disease [11].   (Table-9 and Figure-3A). The fourth sample contains a concentration of manganese (74 ppm) higher than IGB of Mn (64 ppm) this may result from the variations in the source materials from which soils are derived or anthropogenic activities. In comparison with sediment quality guideline, the mean value of Mn exceeds the limits [23]. Copper: Cu concentrations in the soil range from 9.6 to 76.5 ppm with a mean of 32 ppm and in Shatt Al-Hilla sediment samples range from 13 to 31.0 ppm with a mean of 20.9 ppm (Table-9 and Figure  3A). All samples contain a concentration of Cu less than IGB (106), this means that copper exists at levels lower than its natural occurrences in soil or rocks in the study area. In comparison with sediment quality guideline [the mean value of Cu exceed the limits of [23] and [24]. Zinc: Zn concentrations in the soil range from 31 to 131 ppm with a mean of 77.3 ppm and in Shatt Al-Hilla sediment samples ranges from 31.6 to 48 ppm with a mean of 37.5 ppm ( Table-9 and Figure-3A). All samples contain a concentration of Zn less than IGB (135), this means that Zn exists at levels lower than its natural occurrences in soil or rocks in the study area. In comparison with sediment quality guideline, the mean value didn't not exceed [12]. and [24] limits. Nickle: Ni concentrations in the soil range from 8.9 to 68 ppm with a mean of 28.9 ppm and in Shatt Al-Hilla sediment samples range from 12.4 to 21.6 ppm with a mean of 15.9 ppm (Table-9 and Figure-3B). The third sample contains a concentration of Ni (68 ppm) higher than IGB (46.4) this may result from the variations in the sources rocks or anthropogenic activities. In general, Ni means concentration of soil are exceeding the [23] and [24] limits but for river sediments Ni mean (15.9) was very closer to [23] limits and lower than [24] limit. Cobalt: Co concentrations in the soil range from 11.3 to 43 ppm with a mean of 30.3 ppm and in Shatt Al-Hilla sediment samples ranges from 21 to 34.1 ppm with a mean of 28.1 ppm. All samples contain a concentration of Co less than IGB (49) suggest that Co exists at levels lower than its natural occurrences in the soil of the study area (Table-9 and Figure-3B). Lead: Pb concentrations in the soil range from 9.6 to 76.5 ppm with a mean of 32 ppm and in Shatt Al-Hilla sediment samples ranges from 31 to 31 ppm with a mean of 20.9 ppm (Table-9 and Figure-3B). The third sample contains a concentration of pb (76.5 ppm) higher than IGB (53.3). In comparison with sediment quality guideline, the mean value did not exceed the limits, and this result shows that the Shatt Al-Hilla sediments are not polluted by Pb. Chromium: Cr concentrations in the soil range from 9 to 31.6 ppm with a mean of 18.2 ppm and in Shatt Al-Hilla sediment samples ranges from 9 to 15 ppm with a mean of 11.5 ppm ( Table-9 and Figure-3C), the third and eighth samples contains a concentration of Cr 31.6 and 29.3 ppm respectively, higher than IGB (23), this may result from anthropogenic activities. In comparison with sediment quality guideline, the mean value did not exceed the limits. But the soil is contaminated with Cr at site 3 and 8, due to many anthropogenic activities at these two sites, as shown in Table-1. Arsenic: As concentrations in the soil range from 5.1 to 8.2 ppm with a mean of 6.29 ppm and in Shatt Al-Hilla sediment samples ranges from 5.2 to 6.8 ppm with a mean of 6.13 ppm (Table-9 and Figure-3C). When comparing the As concentrations in soil and sediment samples with the IGB of As (12), all samples contain a concentration of As less than IGB, this means that As exists at levels lower than its natural occurrences in the soil in the study area. Cadmium: Cd concentrations in the soil range from 2.4 to 11.5 ppm with a mean of 4.8 ppm and in Shatt Al-Hilla sediment samples range from 2.7 to 3.1 ppm with a mean of 2.9 ppm (Table-9 and Figure-3C). The second, third and fourth samples contain a concentration of Cd 9.6, 7.5 and 11.5 ppm respectively, higher than IGB, this may result from anthropogenic activities that are represented in Table-1. Such activates may lead to increase in Cd concentration at these three sites above the IGB, WHO [12] and [13]. Iron: concentrations in the soil range from 314 to 3120 ppm with a mean of 1021 ppm and in Shatt Al-Hilla sediment samples range from 321 to 745 ppm with a mean of 599 ppm (Table-9 and Figure-3C). The second, third and fourth samples contain a concentration of Fe 1350, 3120 and 2450 ppm respectively, higher than IGB (1098). In comparison with sediment quality guideline, the mean value were exceeded USEPA [12] limit that means the soil and river sediments are polluted with iron. Detail description result of enrichment factor (Ef), Contamination factors (Cf), modified degree of contamination (mCd) and pollution load index (PLI) of the heavy metals for the soil and sediment samples of Shatt Al-Hilla are listed in the Tables-(10 and 11). The results of enrichment factor for heavy metals of the soil and Shatt Al-Hilla Sediment according classification in Table-3 shows that the all heavy metals in samples ( 1, 2, 3, 4, 6, 9, 10, 2S, and 3S) were within Ef<2 indicate to depletion to minimal enrichment (i.e. no or minimal pollution). While Cd in Sample (5), Co in the sample (7), Cr in the sample (8) and Mn in the sample (1S) are within 2 ≤ EF < 5 indicate to moderate enrichment (Table-10.A and Figure-4(A, B, and C).
The pollution load index result of all the soil and Shatt Al-Hilla sediment samples are less than one indicate that "no pollution" are present, except sample 3 where the PLI value higher than 1 indicates the samples have been "polluted " as shown in Table-10 A and Figure-6.
The modified degree of contamination (mCd) data according to classification in the Table-5 indicates nil to a low degree of contamination for all of the soil and sediments samples (Table-10B

Conclusions
In Study area, pH value of Soil and Shatt Al-Hilla sediment within the alkaline range, and the results of the organic matter analysis have relatively low organic matter content.
The results of enrichment factor for heavy metals of the soil and Shatt Al-Hilla sediment show that the all heavy metal in soil samples (1, 2, 3, 4, 6, 9 and 10), and sediment samples (2S, and 3S) within Ef<2 indicate to depletion to minimal enrichment (i.e. no or minimal pollution). While Cd in the sample (5), Co in the sample (7), Cr in the sample (8) and Mn in the sample (1S) are within 2 ≤ EF < 5 indicate to Moderate enrichment. The results of contamination factor (Cf) for heavy metals of the soil and Shatt Al-Hilla sediment show that the all heavy metals in soil samples ( 1, 5, 6, 7, 9, and 10) and sediment samples 1S, 2S, and 3S) within Cf < 1 -Low contamination. While sample "2" (Cd, and Fe) sample "3" (Ni, Cr, Pb, and Cd) sample "4" (Mn, and Fe) and sample "8'(Cr) are within 1 ≤ Cf < 3 moderate contamination. The pollution load index result of all the soil and Shatt Al-Hilla sediment samples are less than one indicate that "no pollution" are present, except sample 3 where the PLI value higher than 1 indicates the samples have been "polluted ". The modified degree of contamination (mCd) data indicates nil to a low degree.