Assessment of the Contamination of Baghdad Soils with Lead Element

Abstract


Introduction
Lead (Pb) is categorized as a heavy metal and considered the most common contaminant in soil.It is widely used to produce batteries, paints, and electronics.Besides, released into the soil as impurities from fertilizers, pesticides, application of municipal, industrial wastewater, and emissions from vehicles exhaust (Markus and McBratney, 2001).The Pb compound particles are suspended in the atmosphere for more than three weeks, and then distributed by the wind over hundreds of kilometers before settling in moist deposits.Particles bigger than 10 mm, which account for up to 95% of the emission, can accumulate over short distances (Binh et al., 2021), Atmospheric deposition continually increases the Pb content of surface soils (WHO, 1989).Pb is very low mobility and non-biodegradable, once incorporated in the soil; it is persisted for a long time and readily accumulated to a toxic level (Kirpichtchikova et al., 2006).This can lead to a decline in biodiversity, animals and plants (Wani et al., 2015).In addition, the increase in Pb concentration above the natural limit leads to the degradation of soil quality and soil erosion is the main causes of the reduction in soil quality where Salah and Al-Madhhachi (2016) have been figured out that the soil erodibility increased directly as Pb concentration increase.As a result, controlling Pb emissions and remediating Pb-polluted soil is critical.Subsequently, Baghdad is regarded as one of Iraq's most significant and most industrialized cities, there are many sources of Pb emissions in Baghdad, industrial factories such as Al-Dora fuel production plants contributes to an increase in Pb concentration about 846 mg/kg due to adding Pb additives during fuel production (Sahib, 2005;Habib et al., 2012) and Babil car Batteries factory in al-waziryah city caused Pb contamination up to 25069.6 mg/kg predominantly according to using the Pb in battery production (Rahi et al., 2014).As well as, smelting processes for metal scrap in Al-Sadr city increasing the Pb concentrations in the environment.These factories employed very old techniques, have weak management, no pollution control system, and no wastewater treatment systems.As a result, some areas of Baghdad are considered to be at high risk of lead contamination.Lead is the most important element that need to disappear from the soil because have a very harmful effect on human health and environment.Lead is a part of many major industries like the Battery industry, motor gasoline, fertilizers, and pesticides so need to monitor it continuously.Thus, this research is very important for the environmental impact assessment to build a database on the Pb concentration in Baghdad's soil (Fakhre and Abdulhussein, 2020).The present study aimed to measure the content and evaluate the spatial distribution of Pb in Baghdad city and to assess the soil samples contamination by using indices Geo-Accumulation (Igeo), Contamination Factor (CF), and Ecological Risk Index (Er).

Study Area
Baghdad is the largest city in Iraq and the second largest capital in the Arab World Region according to the density of inhabitance.The study area is situated in the central of Iraq between UTM coordinates northing (3672000-3704000) and easting (428000-456000), (Fig. 1).The Tigris River passes through the lands of the Baghdad city divides it into two parts (Karkh and Rissafa).The study area is characterized by the presence of Industrial sites, commercial and agriculture land.Baghdad is covered by quaternary sediments (Pleistocene and Holocene) and characterized by flat topography (Jassim and Goff, 2006).

Sampling and Analyses
A total of 20 samples of soil were collected to cover the majority of the city's regions, with an emphasis on the nature of each area (agricultural, commercial, industrial, residential, and roadside).Ten samples are collected from Al-Rissafa side areas (Adhamiya, Al-Wazeeria (Battery Manufacturer), Shikh Omer, Ziyouna, Karada, Shaab, Sadr city, Al-Za'franiya, Al-Dora expressway, and Alselikh) and other 10 samples collected from Al-Krakh side areas (Al-Dora, Al-Masafi junction), Al-Dora, Sayidia, Al-Salam university college, Al-Bayaa (Industrial District), Jehad, Amirya, Abu Ghraib, Al-hurriya, and Kadhimiya.All soil samples were collected in 6 and 7th November 2020 from the surface at a depth between 5-30 cm by hand auger, then transferred into labeled plastic bags.The coordinate of each sample was obtained by using GPS (Table 1).After that, all samples were sent to the laboratory for processing in preparation for the required analysis.The wet samples were dried in the laboratory using an oven set to 40Cº, homogenized, and then sieved with a 2 mm sieve in order to remove large debris, stone, gravel, plant materials, and other materials.The Pb content of the soil was determined using the X-Ray Fluorescence technique (XRF) in XRF Laboratory in Directorate of Environmental and Water Research and Technology, Ministry of Science and Technology.Mineralogical identification was performed for 19 samples by using X-Ray Diffraction (XRD), nineteen samples were subjected to identify the non-clay minerals, and four samples (5,12,13,17) were chosen to identify the clay minerals.XRD analysis was carried out in Directorate of Materials Research, Ministry of Science and Technology The spatial analysis map was designed by Arc GIS 10.4.1.Data obtained from the laboratory analyses have been subjected to descriptive statistics analysis by using IPM SPSS statistics 25.

Soil Pollution Assessment Methods
The evaluation of the soil pollution was carried out with different methods, for this purpose different indices were used for the evaluation of lead (Pb) pollution in different land use in Baghdad soil.The indices used were applied by many researchers for example Awadh (2015).These indices are Geoaccumulation index (Igeo), contamination factor (CF), and Ecological Risk Index (Er).

Index of Geoaccumulation (Igeo)
The index of geoaccumulation (Igeo) is a quantitative measure that compares current and preindustrial concentrations of metals in soil to describe the extent of metal pollution proposed by Muller (1969) and given by Nowrouzi and Pourkhabbaz (2014).This heavy metal index (Igeo) is computed according to the following equation: Where Cn is the measured heavy metal concentration in the soil sample and Bn is the heavy metal geochemical background concentration.The constant 1.5 is used to mitigate the influence of achievable fluctuations in background values caused by lithological variances (Abrahim and Parker, 2008).The values of this 7-grade index range from subzero to more than 5 (Muller, 1969), (Table 2).

Contamination Factor (CF)
The contamination factor (CF) is calculated by dividing the heavy metal concentration in the soil by the same metal's background value (Håkanson, 1980).
Where Cbackground is the average concentration of the corresponding heavy metal in the background samples and Cheavy metal is the measured concentration of heavy metal in a sample.According to Håkanson (1980), there are four types of contamination factors (Table 3).Assesses the toxicity of specific trace elements in sediments (Zheng, 2013) and is presently utilized in soil analysis to identify the ecological risk of lead in the soil of the research region.To determine the Potential of Ecological Risk index (Er) for each metal, the following equation from Håkanson (1980) was used: Where Tr is the toxic response factor, with a standard value of 5 for Pb, CF is the contamination factor.Table 4 shows the categorization of the potential ecological risk index:

Content and Spatial Distribution of Lead in the Soil
Table 5 shows the total lead content in soil samples taken from the study area in mg/kg, as well as national and international background values and the spatial distributions of lead in soil are displaying in Fig. 2.

Mineralogical Identification
The mineralogical analysis results of nineteen samples were subjected to XRD analysis are shown in Table 6.According to these analysis results, quartz, calcite, and albite are the main non-clay mineral, dolomite and gypsum were distinguished as minor minerals.Clay minerals analysis results demonstrate the presence of illite, kaolinite, chlorite, palygorskite, and montmorillonite.

Assessment of Soil Pollution
The normative calculation of the pollution assessment method is presented in Tables 7,8, and 9.

Discussion
The Pb content in soil samples ranged from 1 to 73420 mg/kg in Al-Wazeeria city (battery manufacture) (Table 5).The observed values in the industrial areas (Al-Wazeeria city, Al-Bayaa, Shikh omer and Sadr city) exceed the acceptable limits (100 mg/kg) of a world health organization (WHO, 2003).whereas, the Pb concentration in other sites are within the permissible limits.In comparison with the Iraqi standards 5 mg/kg (AL-Basssam, 2014) industrial areas and roadside are showed high differences.The Mineralogical analysis of soil samples shows the dominance of the non-clay mineral (quartz, calcite, albite, and gypsum) which are common minerals in Iraqi soil whereas, illite is dominant in the clay mineral (Table 6).The kind of clay mineral has an influence on heavy metal absorption.For example, montmorillonite may absorb more trace and heavy metals due to its expandable nature.The observed high concentration of Pb in Al-Wazeeria city (Battery manufacture) is mostly related to the manufacture of lead-acid batteries.lead is mainly the life cycle toxicity potential of lead-acid batteries, particularly the emissions of total lead into the environment (Liu et al., 2015).Whereas, the elevated concentrations of Pb in Al-Bayaa (industrial District) and Shikh Omer could be due to the application of municipal and industrial wastewater, using paints and also petroleum products.In the Sadr city elevated Pb concentration is mainly due to smelting operation which is conducted in primitive method without control.Roadside (Al-Masafi junction site) is considered as a high-density traffic site, thus Pb elevated concentration is due to the vehicles using leaded gasoline and lead-acid batteries and maybe form atmospheric emission of Al_Dora refinery.Generally, the industrial sites have the highest concentrations of Pb than roadside sites and other land-use sites.Thus, conclude the source of high Pb concentrations is anthropogenic activities.
The spatial analysis map elucidates the concentrations of Pb in Al-Rissafa side more than Al-karkh side and the reason is due to the numerous industrial areas in Al-Rissafa side.Table 7 showed the mean values of geoaccumulation index (Igeo) ranged between <0 -2.415.All Igeo mean values for soil samples were less than 0 and within class 0 which indicates that it is practically unpolluted except the industrial area where Igeo mean value was 2.415 within class 3 which indicates that is moderate to strongly polluted.These results support the hypothesis that pollutants from anthropogenic activity, such as industrial activity, which effect on study area.
The Contamination Factor (CF) is recognized as an effective and simple tool for monitoring heavy metal contamination and its high value indicates the state of pollution at that site.The values of CF for the soil samples of the investigated area are shown in Table 8, which ranged between <1 -195.075mg/kg and its value has increased in samples (5,12,13,17) which are industrial areas and this indicates the level of pollution that arise as a result of the anthropogenic effect of human activities.
The Ecological risk index (Er) mean values for Pb element in soil samples of the study area ranged between <1 to 975.375 (Table 9).The observed results reveal that there is a minimal potential ecological risk in all locations except the industrial sites, where the mean values of soil samples exceed 320, indicating a very high potential ecological risk.and world soil mean values showed that the study area has a higher Pb concentration in industrial sites than in those of other studies and the world soil average.

Fig. 1 .
Fig.1.The location map of the soil samples

Fig. 2 .
Fig. 2. The spatial distribution map of Lead (Pb) in soil of study area

Table 1 .
The Site name of land use type and coordinates (UTM)

Table 2 .
Geoaccumulation index (I geo) for soil pollution levels

Table 3 .
Soil pollution classifications depending on the level of contamination (CF)

Table 4 .
The categorization standard for possible ecological risk in soil

Table 5 .
Lead element concentration in the study area

Table 6 .
Mineralogical identification of soil samples collected from Baghdad city

Table 7 .
Mean value of Geoaccumulation Igeo for different land use

Table 8 .
Mean value of Contamination factor for different land use

Table 9 .
Mean value of Ecological Risk Index (Er) for different land use