Distribution and Evaluation of Lead and Cadmium in Some Soils Surrounding East Baghdad Oil Field

Soil acts as a last sink for elements that people release into the environment through a range of activities due to its physiochemical characteristics. These substances, whether are organic or mineral pollutants, accumulate in the soil and constitute a significant risk to the ecosystem in general because they mess with the chemical and physical equilibrium of the soil, get into the food chain, and eventually get to people. When pollutant concentrations during the bioaccumulated process exceed the global standards for what is regarded as a contaminant in water, air, and soil. Nine soil samples were collected from different sites and two samples from each site at two depths (0-20 and 20-40 cm) to determine if there were any differences in element concentrations at each depth near the East Baghdad oil field in Iraq in February 2022 and analyzed to determine the impacts of industrialization and pollutants related to urbanization. When the grain sizes of the soil samples were analysed, the predominated size fractions were Loam + Clay Loam. The trace elements analysis using atomic absorption spectrometry for the examined soil samples showed levels of Pb and Cd within the global average. The physicochemical characteristic of soil samples was examined. The pH of soil samples from the study area ranged from 7.24 to 7.87, with a mean value of 7.631, indicating that the soil is slightly alkaline


Introduction
Oil and gas well drilling produce hazardous compounds that could have an adverse environmental impact [1]. In addition to serving as a geochemical sink for contaminants, soil also functions as a natural buffer, regulating the transport of chemical elements and substances to the atmosphere, hydrosphere, and biota. This makes the soil a very unique component of the biosphere. However, the most important role of soil is its productivity, which is basic for the survival of humans [2]. Heavy metals are particularly of environmental concern because of their potential toxicity and their importance as an essential nutrient background concentrations of heavy metals in soils are, therefore, important due to the recent interest in contamination potential and toxic effects of these elements on humans and the environment [3]. One of the beneficial but poisonous trace elements is lead (Pb), which is also one of the most prevalent and extensively dispersed environmental metal toxins [4]. Since 1920, lead alkyls have been added to gasoline as anti-knocking additives, which has led to an increase in the concentration of lead in the air, surface water, and soil [5]. As well as the few maxima discovered are crucial numbers since cadmium (Cd) is thought to be the most hazardous heavy metal [6]. Significant effects on terrestrial ecosystems, agricultural productivity, and health impacts are caused by Cd-contaminated soils [7].
The purpose of this research is to identify the soil's Pb and Cd concentrations, local distributions, and accumulation locations in some soils surrounding the East Baghdad oil field and compare them to global ratios.

Location and Geological Setting of the study area
The East Baghdad oil field is situated between latitudes 44.31877 and 44.3504 and longitudes 33.50312 and 33.48871 Figure1. The East Baghdad field may extend over 100 km from north to south, with a maximum width of more than 10 km. The field has a complex structure that links to an oil-trapping transverse fault and a central fault that traverses the length of the field [8]. An entire depiction of a flood plain made up of Quaternary deposits may be seen in the study area. Pleistocene and Holocene deposits might be more than 250 meters thick [9]. Most of the Mesopotamian plain is covered by the Holocene strata, which are composed of a complex as well as the alternate sequence of sand, clay, silt, and gravel. The province of Baghdad is mostly situated on the Unstable Shelf of the Arabian Plate in the Tigris Subzone of the Mesopotamian Zone [10].

Figure 1:
Map of the study area shows the location of soil samples.

Sampling and analysis
Eighty soil samples were taken as part of the research that was carried out on 12/2/2022. Each site had two depths of soil analyzed. Each sample comprises a depth component (0-20 cm for sample A and 20-40 cm for sample B). Some samples are situated approximately 5 km to the east of the Baghdad oil field, while other samples are located within the oil field. All samples were kept in sealed Ziploc bags with labels for further inspection, and indeed, the precise location was determined using GPS data, as shown in Table 1. Each sample was then processed in a lab so that it could be used for the required analysis. The humid samples were set apart sufficiently enough to dry completely overnight and dry the soil at 110°± 5° C. after which they were sieved using a 2 mm sieve to remove big debris, stone, gravel, plant matter, and other contaminants. In the laboratory of the Directorate of Environmental and Water Research and Technology, Ministry of Science and Technology, all soil samples were tested for geochemical characteristics such as pH, electrical conductivity (EC), organic matter (OM%), and grain size analyses, while Atomic Absorption Spectrometry (AAS) were analyzed in University of Baghdad, College of sciences Department of Biology.

Pb and Cd abundance
The result of AAS for Pb and Cd are shown in Table 2. They indicated that Pb concentration varied from 7.2 ppm in S9B to 19.5 ppm in S9A, with a mean of 12.777 ppm. While the concentration of Cd ranged from 0.84 ppm in S3B to 1.37 ppm in S (A3 and B7), with a mean of 1.087 ppm The WHO, 2003 [11] for Pb and Cd proposed soil quality standard was used to compare the chemical contamination in the soil, Table 3 displays these requirements. The effects of industrial emissions and leaded gasoline are thought to provide the greatest environmental concern among the different anthropogenic and natural sources of Pb contamination. According to estimates made by [12], the rate of Pb concentration in soil is at least 20 times higher than the rate of natural clearance.
The top 15 cm of soil still contains up to 90% of Cd pollution from various sources. Industrial Cd wastes are a well-known significant cause of illness in farmlands of many different countries [13]. As a Comparison with worldwide soil studies [11] for Pb 100 ppm and Cd 3 ppm. According to the WHO, lead concentrations were all within permissible values, indicating that they are beyond the normal range. The acceptable limit of Cd is because there is no increased amount of Cd in the soil at any of the locations that have been analysed [14].

Spatial distribution of heavy metals
Any estimate of the environmental effect of heavy metals must take into account the geographical distribution of heavy metals in soils. The GIS method creates a map to estimate the spatial distribution of Cd contents in the soil of study area using the spatial analyst extension in Arc Map [15]. As shown in Figures 2, 3, 4, and 5.
The map showed that the concentrations of Pb increased in site 9A and Cd increased in site 7B.

Soil physio-chemistry 3.3.1 Grain Size Analysis
The physical texture of soil comprises a range of minerals, oxides, and organic compounds as well as a particle size distribution [16]. The soil's texture affects the soil's ability to exchange and retain chemicals introduced into the soil by solutions [17]. Contamination frequently affects the texture class because fine earth, like clay, absorbs more cations than coarse fractions [18]. As shown in Table 4, grain size assessments for eighteen soil samples show that soil samples S1(A) and S7(A, B) are clay loam, where (loam) is a soil that is mostly made of sand (particle size > 63 µ), silt (particle size > 2 µ), and a small amount of clay (particle size 2 µ). Its particle composition is roughly 40-40-20% sand-silt-clay by weight. These proportions, however, can vary to some extent, resulting in a variety of loam soils: Some of the terms used to describe different types of soil are sandy loam, silty loam, clay loam, sandy clay loam, silty clay loam, and loam [19]. S1 (B), S2 (A, B), S3 (A, B), S4 (A, B), and S5 (A, B) (A, B), and S10 (A) were of loam, while S6 (A) was of clay size.

pH
The pH of soil samples from the study region varies between 7.44 and 7.87, with an average value of 7.634 (Table 3), indicating that the soil is slightly alkaline. Pb is retained less firmly and is more soluble under low soil pH (pH =5, acidic environments). Lead is retained more tightly in the soil at pH levels that are close to neutral or higher (pH>6.5, neutral to basic conditions), and its solubility is very low [20]. Because the amount of Cd released into solution from adsorption sites is dependent on the pH of the environment, acid soils can be expected to have higher levels of mobility and availability to plants [21] (Table 5, and Figure 6).  To establish the relation between pH, Lead, and Cd concentration correlation coefficient was used in this study. Correlation coefficients often aim to study whether there is some association between 2 observed variables and to estimate the strength of this relationship by using the Pearson equation [22].
Where: X, Y = the variations (in this study Vanadium concentration and pH) r = Correlation coefficient n = Number of observations  The result of the equation indicates that there is a positive relationship between Pb concentration and pH value in the study area that is mean when the pH is high Pb concentration is high too. As shown in Table 7 Cd has a positive relationship with pH.

Electrical conductivity (EC)
The amount of moisture that soil particles contain has an impact on the soil's electrical conductivity. Clays has a high conductivity, silts have a medium conductivity, and sands has a low conductivity. As a result, the size and texture of soil particles have a significant impact on EC correlations [23]. The soil is slightly saline, according to the EC values of the soil samples, which varied from 2.38 to 3.01 and had an average value of 2.571 as in Table 8,9 and figure 7.

Organic matter (OM%)
The portion of the soil that is made up of plant or animal tissue in various stages of decomposition is known as soil organic matter [25]. The test results of all soil samples in the study area showed that the concentration values of organic matter (OM%) ranged from 0.48%-0.89% with a mean of 0.612% as shown in Table 10 and Figure 8.

Discussion
The Pb in soil samples ranged from 7.2-19.5 ppm and Cd concentrations were between 0.84 and 1.37 ppm. These values are all within [11] -permissible limits, suggesting that they are within the usual range. The research soil's pH ranges from 7.44 to 7.87, with a mean of 7.63, indicating a slightly alkaline soil and very little saline in the study area. The concentration values of organic matter (OM%) ranged from 0.48%-0.89% with a mean of 0.60. Grain size analyses showed that the soil ranged between loam-clay loam and clay.

Conclusions
To investigate the effects of oil and oil factories on the local soil and the pollution that emerges from them, this study employed some analyses to determine the pollutant components, including: -The geochemical analysis of the studied soil samples showed that Pb and Cd concentrations in soil samples are within the permitted values in all locations. -According to geographical distribution and contour maps, Pb concentration is at its maximum in the study area in S A9 (19.5) and the maximum concentration of Cd was at SB7 -Grain size analyses of eighteen (18)  -The pH of soil samples from the research region indicates that the soil of the study area is slightly alkaline and very slightly saline.

Recommendation
-Examine the presence of radiation in the study area.
-Research should be conducted regularly seasonally, to determine the change in pollutant concentrations in the soil.
-Check for any potentially dangerous trace elements in food that produce grown near to an oil field site to assess any potential direct health effects.
-Conduct regular blood tests on workers in the oil fields to assess the levels of trace elements in their blood and search for any possible health problems.