Heavy Metals Pollution Assessment in Soil of Al-Zubair Area, Southern Iraq

ABSTRACT


Introduction
With increasing of the industry, there has been a significant increase in industrial waste released into the environment, mostly into the soil, water and air causing heavy metals to accumulate, especially in urban areas.Uncontrolled heavy metal leakage into the land and rivers is a significant environmental problem.They are hazardous and cannot be broken down into non-toxic forms causing a global health issue.The principal causes of pollution in urban environments are population expansion, industrial activity, and cars in large cities.Some indications of environmental urban pollution include top soils, roadside and roadway dusts (Yeung et al., 2003;Sezgin et al., 2004).The accumulation of heavy metals in ecosystems is a global issue.This is because of their hazardous nature, widespread origins, and cumulative effects.Large quantities of heavy and trace metals left to accumulate in soil and water can be toxic to the land, flora and fauna of the sea, disrupting sensitive ecological equilibrium and contaminating food supplies, which could have negative consequences for human health (Hardaway et al., 2004).Metals like copper, nickel, zinc, and manganese are required for soil and plant and have beneficial effects even at low quantities, whereas lead, mercury, and cadmium are non-essential and hazardous even at extremely low concentrations making them possible cofactors in cancer.
Heavy metals found at elevated levels of soil are easily absorbed by humans through inhalation of dust-contaminated air or skin contact (Benhaddya and Hadjel, 2014).High levels of toxic metals have devastating effects on human and animal health including stunted development and growth, damaged organs, blood-forming systems, the cardiovascular, renal, and reproductive systems, harm the neurological system, and even death.In addition, exposure to these metals is associated with deficits in or lowered attention, aberrant behavior (Christoforidis and Stamatis, 2009).Anthropogenic sources of such metal could be found, such as the combustion of gasoline, diesel, and coal, as well as industrial operations (Loredo et al., 2003;Manasreh, 2010), together with the natural geochemical processes, such as weathering, can all contribute to the presence of heavy metals in soil.The study aims to assesst soil pollution of Al-Zubair area after using different pollution indices.

Methodology Study Area
It is located in Al-Zubair district, between latitudes (30° 20'-30° 24' N) and a longitude (47° 40'-47° 44' E) at the southwestern part of Basrah Governorate, with an area about 1134 km²; it is surrounded by many oil and gas fields, Al-Shuaiba oil refinery, State Company for Petrochemical Industry and Fertilizer factory plants (Fig. 1) (Municipality of Zubair Directorate, 2015).

Physiochemical Properties:
Measurements of physiochemical properties such as pH, EC, and TOC were conducted at Chemistry Department at Marine Science Center, University of Basrah.Ec and pH of soil were measured according to Mclean method ((1982).The absolute amounts of total organic carbon (TOC) were measured using Walkey and Black's method (1934) at the Geology Department of the University of Basrah.Eleven soil samples were selected to sieve for determining the particle size distributions.The Pipette method (Folk, 1974) is used to calculate the silt and clay content in soil, heavy metals were measured using an Agilent 7700 ICP-MS technique.Panalytical PW3830 X-ray diffraction analysis is also used to identify the clay and non-clay minerals in soil of at the laboratories of Iran University.

Pollution Assessment 1. Pollution Index (PI) and Integrated pollution index (IPI):
Both PI and IPI are broad indicators for pollution (Faiz et al., 2009).The PI is determined using the equation: where Cn is the concentration of the analyzed element, and Bn shows the geochemical background.
For the first equation, both Cn and Bn were defined according to (Kabata-Pendias, 2011) (Table 1).

Geo-accumulation index:
The geoaccumulation index (Igeo) is a good method to evaluate the pollution developed by Muller (1969) following equation.
Where Cn is the measured concentration of the investigated metal in the soil and Bn is the metal's geochemical background concentration or reference value as determined by Kabata-Pendias (2011).Factor 1.5 is used because natural variation and human activity can both affect the baseline concentration of a given metal, requiring adjustment.

Enrichment Factor (EF):
Metal pollution and its effect on the environment can be gauged by looking at the enrichment ratio (EF).When comparing the levels of contamination in various environmental media, EF is a useful tool because of its universal formula (Benhaddya and Hadjel, 2013).In order to evaluate metal concentration, the EF, a normalization approach established by Simex and Helz (1981), is used.The ratio of metal concentration to another soil component is normalized (Rubio et al., 2000).
Where (CM/CFe) is the ratio of the amount element of concern (CM) to the amount of Fe (CFe) in the soil sample (ppm), and (CM/CFe) is the same ratio in an unpolluted reference sample (Kapata and Pandis, 2011).The classification of enrichment factor is applied according to Jiao et al. (2015).

Physiochemical properties and grain size analysis
The soil's acidity plays an important role to capture elements from the surface (Appel et al., 2002).Acidic conditions make many heavy metals more mobile allowing them to travel with the water through the sediments.In alkaline environment, heavy metals deposited as oxides, hydroxides, phosphates, and carbonates phases (Al-Khafaji and Jalal, 2020).The pH was high at AL-Shuhdaa station and the lowest value was at Hay Al-Askary station.Al-Shuaiba station had the lowest value of TOC (0.21%), while the industrial sector station around Al-Shuaiba Refinery had the highest value due to the oil spill near the refinery.Soil moisture content influenced the electrical conductivity (EC) of the soil.Soil particle size and texture are so closely correlated with EC (Crisso et al., 2005).The salinity (EC) level in Al-Shuaiba station is extremely high (52.8ms/cm).Because the dissolved salt in water, urban areas tend to have higher salinity than rural regions, which may be a result of industrial activities like irrigation of land.Grain size analysis show that the soil is comprised of silty sand with low content of soil.The comparison between the results of the study area and the world soil background (Kabata-Pendias, 2011), and the world soil background (Rudnick et al., 2003) is shown in Tables (2,3).

Mineralogy
The X-ray diffraction patterns of bulk soil samples shows that quartz and calcite are the dominated non-clay minerals (Fig. 2a).The most common clay mineral is mixed layer montmorillonite-chlorite followed by illite, palygorskite, kaolinite, and chlorite (Fig. 2b).Clay minerals (hydrous aluminosilicates) can be found as colloidal form in almost types of soil, sediments, rocks.Clay is able to absorb cations and anions through ion exchange or adsorption, so clay minerals serve as a natural scavenger of contaminants in the environment (Yuan et al., 2013).All tests show that clay dosage is correlated positively with the adsorption rate (Liu et al., 2010).It is clear from the majority of researches that even a very low concentration of clay minerals can remove significant amounts of heavy metals from contaminated media.

Heavy metals
The mean levels of arsenic, cadmium, nickel, lead, and zinc are above a global geochemical background levels for soils (Kabata-Pendias, 2011) (Table 2).In general, the means of Cr, Co, Fe, Mn, and Cu are lower than normal value.Due to the increase of human activity, there is high concentrations of heavy metals in soil effected by industrial waste, vehicle emission, oil and gas exploration around Al-Zubair City.This indicates the discrete inputs from anthropogenic activities, which had a significant impact on soils, especially vehicles and industrial emissions, fossil, garages, metal workshops and waste dumps.The mean concentrations of Pb in soil of study are lower in comparison with the previous studies in Iraq and International Soil (Table 4).The mean of Zn is higher than its concentration reported in some International Soil, but have lower content in comparison to Jeddah City, Saudi Arabia, Hong Kong, and at Highway among Basra-Nasiriya and Samawa (Al-Khafaji and Al-Saleh, 2018), southern Iraq (Table 4).The mean of Co and Cr are lower than in previous studies.Generally, every region has a distinctive heavy metal signature depending on the industrial activity density, used technology, regional weather, and wind patterns .

Pollution Evaluation 1. Evaluation of Geo-accumulation index (Igeo)
According to Igeo values (Table 5), the pollution levels of Cd in all stations are higher than the other metals.Cd falls in unpolluted to moderately polluted' except in Kut Al-Markaz station (center of the city), which fall in moderately to heavily polluted.Other elements fall into the category of practically unpolluted.Zn is practically unpolluted, except in Al-Faraha and Al-Thoahrat stations.Generally, the Igeo of the heavy metals have the order: Cd >As>Ni>Pb>Zn>Fe>Cu>Cr>Mn>Co, suggesting that the main causes of pollution is human activities such as industrialization, urbanization, urban and industrial wastes, and car emissions.

Enrichment Factor (EF)
EF is employed to speculate on whether or not heavy metals have a lithogeny or anthropogenic origin because it is a handy measure of geochemical trends; (Sutherland 2000;Ye et al. 2011).The extreme values, as well as the mean of EF are shown in (Table 6) the maximum value of Pb was recorded Near Al-Shuaiba Refinery (11.729ppm) while the minimum at Mazraea(Khazim Al-Saraifi) station (2.098ppm), the significant enrichment of Pb in the most stations indicate anthropogenic sources (Table 6,Fig 3).Zn have moderate enrichment except in Al-Faraha and Al-Thoahrat station which have very high enrichment of Zn.Whereas Mn, Cu and Cr have minimal enrichment.The EF value of Co was very high Near Al-Al-Shuaiba Refinery and have extremely high enrichment in the most station.The enrichment factor of metals in study area have the order: EFCo>EFCd>EFAs>EFPb>EFZn>EFNi>EFCu>EFCr>EFMn in the most stations the Co, Zn, Cd, Pb and As have higher enrichment in comparison to natural soil, the classification of enrichment factor according to (Jiao et al.,2015) and have high EF confirming an important role of anthropogenic sources of pollution, such as the vehicle emissions incineration of waste, in addition to the pollutants of power stations, the emissions of Al-Shuaiba oil refinery and petrochemical company around Al-Zubair city.

Pollution Index and Integrated pollution index of heavy metals (PI, IPI)
The data of PI exhibited that Mn, Fe, Cu, Cr and Co have lower values of PI, while Pb, Ni, and as have medium pollution indices.Zn and Cd have highly pollution indices (Table 7) (Fig. 4).Therefore, the soils in these locations may have been extensively impacted by traffic and industrial sources.The results show that: Kut Al-Markaz, Al-Faraha and Al-Thoahrat stations have medium to high values of IPI (Table 7).Therefore, the soil in these locations may have been extensively impacted by increase of traffic gases released from nearby Al-Zubair oil fields in addition to the effect of Al-Shuaiba refinery.

Fig. 4 .
Fig.4 .Integrated pollution index (IPI) of heavy metals in the soils