Spatial Distribution of Heavy Element in Erbil's Municipal Landfills by Using GIS

Untreated municipal solid waste (MSW) release onto land is prevalent in developing countries. To reduce the high levels of harmful components in polluted soils, a proper evaluation of heavy metal concentrations in Erbil's Kani Qrzhala dump between August 2021 and February 2022 is required. The purpose of this research was to examine the impact of improper solid waste disposal on soil properties within a landfill by assessing the risks of contamination for eight heavy elements in two separate layers of the soil by using geoaccumulation index (I-geo) and pollution load index (PLI) supported. The ArcGIS software was employed to map the spatial distribution of heavy element pollution and potential ecological risks. The I-geo values in summer varied from -1.700 to 3.560 for Zn, 5.045 to 8.175 for Cd, 2.318 to 4.329 for Pb, 0 to 3.374 for Mn, 1.439 to 3.880 for Ni, 0.638 to 2.278 for Cu, - 0.541 to 2.665 for Cr, and -2.495 to 0.778 for Hg. Based on the I-geo categorization, the contamination levels of Zn, Cd, Pb, Mn, Ni, Cu, and Hg ranged from uncontaminated to extremely contaminated. However, all metals were assessed as uncontaminated throughout winter, except I-geo (Cd) and I-geo (Ni) varied from -0.467 to 3.966 and -5.720 to 2.015 were classified from as uncontaminated to strong and uncontaminated to moderately/strongly contaminated respectively. According to the PLI category, most samples were rated as "highly polluted" during summer, but during the rainy season, all samples were rated as "unpolluted".


Introduction
Heavy element contamination of soil has received significant environmental focus in recent years.Industry, coal and fuel burning, and car emissions, mining operations, use of fertilizers and pesticides, municipal solid waste disposal, and other activities are the sources of trace element releases into the soil, particularly urban soils 1,2 .
In developing countries, ineffective solid waste management is a significant issue.So, the ecosystem has become contaminated with potentially hazardous substances.The absence of a clear approach for source segregation can intensify contamination of the environment.Waste disposal has emerged as an essential component of integrated solid waste management when Landfilling is the most popular method for disposing of various solid wastes worldwide 3 .
The geochemical characteristics of agricultural soils, especially the concentrations of heavy elements, determine the quality of the soil 4,5 .Accumulation of heavy elements may endanger humans and natural systems via exposure to polluted soil or food, Phytotoxicity endangers the food chain (plant-soil-human), pollutes groundwater, and degrades food quality (safety and commercial viability), and declining soil use for crop output, resulting in food shortages and communal land issues 6 .
Crop development requires the frequent application of substantial volumes of nitrogen, phosphorus and potassium fertilizers in modern agricultural practices.Compounds containing trace amounts of these elements, but when applied continuously in the form of fertilizers, they can greatly enhance the soil mineral composition 7 .
In addition, heavy elements such as nickel, boron, cadmium, lead, arsenic, cobalt, and chromium make significant health risks to humans, animals, and vegetation.Ni, for instance, promotes plant growth, but excessive Ni can increase likelihood to both humans and other animals.But presence of too much Ni within soil can raise the probability of skin, nose, and lung cancers 8 .Soil pollution causes foundation failure, land subsidence, landslides, contamination of groundwater quality, etc.Therefore, it is crucial to understand the contamination properties of soils to guarantee the integrity of structural components and inhibit the failure of existing structures 9 .Physical, chemical, index, and engineering properties can be used to deduce the contamination characteristics of the soil.The manual processes of spatial model evaluation, interpolation, and generation are difficult and time-consuming.GIS can be useful in such situations.Because of the rapid development of GIS applications in fields such as contamination, noise pollution, commercial and utility GIS, and so on, in which data is gathered in discrete form, interpolation methods can be employed to acquire continuous data 10 .
Globalization and unregulated agricultural activities have altered natural landscapes and ecosystems 11 .Hence, the assessment of soil contamination must take into account a deep understanding of the spatial distribution of contaminants 12 .
A GIS database would provide comprehensive information for low-cost soil monitoring 13 .heavy elements distribution and concentration must be analyzed.This will allow the determination of pollutant levels and the evaluation of their effects on the environment and human health.Soil toxic element analysis and mapping can aid in the development of strategies that encourage the appropriate utilization of soil nutrients, decrease soil degradation, and increase agricultural output.Soil pollutants are surveyed and their spatial distributions are analyzed using geophysical survey 14   .The Kriging function is helpful for assessing pollution levels comprehensively 15 .To reduce the excessive concentrations of toxic components in polluted soil, precise estimation of toxic element concentrations in soils, backed by GIS database systems, is necessary 16 .
So, the objectives of this study were to (i) map soil contamination based on three heavy elements (Cd, Pb, and Ni) using (GIS) in 26 soil sites and two soil layers; and (ii) evaluate the possible contamination for eight heavy elements using I-geo and PLI in two distinct soil strata.

The Study Area
The study area is located north of Kani Qrzhala Sub District Fig. 1 in Erbil City, on the left side of Erbil-Mosul major road, Iraq.The location's longitude and latitude belong to (latitudes 36°10'23" north and longitudes 43°35'32" east; Fig. 1).In which, the landfill, began operations in 2001, covers an area of 37 acres.The vast bulk of the landfill area has already been occupied.The location gets almost 2000 t of municipal solid waste every day (based on data collected from ELS administrative staff).The waste is transported into landfills, which are then filled without separation and covered with layers of soil.The site was selected because it is now used as a rubbish dump and septic tank discharge region, highlighting the environmental repercussions that are developing.

Soil Analysis:
Samples of soil were collected from 26 representative sites in Erbil's Kani Qrzhala subdistricts between August 2021 and February 2022.Soil sites were selected on the basis of local geological characteristics to show how the different landfill processes work.Different layers of soil were sampled depending on their distinct shapes.Since each physiographic unit encompasses contains multiple profiles, the level of certainty in the distribution is high due to the extensive coverage of the physiographic units.As illustrated in Fig. 1, the investigated profiles and soil sample sites were ascertained utilizing a Global Positioning System (GPS) unit German-made.
Soil samples were gathered from the preferred top layers.Because there are no morphological variations in the soil profiles in the investigation area, soil samples were taken at two depths.At levels of, 0-5 cm and 5-30 cm, two soil samples were obtained from each profile and collecting soil samples was at summer and winter.All samples were packed in plastic bags and returned to the lab.The samples were composited, homogenized, dried at temperatures ranging from 25 -35 degrees Celsius, crushed, and sieved to 2 mm 17 .
Aqua regia (EDTA 0.05M) was used to take a sample of 5 g of powdered soil to determine element concentration.The concentration of Zn, Cd, Pb, Mn, Ni, Cu, Cr, and Hg was measured by an atomic absorption spectrometer (Atomic Absorption Spectrometer, Perkins Elmer, USA 1100D).Furthermore, heavy elements levels in soil were compared to threshold levels in mg kg -1 dry soil 18 .

GIS Application:
Throughout this investigation, GPS was used to obtain data from Erbil and coordinate points.Every location's latitude and longitude were recorded, and all received data were processed using ArcGIS version 10.8 from 2 .The Kriging interpolation method software was used to calculate the intensity of each of the three heavy elements (Cd, Pb, and Ni).Kriging produces a satisfactory outcome when the points are distributed uniformly and a significant number of elevation points exist in a particular region.Furthermore, sample points are assumed to be independent of one another 19,20 .Interpolation is typically used to forecast cell values in a pattern format using a given number of sample data points.It is a useful technique for predicting unknown values for a specific set of geographical location information.

Assessment of Contamination: Geoaccumulation Index (I-geo)
The I-geo reflects contamination by comparing heavy elements levels determined with background values previously used to evaluate bottom sediments 21 .The geographic accumulation index (Igeo) was used to measure heavy elements contamination with the following Eq.1: where Cn is the observed concentration of heavy element in the soil and Bn is their geochemical background concentration (medium crust) 22 .To limit the impact of any changes in threshold values that might be attributable to variations in sedimentary rocks, the constant 1.5 was included in Eq 1.Although soil is a component of the earth's surface and its chemical structure is related to that of the crust, this concentration falls between the concentration observed and that of the elements in the crust 23 .Table 1 depicts the I-geo classification.

The Pollution Load Index (PLI)
The PLI is a geometric mean of impurity coefficients (Cif) that characterizes the donation of all heavy metals in a given location 24 .The contamination factor (CF) was calculated by dividing the heavy element content by the reference value using the following Eq 2 25 : CF= The following Eq 3 was employed to construct the pollution load index (PLI), which is used to evaluate element contents in soils in relation to the background level 26 : Where CF represents the contamination factor and n represents the total number of elements.This variable can be employed to assess the degree of environmental contamination in addition to improving and observably enhancing the quality of the soil.The classification of PLI is displayed in Table 2.

Results and Discussion
The Variation of Eight Heavy Metals in Two Different Layers of Soil: In this study, contamination with Zn, Cd, Pb, Mn, Ni, Cu, Cr, and Hg was examined in two distinct soil layers, during summer and winter.In summer, the zinc concentration at the landfill site was between 32,312 to 1,238,230 mg kg -1 .Statistically, there were significant differences p <0.05 between the Zn concentrations at the down site, landfill site, and top site.As predicted, the maximum concentration of Zn metal was found at the landfill's down-site location, with a value of 1238.230mg kg -1 , while the lowest concentration was found at the top-site (32.312 mg kg -1 ).The existence of Zn within the landfill site could be related to heavy element disposal, which also contains the dry cells and the combustion of electrical waste 27 .Zn is a micronutrient that plays an important role in enzymatic processes, and its availability in the soil can result in decreased Cd uptake by plants 28 .Even if the Zn content exceeded the allowable concentration level, excessive consumption may be harmful to human health.
Cadmium is an infrequent heavy element, but it is the most harmful heavy element to human health 29 .Cadmium concentrations were found to be significantly different p <0.05 between sampling sites in this study, Table 3.The lowest Cd content was 20.165 mg kg -1 and the highest concentration was 177.715 mg kg -1 of the metal, Table 3 Pb contents were found at site 13, indicating that the element is highly mobile Table 4.
Mn varied from 731.971 to 7589.760 mg kg -1 , the accumulation of Mn could be attributable to the careless dumping of solid waste and the introduction of leachate into the soil.Furthermore, a high concentration of manganese might be the result of garbage containing dry cell batteries, paints, glasses, and ceramics that were dumped at the landfill sites, as well as contamination from manganese dioxide cells, for which the city has no regulated disposal techniques 33 .
The mean Ni concentrations varied from 117.927 to 640.340 mg kg -1 in landfill soils were greater than at the background level Table 5. Nickel is a harmful element typically found in leachate from hazardous waste landfills.It is generated through metal finishing, electroplating, organic waste, and the combustion waste of fossil fuels 34 .The existence of Ni in soils near the landfill may reveal that it did receive some industrial waste.There were considerable differences in Ni content between different layers at p <0.05.
Cu concentration varied from 90.804 to 283.024 mg kg -1 .Both 35 and 36 elevated levels of Cu were discovered in the soils surrounding landfills.Copper is utilized in the production of numerous goods, such as wires, automotive components, pipelines, and alloy wheels that end up in landfills.
Chromium is an essential trace element for human health and well-being.Chromium pollution is a significant environmental threat that has negative effects on our surroundings and natural resources, particularly soil and water.Overexposure may lead to increased accumulation in human and animal tissues, resulting in toxic and negative health impacts.Several studies have found that chromium is a poisonous substance that interferes with plant metabolic processes, reducing crop yield and growth and decreasing grain and vegetable quality 37 .Cr varied from 261.797 to 566.048 mg kg -1 .
Hg ranged from 0.133 to 1.286 mg kg -1 , Tables.3, 4, 5, and 6 along the two different layers in summer, the elevated levels of mercury associated with nearly three-quarters of the mercury in municipal solid waste come from battery packs and fluorescent lighting, which are expected to continue to be major mercury sources in the near future.
Reduced or eliminated mercury levels in household items, especially batteries and fluorescent lights, ought to be the primary concern in mercury control in municipal solid waste, whereas mercury concentrations in consumer goods must also be set at appropriate and attainable levels using a lifecycle approach 38 .
In contrast, the low amount of heavy elements in the soil during the winter months is a result of heavy elements infiltrating the soil even during the cold season 39 , the Zn ranged from 9.021 to 138.788 mg kg -1 , Cd ranged from 0.445 to 9.611 mg kg -1 , Pb ranged from 12.418 to 73.303 mg kg -1 , Mn ranged from 1.014 to 175.829 mg kg -1 , Ni ranged from 0.240 to 8.373 mg kg -1 , Cu ranged from 0.743 to 101.476 mg kg -1 , Cr ranged from 4.717 to 12.547 mg kg -1 and Hg ranged from 0.005 to 0.038 mg kg -1 Tables 7, 8, 9 and 10 all over the two different layers.
In accordance with the research findings, all heavy elements were greater than permissible limits during summer, with the exception of Hg, which was within permissible limits in several sites.heavy elements in solid waste are mostly made up of toxic waste, such as batteries, paints, and inks 40 .As a result, the amounts of heavy elements are much lower in winter than in summer because the unequal slope and wet climate of our landfill encourage drainage and leaching of heavy elements by rainwater, resulting in lower percentages.Nevertheless, concentrations of heavy elements in household waste are lower than in industrial waste

41
. According to 42 , the majority of heavy elements existing in soils contaminated by household solid waste could be removed through runoff, draining out, and infiltration.

Assessment of Contamination Risk Using Geoaccumulation Index:
In this investigation, soil contamination was evaluated using I-geo.In the various soil layers, the I-geo results showed widespread contamination by Zn, Cd, Pb, Mn, Ni, Cu, Cr, and Hg.In summer, Igeo (Zn) ranged from -1.700 to 3.560, indicating that the concentration of Zn in landfill soils ranges from uncontaminated to strongly contaminated ,Tables 11 and 12 13 and 14.Lower levels of heavy metals in winter due to the leaching of heavy metals by precipitation.Cd contamination in the different soil layers.Thus, according to Pb maps, the majority of the investigation sites are green, implying that a significant part of the study areas was uncontaminated by Pb during the winter due to metals leaching into the lower part of the soil.Furthermore, the Ni maps 5-30 cm of soil were mostly pink, indicating that the soil was uncontaminated/moderately contaminated to moderately/strongly contaminated, but the upper portion of the soil was mostly green, denoting that the majority of the soil was uncontaminated by Ni.According to the data, the I-geo values of three heavy metals were detected as non-polluted in highly polluted environments.In the different soil strata, the Cd, Pb, and Ni concentrations measured by I-geo vary significantly, Figs.5-10.According to I-geo categorization, the Cd, Pb, and Ni varied from uncontaminated to extremely contaminated.The I-geo (Cd) exhibited a high accumulation influence in numerous samples, indicating high rates in the majority of samples during summer.In winter, there was also non-polluted soil in sample soil 6, as shown in Table 13.These data suggest that the two soil layers in Erbil's Kani Qrzhala Subdistrict are rich in Cd, Cr, Ni, Cu, Pb, Zn, Hg, and Mn.The primary causes of soil contamination with Cd, Cr, Ni, Cu, Pb, Zn, Hg, and Mn are electronic products, electroplating waste, paint waste, spent batteries, etc. 44 .

Conclusion
This study reveals environmental contamination near the landfill site, emphasizing the importance of a comprehensive public health approach to deal with environmental contamination in local communities.Heavy elements were found in soils at the Erbil municipal waste landfill, including zinc, cadmium, lead, manganese, nickel, copper, chromium and mercury.Elements concentrations ranged as follows: Mn > Zn > Pb > Ni > Cr > Cu > Cd > Hg.Heavy element concentrations were generally highest at the landfill site.Furthermore, the soils at the landfill are highly contaminated with Mn (> 7000 mg kg -1 ).The presence of metallic substances in the earth's crust, as well as Mncontaining waste, is attributed to the high level of Mn content in the soil.The findings indicated that a solid waste open dump site has a negative impact on soil quality in the study area and is a possible source of risk to human health via the food chain.
According to the findings of this study, the soils surrounding the landfill are not suitable for agricultural activities due to heavy element leaching that may be picked up by food crops.These heavy element contaminants, however, were all below the allowable limits for agricultural soils.The EPA must conduct regular monitoring and raise awareness to ensure waste segregation prior to dumping in order to reduce elevated levels of contaminants (heavy elements) at the landfill, which may pose serious health risks.Alternatively, remediation technologies (for example, phytoremediation) could be introduced at the site to aid in the decontamination of the landfill area, particularly Mn.Eventually, it will be clear that a methodical and ongoing heavy element pollution control program is required, as well as other mitigation measures to reduce the rate and extent of pollution issues in the future.

Figure 1 .
Figure 1.Study area location and sites of sample collection.
43 , I-geo (Cd) values varied from 5.045 to 8.175 are classified as extremely contaminated; I-geo (Pb) values varied from 2.318 to 4.329 are classified as moderately/strongly contaminated to strongly/extremely contaminated; I-geo (Mn) values varied from 0 to 3.374 are classified as uncontaminated to strongly contaminated, and I-geo (Ni) values ranging from 1.439 to 3.880, I-geo (Cu) values between 0contaminated.I-geo (Cr) ranged from -0.541 and 2.665 are categorized as uncontaminated

Figure 2 .
Figure 2. Spatial distribution of I-geo (Cd) in the two different layers of soils at study sites during summer.

Figure 3 .
Figure 3. Spatial distribution of I-geo (Pb) in the two different layers of soils at study sites during summer.

Figure 4 .Figure 5 .
Figure 4. Spatial distribution of I-geo (Ni) in the two different layers of soils at study sites during summer.

Figure 6 .
Figure 6.Spatial distribution of I-geo (Pb) in the two different layers of soils at study sites during winter.

Figure 7 .
Figure 7. Spatial distribution of I-geo (Ni) in the two different layers of soils at study sites during winter.Assessment of Contamination Risk Using Pollution Load Index:Elsayed et al.,45 developed the "pollution load index" (PLI) as a straightforward and proportional approach for determining the degree of heavy metal pollution.Hence, it is a unique indicator for comparing the level of pollution in various areas.The PLI outcomes, Figs.8 and 9, were observed to be very high PLI > 1 for all of the analyzed samples during summer.Due to the influence of distinct outer causes of soil pollution, such as solid waste, industrial and agricultural operations, the PLI

Figure 8 .
Figure 8. Pollution load index values and pollution levels in (0-5 cm) soil at study sites during summer.

Figure 9 .Figure 10 .
Figure 9. Pollution load index values and pollution levels in (5-30 cm) soil at study sites during summer.

Figure 11 .
Figure 11.Pollution load index values and pollution levels in (5-30 cm) soil at study sites during winter.

Table 14 . Geoaccumulation index (I-geo) for (Ni, Cu, Cr and Hg) during winter.
Baghdad Science Journal layers were noted with increasing concentrations towards the middle portions of the study area, which might be related to the proximity to significant waste accumulations that may encompass batteries.Most of the work area is orange on the Ni maps, which means that a large part of the area being looked into was moderate to strongly contaminated with Ni.
Figs. 5-7 depict the spatial distributions of I-geo during summer for heavy metals in the study area.The maps of the Cd distributions are entirely colored differently, showing that the soil layers of study sites were extremely contaminated with Cd.Furthermore, increasing concentrations of Pb in soil 2024, 21(3): 0867-0893 https://dx.doi.org/10.21123/bsj.2023.8382P-ISSN: 2078-8665 -E-ISSN: 2411-7986