Evaluation Heavy Metals Pollution in the Soil from some Regions of Al-Diwaniyah City / Iraq

Soil is the surface layer of the earth’s crust in which plant roots grow and some animals and other microorganisms live in it and it is considered the basis of the ecosystem, so its contamination negatively impact the health of all living organisms, especially humans who are at the top of the food chain. Heavy metals are considered among the most prominent inorganic pollutants in the soil, so this study came to evaluate the concentrations of some toxic heavy metals in areas with different activities in the city of Diwaniyah. The results of the study showed that the concentrations of heavy metals in the surface soil ranged between (0.958-2.292 mg/kg) and (19.132-73.907 mg/kg), (14.882 - 50.012 mg/kg) and (29.689-62.109mg/kg) for cadmium, lead, copper and chromium, respectively, and their concentrations in the soil at depth of 30 cm ranged between (1.529-1.971 mg/kg), (22.160 - 99.885 mg/kg), (12.790-55.630 mg/kg) and (41.278-75.467 mg/kg) for cadmium, lead, copper and chromium, respectively. Soil pollution was evaluated by using some pollution indices such as the geological accumulation index, pollution load index, contamination factor and degree of pollution. The results of pollution indices showed that the surface soil of the surface study sites and depth of 30 cm is contaminated with a very high degree of cadmium. Medium pollution with lead and little pollution with copper and chromium, and this requires great attention in order to reduce soil pollution with heavy metals, especially cadmium and lead.


Introduction
Environmental pollution with heavy metals is a widespread problem all over the world, especially in recent decades, due to the industrial development that took place in the world, which led to a significant increase in the risks of environmental pollution with heavy metals.Rapid industrialization and irregular urbanization, together with the long-term use of large amounts of fertilizers and pesticides, lead to the accumulation of toxic substances in the soil, water and air [1], [2].Soil is the upper most part of the earth's crust, which has been transformed by physical, chemical, and biological processes and atmospheric factors.It consists of mineral particles, organic materials, water, air, and living organisms organized in the horizons of the soil [3].Soil pollution is defined as the presence of a 1259 (2023) 012013 IOP Publishing doi:10.1088/1755-1315/1259/1/012013 2 chemical or substance out of place or present in a concentration higher than the normal limit that has harmful effects on any non-target organism [4].As for soil pollutants, it is defined as any substance or factor present in the soil as a result of an human activity [3] .Heavy metals enter the soil from several sources, including waste of all kinds, atmospheric deposition, animal dung, sewage sludge, inorganic fertilizers, emissions resulting from human activities as a result of industrial processes, and household and municipal waste [5].Once heavy metals enter the soil, they remain for long periods and have a long half-life of up to thousands of years depending on the type of metal.Heavy metals can only be removed from the soil by removing the soil itself [6].Exposure to heavy metals, especially compounds of cadmium and lead, is dangerous to human health, especially before birth and during the lactation period, as it causes changes in the nervous system.Exposure to lead also leads to heart and blood vessel diseases, impaired kidney function, and disorders in the immune system and liver.Cadmium is considered a carcinogen and toxic to nerves that cause skeletal disorders and liver damage.The problem of heavy metals is not only from its toxic properties, but also comes from its ability to Accumulation in the body of a living organism, when exposed to it at a low level, its symptoms do not appear directly, and its effects can be observed at the physiological and chemical levels [7], [8].Concerns about soil pollution are increasing in all regions of the world, and the United Nations Assembly adopted UNEA-3 a resolution calling for accelerating procedures and cooperation to address and manage soil pollution.This consensus achieved by more than 170 countries of the world is a clear sign of the global importance of soil pollution and the willingness of these countries to develop Concrete solutions to address the causes and effects of this major threat [4].Many studies have been conducted on environmental pollution with heavy metals in large parts of the world.Solgi et al., 2012 studied soil pollution with heavy metals in industrial areas in Iran and found that the soil of all industrial areas is contaminated with heavy metals, especially with cadmium, which recorded the highest value in average of geological accumulation [9].Also Chen et al., 2005 studied the concentration of heavy metals in the soil of gardens and found that the agricultural soil is polluted with lead and copper and has little nickel and zinc contamination [5].And also Huang et al., 2019 studied the contamination of agricultural soils in China with heavy metals and found that the concentrations of cadmium and mercury exceeded the permissible global limits, while the averages of chromium, copper, lead, zinc, nickel and arsenic did not exceed the permissible limits [10] .This study came in order to measure the concentrations of heavy metals in the surface soil and the soil at a depth of 30 cm, as well as to know the extent of soil pollution through the use of pollution indices.

The Steady Area
The current study was conducted in the Iraqi city of Diwaniyah, one of the Middle Euphaverages governoaverages, 180 km south of the capital, Baghdad.The city located between latitudes 31.8 and 32.2 north and longitudes 44.2 and 45.46 east.Five sites were chosen to conduct the study to take soil samples, as shown in table 1.

Extraction of Heavy Metals
The heavy metals were extracted in the soil by using the hot acid extraction method, as 1 gram of soil samples were placed in a glass beaker with a capacity of 100 ml, then placed in the fume hood apparatus, after that 10 ml of a mixture of concentaveraged hydrochloric acid and nitric acid was added to it in a ratio of 1:3 with ensure that the sample is completely covered with acid, then place the beaker containing the sample on a hot plate at a temperature of 80 °C for half an hour, ensuring that the extract does not dry out, then the extract is placed in a plastic container of 25 ml and 10 ml of distilled water is added to it, after that the container is placed in a centrifuge for 15 minutes at a speed of 3000 revolutions / minute, after that, the extract was placed in a 25ml volumetric flask, and the volume was filled with distilled water to the mark.The sample was kept in the refrigerator until measurement [11] and the final samples were measured using Atomic absorption spectrophotometer acetylene flame (SHIMADZU AA-7000) to extract the concentration of heavy metals in the surface soil and soil at a depth of 30 cm.The concentration of heavy metals was calculated using the following equation: Where : A: The concentration of the element after being examined in the device in ppm , B: final volume of the sample after dilution , D: sample dry weight (grams).

Geo Accumulation Index (Igeo)
It is an indicator used to evaluate soil contamination with heavy metals.It was proposed by Muller, 1969 [12].It is used by comparing the current concentrations of heavy metals in the soil with their concentrations in the pre-industrial era [13], taking into account the effects of natural decomposition, as well as human activities, environmental changes, and geological changes at the work site [14], [15] , degree of heavy metal contamination of the soil were evaluated using the global average shale [16].
Igeo = log2(Cn / 1.5Bn( where : Cn: heavy metal content in the soil , Bn: metal abundance in the preindustrial crust, 1.5: Constant is used to compensate for natural fluctuations of the heavy metals [16]. Table 2. Heavy metal pollution classification and the geographic accumulation index (Igeo).

Contamination Factor and Contamination Degree
The contamination factor is calculated for the studied samples in order to determine the extent of contamination of soil samples with toxic heavy metals and to compare the polluted and unpolluted places, where the following equation is used to calculate the contamination factor [17], [18] cf= Cm/(Bm ) Where Cf : represent contamination factor, Cm : average concentration of the heavy element in the sample, Bm: The reference value of the element in shale [16].To find out the state of pollution according to the contamination factor, we use the fallowing parameters: Cf < 1 minimal pollution, 1 ≤ Cf < 3 medium pollution , 3≤ Cf < 6 considered pollution , Cf > 6 Very high pollution Contamination degree represents the total number of pollution factors, for which the following equation is used to calculate it [17] .

Type of pollution Degree of pollution (c d )
Low contamination C d < 5 medium pollution c d ≤ 10 5 < high pollution 10 < c d ≤ 20 very high pollution C d ≥ 20

Pollution Load Index (PLI)
The pollution load index was used to find out the contamination extent of the soil of the study areas with toxic heavy metals, which was formulated by Tomlinson,1980 [19], and the average shale was used as a reference value for minerals in the soil .

PLI=√(n&CF1×CF2×…×CFn)
Where n: represents the number of heavy metals, Cf contamination factor If the PLI value is less than 1, then the soil is considered to be in an ideal condition, but if it is more than 1, then the soil is very polluted.

Concentrations of Heavy Metals in the Surface Soil
The results (Table 4 and Appendix 1) showed that the highest average of cadmium concentration in the surface soil was recorded in the first site and reached (2.292 mg/kg), while the lowest average was recorded in the fourth site and amounted to (0.958 mg/kg) and the highest concentration was recorded during study period was in July in the second site and (3.875 mg/kg), while the lowest concentration was recorded in the fourth site during December (0.053 mg/kg) .The levels of cadmium during the summer were higher than those during the winter .When comparing the results of the study with the global benchmarks and values of shale (Table 5) [10][11](22) [16], it was found that the values of cadmium levels exceed the average values of shale , Dutch and American soil determinants in all study sites are within the range allowed by the World Health Organization.The results (Table 4 and Appendix 1) also showed that the highest average of lead concentration in the surface soil was recorded in the first site and reached (56.024 mg/kg), while the lowest average was recorded in the fifth site and amounted to (19.132 mg/kg) and the highest concentration was recorded during the study period In August in the first site (107.299mg/kg), while the lowest concentration was recorded in the fourth site in June and (7.664 mg/kg) .The lead levels during the winter season were higher than the averages during the summer season .When comparing the results of the study for the lead metalwith the global determinants, it was found that the values of lead averages exceeded the average values of shale and the American determinants, and fell within the permissible level of the World Health Organization and the Dutch soil determinants.The results (Table 4 and Appendix 1) also showed that the highest average of copper concentration in the surface soil was recorded in the first site and reached (50.012 mg/kg), while the lowest average was recorded in the third site and amounted to (14.882 mg/kg) and the highest concentration was recorded in August in the first site (72.662mg/kg), while the lowest concentration was recorded in the third site in July (12.175mg/kg) .The levels of copper in the surface soil during the winter season were higher than the averages of the summer season..When comparing the levels of copper in the study areas with the global determines , it was found that its averages are within the limits allowed by the World Health Organization and less than the values of shale and the Dutch parameters, except for the first site, whose average exceeded the values of shale and the Dutch parameters.The results (Table 4and Appendix 1) also showed that the highest average of chromium concentration in the surface soil was recorded in the fourth site and amounted to (62.109 mg/kg), while the lowest average was recorded in the third location and amounted to (29.689 mg/kg).The highest concentration was recorded during the study period in August in the fourth location (102.997mg/kg), while the lowest concentration was recorded in the third site in the same month (23.638 mg/kg) .The levels of chromium in the surface soil during the summer were higher than the averages The winter season, when comparing the chromium averages in the study areas with the global determinants, it was found that they are within the internationally permissible limits and less than the average values of shale .Heavy metals are one of the natural soil components, but at specific levels.When these levels are exceeded, the soil is considered polluted [21].Soil contamination with heavy metals is a worldwide concern due to the difficulty of their removal and their accumulation, which causes toxic effects on the agricultural system, humans and animals [23],[24] [25].Heavy metals reach the soil's surface, either naturally, such as falling dust, or due to human activities through the throwing of industrial and household waste, paints, fertilizers, pesticides, etc. [26][27] .The highest averages of concentrations of cadmium, lead and copper were recorded in the surface soil in the first location represented in the industrial district, and the reason is mostly due to the proliferation of car repair shops, the continuous movement of means of transport, throwing industrial waste and damaged car paints, in addition to the presence of damaged batteries, which are considered one of the most prominent sources of lead, cadmium and other minerals harmful substances [28], [29].As for the lowest average of these metals, it was recorded in the fourth site in relation to cadmium and lead, and the third site in relation to copper.The reason is mostly due to the absence of car repair shops, and perhaps to the fact that the fourth site is characterized by being an open area, as well as not using pesticides in these areas because these areas are non-agricultural and other reasons.As for chromium The fourth site recorded the highest concentration and the reason is the proximity of this site to the electric power generation station and its emissions, of which chromium is one of its emissions.station, while the lowest average concentration of chromium in the surface soil was in the third location.

Concentrations of Heavy Metals in the Soil at a Depth of 30 cm
The results of (Table 6 and Appendix 2) showed that the highest average of cadmium concentration in soil with a depth of (30 cm) was recorded in the first site and reached (1.971 mg/kg), while the lowest average was recorded in the fourth site and reached (1.529 mg/kg).The highest concentration during the study period was in January in the first site (3.775 mg/kg), while the lowest concentration was recorded in the second site in August and it reached (0.006 mg/kg) .The levels of cadmium during the summer were higher than those during the winter.When comparing the results of the study for the soil depth of 30 cm with the international standard determents and the values of the shale (Table 5), it was found that the values of the cadmium averages exceed the average values of the shale and the Dutch and American soil determination in all study sites and fall within the permissible range by the World Health Organization.
The results (Table 6 and Appendix 2) also showed that the highest average of lead concentration in the soil at a depth of 30 cm was recorded in the first site and amounted to (99.885 mg / kg), while the lowest average was recorded in the fourth site and amounted to (22.160 mg / kg) and the highest concentration was recorded during The study period in August in the first site (120.711mg / kg), while the lowest concentration was recorded in the fourth site in June (9.580mg / kg).As for the lowest monthly average, it was during the month of February, which amounted to (38.845 mg / kg).The levels of lead during the summer season were higher than the averages of the winter season.When comparing the results of the study for the lead element in the soil at a depth of 30 cm with the international determinants (table 5), it was found that the values of lead averages exceeded the average values of shale and the American determinants for all sites and fell within the permissible level of the World Health Organization and the Dutch soil determinants except for the first site that exceeded the Dutch determinants.
The results (Table 6 and Appendix 2) also showed that the highest average of copper concentration in the soil at a depth of 30 cm was recorded in the first site and amounted to (55,630 mg / kg), while the lowest average was recorded in the second site and amounted to 12,796 (mg / kg).During the month of December, the study was conducted in the first site, and it reached (71.091 mg / kg), while the lowest concentration was recorded in the second site during the same month and amounted to (8.051 mg / kg).The levels of copper in the soil at a depth of 30 cm during the winter season were higher than the averages of the summer season.When comparing copper levels in the study areas with international standards (Table 5), it was found that its averages are within the limits allowed by the World Health Organization and less than the values of oil shale and Dutch limits, except for the first site whose average exceeded the values of shale and Dutch limits.
The results (Table 6 and Appendix 2) also showed that the highest average of chromium concentration in the soil at a depth of 30 cm was recorded in the fourth site and amounted to (75.325 mg / kg), while the lowest average was recorded in the second site and amounted to (41.278 mg / kg).The highest concentration was recorded during The study period was in June in the fourth site (94.555mg / kg), while the lowest concentration was recorded in the second site in January (34.225 mg / kg) .The levels of chromium in the soil at a depth of 30 cm during the summer were higher than those in the winter.When comparing the chromium averages in the study areas with the international determinants, it was found that they are within the internationally permissible limits and less than the average values of shale.
The highest concentrations of cadmium, lead and copper metals were recorded in the soil at a depth of 30 cm in the first location.The lowest concentrations of these metals were recorded in the fourth location for cadmium and lead, and the second location for copper.This is mostly due to the same reasons mentioned in the concentration of these minerals in the surface soil.As for chromium, the highest average was recorded.concentration in the soil at a depth of 30 cm in the fourth site, and its lowest average was recorded in the second site.

Contamination Factors and Contamination Degree
The results table (7) showed that the values of the contamination factors for surface soil ranged between (3.1957 -7.6420), (0.9566 -2.8012), (0.3307 -1.1113) and (0.3307 -0.6901) for cadmium, lead, copper and chlorine, respectively.According to these values, surface soil is described.It is highly polluted with cadmium, moderately polluted with lead, and slightly polluted with chromium and copper.
The results table (7) showed that the values of the degree of pollution ranged between (5.3512-12.134),where the first site recorded the highest degree of pollution, while the fourth site recorded the lowest degree of pollution.According to the values of the contamination degree, the surface soil of the study areas is moderately polluted in all study areas except for the first, which is considered high polluted, and this increase in the degree of pollution in the first site is due to the high value of the contamination factor for the cadmium element in this site, which is originally due to the high concentration of this element in the first site (Appendix 1).Also, the results table (8) showed that the values of the pollution coefficient in the soil at depth of 30 cm ranged between (5.0976-6.5707), (1.080-4.9942), (1.2362-0.2842)and (0.8385-0.4586) for cadmium, lead, copper and chlorine, respectively, and according to these the values describe the soil at a depth of 30 cm as being contaminated with considerable to very high degree of cadmium, medium to considerable contamination for lead, low to moderately contamination for copper, and low contamination for chromium .The results table (8) showed that the values of the degree of pollution ranged between (7.5570 -13.3198),where the first site recorded the highest degree of pollution, while the fourth site recorded the lowest degree of pollution .According to the values of the degree of pollution, the soil with a depth of 30 cm is considered modeaveragely polluted in all study areas except The first site, which is considered polluted to contamination degree, and this increase in the degree of pollution in the first site is due to the high value of the pollution factor for the cadmium and lead metals in this site, which is originally due to the high concentration of these two metals in the first site (Appendix 2).

Pollution Load Index (PLI)
The results of Table (7) showed that the values of the pollution load index for the study areas ranged between (0.9796 -1.9271),where the first site recorded the highest value of the pollution load index, while the third site recorded the lowest value.According to the values of the pollution load index, the surface soil of the study areas is described as very polluted in all study areas except for the third site which is described as somewhat ideal.Also The results of Table (8) showed that the values of the pollution load index in the soil at a depth of 30 cm for the study areas ranged between (1.0388-2.1417)where the first site recorded the highest value of the pollution load index, while the second site recorded the lowest value according to the values of the pollution load index, the soil with a depth at 30 cm is described as very polluted in all study areas, especially the first site, whose soil is considered highly polluted.The results table 10 showed that the values of the geological accumulation index in the soil at a depth of 30 cm ranged between (1.0195-1.3141),(0.2216-0.9988), (0.0568-0.2472), and (0.0417-0.1377) for cadmium, lead, copper and chromium, respectively, according to the values of the accumulation index.
According to the values of the geological accumulation index, the soil with a depth of 30 cm is described as moderately polluted with cadmium in all study sites and not contaminated to less contamination with other metals.

Conclusion
The results of the study showed that the concentrations of cadmium in the surface soil and the soil at a depth of 30 cm exceeded the American and Dutch limitation and the values of shale and did not exceed the WHO within the internationally permitted determinants, soil contamination with cadmium at a high average is considered dangerous because of the toxic effects this metal causes on living organisms in general and plants in particular, being the basis of the food chain, and this requires great attention in order to reduce the sources of pollution with this metal.Therefore, the results of this study Important in order to improve the soil and reduce its contamination with toxic metals.

Table 1 .
Locations, details, and settings of the study area.
2.2.Sample CollectionSamples were collected from the surface soil and from the soil at depth of 30 cm monthly from the study sites during the summer and winter seasons (2022-2023) using the individual method for 1259 (2023) 012013

Table 4 .
Concentrations of heavy metals in the surface soil of the study areas during the summer and winter seasons (the first line is the range, the second line is the average ± the standard deviation).

Table 5 .
Standard determinants of heavy metals in soil.

Table 6 .
Concentrations of heavy metals in the soil at a depth of 30 cm of the study areas during the summer and winter seasons (the first line is the range, the second line is the average ± the standard deviation).

Table 7 .
Indicators of surface soil contamination with heavy metals at the study sites.

Table 8 .
Indicators of soil contamination with a depth of 30 cm with heavy metals in the study sites.The results table9showed that the values of the geological accumulation index ranged between (0.6391-1.5284), (0.1913-0.5602), (0.0661-0.222) and (0.0659-0.1380) for cadmium, lead, copper and chromium, respectively According to the values of the geological accumulation index, the surface soil is described as low to medium contamination with cadmium and not contaminated with other metals.

Table 9 .
Geological accumulation index of heavy metals in the surface soil of the study sites.

Table 10 .
The geological accumulation index of heavy metals in the soil at a depth of 30 cm for the study sites.