Evaluation of Heavy Metals of Lead, Nickel, Cadmium, Vanadium and Some Chemical Parameters in Surface Soils of the City of Khorramabad

This study was conducted in 2017 with the aim of determining the distribution of heavy metals lead, nickel, cadmium, vanadium and the parameters of acidity, electrical conductivity and organic matter in the surface soils of the city of Khorramabad. Sampling was performed monthly from 12 stations and was repeated 3 times in the autumn. The highest amount of cadmium was observed in the soil samples of industrial areas of the city in the two sampling periods of October and December to be 7 ppm. A comparison of the mean measured values of heavy elements showed that the highest average amounts of heavy elements are in industrial areas and the lowest in residential areas. The lowest amount was measured in 8 th and 11 th stations at 2 ppm. The highest amount of lead in the 6 th station, a bustling area, was measured to be 22 ppm. The average nickel in industrial areas was higher than other areas. In industrial area, during the sampling period of October, its amount was determined to be 58 mg/kg. The highest amount of vanadium was recorded in staion9 at 52 mg/kg. Lead has a significant correlation with nickel, cadmium and soil acidity. This correlation is 0.01% for acidity and cadmium variables and 0.03% for nickel. Nickel has a significant correlation with cadmium and vanadium at the level of 0.01%. The results indicate that the surface soil of the city of Khorramabad is not contaminated with the studied metals. In general, the results showed that both human and natural factors are always involved in the distribution and concentration of heavy metals.


INTRODUCTION 1
Soil pollution due to heavy metal pollution is one of the most serious environmental threats to soil quality [1,2]. The severity of this problem has increased in industrialized countries in recent decades [3]. Recent developments in the global economy have led to an increase in heavy metals in soil, both in type and amount [4]. In particular, the contamination of agricultural soils due to the widespread use of chemical fertilizers, natural pesticides, animal manures, irrigation with sewage and sewage sludge, solid wastes, chemical compounds and atmospheric sediments in an effort to increase crop yield [5,6].
Heavy metals have negative effects on human health because of their stability and toxicity [12] and may be transmitted to the human body through ingestion, inhalation and skin contact or through the food chain [13]. Although dust inhalation is primarily hazardous to human health, heavy metal dust is also concentrated in the soil and with the migration of metals may become a secondary environmental hazard in terms of agricultural and vegetable contamination and ground water pollution [14]. Cadmium is a heavy metal with significant toxicity and has a destructive effect on most organs. The metal can be widely distributed in the human body, and its main sources are contamination from cigarette smoke, welding, and cadmium-contaminated foods and beverages [15,16]. Lead is the most importanttoxic heavy element in the environment. Due to its important physical and chemical properties, its use is very common and important. It is a very important environmental chemical that is distributed on the surface of the earth and is very dangerous. Of all the organs, the nervous system is the most affected by lead metal. However, the toxicityof this metalhas more effect on children than on adults. This is because their internal and external tissues are softer than adults [17,18]. Nickel is found in very low levels in the environment. Itis present in a variety of soils and meteorites, and also erupts from the release of volcanic gases. Inhaling nickel fro m smoke of fossil fuels, fires and cigarettes can be very dangerous for the human respiratory and circulation system [19,20]. Vanadium is an element found naturally in the environment and is distributed in the earth's crust at an average concentration of 100 mg/kg. In general, vanadium compounds have the low toxicity. Most of the toxic effects of vanadium compounds cause local irritation of the eyes and upper respiratory tract [21]. According to the studies conducted in the field of environmental pollution and human health risk of heavy metals, it is necessary to study the spatial distribution of metals. Heavy metal spatial distribution data helps researchers identify areas where hazards are high and then present them to decision makers so that repairing methods can be implimented [22,23]. In recent years, many studies have been conducted on heavy metal pollution, source identification, distribution pattern, pollution rate and human health risks worldwide [2,4,[24][25][26]. Ruiz-Fernandez et al. [9] showed the spatial and temporal distribution of heavy metal concentrations and their enrichment in Mexican soils. Manjuladevi et al. [19] reported that the distribution of heavy metals was larger than the previously measured values in Murcia, Spain. They pointed out that heavy metal contamination in soils was mainly caused by industrial activities in the city of Murcia [19]. Zhao et al. [4] reported that potentially hazardous metals in agricultural soils are contaminated with the cadmium, copper, zinc and nickel metals in southeastern China. They also said that higher concentrations of heavy metals in the soil could adversely affect soil quality, reduce crop yields, and also contaminate crops, resulting in potential health risks to humans [4]. Jiang et al. [27] also proved that human activities have had a significant impact on the accumulation of heavy metals in urban soil in China's Jiangsu Province. Determination of heavy metal concentrations in urban soils of Rawalpindi, Pakistan showed that soil contamination by the studied cadmium, cobalt, chromium, copper, manganese, nickel, lead and zinc metals has been due to vehicle traffic and traffic and industrial effluents [28].
Therefore, due to the importance of heavy metal hazards, this study was conducted to investigate the spatial distribution of cadmium, lead, nickel and vanadium heavy metals and to determine the physical and chemical parameters of electrical conductivity, acidity and organic carbon in surface soils of Khorramabad.

Study area
The city of Khorramabad has a position of 48 degrees and 20 minutes to 48 degrees and 23 minutes east longitude and 33 degrees and 27 minutes to 33 degrees and 33 minutes north latitude and has three urban areas and is located in Dalon north-south of the country. This has caused a large number of vehicles to pass through the crossing and communication line that passes between the city of Khorramabad, and also during the last decade, the city of Khorramabad has grown rapidly in terms of population, size and location of industries and workshops. Which all caused the spread of various types of infections.

Sampling
This descriptive cross-sectional study was conducted in 2017. In order to determine the number of sampling points according to the area of Khorramabad city, the types of land uses in the city and financial constraints; 12 sampling points were selected to conduct research ( Figure 1). This choice was based on different uses

Measurement of parameters
Using the standard method of the US Environmental Protection Agency, chemical digestion of soil samples and measurement of heavy metal concentrations were performed by ICP-MS method, Varian 710-ES model made in the USA. First, the soil samples were passed through a sieve with a 2 mm holes and worn with a porcelain mortar and turend into a soft powder for testing, then weighed 0.5 g for testing. For chemical digestion of soil samples, 3 to 4 drops of 1 N hydrochloric acid were added to it and 5 ml of Soltani acid was added to 0.5 g of soil sample;and the solution was placed on the heater. Then 3 ml of perchloric acid was added and heating was continued until the mix became almost dry. The solution was then diluted using 50 ml of 1 Normal hydrochloric acid solution [29].
To determine the acidity of soil hub, samples were prepared according to ISO10390 standard method and then the pH of the sample was measured by a pH meter. To do this, soil samples were sieved using a sieve with a 2 mm Pores. Afterwards 20g of each soil sample was weighed and dissolved in 50 ml of water and mixed well, the sample was kept stationary for 17 hours and then the acidity of the smaple was measured using the device. To determine the electrical conductivity, the sample was prepared according to the ISO11265 standard method and then the electrical conductivity of the sample was measured by an EC meter. The percentage of soil's organic matter was determined by LOI (Loss On Ignition) method. Samples were prepared according to ASTM 2974-00D standards method and then the amount of organic matter was measured [30].

Pollution factor
Pollution factor (CF) was used to determine the contamination of elements in the studied top soils. In this equation, Cn is the concentration of each element in the soil and Co is the average concentration of each element in the field. According to the classification provided by Hakanson, CF<1 shows low pollution, 1≤CF<3 shows moderate pollution, 3≤CF<6 shows high pollution and CF≥6 shows severe pollution [31]:

Pollution load index
The pollution load index (PLI) was calculated using the following equation. In this formula, CF is the pollution factor, which is obtained from the pollution factor equation for each metal, and n is the number of metals studied. Pollution load index values vary from zero (noncontaminated) to 10 (highly contaminated). Typically , values less than 1 indicate no contamination, and values greater than 1 indicate contamination with heavy metals [31]:

Enrichment factor
The enrichment factor (EF) for each metal was calculated from the ratio between the normalizing element to the background value of the elements, according to the following equation. The reference element in determinin g the enrichment factor is an element that has a purely geological origin. In this research, the iron element was used as a reference metal. According to the proposed classification, EF<2 shows low pollution, 2≤EF <5 shows moderate pollution, 5≤EF<20 shows high pollution, 20≤EF<40 shows very high pollution, and EF≥40 shows extremely high pollution [31]:

Ecological risk
Ecological risk (Er) assessment was calculated fro m Equation (5). In this regard, CF stands for pollution factor, and Er shows the ecological risk of each element under study. Hakanson [31] defined the TR value, which is an indicator of the toxicity of heavy metals, for the analysis of the obtained values into four different groups. Ecological risk for each element is classified into five levels: low risk Er<40, medium risk 40≤Er <80, significant risk 80≤Er<160, high risk 160≤Er<320 and very high risk Er≥320 [31]:

Accumulation index
Accumulation index (Igeo) can determine the degree of soil pollution. This index, first proposed by Muller, is used in environmental analysis to identify contaminated surfaces and was calculated from Equation (6). In this regard, Igeo is the land accumulation index, Cn is the concentration of heavy metal in the soil, Bn is the concentration of the ground (average shale). In this regard, in order to modify the effects of soil parent materials and natural fluctuations in the given substance' s content in the environment, a coefficient of 1.5 was used. It also corrects very little change caused by human activities. Muller Classification Basis classifies into seven classes of contamination: Igeo<0 non-contaminated, 0≤Igeo<1 non-contaminated to slightly contaminated, 1≤Igeo<2 slightly contaminated, 2≤Igeo<3 slightly contaminated to highly contaminated, 3≤Igeo<4 highly contaminated, 4≤Igeo<5 highly contaminated Severely infected and highly Igeo≥5 highly classified [33]:

Statistical analysis
In order to statistically process the data, SPSS V.18 software was used. The normality of the data was checked by the Kolmograph-Smirnov test. To confirm the type of data distribution, the Kolmogorov-Smirnov test was used at 95% confidence level. One-way analysis of variance (ANOVA) was used to compare the mean concentrations of the evaluated elements between sampling stations. The relationship between variables was examined using the Pearson correlation test. The Microsoft Excel software was used to draw tables and graphs.

RESULTS AND DISCUSSION
The results of measuring the physicochemical parameters of the soil of the region, which include the parameters of acidity, organic matter, and soil texture, are summarized in Table 1. The highest amount of pH in the 4 th station is 7.7 and the lowest amount is in the 6 th stationis 6.9. The highest electrical conductivity was measured in the 12 th stationat the rate of 4.8 microsiemens per centimeter and the lowest in the 7 th stationat 0.74. The highest amount of organic matter observed in the 5 th station was 3.21% and the lowest amount was recorded in the first station at 0.06%. Descriptive statistics for heavy metals including mean, standard deviation, standard error, variance, skewness, and elongation coefficients are presented in Table 2. Apart from the mean, other statistics are part of the dispersion indices and are used to determine the type of test used (parametric or non-parametric). Results are also provided for verification and validation. The standard deviation in the nickel parameter is 46.41, which shows a relatively large dispersion. However, this value for the cadmium parameter is 4.58.
Temporal and spatial variations of the measured elements in the 12 sampling areas are presented in Figures  ppm. The lowest amount was measured in the 8 th station and 11 th station to be 2 ppm. The measurement showed that the maximu m amount of lead is equal to 22 ppm at the sixth station, which is a busy area. The average nickel in industrial areas was higher than in other areas. In industrial town No. 1, during the sampling period o f October, its amount was measured to be 58 mg/kg. The highest amount of vanadium was recorded in 9 th station to be 52 mg/kg. A comparison of the mean measured values of heavy elements in residential, traffic, and industrial sampling areas is shown in Figure 6. These results showed that the highest average amount of heavy elements are in industrial areas and the lowest in residential areas.
The results of Pearson correlation test between the studied variables are shown in Table 3. Lead has a significant correlation with nickel, cadmium and soil acidity. This correlation is 0.01% for acidity and cadmium variables and 0.03% for nickel. Nickel has a    Figure 7. Based on cluster analysis, metals and parameters were divided into two main groups; The first group includes cadmium, lead, acidity, electrical conductivity, and soil organic carbon and the second group includes vanadium and nickel.
According to the results of the pollution factor, heavy metals cadmium, lead, nickel, and vanadium in the surface soils of Khorramabad had low pollution, with the highest amount of pollution factor being related to cadmium metal at the first station (1.4) and the lowest level of this index being related to Vanadium metal was obtained in 12 th station (0.11) ( Table 4).
The results of land accumulation index showed that the heavy metals cadmium, lead, nickel, and vanadium in the surface soils of Khorramabad were free of contamination, cadmium metal was moderately contaminated only in the first and second stations. Also,   the highest values of land accumulation index of cadmium metal were 2.27 and 1.31. However the lowest value of this metal was 0.075 in 12 th station (Table 5).
According to the results of the pollution index, heavy metals cadmium, lead, nickel and vanadium in the surface soils of Khorramabad had low pollution, with the highest amount of nickel-metal pollution factor was measured 10th station (0.369) and the lowest level of this index was related to Vanadium and was obtained at 12 th station (0.0563) ( Table 6).
The results of Nemro contamination index also showed the absence of heavy metal contamination in the surface soils of Khorramabad, only cadmium metal in first station (1.34) had moderate contamination. The highest score index values for lead, nickel and vanadium were obtained in second,10 th , and 9 th stations to be 0.37, 0.63, and 0.276, respectively. Also, the lowest values of the Nemro pollution index for nickel and vanadium in 12 th and 6 th stations were 0.28 and 0.101, respectively ( Table 7).
The results of the enrichment factor showed that the heavy metals cadmium, lead, nickel and vanadium in the surface soils of Khorramabad in all stations studied are of natural origin and anthropogenic activities had a small role in the pollution of these metals. The highest values of enrichment factor related to nickel metal in tenth station were 0.738, but the lowest value of this index was related to vanadium metal and was measured to be 0.1125 in 12 th station (Table 8).
Ecological risk assessment of heavy metals cadmiu m, lead, nickel and vanadium in the surface soils of Khorramabad in all studied stations showed that they were at low risk. The highest ecological risk values of cadmium, lead, nickel, and vanadium were obtained in second, third, 10 th , and 9 th stationsto be 24.733, 21.78, 20.65 and 11.05 respectively (Table 9).     In this study, the average amount of cadmium and nickel metals in the surface soils of Khorramabad was higher than the concentration of these elements in the earth's crust, but the amount of lead and vanadium was lower. The mean background concentrations of cadmium, lead, nickel and vanadium are 0.25, 57.57, 40.74 and 110 mg/kg, respectively [29,34]. According to the obtained results, it can be stated that higher levels of cadmium and nickel metals than the concentration of the field indicate that anthropogenic activities have increased the amount of metals' concentration in the soil of the study area.
The variable of sampling area had a significant effect on the concentration of heavy elements (P<0.05). For nickel and cadmium, the P-value is less than 0.01, so spatial variations have a great impact on the concentration of these two elements. The value of P in the lead element is calculated to be 0.032, which indicates the existence of a significant difference between the stations at the level of 0.05. Although spatial changes in this element had less effect than other elements. However, these changes are statistically significant (P<0.05). The value of P was calculated to be 0.02 for the element vanadium, which shows that the concentration of this element in the measuring stations was significantly different at the level of 0.003 (P<0.05). Leads are derived from fossil fuels and their main source in urban environments is vehicle traffic [17,18], Therefore, a significant difference in lead concentrations in traffic stations with other areas can be explained. Many studies attribute high levels of lead in soil to industrial and anthropogenic activities [7,[9][10][11].
Sampling areas (residential, industrial and traffic) were not effective in the concentrations of the studied elements for lead, nickel and vanadium (P>0.05). But, for the element nickel, these values had a significant difference at the level of 0.05 (P<0.05). However, the average concentration of all elements in industrial areas was more than traffic and residential areas. Statistical analysis shows that there was a significant difference between traffic and industrial areas as well as industrial (P<0.05). The average concentration of vanadium and nickel in industrial areas was higher than residential areas. Therefore, it can be inferred that because nickel is released from fossil fuels into the environment [20,26], through the ceramics industry, the production of special batteries, electronics industry, manufacturing of steel tools and equipment enters the environment [35], and the release of vanadium into the environment is mainly associated with industrial resources, especially oil refineries and coal power plants [21,36], for these reasons, the amount of nickel and vanadium in the soil of industrial areas were higher than residential areas.
Cadmium levels in traffic and industrial areas are higher than in residential areas, which is obvious; but, it should be noted that the amount of cadmium in residential areas is also higher than the concentration of this element in the earth's crust. It should also be noted that soil cadmium levels are strongly influenced by human agricultural and industrial activities [16,27]. The metal enters the environment through activities such as mining, metal industry, chemical industry, metal working water, superphosphate fertilizers, cadmium-containin g pesticides, as well as the production of some metal alloys and battery manufacturing [35].
Correlation analyzes show a correlation between lead and nickel, cadmium and acidity. This correlation is 0.01 for acidity and cadmium variables and 0.03 for nickel and lead. Nickel has a significant correlation with cadmiu m and vanadium at the level of 0.01. The element vanadium has a significant correlation with the values of electrical conductivity and nickel. Based on cluster analysis, metals and parameters were divided into two main groups; The first group included cadmium, lead, acidity, electrical conductivity, and soil organic carbon and the second group included vanadium and nickel. Different cluster groups represent differences in the geochemical behavior and different origins of metals. Therefore, the metals in a group have the same and natural origin. Cluster analysis is a multivariate statistical method used in this study to identify the origin of elements. The cluster tree connects homogenous options to create larger clusters and to measure similarities between specimens [37,38].
The mean concentrations of heavy metals lead and cadmium in the surface soils of Bojnourd were 9.10, 63, 3.63 and 0.20, 18, 0.18 mg/kg, respectively. The concentration of heavy metals in the urban soil of Bojnourd may be due to traffic and industrial activities [39]. Heavy metal contamination has also been reported in surface soils around Ahvaz Industrial Town No. 2 [40]. In all areas of Zahedan (except residential areas), the average concentration of cadmium, chromium, copper, nickel, lead, and zinc was higher than the concentration of the background. Concentrations of cadmiu m, chromium, copper, nickel, lead and zinc were 0.1, 37.53 96 6.96, 29.54 10 10.25, 51.9 8 8.53, 25.25, respectively. It was 28.37 6, 184.30 94 25.94 mg/kg of soil. The results of this study showed that land use has a significant effect on increasing the concentration of heavy metals in the surface soil of Zahedan. The highest concentrations of metals were obtained in commercial and high-traffic areas where there was higher vehicle traffic in the mentioned areas, so reducing traffic and improving the public transportation system in these areas can lead to improved soil quality in these areas [25]. In another study, the concentration of lead and cadmium in soils of different regions of Isfahan has been reported to be higher than the global average [41]. The average concentrations of heavy metals vanadium and nickel in roadside soils around the Rasht-Qazvin freeway were 46.63 and 9.48 mg/kg. Based on the results obtained in this study, the surface soils of the study area are slightly polluted in terms of the studied metals, but studies of environmental conditions showed that despite the results, concerns about the release of pollution load in the soils around the freeway should always be present; because due to the existence of agricultural fields in the region, a significant part of the metals are removed from the environment by crops every year during the process of biosorption [42]. According to the results of the mentioned studies, various industries such as metal mining to computers and electronics, chemical fertilizer factories, dyeing, textile, weapons and thermal power plants, oil and petrochemical industries, steel and piping industries, hospitals and slaughterhouses livestock, and poultry are involved in causing heavy metal pollution [43,44]. Metallic elements such as copper, nickel, lead and cadmium are in the group of human activities and enter the soil through the use of chemical fertilizers, fungicides, industry, and sewage sludge [45]. In other words, human activities, especially agricultural effluents, industrial wastewaters, and pollution from the transportation industry cause a significant amount of heavy metals to enter the environment [46]. Assessment of soil heavy metals for the environment and human health in Yangtze Basin region of China shows a moderate enrichment factor for cadmium and selenium was observed. The potential ecological risk index shows a significant difference in the areas with moderate risk. However, several relatively severe areas were contaminated with cadmium, arsenic, and mercury by the land accumulation index, and as a result, these areas were classified as a significant risk or high risk [47] Adedeji et al. [48] investigated the spatial distribution and health risk assessment of soil contamination by the heavy metals cadmium, chromium, copper, manganese, nickel, lead, and zinc in Ijebu-Ode, Nigeria. Geographic Information System (GIS) data, pollution indices (enrichment factor, Igeo index) and health risk assessment model were used to analyze the spatial distribution, pollution level and potential health risk of heavy metals, respectively. The average concentrations of the seven heavy metals studied are as follows s: zinc> lead> manganese> copper> cadmium> nickel> chromium, respectively. There is a great deal of spatial variation in the distribution patterns of heavy metals. Cancer risks of copper, manganese, lead and zinc for children and manganese, lead and zinc for adults were higher than acceptable. Anthropological activities resulting from various urban uses are involved in the level of pollution and spatial distribution of heavy metals in the soil. Increased urban soil pollution may contribute to some health risks for residents of the study area [48]. According to the results presented in this study and other studies and research, biological monitoring of heavy metals in soil and plants should be carried out continuously and intermittently, because studies and research on heavy metals show that if, in the coming years, safety rules are not implemented environmentally the concentration of heavy metals in the soil will increase and as a result, they will be transferred to plants and enter the human food cycle, and diseases caused by heavy metals will be more prevalent [49,50].

CONCLUSIONS
The results of the calculations of the studied pollution indices showed that the intensity of pollution in first and second stations (industrial towns) is high. In third station is at the the middle level and other stations are free of pollution. In fact, first and second stations are moderately polluted and other stations are free of pollution. The results of the ecological risk assessment also showed that only in the industrial town's stations the ecological risk is at a moderate level for the cadmium element. At other stations, the ecological risk is low. The results showed that the natural share of each of the studied heavy metals is more than the share of man-made effects in a way that the man-made effects reache zero, the highest share of man-made effectsare cadmium and then lead. For the elements of nickel and vanadium, the man-mad e component is negligible. The results indicate that the surface soil of Khorramabad is not contaminated with the studied metals. In general, the results showed that human and natural factors are always involved in the distribution and concentration of heavy metals.