Mercury Content, and Health Risks Assessment in the Surface Soil from Selected Sites in Kirkuk, Northern Iraq

Abstract


Introduction
Mercury (Hg) is one of the natural components of the earth's crust, as it exists in the form of a metal element or organic and inorganic compounds (Jaishankar et al., 2014).Mercury was found in ancient egyptian tombs dating back to 1500 years BC, and was named after the Roman God Mercury, known for speed and mobility, relative to the name of the fastest moving planet in the solar system, Mercury (Prakash, 2019).This element is attention because of its potential to cause adverse effects on human health and the environment worldwide (Kim et al., 2016), as a global pollutant produced by human and natural means , it acts on bioaccumulator and has a strong impact on the environment and in addition to being a strong neurotoxin.Mercury also has many harmful effects on all major body systems, especially the nervous system and the brain (Kumari et al., 2020).The element mercury also has harmful effects on the heart, blood vessels, immune system, nervous, reproductive system (Al-Jumaily& Hasseb, 2021).It is ranked 123th in the list of priority pollutants of the US Environmental Protection Agency (USEPA, 2014), as well as being a fixed and mobile toxic pollutant, this pollutant does not decompose easily in the environment and is mobile due to the volatility of the element into many of its compounds .(Gworek et al., 2020) .The most important sources of this element in natural processes and human activities are volcanic and hydroelectric activities, primary natural emissions, as well as in abandoned mines (with deposited waste), Its also resence large levels resulting from coal combustion, cement production, waste incineration, as well as anthropogenic emissions and events (Pacyna, 2020).Deposition of previously re-emitted mercury, which is deposited in the soil, is the largest storehouse of heavy elements, including mercury (Wang et al., 2019), and Mercury deposited by dry and wet sedimentation processes can react with organic matter in the surface layers of the soil, which has a high adsorption capacity at a pH(4-5) (Kabata-Pendias and Szteke, 2015).Organic matter plays a major role in the distribution of total mercury in the soil and its transport routes through the soil (Wang et al., 2012), since Mercury deposited by soil bacteria can be converted to methylmercury (MeHg), which is one of the most toxic types of mercury (Ullrich et al.,2001).The current study aims to find the levels of mercury concentrations in the surface soil in selected locations of Kirkuk Governorate and assess the environmental and health risks from it.

Study Area
The study area is located in the northern part of Iraq in the Governorate of Kirkuk between longitudes (44° 17' 06" E -44° 29' 30" E ) and latitudes (N 35° 33' 50" N -35° 19' 34") (Fig. 1) and area of 9679 km 2 and an altitude of about 350 m above sea level.The tectonic division of the study area was based on the theory of plate tectonics according to (Jassim and Goff,2006) where the study area is located within the unstable pavement (Unstable-shelf) in the well-known secondary range (foothill zone).As for the stratigraphic aspect, the city of Kirkuk includes four formations visible on the surface, which are the formation of the opening ،Wangana, makdadiya , Bay Hassan, as well as modern deposits, as they are among the oldest up to date (Jassim and Goof, 2006;Metwalli et al., 1974).

Materials and Methods
Samples are collected from topsoil at a depth of 0-20cm from various areas of Kirkuk city, Most of locations are industrial areas (Table1).Field work began on December 10, 2021 using the auger manual device and weighing (1kg), after which the samples were dried in the laboratory using an electric oven at 40 degrees Celsius, then they were ground and sieved by a sieve (mesh 200), then 10 g of each sample was placed in bags Court, labeled and sent to the laboratories of Ankara University Faculty of Engineering, Department of Geology to conduct appropriate analyses using a plasma device with a inductively coupled plasma mass spectrometry (ICP-MS).

Enrichment Factor (EF)
It is a widely used measure to determine the extent to which the presence of an element in the sample is increased in order to assess the level of soil contamination with heavy elements relative to the average natural abundance resulting from anthropogenic activity (Iqbal and Shah, 2011;Bern et al., North Gas Company Sanitary landfill 2019), and the enrichment factor was calculated according to the equation proposed by (Sinex and Helz, 1981) as follows: EF=(CHg/CFe)Sample/(CHg/CFe) reference (1) Representing CHg/CFe (sample) the ratio of the concentration of the element mercury to the concentration ratio of the element iron in the sample, and CHg/CFe (reference)is the ratio of the concentration of the reference element mercury to iron concentration ratio is a reference, and it is classified into five groups according to (Kowalska et al., 2018) (Table 2).

Contamination Factor (CF)
contamination factor is among the most important environmental factors used in assessing soil pollution by calculating the concentration of the element in the sample on its reference value,and (CF) is calculated through the following equation (Hakanson, 1980): (2) C (sample) represents: the measured concentration of the elemental mercury in the sample for the location of the study area C (background) represents: the concentration of the reference element mercury in the Earth's crust according to ( Kabata-Pendias, 2011), which is (70 μg/kg), and is divided into four categories according to (Hakanson, 1980) Table (2).

Ecological Risk Factor (Er)
The environmental risk factor (Er) is calculated to express the level of environmental risk for a particular element, as this factor was proposed by ( Hakanson, 1980) and calculated through the following equation : Er = Tf × CF (3) Where Tf represents: the toxic response factor to the element,knowing that the toxic response factor to the element mercury is (40) according to ( Hakanson,1980), and CF represents the concentration of the element on its reference ratio, and the environmental hazard factor was classified according to (Hakanson, 1980) into five categories (Table 2) .

Health Transactions
The average daily dose of the element mercury (ADD)for the element mercury was calculated with the calculation of the HQ risk factor and the HHI hazard index for the purpose of assessing the health risks of the soil in the study area and by the three tracks: ingestion ingestion, inhalation Inhalation, and dermal skin contact.The daily absorption dose of soil particles was calculated in the three tracks according to (USPES, 2011) (Table 3) based on the following equations :

Results and Discussion
Concentration of elemental mercury in the surface soil of the study area The mean concentration of the element mercury in the surface soil of the study area reached (47.19 μg/kg) and in the range of (19.8 μg/kg -89 μg/kg) at the sites of the study area (Table 4).The results showed that the highest concentration of mercury was found at the sites of Al-Nasr hospital(Health burn area) with a value of (67 μg/kg), exceeding the average concentration of Hg in the earth's crust according ( Kabata-Pendias, 2011) at the site (M41) with a value of 72 μg/kg this may be due to its proximity to the sanitary burn residues resulting from the crematorium located in the hospital, this corresponds to what mentioned by Hu et al. (2018), that waste incineration processes are one of the anthropogenic factors for the presence of the element mercury .An increase in Hg concentration at the site(M40) also noted , which represents the waste site before the sanitary incineration process at Al-Nasr hospital with a value of 62 μg/kg and this may also be due to its proximity to incineration waste, and this corresponds to what refered by (Pacyna, 2020), that the areas of mercury presence are the result of incineration of sanitary waste.
The concentration of mercury in the sanitary landfill sites reached a value of 54.68 μg/kg and the highest value was recorded in the sanitary landfill sites of the Al-Zandan area, represented by the two sites (M12 and M13) reached 77 μg/kg and 89 μg/kg respectively, which is higher than exceeding the average concentration of Hg in the earth's crust ( 70 μg/kg) according to Kabata-Pendias (2011), which are located within the landfill areas of Household, Health, cosmetics and other wastes, and this corresponds to what mentioned by (Tao et al., 2020), which showed that landfills may be an important source of mercury emissions, as landfills contribute about 5% of anthropogenic mercury emissions into the atmosphere (Pacyna et al. 2010).As for the sites near the sanitary landfill of area specifically in the two sites (M18 and M19), the concentration of mercury in them reached 37 μg/kg and 58 μg/kg respectively, due to the presence of waste in large quantities in the area, which may be reflected in its effect to increase the concentration of mercury in it, as well as the sanitary landfill site of the (Jiman area), which also had high concentrations of mercury and appeared by (65 μg/kg), which may be caused by waste decomposition processes, and this is consistent with what indicated by Tao et al. (2017), that landfills are an important source of mercury emission .The average concentration of elemental mercury in the aquarium sites of my region reached (Leylan and Bajwan) with a ratio of (49.16 μg/kg), if its concentrations of sites ( M34 ,M35 ,M36 ) were worth 58 μg/kg, 45 μg/kg,36 μg/kg respectively , this may be attributed to emissions from the Kirkuk cement plant and near the fish ponds, and this is consistent with what mentioned by Li et al. (2019), that cement plants are one of the largest anthropogenic sources of mercury emissions, At the sites (M37, M38, M39) the mercury concentration reached 56 μg/kg, 54 μg/kg, 46 μg/kg respectively in the fish ponds of the Bajwan region, and this may be due to its proximity to industrial sites such as the emissions from the North Oil Company caused by increased mercury concentrations.This is consistent with what indicated by Antuña-Nieto et al. ( 2020), that the increased concentration of mercury is a result of oil and natural gas refining processes, which are anthropogenic factors, the concentration of mercury at the Kirkuk mill sites reached 48.33 μg/kg and its concentrations at the sample sites reached M31, M32, M33 to 56 μg/kg,43 μg/kg,46 μg/kg respectively, which is less than which is higher than exceeding the average concentration of Hg in the earth's crust (70 μg/kg) according to Kabata-Pendias (2011), which is close to the industrial district area .The average concentration of the mercury in the North Gas Company reached 46.56 μg/kg and the results showed that the highest concentration of this element was found at the site M6 with a value of 68.4 μg/kgand this site is located within the company and is located on the western side and near large gas reservoirs, This is consistent with what was stated by Chalkidis et al., 2020 that the increase in mercury pollution may be a result of gas production processes.in the site M3 located on the western side of the North Gas Company, its concentration has reached 55 μg/kg and this increase may be due to the impact of the water supplied by the company and used in the gas treatment stages, while it reached on-site (M1) (51.4 μg/kg), represented by the eastern side of the North Gas Company and close to agricultural areas.The concentration at the sites (M7, M8, M9, M10)within the North Gas Company has reached48 μg/kg, 47 μg/kg, 48 μg/kg, 47 μg/kg respectively.While in the site M2 it reached 19.8 μg/kg represented by the opposite side of the North Gas Company .The concentration of the mercury at the sites of the North Oil Company reached 36.72 μg/kg and its highest concentration at the site (M29) was 49.5 μg/kg which is located on the front side of the refinery and close to the discharge of the waste raised, and its concentration was also on the left of the concentration site (M28) (41 μg/kg), which is close to the valle oil stream, and this is consistent with what ( Ezzeldin et al., 2016), stated that untreated hydrocarbons contain high concentrations of mercury, The concentration at the site M30 reached 41.9 μg/kg which is the site near the eternal fire, and this relatively high concentration is due to gas emissions in the region.

Environmental Transactions
The rate of the EF for mercury in the soil of the study area reached 0.669 with a range of 0.051-1.353 it reached its highest level at the site of the Sanitary landfill (M13), which was 1.353 while all of samples were less than 2 and they are within a low-category enrichment factor (Deficiency to minimal enrichment) .
After calculating the contamination factor of the surface soil samples in the study area, it reached 0.674 and in the range of 1.271-0.258(Table 5).It is revealed that in all the samples under study it is of low-pollution type ( low contamination) except for the two sites M12 and M13 represented by the sanitary landfill sites in the Al-Zandan area, which were with values up to1.10 and 1.27 respectively.In the Al-Nasr hospital Crematorium site (M41), the index was (1.02) with in the category of medium pollution (moderate contamination) (Table 3).
By applying the ecological risk factor of mercury in the surface soil samples in the study area of the mercury,it was found that the sanitary landfill sites of the two samples (M12 and M13), which were 50.8 and 40 respectively (Table 5) and resulting from landfill and decomposition of waste by discharge sites in Al-Zandan area, as well as the site of the crematorium of Al-Nasr hospital (M41), which was 41.14 and resulting from the burning of sanitary waste, and after comparison with the classification (Hakanson, 1980) it these sites were of medium risk (moderate potential ecological risk), while all samples for the other sites under study were of low risk( low potential ecological risk) (Table 3).

Fish ponds
The lowest and highest value with the overall sample Table 5. Indicators of environmental pollution of mercury in the study area

Non-Cancerogenic Risk Assessment
The hazard Quotient HQ factor is defined as the result of the quotient of the average dailiy dose ADD of the element mercury to the known reference dose value according to (USEPA, 2002) and for the three routes of ingestion, inhalation and skin contact separately and according to the formula : HQ=ADD/Rfd (6) The (ADD) represents the daily dose rate of the three routes in the soil, and the (Rfd) the reference dose represents the estimate of the maximum allowable element mercury where the reference value was in the route of ingestion (3×10-4 mg/kg.day ) and in the course of inhalation with a value of (8.57×10-5 mg/kg.day)and in the course of skin contact were mg/kg.day2.10×10-5 (Ferreira-Baptista and De Miguel, 2005;Li et al ., 2017) After calculating the Hazard Quotient (HQ), the hazard index(HI) for mercury was calculated according to (USEPA, 2002), the product of the sum of the risk factor (HQ) in the three tracks (ingestion, inhalation, contact and skin) and according to the following equation HI=∑〖HQing+HQinh+HQderm〗 (7) If the HQ or HI value is less than(1), there is no risk to the population, while an HQ Or HI than one (1) indicates the likelihood of non-carcinogenic health effects (Nazarpour et al., 2018).
After applying the equations of the hazard quotient HQ and the hazard index HI, it turned out that the hazard quotient and the hazard index of the three pathways were all less than 1 (Table 6), there are no non-carcinogenic health effects of mercury on the population of the study area, and they are in the following order : ingestion path > skin contact path > inhalation path for adults and children, as well as the possibility of children to be exposed faster than adults due to their spontaneous nature of inserting the hand into the mouth (Zhao et al., 2014).

Conclusions
• The concentration of mercury in the topsoil of the study area did not exceed the globally recorded geochemical value.• The study showed an increase in the concentration of mercury in some different locations, namely(Sanitary incineration in Al-Nasr hospital, sanitary landfill, north gas company and North Oil Company, fish ponds in the areas of leylan and bajwan, as well as the Kirkuk mill and the industrial district area), this increased values may be attributed to the incineration of sanitary waste, sanitary landfill, automotive waste and other industrial and anthropogenic waste.• The results of soil contamination according to the rate of the enrichment factor (EF) in the surface soil of the study area showed that mercury in all samples falls into the category of a low enrichment factor.• The contamination index (CF) result rate of the topsoil samples showed that they had low contamination.• The indicator of the ecological risk factor (ER) in the surface soil samples of the study area showed that it was of low potential ecological risk.• The results of the hazard quotient and health hazard index of the surface soil samples of the element mercury showed that they were less than one, which indicates that there is no hazardous effect on human health for adults and children.

Fig. 1 .
Fig.1.Location of the study area

Table 1 .
Locations and coordinates of samples in the study area

Table 2 .
Divisions of the EF, CF, and Er

Table 3 .
Standard values used to assess the health risk in the study area for adults and children according to(USPES, 2011)

Table 4 .
Concentrations of elemental mercury in the study area

Table 6 .
hazard index and Hazard quotient in the soil of the study area