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Pollution and health risk assessment of heavy metals in agricultural soil, atmospheric dust and major food crops in Kermanshah province, Iran
Ecotoxicology and Environmental Safety 163 (2018) 153–164
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Pollution and health risk assessment of heavy metals in agricultural soil, atmospheric dust and major food crops in Kermanshah province, Iran
T
⁎
Shahab Ahmadi Doabia, , Mahin Karamib, Majid Afyunia, Mojgan Yeganehc a
Department of Soil Science, College of Agriculture, Isfahan University of Technology, Isfahan 84156-83111, Iran Department of Soil Science, Faculty of Agriculture, Razi University, Kermanshah 6715685438, Iran c Soil and Water Research Institute (SWRI), Agricultural Research Education and Extension Organization, Karaj 31785-311, Iran b
A R T I C LE I N FO
A B S T R A C T
Keywords: Heavy metals Agricultural soil Atmospheric dust Pollution levels Health risk assessment Kermanshah
A total of 167 samples of agricultural soil, atmospheric dust and food crops (wheat and maize) were collected, and four heavy metals, including Zn, Cu, Ni, and Cr, were analyzed for their concentrations, pollution levels and human health risks. The mean heavy metal contents in the agricultural soil and atmospheric dust were exceeds background values and lower than their IEQS (Iranian Environmental Quality Standard) with an exception of Ni. A pollution assessment by Geo-accumulation Index (Igeo) showed that the pollution levels were in the order of Ni > Cu > Cr > Zn for agricultural soils and Ni > Cu > Zn > Cr for atmospheric dust. The Ni levels can be considered “moderately to heavily contaminated” status. The human health risk assessment indicated that noncarcinogenic values were below the threshold values (1), and main exposure pathway of heavy metals to both children and adults are ingestion. The carcinogenic risks values for Ni and Cr were higher than the safe value (1 × 10−6), suggesting that all receptors (especially wheat) in Kermanshah province might have significant and acceptable potential health risk because of exposure to Ni and Cr. The carcinogenic risk for children and adults has a descending order of Ni > Cr, except for wheat. These results provide basic information on heavy metal contamination control and human health risk assessment management in the Kermanshah province.
1. Introduction The potential public health risk associated with the intake of metals from dust and soil has been the subject of discussion in recent years (Wei and Yang, 2010). Heavy metals (HMs) in dust and soil can be easily transferred into human body via three routes: ingestion, inhalation and dermal contact (De Miguel et al., 1998; Madrid et al., 2002; Aelion et al., 2008; Li et al., 2013; Qing et al., 2015; Wu et al., 2015). Agricultural, industrial, and urban developments have raised the possibility of metals’ accumulation in food crops and as a consequence, their risk for human health and well-being (Huang et al., 2007). Pollutant metals are usually non-degradable and there is no known homeostasis mechanism for them. Thus, any high levels of HMs will threaten biological life (Tong and Lam, 2000). Many investigations have confirmed that HMs accumulate in fatty tissues and then affect the functions of nervous system, endocrine system, immune system, cardiovascular system, urogenital system, normal cellular metabolism, etc. (Waisberg et al., 2003; Bocca et al., 2004; Li et al., 2013; Wang, 2013) and significant negative effects on human health, ranging from acute reactions to chronic illnesses (Kampa and Castanas, 2008; Shi et al.,
⁎
2008; Pei et al., 2015; Wang et al., 2015). The Chromium (Cr) is toxic or carcinogenic even at low concentrations when people are exposed for a long time (Angelone and Udovic, 2014; Khan et al., 2015; Zhang et al., 2015). The toxicity of Zn and Cu can change the function of the human central nervous system and respiratory system, and disrupt the endocrine system (Ma and Singhirunnusorn, 2012). Oral exposure to Ni can result in an increased incidence of allergic contact dermatitis, eczema, and respiratory effects in humans (ANL, 2001). Heavy metals are ubiquitous in the environment, as a result of both natural and anthropogenic activities, and humans are exposed to them through various pathways (Wilson and Pyatt, 2007). According to numerous studies, the pollution sources of HMs in environment are mainly derived from anthropogenic sources. The anthropogenic sources of metals in urban areas include traffic emission (vehicle exhaust particles, tire wear particles, weathered street surface particles, brake lining wear particles), industrial emission (power plants, coal combustion, metallurgical industry, auto repair shop, chemical plant, etc.), domestic emission, weathering of building and pavement surface, atmospheric deposited (Sezgin et al., 2004; Ahmed and Ishiga, 2006; Morton-Bermea et al., 2009), and in agricultural areas include mining, waste disposal,
Corresponding author. E-mail address: [email protected] (S.A. Doabi).
https://doi.org/10.1016/j.ecoenv.2018.07.057 Received 13 January 2018; Received in revised form 3 July 2018; Accepted 14 July 2018 0147-6513/ © 2018 Elsevier Inc. All rights reserved.
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to high population growth rate, the rate of urbanization has also accelerated and is now one of the highest in Iran.
sewage, pesticides, fertilizers, and vehicle exhausts (Montagne et al., 2007; Yu et al., 2008). The perusal of related literature revealed that the few studies carried out in Iran were mostly focused on monitoring the concentrations, identifying the enrichment factors and sources, and assessing the pollution levels of HMs in the soil and dust (Saeedi et al., 2012; Kamani et al., 2015; Keshavarzi et al., 2015; Soltani et al., 2015; Ahmadi Doabi et al., 2017). However, there is no information available about health risk assessment of HMs for humans residing in Kermanshah province, Iran. Health risk assessment is an effective approach to determine the risk to human health quantitatively posed by several various contaminants through different exposure pathways (Kampa and Castanas, 2008; Luo et al., 2012). Therefore, to enact an effective policy to quantify and control further harm on human health risk by HMs, a comprehensive health risk assessment in agricultural soil, atmospheric dust and major food crops throughout Kermanshah province is needed. Keeping in view the importance of health risk assessment, the current study aimed elaborate the following objectives: 1) to determine total concentrations of four heavy metals (Zn, Cu, Ni and Cr); 2) to assess levels of heavy metals pollution in agricultural soil, atmospheric dust on the basis of geo-accumulation index; and 3) to evaluate the potential non-carcinogenic and carcinogenic health risks of heavy metals for children and adults via different exposure pathways by using health risk assessment models described by United states Environmental protection agency (US EPA). To our knowledge, this study is the first attempt to assess the potential health human risk in agricultural soils, atmospheric dusts and major food crops of Kermanshah province.
2.2. Sample collection and preparation 2.2.1. Agricultural soil and food crops sampling Based on the predominant crop distribution, sizes of agricultural area, and probable sources of soil pollution, 53 agricultural soil samples (AS) were collected from 0 to 20 cm depth across Kermanshah province (including counties: Kermanshah, Sonqor, Gilan-e Gharb, Qasr-e Shirin, Sahneh, Sarpol-e Zahab, Kangavar, Paveh, Javanrud and Eslamabad-e Gharb) based on a randomized design in May 2013 (Fig. 1). Samples were taken from the designated locations by a process of composite sampling (quincunx sampling pattern), using a stainless steel auger. Five soil subsamples were taken and mixed together at each sampling point. These composite soil samples were transmitted to a central laboratory for physical and chemical analyses. All soil samples were airdried at room temperature. After removing the stones and other debris, samples were passed through 2 mm polyethylene sieve. Portions of all samples (~50 g) were ground in a grinder and sieved through 0.15 mm (100-mesh) for soil heavy metal analysis (Micó et al., 2006; Lu et al., 2012). In addition, at the harvest time (July and September 2013), 16 samples from edible parts (grain) of wheat (10 samples) and maize (6 samples) were also collected from different areas of Kermanshah province in the same sites where soils were collected. Fields were chosen randomly considering the size of them and their crops. 2.2.2. Atmospheric dust sampling A total of 98 atmospheric dust samples (AD) were collected in a temporal range from spring to summer 2013, each sample lasting 87 days in different cities of Kermanshah province (including counties: Kermanshah, Sonqor, Gilan-e Gharb, Qasr-e Shirin, Sahneh, Sarpol-e Zahab, Kangavar, Paveh and Javanrud) (Fig. 1). Kermanshah province meteorological organization statistics showed dusty days occur mainly in spring and summer seasons. The sampling sites were selected based on the following criteria. They were not shaded by trees or buildings, were easily accessible and secure against interference by animals, humans and upwind obstructions. Accordingly, dust collectors (passive samplers) were installed on the roof of buildings about 3–4 m above the ground level. Each collection tray consisted of a circular plastic surface (320 mm in diameter, 120 mm depth) fixed on holders with 33 cm height and were covered with a 2 mm PVC mesh on the top to form a rough area for trapping saltant particles. Dust samples were collected
2. Materials and methods 2.1. Study area Kermanshah province is situated in the west of Iran. It is mountainous and the climate is arid and semi-arid (Fig. 1). The population of this region is about 1.94 millions. The annual mean precipitation and temperature in the province is 450 mm and 16 °C, respectively. The prevailing wind directions are west to east with northwest and southwest fluctuations (IRIMO, 2013). The gaseous wastes in the form of automobile exhaust, chemicals factories emissions, different kinds of industries (including oil refinery and petrochemical factory) and primitive forms of heating, as well as dust input from Iraq, the neighboring country, are the major sources of pollution in the province. In addition
Fig. 1. Study area and sampling points in Kermanshah province. 154
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equation to minimize the effect of possible variations in the background values (Muller, 1969). The geo-accumulation index consists of seven grades or classes (Muller, 1969; Bhuiyan et al., 2010). According to Muller (1969), the Igeo for each metal is calculated and classified as: uncontaminated (Igeo ≤ 0); uncontaminated to moderately contaminated (0 < Igeo ≤ 1); moderately contaminated (1 < Igeo ≤ 2); moderately to heavily contaminated (2 < Igeo ≤ 3); heavily contaminated (3 < Igeo ≤ 4); heavily to extremely contaminated (4 < Igeo ≤5); extremely contaminated (Igeo > 5).
carefully with distilled water and stored in sealed polyethylene bags, labeled and then transported to the laboratory. Total of 98 atmospheric dust samples for two seasons were oven dried for 24 h at temperature 105 °C to a constant mass, and then sieved through a 1.0 mm mesh nylon sieve to remove refuse and small stones. For measuring heavy metals concentrations, the samples were passed through a 63 µm nylon sieve. This fraction of particles are known to be easily transported in suspension, with the finest particles being capable of remaining airborne for considerable durations (Shilton et al., 2005; Soltani et al., 2015; Keshavarzi et al., 2015). Furthermore, environmental and health risks are usually associated with fine particles rather than coarser fractions (Wei and Yang, 2010; Zheng et al., 2010; Charlesworth et al., 2011; Li and Zuo, 2013; Liu et al., 2014).
2.6. Health risk assessment Local residents are exposed to metals through the following main pathways: (a) direct ingestion of substrate particles (Ding); (b) inhalation of re-suspended particles through mouth and nose (Dinh); and (c) dermal absorption of trace elements in particles adhered to exposed skin (Ddermal). The dose received through each of the three paths was evaluated using Eqs. (2)–(4) (US EPA, 1996, 1989). According to the International Agency for Research on Cancer, Ni and Cr are considered to have a carcinogenic effect (Cao et al., 2014). Due to the lack of carcinogenic slope factors for Zn and Cu, the carcinogenic risks of Ni and Cr through ingestion and inhalation were assessed.
2.3. Chemical analysis In order to heavy metal measurements, an accurately weighed 0.5 g of agricultural soil and atmospheric dust was placed in a test tube, 10 ml of a 3:1 concentrated HCl/HNO3 mixture was added to each test tube, and the mixture was left at room temperature overnight. Each test tube was covered with an air condenser and refluxed gently at 80 °C for 2 h. After cooling, the solution was filtered through a moistened Whatman 42 filter paper and diluted to 50 ml volume with distilled water (Sparks et al., 1996; Karimi et al., 2009). Analysis of the total Zn, Cu, Ni and Cr content of plants was carried out using method 3051A of the US Environmental Protection Agency (US EPA, 1998). The total concentrations of Zn, Cu, Ni and Cr were determined using an Atomic Absorption Spectrophotometer (AAS: model Perkin Elmer 3030, USA). The detection limit values for all studied elements were between 0.01 and 0.02 ppm, with wavelengths of 213.9, 324.8, 232 and 357.9 for Zn, Cu, Ni and Cr, respectively. The standard solution concentrations were 0.5, 1.5, 3, for Zn and Cr, 0.5, 1.5, 3 or 2, 6, 12 for Cu, and 0.5, 1.5, 3 or 1, 3, 6 for Ni. For Cu and Ni one of the two groups of standard solutions was used based on the sample content of the element. In fact, first group were applied for samples with less element content and second group for samples with greater concentration of the element (Ahmadi Doabi et al., 2017).
IngR × EF × ED ×CF BW × AT
(2)
Dinh = C ×
InhR × EF × ED PEF × BW × AT
(3)
Ddermal = C ×
AF × SA × ABS × EF × ED ×CF BW × AT
(4)
Description and values of factors used in formulas (2–4) are given in Table 1. Reference dose (RfD) values (Table 3), which were used for assessment of non-carcinogenic risk, were taken from the integrated risk information system (US EPA, 1993; Du et al., 2013). C (exposurepoint concentration, mg kg−1) in Eqs. (2)–(4), combined with the values for the exposure factors shown above, is considered to yield an estimate of the “reasonable maximum exposure” (US EPA, 1989), which is the upper limit of the 95% confidence interval for the mean. In this study, the 95% upper confidence limits (UCL) were performed using Pro-UCL package version 4.1.00 for Windows. After calculating the average daily dose (Ds) for the three exposure routes (Ding, Dinh and Ddermal) non-carcinogenic and carcinogenic risks were calculated.
2.4. Statistical analysis Descriptive statistical parameters such as minimum, maximum, mean, median, standard deviation (S.D.), standard error (S.E.) and coefficient of variation (CV %) were calculated for the metals concentrations in studied samples. The geo-accumulation index (Igeo) was calculated to evaluate the pollution extent to which the AS and AD samples were contaminated (Angulo, 1996; Muller, 1969). Statistical analyses were performed using SPSS 16.0. Spatial distribution maps of HMs concentrations for AS and AD, and Igeo values were prepared using the Inverse Distance Weighting (IDW) method in Arc GIS (version 10.3).
2.6.1. Non-carcinogenic and carcinogenic risk According to EPA's guideline on risk assessment, we have separate discussions for carcinogenic and non-carcinogenic effects because the methods used are different for these two modes of chemical toxicity. In this study, quantified risk or hazard indexes (HIs) for both carcinogenic and non-carcinogenic effects was applied for all exposure pathways by dividing the doses by the corresponding RfD in non-carcinogenic risk and multiplying the doses by the corresponding slope factor (SF) in carcinogenic risk. Hazard index refers to the “sum of more than one hazard quotient (HQ) for multiple substances and/or multiple exposure pathways” (US EPA, 1989). Hence, a combination of non-carcinogenic risk for humans from different exposure pathways can be estimated by adding the HI of each exposure pathway (ingestion, dermal contact and inhalation) together (US EPA, 1989). If the value of HQ or HI is ≤ 1, it is believed that there is no significant risk of non-carcinogenic effects. If the value of HQ or HI is > 1, it means that there is a great chance of non-carcinogenic effects, with a probability increasing with the increasing value of HQ or HI (US EPA, 2001c; Zheng et al., 2010). The estimated value for the carcinogenic risk (CR) is the probability that if an individual will develop any type of cancer from lifetime exposure to carcinogenic hazards. In general, the US EPA recommends that and CR lower than 1 × 10−6 can be regarded as negligible and a
2.5. Pollution assessment The contamination levels of HMs in AS and AD are assessed by using geo-accumulation index (Igeo) introduced by Muller (1969). This method evaluates the enrichment of metal levels above baseline or background values. This method has been widely applied in European trace metal studies since the late 1960s and it is also employed in pollution assessment of soil and dust (Lu et al., 2009; Wei and Yang, 2010; Zhuang et al., 2013; Tang et al., 2015; Ahmadi doabi et al., 2017; El Azhari et al., 2017), which is calculated using the follow equation:
Igeo = log 2(Ci /kBi)
Ding = C ×
(1)
where Ci is the measured concentration of the elements in environment and Bi is the geochemical background value of heavy metal (i) in world soils (Alloway, 2010). The factor k (= 1.5) is introduced in this 155
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Table 1 Description and values of factors used in the risk assessment equations. Factors
Description
Unit
Values
Source
Child C IngR
−1
Exposure-point concentration Ingestion rate (soil and dust) (Wheat) (Maize) Inhalation rate Exposure frequency (soil) (dust) (Wheat) (Maize) Exposure duration (soil and dust) (crop) Conversion factor Exposed skin area Skin adherence factor Dermal absorption factor Particle emission factor Average body weight Average time (non-carcinogens) (carcinogens)
InhR EF
ED CF SA AF ABS PEF BW AT
Adult
95% UCL 200 100 129 388 0.63 2.19 7.6 20 350 350 180 180 365 365 100 100 6 24 4 27 1 × 10−6 1 × 10−6 2800 5700 0.2 0.07 0.001 0.001 1.36 × 109 1.36 × 109 15 70 ED × 365 70 × 365 = 25,550
mg kg mg day−1 g day−1 m3 day−1 day year−1
year kg mg−1 cm2 mg cm−2 h−1 unitless m3 kg−1 kg day
This study US EPA (2002) GFBIC (2014) Yeganeh et al. (2013) US EPA (2002) EFH (2009) Ferreira-Baptista and De Miguel (2005) Yeganeh et al. (2013) Observation US EPA (2002) Aghili et al. (2009) US EPA (2002) US EPA (2002) US EPA (2011) US EPA (2002) Afiuni (2013) US EPA (1989)
Table 2 Descriptive statistics of the heavy metals contents in agricultural soil, atmospheric dust and food crops of Kermanshah province (mg kg−1).
Agricultural Soils (n = 53)
Atmospheric Dusts (n = 98)
Wheat (n = 10)
Maize (n = 6)
Element
Minimum
Maximum
Mean
Median
S.D.
S.E.
CV %
Guideline criterion
IEQSc
Zn Cu Ni Cr Zn Cu Ni Cr Zn Cu Ni Cr Zn Cu Ni Cr
40 10 48 32 88 24 60 44 26.4 6.5 0.5 2.5 20.5 2.5 2 2.5
113 83 306 235 700 256 245 147 46.4 9 2 8 64.5 7.5 8 4
74.62 41.21 131.46 79.21 210.29 47.63 119.53 73.74 34.25 7.85 1.35 4.90 38.33 4.83 5.58 3.25
72 41 125 76 173.17 44 100 66.65 31.15 8 1.25 4.50 35.50 4.75 6.5 3.25
16.24 12.09 47.17 28.73 113.14 25.73 44.33 21.96 7.70 0.78 0.53 1.84 17.78 2.09 2.69 0.69
2.23 1.66 6.48 3.95 11.43 2.60 4.48 2.22 2.44 0.25 0.17 0.58 7.26 0.85 1.10 0.28
22 29 36 36 54 54 37 30 22 10 39 38 46 43 48 21
62a 14a 18a 42a 62a 14a 18a 42a 100–500b 10–30b 10–30b 1–10b 100–500b 10–30b 10–30b 1–10b
500 200 110 110 500 200 110 110
a
Background values of world soils (Alloway, 2010). Critical limits introduced by Kabata-Pendias (2001). c Allowable contents of potential toxic elements for agricultural soils with pH > 7 given in the directive of Iranian Environmental Quality Standard (IEQS) in 2013. b
CR above 1 × 10−4 are likely to be harmful to human beings. A CR within a range from 1 × 10−6 ~ 1 × 10−4 indicates an acceptable or tolerable risk for regulatory purposes and desirable remediation, social stability and to human health (US EPA, 2001a, 2001b; Wu et al., 2015). The SF (mg kg−1 day−1)−1 is the slope factor for carcinogenic exposure. The values for SF and RfD are listed in Table 3. The potential non-carcinogenic (Li et al., 2013) and carcinogenic risks (Dehghani et al., 2017) for individual metals were calculated by using the following equations:
HQ =
Di RfD
3. Results and discussion 3.1. Heavy metal contents The concentrations of Zn, Cu, Ni, and Cr in AS, AD and food crops are shown in Table 2. To facilitate evaluation and comparison the values, the background values of the metals in soil derived from considered localities of the world soils (Alloway, 2010). According to the inter-comparison of the heavy metal concentrations in AS and AD, the concentrations of the metals in different environments are followed a descending order as: AS > AD for Ni and Cr, and AD > AS for Zn and Cu. The coefficient of variance (CV) indicates the degree of variability within the concentrations of a metal in the AS, AD and food crops. If CV ≤ 20%, it shows low variability, 21% ≤ CV ≤ 50% is considered as moderate variability, 50% ≤ CV ≤ 100% is suggested high variability and CV above 100% is regarded as exceptionally high variability (Karimi Nezhad et al., 2015). The CV for all elements in AS, food crops (except for Cu in wheat) and Ni and Cr in AD indicated a moderate degree of variability, while the CV for Zn and Cu in AD indicated a high degree of variability reflecting the non-homogeneous distribution of Zn
(5)
HI = ∑ HQ i
(6)
CRi = Di × SF
(7)
CR = ∑ CRi
(8) 156
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Fig. 2. Spatial distribution maps of Zn, Cu, Ni, and Cr concentration (mg kg−1) in agricultural soil (AS) and atmospheric dust (AD) of the study area.
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Igeo values for Cr indicate that the AD in the province is lowly contaminated by this metal. While, for Ni and Cu indicate that the AD in the province are heavily contaminated by the two metals. Moreover, the mean Igeo values for Zn, Cu, Ni and Cr in AD of the province are 1.03 (29%), 1.08 (48%), 2.06 (36%) and 0.17 (53%), respectively. The data indicates that there is the widespread pollution of Zn, Cu, Ni and Cr is in AD of Kermanshah (Fig. 4). As far as the overall behavior of HMs under study is concerned, on the basis of Igeo it can be said that the AS and AD samples in Kermanshah province are practically uncontaminated for Zn in AS, uncontaminated to moderately contaminated for Cu and Cr in AS and Cr in AD, moderately contaminated for Zn and Cu in AD, and moderately to heavily contaminated for Ni in AS and AD. The concentrations and Igeo values of Ni and Cu in agricultural soils and atmospheric dusts indicate that the contamination of the HMs is widespread in the environment in Kermanshah (Figs. 2 and 4). In general the sources of Zn, Cu, Ni and Cr in AD are probably traffic emission and industrial emission, while the metals in AS may be derived from parent materials, mining, sewage sludge, pesticides and fertilizers. The main pollution sources of the metals are also different among the province. The pollution sources of the HMs in the AD of Kermanshah province for Zn and Cu are probably traffic emission, as well as industrial emission, and for Ni and Cr are industrial emission and partly traffic and combustion processes (Ahmadi Doabi et al., 2017). The Zn and Cu in the AS of Kermanshah may be derived from anthropogenic activities (such as manures, municipal waste compost, and mineral fertilizers, etc.), whereas Ni and Cr are probably influenced by parent materials, combined with less traces of anthropogenic origins (Ahmadi Doabi et al., 2018).
Fig. 3. Boxplot Geo-accumulation index (Igeo) for heavy metals in the agricultural soil (AS) and atmospheric dust (AD) samples of Kermanshah province.
and Cu concentrations, which is probably related to the human activities. The non-homogeneous distribution may suggest the presence of local enrichment sources. The spatial distribution maps of heavy metals in AS and AD are shown in Fig. 2. The mean concentrations of Zn (74.62), Cu (41.21), Ni (131.46) and Cr (79.21) mg kg−1 in AS of province are higher than their background values (Table 2). However, the metal concentrations in AS of the entire province are lower than their IEQS with an exception of Ni concentrations in province. Also in food crops, except for Cr, the mean concentrations are less than the critical limits introduced by KabataPendias (2001). Concentrations of Cr in wheat (4.90 mg kg−1) and maize (3.25 mg kg−1) are greater than the lower boundary of the critical range (1–10 mg kg−1) for this metal according to the German Federal Ministry of the Environment (1992). Similar results were obtained by Yeganeh et al. (2012). The mean concentrations of Zn (210.29), Cu (47.63), Ni (119.53) and Cr (73.74) mg kg−1 in AD of the entire province from Kermanshah are much higher than their background values in soil of world (Table 2). The concentration ranges of the metals are observed to be 88–700, 24–256, 60–245 and 44–147 mg kg−1 for Zn, Cu, Ni and Cr, respectively. The concentrations of the metals in AD of the entire province are higher than their background values. However, the concentrations of Zn, Cu and Cr in province are lower than the IEQS with an exception of Ni.
3.3. Human health risk assessment of HMs 3.3.1. Non-carcinogenic risk Results of non-carcinogenic human health risk assessment of HMs in the AS and AD through possible exposure pathways (ingestion, dermal contact, and inhalation), and food crops (ingestion) for children and adults were shown in Table 3. Ingestion of AS, AD particles and food crops appeared to be the main exposure pathway for Zn, Cu, Ni and Cr to children and adult, followed by dermal contact and inhalation routes, respectively. Similar results were obtained by Ferreira-Baptista and De Miguel (2005), Zheng et al. (2010) and Dehghani et al. (2017). The contributions of HQing of Zn, Cu, Ni and Cr to HI in AS and AD were 99.98%, 99.94%, 99.94% and 99.94% for children, and 99.97%, 99.50%, 99.91% and 99.50% for adults, respectively (Table 3). These results suggest that ingestion is the main exposure route that threatens human health (especially via wheat). This result is consistent with other studies (Yeganeh et al., 2012, 2013; Chabukdhara and Nema, 2013; Qing et al., 2015; Wei et al., 2015; Salah Al-Heety et al., 2017). HQ (non-carcinogenic risk) due to inhalation of AS and AD particles is 1–7 orders of magnitude lower than the other two exposure pathways, and it is unlikely that this exposure route would pose a higher risk than ingestion. Therefore, inhalation of re-suspended particles through the mouth and nose is almost negligible compared with the other routes of exposure. HQ values in AS and AD from ingestion, inhalation and dermal contact in children were higher than those for adults. The only exception was Cu with higher HQinh for adults compared with children. Fig. 5 shows HI values for non-carcinogenic health risks among adults and children involving Kermanshah province AS, AD, and food crops (wheat and maize) samples associated with exposure to Zn, Cu, Ni, and Cr. The orders of non-cancer HI of HMs for both children and adults in AS, AD and maize were Zn > Ni > Cu > Cr, while for wheat were Zn > Cu > Ni > Cr (Table 3). HI values for all studied heavy metals were below 1. Zinc displayed the highest HI values among the investigated metals (especially in wheat), while potential health risk from Cr is the least. This result is originated from the high
3.2. Contamination levels of HMs The calculated results of Igeo of HMs in AS and AD are presented in Fig. 3. The mean values of Igeo decrease in the order of Ni > Cu > Cr > Zn for AS and Ni > Cu > Zn > Cr for AD. Fig. 3 shows that nearly the Igeo value for Zn (91%) in AS of the Kermanshah province is lower than 0. This indicates that the AS is uncontaminated or slightly contaminated by this metal. The Igeo values for Cu (58%) and Cr (66%) in AS in the province are lower than 1. This suggests that the AS in the province is uncontaminated to moderately contaminate by the two metals. The highest Igeo values for Ni (3.50) are found in the AS of province. In the province, the AS may be considerably contaminated by Ni. The mean Igeo values also indicate that the pollution of Ni (58%) is widespread in AS in Kermanshah province. However, the AS in Kermanshah is lowly or moderately contaminated by the other Zn, Cu and Cr. The spatial distribution maps of Igeo values in AS and AD are shown in Fig. 4. Nearly all the Igeo values for Zn, Cu and Ni in AD in the province are higher than 0 (Fig. 3). This indicates that the AD in this province is contaminated by the metals derived from anthropogenic sources. The 158
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Fig. 4. Spatial distribution maps of Geo-accumulation index (Igeo) values for Zn, Cu, Ni, and Cr in the agricultural soil (AS) and atmospheric dust (AD) of the study area.
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Table 3 Exposure dose, hazard quotient and risk for each element and exposure pathway (mg kg−1 d−1) in agricultural soil, atmospheric dust and food crops.
RfDing RfDinh RfDdermal SFing SFinh Agricultural Soil C (95% UCL) distributions Non-Carcinogenic risk Children Ding Dinh Ddermal HQing HQing / HI (%) HQinh HQdermal HI Adults Ding Dinh Ddermal HQing HQing / HI (%) HQinh HQdermal HI Carcinogenic risk Children CRing CRinh Adults CRing CRinh Atmospheric Dust C (95% UCL) distributions Non-Carcinogenic risk Children Ding Dinh Ddermal HQing HQing / HI (%) HQinh HQdermal HI Adults Ding Dinh Ddermal HQing HQing / HI (%) HQinh HQdermal HI Carcinogenic risk Children CRing CRinh Adults CRing CRinh Food Crops C (95% UCL) distributions Non-Carcinogenic risk Children Ding HQing HI Adults Ding
Zn
Cu
Ni non-canc.
3.00E-01 3.00E-01 6.00E-02
3.70E-02 4.02E-02 1.90E-03
2.00E-02 2.06E-02 1.00E-03
Ni canc.
Cr non-canc.
Cr canc.
5.00E-03 2.86E-05 2.50E-04 0.91 0.91
0.5 510
78.36 normal
43.99 normal
142.2 gamma
142.2 gamma
85.11 gamma
1.00E-03 2.80E-08 2.80E-06 3.34E-05 99.98 9.33E-10 4.67E-09 3.34E-05
5.62E-04 1.57E-08 1.57E-06 1.52E-06 99.94 3.91E-11 8.29E-10 1.52E-06
1.82E-03 5.08E-08 5.09E-06 9.09E-06 99.94 2.47E-10 5.09E-09 9.10E-06
1.09E-03 3.04E-08 3.05E-06 2.18E-07 99.94 1.06E-13 1.22E-10 2.18E-07
1.07E-04 1.58E-08 4.28E-07 3.58E-06 99.97 5.26E-10 7.14E-10 3.58E-06
6.03E-05 8.86E-09 2.40E-07 1.63E-07 99.50 3.56E-10 4.57E-10 1.64E-07
1.95E-04 2.86E-08 7.77E-07 9.74E-07 99.91 1.39E-10 7.77E-10 9.75E-07
1.17E-04 1.71E-08 4.65E-07 2.33E-08 99.50 5.99E-14 1.16E-10 2.34E-08
1.65E-03 4.62E-08
5.44E-04 1.55E-05
1.77E-04 2.61E-08
5.83E-05 8.74E-06
229.7 nonparametric
52.21 nonparametric
127 nonparametric
1.51E-03 4.22E-08 4.23E-06 5.03E-05 99.98 1.41E-09 7.05E-09 5.04E-05
3.43E-04 9.59E-09 9.61E-07 9.28E-07 99.94 2.39E-11 5.06E-10 9.28E-07
8.35E-04 2.33E-08 2.34E-06 4.18E-06 99.94 1.13E-10 2.34E-09 4.18E-06
5.09E-04 1.42E-08 1.43E-06 1.02E-07 99.94 4.98E-14 5.71E-11 1.02E-07
3.15E-04 4.63E-08 1.25E-05 5.39E-06 99.97 7.93E-10 1.08E-09 5.40E-06
7.15E-05 1.05E-08 2.85E-06 9.94E-08 99.50 2.17E-10 2.79E-10 9.99E-08
1.74E-04 2.56E-08 6.94E-06 4.47E-07 99.91 6.39E-11 3.57E-10 4.48E-07
1.06E-04 1.56E-08 4.23E-06 1.09E-08 99.50 2.81E-14 5.44E-11 1.10E-08
Wheat 38.72 normal
Maize 52.96 normal
Wheat 8.3 normal
Maize 6.55 normal
Wheat 1.66 normal
Maize 7.8 normal
3.33E-01 1.11E-02 1.11E-02
6.10E-04 2.03E-05 2.03E-05
7.14E-02 1.93E-04 1.93E-04
7.50E-05 2.04E-07 2.04E-07
1.43E-02 7.14E-05 7.14E-05
2.15E-01
4.50E-04
4.60E-02
5.60E-05
9.20E-03
85.11 gamma
127 nonparametric
77.47 nonparametric
77.47 nonparametric
7.60E-04 2.12E-08
2.55E-04 7.26E-06
8.14E-05 1.20E-08
2.73E-05 4.09E-06
Wheat 1.66 normal
Maize 7.8 normal
Wheat 5.96 normal
Maize 3.82 normal
9.00E-05 4.49E-07 4.49E-07
5.13E-02 1.03E-05 1.03E-05
4.40E-05 8.79E-09 8.79E-09
6.70E-05
3.30E-02
3.30E-05
Wheat 5.96 normal
Maize 3.82 normal
(continued on next page) 160
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Table 3 (continued) Zn HQing HI Carcinogenic risk Children CRing Adults CRing
Cu
7.15E-03 7.15E-03
1.51E-05 1.51E-05
Ni non-canc.
1.24E-04 1.24E-04
1.52E-07 1.52E-07
4.60E-05 4.60E-05
Ni canc.
Cr non-canc.
3.34E-07 3.34E-07
6.61E-06 6.61E-06
Cr canc. 6.55E-09 6.55E-09
1.30E-02
8.17E-05
2.56E-02
2.20E-05
8.37E-03
6.08E-05
1.65E-02
1.64E-05
4.00E-05
AS Children
6.00E-05
AD Children
3.50E-05
AS Adult
5.00E-05
AD Adult
4.00E-05
2.50E-05
HI Value
HI Value
3.00E-05
2.00E-05 1.50E-05
3.00E-05 2.00E-05
1.00E-05 1.00E-05
5.00E-06
0.00E+00
0.00E+00
Zn 1.20E-02
Ni
Zn
Cr 2.50E-05
Wheat Children Wheat Adult
1.00E-02 8.00E-03 6.00E-03 4.00E-03
Cu
Ni
Cr
Maize Children Maize Adult
2.00E-05
HI Value
HI Value
Cu
1.50E-05 1.00E-05 5.00E-06
2.00E-03 0.00E+00
Zn
Cu
Ni
0.00E+00
Cr
Zn
Cu
Ni
Cr
Fig. 5. Hazard index (HI) values for non-carcinogenic health risks for adults and children involving Kermanshah province agricultural soil (AS), atmospheric dust (AD) and food crops (Wheat and Maize).
samples through the ingestion. The CR values of Ni and Cr in AS, AD, wheat, and maize were 1.65E-03, 5.60E-04; 7.60E-04, 2.62E-04; 1.30E02, 2.56E-02, and 8.17E-05, 2.20E-05 for children and 1.77E-04, 6.70E05; 8.14E-05, 3.14E-05; 8.37E-03, 1.65E-02, and 6.08E-05, 1.64E-05 for adults, respectively. Carcinogenic risk values for children were higher than adults. The contribution order of CR of each metal to the overall CR values in AS, AD, wheat and maize was 74.7% (Ni) > 25.3% (Cr); 74.4% (Ni) > 25.6% (Cr); 66.4% (Cr) > 33.6% (Ni) and 78.8% (Ni) > 21.2% (Cr) for children and 72.6% (Ni) > 27.4% (Cr); 72.2% (Ni) > 27.8% (Cr); 66.4% (Cr) > 33.6% (Ni) and 78.8% (Ni) > 21.2% (Cr) for adults, respectively. The majority of the CR lay between 1 × 10−5 and 1 × 10−4; only observed high risk levels that exceeded 1 × 10−4 in wheat samples for Ni and Cr, and in AS samples for Ni. Fig. 6 shows that the cumulative CR values of Ni and Cr have exceeded incremental lifetime of 1 × 10−6. Thus, the possibilities of having cancer in the long term are evident for children and adults. The CR obtained for adults was all within the acceptable range (except for Ni in AS, and Ni and Cr in wheat), therefore, it may conclude that there would not occur serious long-term health impacts for adults with respect to Ni and Cr in AD and maize samples, and to Cr in AS samples. In contrast, for children, the total carcinogenic risks (CRs) of Ni and Cr
concentration of Zn in AS, AD and food crops (wheat and maize). The HI values of these HMs in AS and AD was about 9 times and in food crops about 1.3 ~ 1.5 times higher for children compared to adults suggesting that children have much more chance for non-carcinogenic risk in Kermanshah province than adults. The high non-carcinogenic risk of children is mostly due to their pica behavior and hand or finger sucking (Wei et al., 2015; Zhao et al., 2014). The HQs and HIs for all HMs are lower than the safe level (1), indicating low detrimental health risk to children and adults due to heavy metal exposure. The results reflected that exposure to HMs in AS, AD and food crops solely would not cause serious health impacts in Kermanshah province. However, the calculated risk is affected by a high degree of uncertainty. On the other hand, the adverse effects of HMs accumulations in human body for a long time are not considered here. 3.3.2. Carcinogenic risk To assess carcinogenic risk (CR) of Ni and Cr, appropriate SF values were taken from RAIS (2017) and OEHHA (2017). The CR levels of Ni and Cr in AS, AD and food crops in Kermanshah province are listed in Table 3. The CR of Ni and Cr was calculated in AS and AD samples through the ingestion and inhalation, and in food crops 161
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1.80E-03 1.60E-03
8.00E-04
AD Children
AS Adult
7.00E-04
AD Adult
6.00E-04
Cumulative CR
Cumulative CR
1.40E-03
AS Children
1.20E-03 1.00E-03 8.00E-04 6.00E-04 4.00E-04
5.00E-04 4.00E-04 3.00E-04 2.00E-04 1.00E-04
2.00E-04 0.00E+00
0.00E+00
Ni 3.00E-02
Ni
Wheat Children
9.00E-05
Wheat Adult
8.00E-05
Cr Maize Children Maize Adult
7.00E-05
Cumulative CR
Cumulative CR
2.50E-02
Cr
2.00E-02 1.50E-02 1.00E-02 5.00E-03
6.00E-05 5.00E-05 4.00E-05 3.00E-05 2.00E-05 1.00E-05 0.00E+00
0.00E+00
Ni
Ni
Cr
Cr
Fig. 6. Total cancer risk (CR) values for carcinogenic health risks for adults and children involving Kermanshah province agricultural soil (AS), atmospheric dust (AD) and food crops (Wheat and Maize).
of this study would facilitate the decision-makers to manage contaminated AS, AD and food crops, and minimize health risks to province inhabitants and also could serve as a useful case study for the assessment of health risks posed by urban environment in other provinces or countries.
(except for Ni and Cr in maize) were higher than the threshold value (1 × 10−4), highlighting that children may suffer more potentially carcinogenic risks in their daily life via unconscious ingestion pathways. Moreover, the health risk posed by heavy metals via ingestion is higher than that by inhalation for both adults and children. Carcinogenic risks of Ni and Cr for both children and decreased in this order: wheat > AS > AD > maize. On the other hand, CRs of Ni for both children and adults in AS, AD and maize was more than Cr (except via wheat). From the results, we also can conclude that the ingestion of wheat was the most important exposure pathway for children and adults and could have more potential to threaten human health compared to AS, AD and maize. According to the current results, Ni and Cr should be paid more attention for the potential occurrence of carcinogenic risk to threaten human health in the study area. However, further studies are needed to explain the higher CR caused by Ni and Cr in this region.
4. Conclusion The concentrations, pollution levels, and health risks of HMs (Zn, Cu, Ni and Cr) in AS, AD and food crops from Kermanshah province were studied. The obtained results show that mean contents of all studied elements in AS and AD samples exceed background values, indicating that the pollution may come from anthropogenic sources. Compared with the IEQS guidelines for agricultural soil quality of Iran, AS and AD of Kermanshah province have elevated concentrations of Ni. The Ni should be paid more attention. Statistical descriptions of the contents indicate that pollution sources of the HMs in the AS and AD of Kermanshah province for Zn and Cu are due to man-made sources, while Ni and Cr probably have mixed sources of natural and anthropogenic origins in the AS (with less traces of anthropogenic influence) and AD (with less traces of natural influence). The Igeo values reveals that Ni in AS and AD were moderately to heavily contaminated. The results of risk analysis suggest that ingestion of food crops especially wheat is the main pathway for entering the metals to human body and threaten their health. Both the HQ values and the HI value for all studied metals are far lower than the safe level (= 1) for children and adults, indicating there is no non-carcinogenic risk from these metals. The carcinogenic risk values of Ni and Cr for children and adults were above the threshold value (1 × 10−6). On the other hand, children are likely under a higher health risk than adults, especially where the carcinogenic risk is higher than 1 × 10−4, indicating that children may be facing the threat of serious carcinogenic risk over a lifetime.
3.3.3. Uncertainties It is considered to be most accurate and reliable to use the bio-accessible concentrations of elements to determine health risks (Oomen et al., 2002). However, the calculated risk of both non-carcinogenic and carcinogenic of metals via AS, AD and food crops exposure pathways was influenced by several other uncertainty factors (Qing et al., 2015). In this study local parameters used as much as possible, but in some cases, there was not any local data or information, then we had to use the international data bases such as US EPA exposure handbook. The other source of uncertainty is that other elements (e.g., As, Pb, Cd, and Sr) and other exposure pathways (e.g., water or contaminated food) were not considered in this study. Despite the uncertainties involved, the model proved to be a robust tool for assessing human health risks in recognizing the dangerous metals and identifying the exposure pathways of most concern (Wei et al., 2015; Wang et al., 2016). The findings 162
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These findings indicate that more consideration ought to be paid to HM contamination of AS, AD and food crops in Kermanshah province.
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Pollution and health risk assessment of heavy metals in agricultural soil, atmospheric dust and major food crops in Kermanshah province, Iran
T
⁎
Shahab Ahmadi Doabia, , Mahin Karamib, Majid Afyunia, Mojgan Yeganehc a
Department of Soil Science, College of Agriculture, Isfahan University of Technology, Isfahan 84156-83111, Iran Department of Soil Science, Faculty of Agriculture, Razi University, Kermanshah 6715685438, Iran c Soil and Water Research Institute (SWRI), Agricultural Research Education and Extension Organization, Karaj 31785-311, Iran b
A R T I C LE I N FO
A B S T R A C T
Keywords: Heavy metals Agricultural soil Atmospheric dust Pollution levels Health risk assessment Kermanshah
A total of 167 samples of agricultural soil, atmospheric dust and food crops (wheat and maize) were collected, and four heavy metals, including Zn, Cu, Ni, and Cr, were analyzed for their concentrations, pollution levels and human health risks. The mean heavy metal contents in the agricultural soil and atmospheric dust were exceeds background values and lower than their IEQS (Iranian Environmental Quality Standard) with an exception of Ni. A pollution assessment by Geo-accumulation Index (Igeo) showed that the pollution levels were in the order of Ni > Cu > Cr > Zn for agricultural soils and Ni > Cu > Zn > Cr for atmospheric dust. The Ni levels can be considered “moderately to heavily contaminated” status. The human health risk assessment indicated that noncarcinogenic values were below the threshold values (1), and main exposure pathway of heavy metals to both children and adults are ingestion. The carcinogenic risks values for Ni and Cr were higher than the safe value (1 × 10−6), suggesting that all receptors (especially wheat) in Kermanshah province might have significant and acceptable potential health risk because of exposure to Ni and Cr. The carcinogenic risk for children and adults has a descending order of Ni > Cr, except for wheat. These results provide basic information on heavy metal contamination control and human health risk assessment management in the Kermanshah province.
1. Introduction The potential public health risk associated with the intake of metals from dust and soil has been the subject of discussion in recent years (Wei and Yang, 2010). Heavy metals (HMs) in dust and soil can be easily transferred into human body via three routes: ingestion, inhalation and dermal contact (De Miguel et al., 1998; Madrid et al., 2002; Aelion et al., 2008; Li et al., 2013; Qing et al., 2015; Wu et al., 2015). Agricultural, industrial, and urban developments have raised the possibility of metals’ accumulation in food crops and as a consequence, their risk for human health and well-being (Huang et al., 2007). Pollutant metals are usually non-degradable and there is no known homeostasis mechanism for them. Thus, any high levels of HMs will threaten biological life (Tong and Lam, 2000). Many investigations have confirmed that HMs accumulate in fatty tissues and then affect the functions of nervous system, endocrine system, immune system, cardiovascular system, urogenital system, normal cellular metabolism, etc. (Waisberg et al., 2003; Bocca et al., 2004; Li et al., 2013; Wang, 2013) and significant negative effects on human health, ranging from acute reactions to chronic illnesses (Kampa and Castanas, 2008; Shi et al.,
⁎
2008; Pei et al., 2015; Wang et al., 2015). The Chromium (Cr) is toxic or carcinogenic even at low concentrations when people are exposed for a long time (Angelone and Udovic, 2014; Khan et al., 2015; Zhang et al., 2015). The toxicity of Zn and Cu can change the function of the human central nervous system and respiratory system, and disrupt the endocrine system (Ma and Singhirunnusorn, 2012). Oral exposure to Ni can result in an increased incidence of allergic contact dermatitis, eczema, and respiratory effects in humans (ANL, 2001). Heavy metals are ubiquitous in the environment, as a result of both natural and anthropogenic activities, and humans are exposed to them through various pathways (Wilson and Pyatt, 2007). According to numerous studies, the pollution sources of HMs in environment are mainly derived from anthropogenic sources. The anthropogenic sources of metals in urban areas include traffic emission (vehicle exhaust particles, tire wear particles, weathered street surface particles, brake lining wear particles), industrial emission (power plants, coal combustion, metallurgical industry, auto repair shop, chemical plant, etc.), domestic emission, weathering of building and pavement surface, atmospheric deposited (Sezgin et al., 2004; Ahmed and Ishiga, 2006; Morton-Bermea et al., 2009), and in agricultural areas include mining, waste disposal,
Corresponding author. E-mail address: [email protected] (S.A. Doabi).
https://doi.org/10.1016/j.ecoenv.2018.07.057 Received 13 January 2018; Received in revised form 3 July 2018; Accepted 14 July 2018 0147-6513/ © 2018 Elsevier Inc. All rights reserved.
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to high population growth rate, the rate of urbanization has also accelerated and is now one of the highest in Iran.
sewage, pesticides, fertilizers, and vehicle exhausts (Montagne et al., 2007; Yu et al., 2008). The perusal of related literature revealed that the few studies carried out in Iran were mostly focused on monitoring the concentrations, identifying the enrichment factors and sources, and assessing the pollution levels of HMs in the soil and dust (Saeedi et al., 2012; Kamani et al., 2015; Keshavarzi et al., 2015; Soltani et al., 2015; Ahmadi Doabi et al., 2017). However, there is no information available about health risk assessment of HMs for humans residing in Kermanshah province, Iran. Health risk assessment is an effective approach to determine the risk to human health quantitatively posed by several various contaminants through different exposure pathways (Kampa and Castanas, 2008; Luo et al., 2012). Therefore, to enact an effective policy to quantify and control further harm on human health risk by HMs, a comprehensive health risk assessment in agricultural soil, atmospheric dust and major food crops throughout Kermanshah province is needed. Keeping in view the importance of health risk assessment, the current study aimed elaborate the following objectives: 1) to determine total concentrations of four heavy metals (Zn, Cu, Ni and Cr); 2) to assess levels of heavy metals pollution in agricultural soil, atmospheric dust on the basis of geo-accumulation index; and 3) to evaluate the potential non-carcinogenic and carcinogenic health risks of heavy metals for children and adults via different exposure pathways by using health risk assessment models described by United states Environmental protection agency (US EPA). To our knowledge, this study is the first attempt to assess the potential health human risk in agricultural soils, atmospheric dusts and major food crops of Kermanshah province.
2.2. Sample collection and preparation 2.2.1. Agricultural soil and food crops sampling Based on the predominant crop distribution, sizes of agricultural area, and probable sources of soil pollution, 53 agricultural soil samples (AS) were collected from 0 to 20 cm depth across Kermanshah province (including counties: Kermanshah, Sonqor, Gilan-e Gharb, Qasr-e Shirin, Sahneh, Sarpol-e Zahab, Kangavar, Paveh, Javanrud and Eslamabad-e Gharb) based on a randomized design in May 2013 (Fig. 1). Samples were taken from the designated locations by a process of composite sampling (quincunx sampling pattern), using a stainless steel auger. Five soil subsamples were taken and mixed together at each sampling point. These composite soil samples were transmitted to a central laboratory for physical and chemical analyses. All soil samples were airdried at room temperature. After removing the stones and other debris, samples were passed through 2 mm polyethylene sieve. Portions of all samples (~50 g) were ground in a grinder and sieved through 0.15 mm (100-mesh) for soil heavy metal analysis (Micó et al., 2006; Lu et al., 2012). In addition, at the harvest time (July and September 2013), 16 samples from edible parts (grain) of wheat (10 samples) and maize (6 samples) were also collected from different areas of Kermanshah province in the same sites where soils were collected. Fields were chosen randomly considering the size of them and their crops. 2.2.2. Atmospheric dust sampling A total of 98 atmospheric dust samples (AD) were collected in a temporal range from spring to summer 2013, each sample lasting 87 days in different cities of Kermanshah province (including counties: Kermanshah, Sonqor, Gilan-e Gharb, Qasr-e Shirin, Sahneh, Sarpol-e Zahab, Kangavar, Paveh and Javanrud) (Fig. 1). Kermanshah province meteorological organization statistics showed dusty days occur mainly in spring and summer seasons. The sampling sites were selected based on the following criteria. They were not shaded by trees or buildings, were easily accessible and secure against interference by animals, humans and upwind obstructions. Accordingly, dust collectors (passive samplers) were installed on the roof of buildings about 3–4 m above the ground level. Each collection tray consisted of a circular plastic surface (320 mm in diameter, 120 mm depth) fixed on holders with 33 cm height and were covered with a 2 mm PVC mesh on the top to form a rough area for trapping saltant particles. Dust samples were collected
2. Materials and methods 2.1. Study area Kermanshah province is situated in the west of Iran. It is mountainous and the climate is arid and semi-arid (Fig. 1). The population of this region is about 1.94 millions. The annual mean precipitation and temperature in the province is 450 mm and 16 °C, respectively. The prevailing wind directions are west to east with northwest and southwest fluctuations (IRIMO, 2013). The gaseous wastes in the form of automobile exhaust, chemicals factories emissions, different kinds of industries (including oil refinery and petrochemical factory) and primitive forms of heating, as well as dust input from Iraq, the neighboring country, are the major sources of pollution in the province. In addition
Fig. 1. Study area and sampling points in Kermanshah province. 154
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equation to minimize the effect of possible variations in the background values (Muller, 1969). The geo-accumulation index consists of seven grades or classes (Muller, 1969; Bhuiyan et al., 2010). According to Muller (1969), the Igeo for each metal is calculated and classified as: uncontaminated (Igeo ≤ 0); uncontaminated to moderately contaminated (0 < Igeo ≤ 1); moderately contaminated (1 < Igeo ≤ 2); moderately to heavily contaminated (2 < Igeo ≤ 3); heavily contaminated (3 < Igeo ≤ 4); heavily to extremely contaminated (4 < Igeo ≤5); extremely contaminated (Igeo > 5).
carefully with distilled water and stored in sealed polyethylene bags, labeled and then transported to the laboratory. Total of 98 atmospheric dust samples for two seasons were oven dried for 24 h at temperature 105 °C to a constant mass, and then sieved through a 1.0 mm mesh nylon sieve to remove refuse and small stones. For measuring heavy metals concentrations, the samples were passed through a 63 µm nylon sieve. This fraction of particles are known to be easily transported in suspension, with the finest particles being capable of remaining airborne for considerable durations (Shilton et al., 2005; Soltani et al., 2015; Keshavarzi et al., 2015). Furthermore, environmental and health risks are usually associated with fine particles rather than coarser fractions (Wei and Yang, 2010; Zheng et al., 2010; Charlesworth et al., 2011; Li and Zuo, 2013; Liu et al., 2014).
2.6. Health risk assessment Local residents are exposed to metals through the following main pathways: (a) direct ingestion of substrate particles (Ding); (b) inhalation of re-suspended particles through mouth and nose (Dinh); and (c) dermal absorption of trace elements in particles adhered to exposed skin (Ddermal). The dose received through each of the three paths was evaluated using Eqs. (2)–(4) (US EPA, 1996, 1989). According to the International Agency for Research on Cancer, Ni and Cr are considered to have a carcinogenic effect (Cao et al., 2014). Due to the lack of carcinogenic slope factors for Zn and Cu, the carcinogenic risks of Ni and Cr through ingestion and inhalation were assessed.
2.3. Chemical analysis In order to heavy metal measurements, an accurately weighed 0.5 g of agricultural soil and atmospheric dust was placed in a test tube, 10 ml of a 3:1 concentrated HCl/HNO3 mixture was added to each test tube, and the mixture was left at room temperature overnight. Each test tube was covered with an air condenser and refluxed gently at 80 °C for 2 h. After cooling, the solution was filtered through a moistened Whatman 42 filter paper and diluted to 50 ml volume with distilled water (Sparks et al., 1996; Karimi et al., 2009). Analysis of the total Zn, Cu, Ni and Cr content of plants was carried out using method 3051A of the US Environmental Protection Agency (US EPA, 1998). The total concentrations of Zn, Cu, Ni and Cr were determined using an Atomic Absorption Spectrophotometer (AAS: model Perkin Elmer 3030, USA). The detection limit values for all studied elements were between 0.01 and 0.02 ppm, with wavelengths of 213.9, 324.8, 232 and 357.9 for Zn, Cu, Ni and Cr, respectively. The standard solution concentrations were 0.5, 1.5, 3, for Zn and Cr, 0.5, 1.5, 3 or 2, 6, 12 for Cu, and 0.5, 1.5, 3 or 1, 3, 6 for Ni. For Cu and Ni one of the two groups of standard solutions was used based on the sample content of the element. In fact, first group were applied for samples with less element content and second group for samples with greater concentration of the element (Ahmadi Doabi et al., 2017).
IngR × EF × ED ×CF BW × AT
(2)
Dinh = C ×
InhR × EF × ED PEF × BW × AT
(3)
Ddermal = C ×
AF × SA × ABS × EF × ED ×CF BW × AT
(4)
Description and values of factors used in formulas (2–4) are given in Table 1. Reference dose (RfD) values (Table 3), which were used for assessment of non-carcinogenic risk, were taken from the integrated risk information system (US EPA, 1993; Du et al., 2013). C (exposurepoint concentration, mg kg−1) in Eqs. (2)–(4), combined with the values for the exposure factors shown above, is considered to yield an estimate of the “reasonable maximum exposure” (US EPA, 1989), which is the upper limit of the 95% confidence interval for the mean. In this study, the 95% upper confidence limits (UCL) were performed using Pro-UCL package version 4.1.00 for Windows. After calculating the average daily dose (Ds) for the three exposure routes (Ding, Dinh and Ddermal) non-carcinogenic and carcinogenic risks were calculated.
2.4. Statistical analysis Descriptive statistical parameters such as minimum, maximum, mean, median, standard deviation (S.D.), standard error (S.E.) and coefficient of variation (CV %) were calculated for the metals concentrations in studied samples. The geo-accumulation index (Igeo) was calculated to evaluate the pollution extent to which the AS and AD samples were contaminated (Angulo, 1996; Muller, 1969). Statistical analyses were performed using SPSS 16.0. Spatial distribution maps of HMs concentrations for AS and AD, and Igeo values were prepared using the Inverse Distance Weighting (IDW) method in Arc GIS (version 10.3).
2.6.1. Non-carcinogenic and carcinogenic risk According to EPA's guideline on risk assessment, we have separate discussions for carcinogenic and non-carcinogenic effects because the methods used are different for these two modes of chemical toxicity. In this study, quantified risk or hazard indexes (HIs) for both carcinogenic and non-carcinogenic effects was applied for all exposure pathways by dividing the doses by the corresponding RfD in non-carcinogenic risk and multiplying the doses by the corresponding slope factor (SF) in carcinogenic risk. Hazard index refers to the “sum of more than one hazard quotient (HQ) for multiple substances and/or multiple exposure pathways” (US EPA, 1989). Hence, a combination of non-carcinogenic risk for humans from different exposure pathways can be estimated by adding the HI of each exposure pathway (ingestion, dermal contact and inhalation) together (US EPA, 1989). If the value of HQ or HI is ≤ 1, it is believed that there is no significant risk of non-carcinogenic effects. If the value of HQ or HI is > 1, it means that there is a great chance of non-carcinogenic effects, with a probability increasing with the increasing value of HQ or HI (US EPA, 2001c; Zheng et al., 2010). The estimated value for the carcinogenic risk (CR) is the probability that if an individual will develop any type of cancer from lifetime exposure to carcinogenic hazards. In general, the US EPA recommends that and CR lower than 1 × 10−6 can be regarded as negligible and a
2.5. Pollution assessment The contamination levels of HMs in AS and AD are assessed by using geo-accumulation index (Igeo) introduced by Muller (1969). This method evaluates the enrichment of metal levels above baseline or background values. This method has been widely applied in European trace metal studies since the late 1960s and it is also employed in pollution assessment of soil and dust (Lu et al., 2009; Wei and Yang, 2010; Zhuang et al., 2013; Tang et al., 2015; Ahmadi doabi et al., 2017; El Azhari et al., 2017), which is calculated using the follow equation:
Igeo = log 2(Ci /kBi)
Ding = C ×
(1)
where Ci is the measured concentration of the elements in environment and Bi is the geochemical background value of heavy metal (i) in world soils (Alloway, 2010). The factor k (= 1.5) is introduced in this 155
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Table 1 Description and values of factors used in the risk assessment equations. Factors
Description
Unit
Values
Source
Child C IngR
−1
Exposure-point concentration Ingestion rate (soil and dust) (Wheat) (Maize) Inhalation rate Exposure frequency (soil) (dust) (Wheat) (Maize) Exposure duration (soil and dust) (crop) Conversion factor Exposed skin area Skin adherence factor Dermal absorption factor Particle emission factor Average body weight Average time (non-carcinogens) (carcinogens)
InhR EF
ED CF SA AF ABS PEF BW AT
Adult
95% UCL 200 100 129 388 0.63 2.19 7.6 20 350 350 180 180 365 365 100 100 6 24 4 27 1 × 10−6 1 × 10−6 2800 5700 0.2 0.07 0.001 0.001 1.36 × 109 1.36 × 109 15 70 ED × 365 70 × 365 = 25,550
mg kg mg day−1 g day−1 m3 day−1 day year−1
year kg mg−1 cm2 mg cm−2 h−1 unitless m3 kg−1 kg day
This study US EPA (2002) GFBIC (2014) Yeganeh et al. (2013) US EPA (2002) EFH (2009) Ferreira-Baptista and De Miguel (2005) Yeganeh et al. (2013) Observation US EPA (2002) Aghili et al. (2009) US EPA (2002) US EPA (2002) US EPA (2011) US EPA (2002) Afiuni (2013) US EPA (1989)
Table 2 Descriptive statistics of the heavy metals contents in agricultural soil, atmospheric dust and food crops of Kermanshah province (mg kg−1).
Agricultural Soils (n = 53)
Atmospheric Dusts (n = 98)
Wheat (n = 10)
Maize (n = 6)
Element
Minimum
Maximum
Mean
Median
S.D.
S.E.
CV %
Guideline criterion
IEQSc
Zn Cu Ni Cr Zn Cu Ni Cr Zn Cu Ni Cr Zn Cu Ni Cr
40 10 48 32 88 24 60 44 26.4 6.5 0.5 2.5 20.5 2.5 2 2.5
113 83 306 235 700 256 245 147 46.4 9 2 8 64.5 7.5 8 4
74.62 41.21 131.46 79.21 210.29 47.63 119.53 73.74 34.25 7.85 1.35 4.90 38.33 4.83 5.58 3.25
72 41 125 76 173.17 44 100 66.65 31.15 8 1.25 4.50 35.50 4.75 6.5 3.25
16.24 12.09 47.17 28.73 113.14 25.73 44.33 21.96 7.70 0.78 0.53 1.84 17.78 2.09 2.69 0.69
2.23 1.66 6.48 3.95 11.43 2.60 4.48 2.22 2.44 0.25 0.17 0.58 7.26 0.85 1.10 0.28
22 29 36 36 54 54 37 30 22 10 39 38 46 43 48 21
62a 14a 18a 42a 62a 14a 18a 42a 100–500b 10–30b 10–30b 1–10b 100–500b 10–30b 10–30b 1–10b
500 200 110 110 500 200 110 110
a
Background values of world soils (Alloway, 2010). Critical limits introduced by Kabata-Pendias (2001). c Allowable contents of potential toxic elements for agricultural soils with pH > 7 given in the directive of Iranian Environmental Quality Standard (IEQS) in 2013. b
CR above 1 × 10−4 are likely to be harmful to human beings. A CR within a range from 1 × 10−6 ~ 1 × 10−4 indicates an acceptable or tolerable risk for regulatory purposes and desirable remediation, social stability and to human health (US EPA, 2001a, 2001b; Wu et al., 2015). The SF (mg kg−1 day−1)−1 is the slope factor for carcinogenic exposure. The values for SF and RfD are listed in Table 3. The potential non-carcinogenic (Li et al., 2013) and carcinogenic risks (Dehghani et al., 2017) for individual metals were calculated by using the following equations:
HQ =
Di RfD
3. Results and discussion 3.1. Heavy metal contents The concentrations of Zn, Cu, Ni, and Cr in AS, AD and food crops are shown in Table 2. To facilitate evaluation and comparison the values, the background values of the metals in soil derived from considered localities of the world soils (Alloway, 2010). According to the inter-comparison of the heavy metal concentrations in AS and AD, the concentrations of the metals in different environments are followed a descending order as: AS > AD for Ni and Cr, and AD > AS for Zn and Cu. The coefficient of variance (CV) indicates the degree of variability within the concentrations of a metal in the AS, AD and food crops. If CV ≤ 20%, it shows low variability, 21% ≤ CV ≤ 50% is considered as moderate variability, 50% ≤ CV ≤ 100% is suggested high variability and CV above 100% is regarded as exceptionally high variability (Karimi Nezhad et al., 2015). The CV for all elements in AS, food crops (except for Cu in wheat) and Ni and Cr in AD indicated a moderate degree of variability, while the CV for Zn and Cu in AD indicated a high degree of variability reflecting the non-homogeneous distribution of Zn
(5)
HI = ∑ HQ i
(6)
CRi = Di × SF
(7)
CR = ∑ CRi
(8) 156
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Fig. 2. Spatial distribution maps of Zn, Cu, Ni, and Cr concentration (mg kg−1) in agricultural soil (AS) and atmospheric dust (AD) of the study area.
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Igeo values for Cr indicate that the AD in the province is lowly contaminated by this metal. While, for Ni and Cu indicate that the AD in the province are heavily contaminated by the two metals. Moreover, the mean Igeo values for Zn, Cu, Ni and Cr in AD of the province are 1.03 (29%), 1.08 (48%), 2.06 (36%) and 0.17 (53%), respectively. The data indicates that there is the widespread pollution of Zn, Cu, Ni and Cr is in AD of Kermanshah (Fig. 4). As far as the overall behavior of HMs under study is concerned, on the basis of Igeo it can be said that the AS and AD samples in Kermanshah province are practically uncontaminated for Zn in AS, uncontaminated to moderately contaminated for Cu and Cr in AS and Cr in AD, moderately contaminated for Zn and Cu in AD, and moderately to heavily contaminated for Ni in AS and AD. The concentrations and Igeo values of Ni and Cu in agricultural soils and atmospheric dusts indicate that the contamination of the HMs is widespread in the environment in Kermanshah (Figs. 2 and 4). In general the sources of Zn, Cu, Ni and Cr in AD are probably traffic emission and industrial emission, while the metals in AS may be derived from parent materials, mining, sewage sludge, pesticides and fertilizers. The main pollution sources of the metals are also different among the province. The pollution sources of the HMs in the AD of Kermanshah province for Zn and Cu are probably traffic emission, as well as industrial emission, and for Ni and Cr are industrial emission and partly traffic and combustion processes (Ahmadi Doabi et al., 2017). The Zn and Cu in the AS of Kermanshah may be derived from anthropogenic activities (such as manures, municipal waste compost, and mineral fertilizers, etc.), whereas Ni and Cr are probably influenced by parent materials, combined with less traces of anthropogenic origins (Ahmadi Doabi et al., 2018).
Fig. 3. Boxplot Geo-accumulation index (Igeo) for heavy metals in the agricultural soil (AS) and atmospheric dust (AD) samples of Kermanshah province.
and Cu concentrations, which is probably related to the human activities. The non-homogeneous distribution may suggest the presence of local enrichment sources. The spatial distribution maps of heavy metals in AS and AD are shown in Fig. 2. The mean concentrations of Zn (74.62), Cu (41.21), Ni (131.46) and Cr (79.21) mg kg−1 in AS of province are higher than their background values (Table 2). However, the metal concentrations in AS of the entire province are lower than their IEQS with an exception of Ni concentrations in province. Also in food crops, except for Cr, the mean concentrations are less than the critical limits introduced by KabataPendias (2001). Concentrations of Cr in wheat (4.90 mg kg−1) and maize (3.25 mg kg−1) are greater than the lower boundary of the critical range (1–10 mg kg−1) for this metal according to the German Federal Ministry of the Environment (1992). Similar results were obtained by Yeganeh et al. (2012). The mean concentrations of Zn (210.29), Cu (47.63), Ni (119.53) and Cr (73.74) mg kg−1 in AD of the entire province from Kermanshah are much higher than their background values in soil of world (Table 2). The concentration ranges of the metals are observed to be 88–700, 24–256, 60–245 and 44–147 mg kg−1 for Zn, Cu, Ni and Cr, respectively. The concentrations of the metals in AD of the entire province are higher than their background values. However, the concentrations of Zn, Cu and Cr in province are lower than the IEQS with an exception of Ni.
3.3. Human health risk assessment of HMs 3.3.1. Non-carcinogenic risk Results of non-carcinogenic human health risk assessment of HMs in the AS and AD through possible exposure pathways (ingestion, dermal contact, and inhalation), and food crops (ingestion) for children and adults were shown in Table 3. Ingestion of AS, AD particles and food crops appeared to be the main exposure pathway for Zn, Cu, Ni and Cr to children and adult, followed by dermal contact and inhalation routes, respectively. Similar results were obtained by Ferreira-Baptista and De Miguel (2005), Zheng et al. (2010) and Dehghani et al. (2017). The contributions of HQing of Zn, Cu, Ni and Cr to HI in AS and AD were 99.98%, 99.94%, 99.94% and 99.94% for children, and 99.97%, 99.50%, 99.91% and 99.50% for adults, respectively (Table 3). These results suggest that ingestion is the main exposure route that threatens human health (especially via wheat). This result is consistent with other studies (Yeganeh et al., 2012, 2013; Chabukdhara and Nema, 2013; Qing et al., 2015; Wei et al., 2015; Salah Al-Heety et al., 2017). HQ (non-carcinogenic risk) due to inhalation of AS and AD particles is 1–7 orders of magnitude lower than the other two exposure pathways, and it is unlikely that this exposure route would pose a higher risk than ingestion. Therefore, inhalation of re-suspended particles through the mouth and nose is almost negligible compared with the other routes of exposure. HQ values in AS and AD from ingestion, inhalation and dermal contact in children were higher than those for adults. The only exception was Cu with higher HQinh for adults compared with children. Fig. 5 shows HI values for non-carcinogenic health risks among adults and children involving Kermanshah province AS, AD, and food crops (wheat and maize) samples associated with exposure to Zn, Cu, Ni, and Cr. The orders of non-cancer HI of HMs for both children and adults in AS, AD and maize were Zn > Ni > Cu > Cr, while for wheat were Zn > Cu > Ni > Cr (Table 3). HI values for all studied heavy metals were below 1. Zinc displayed the highest HI values among the investigated metals (especially in wheat), while potential health risk from Cr is the least. This result is originated from the high
3.2. Contamination levels of HMs The calculated results of Igeo of HMs in AS and AD are presented in Fig. 3. The mean values of Igeo decrease in the order of Ni > Cu > Cr > Zn for AS and Ni > Cu > Zn > Cr for AD. Fig. 3 shows that nearly the Igeo value for Zn (91%) in AS of the Kermanshah province is lower than 0. This indicates that the AS is uncontaminated or slightly contaminated by this metal. The Igeo values for Cu (58%) and Cr (66%) in AS in the province are lower than 1. This suggests that the AS in the province is uncontaminated to moderately contaminate by the two metals. The highest Igeo values for Ni (3.50) are found in the AS of province. In the province, the AS may be considerably contaminated by Ni. The mean Igeo values also indicate that the pollution of Ni (58%) is widespread in AS in Kermanshah province. However, the AS in Kermanshah is lowly or moderately contaminated by the other Zn, Cu and Cr. The spatial distribution maps of Igeo values in AS and AD are shown in Fig. 4. Nearly all the Igeo values for Zn, Cu and Ni in AD in the province are higher than 0 (Fig. 3). This indicates that the AD in this province is contaminated by the metals derived from anthropogenic sources. The 158
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Fig. 4. Spatial distribution maps of Geo-accumulation index (Igeo) values for Zn, Cu, Ni, and Cr in the agricultural soil (AS) and atmospheric dust (AD) of the study area.
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Table 3 Exposure dose, hazard quotient and risk for each element and exposure pathway (mg kg−1 d−1) in agricultural soil, atmospheric dust and food crops.
RfDing RfDinh RfDdermal SFing SFinh Agricultural Soil C (95% UCL) distributions Non-Carcinogenic risk Children Ding Dinh Ddermal HQing HQing / HI (%) HQinh HQdermal HI Adults Ding Dinh Ddermal HQing HQing / HI (%) HQinh HQdermal HI Carcinogenic risk Children CRing CRinh Adults CRing CRinh Atmospheric Dust C (95% UCL) distributions Non-Carcinogenic risk Children Ding Dinh Ddermal HQing HQing / HI (%) HQinh HQdermal HI Adults Ding Dinh Ddermal HQing HQing / HI (%) HQinh HQdermal HI Carcinogenic risk Children CRing CRinh Adults CRing CRinh Food Crops C (95% UCL) distributions Non-Carcinogenic risk Children Ding HQing HI Adults Ding
Zn
Cu
Ni non-canc.
3.00E-01 3.00E-01 6.00E-02
3.70E-02 4.02E-02 1.90E-03
2.00E-02 2.06E-02 1.00E-03
Ni canc.
Cr non-canc.
Cr canc.
5.00E-03 2.86E-05 2.50E-04 0.91 0.91
0.5 510
78.36 normal
43.99 normal
142.2 gamma
142.2 gamma
85.11 gamma
1.00E-03 2.80E-08 2.80E-06 3.34E-05 99.98 9.33E-10 4.67E-09 3.34E-05
5.62E-04 1.57E-08 1.57E-06 1.52E-06 99.94 3.91E-11 8.29E-10 1.52E-06
1.82E-03 5.08E-08 5.09E-06 9.09E-06 99.94 2.47E-10 5.09E-09 9.10E-06
1.09E-03 3.04E-08 3.05E-06 2.18E-07 99.94 1.06E-13 1.22E-10 2.18E-07
1.07E-04 1.58E-08 4.28E-07 3.58E-06 99.97 5.26E-10 7.14E-10 3.58E-06
6.03E-05 8.86E-09 2.40E-07 1.63E-07 99.50 3.56E-10 4.57E-10 1.64E-07
1.95E-04 2.86E-08 7.77E-07 9.74E-07 99.91 1.39E-10 7.77E-10 9.75E-07
1.17E-04 1.71E-08 4.65E-07 2.33E-08 99.50 5.99E-14 1.16E-10 2.34E-08
1.65E-03 4.62E-08
5.44E-04 1.55E-05
1.77E-04 2.61E-08
5.83E-05 8.74E-06
229.7 nonparametric
52.21 nonparametric
127 nonparametric
1.51E-03 4.22E-08 4.23E-06 5.03E-05 99.98 1.41E-09 7.05E-09 5.04E-05
3.43E-04 9.59E-09 9.61E-07 9.28E-07 99.94 2.39E-11 5.06E-10 9.28E-07
8.35E-04 2.33E-08 2.34E-06 4.18E-06 99.94 1.13E-10 2.34E-09 4.18E-06
5.09E-04 1.42E-08 1.43E-06 1.02E-07 99.94 4.98E-14 5.71E-11 1.02E-07
3.15E-04 4.63E-08 1.25E-05 5.39E-06 99.97 7.93E-10 1.08E-09 5.40E-06
7.15E-05 1.05E-08 2.85E-06 9.94E-08 99.50 2.17E-10 2.79E-10 9.99E-08
1.74E-04 2.56E-08 6.94E-06 4.47E-07 99.91 6.39E-11 3.57E-10 4.48E-07
1.06E-04 1.56E-08 4.23E-06 1.09E-08 99.50 2.81E-14 5.44E-11 1.10E-08
Wheat 38.72 normal
Maize 52.96 normal
Wheat 8.3 normal
Maize 6.55 normal
Wheat 1.66 normal
Maize 7.8 normal
3.33E-01 1.11E-02 1.11E-02
6.10E-04 2.03E-05 2.03E-05
7.14E-02 1.93E-04 1.93E-04
7.50E-05 2.04E-07 2.04E-07
1.43E-02 7.14E-05 7.14E-05
2.15E-01
4.50E-04
4.60E-02
5.60E-05
9.20E-03
85.11 gamma
127 nonparametric
77.47 nonparametric
77.47 nonparametric
7.60E-04 2.12E-08
2.55E-04 7.26E-06
8.14E-05 1.20E-08
2.73E-05 4.09E-06
Wheat 1.66 normal
Maize 7.8 normal
Wheat 5.96 normal
Maize 3.82 normal
9.00E-05 4.49E-07 4.49E-07
5.13E-02 1.03E-05 1.03E-05
4.40E-05 8.79E-09 8.79E-09
6.70E-05
3.30E-02
3.30E-05
Wheat 5.96 normal
Maize 3.82 normal
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Table 3 (continued) Zn HQing HI Carcinogenic risk Children CRing Adults CRing
Cu
7.15E-03 7.15E-03
1.51E-05 1.51E-05
Ni non-canc.
1.24E-04 1.24E-04
1.52E-07 1.52E-07
4.60E-05 4.60E-05
Ni canc.
Cr non-canc.
3.34E-07 3.34E-07
6.61E-06 6.61E-06
Cr canc. 6.55E-09 6.55E-09
1.30E-02
8.17E-05
2.56E-02
2.20E-05
8.37E-03
6.08E-05
1.65E-02
1.64E-05
4.00E-05
AS Children
6.00E-05
AD Children
3.50E-05
AS Adult
5.00E-05
AD Adult
4.00E-05
2.50E-05
HI Value
HI Value
3.00E-05
2.00E-05 1.50E-05
3.00E-05 2.00E-05
1.00E-05 1.00E-05
5.00E-06
0.00E+00
0.00E+00
Zn 1.20E-02
Ni
Zn
Cr 2.50E-05
Wheat Children Wheat Adult
1.00E-02 8.00E-03 6.00E-03 4.00E-03
Cu
Ni
Cr
Maize Children Maize Adult
2.00E-05
HI Value
HI Value
Cu
1.50E-05 1.00E-05 5.00E-06
2.00E-03 0.00E+00
Zn
Cu
Ni
0.00E+00
Cr
Zn
Cu
Ni
Cr
Fig. 5. Hazard index (HI) values for non-carcinogenic health risks for adults and children involving Kermanshah province agricultural soil (AS), atmospheric dust (AD) and food crops (Wheat and Maize).
samples through the ingestion. The CR values of Ni and Cr in AS, AD, wheat, and maize were 1.65E-03, 5.60E-04; 7.60E-04, 2.62E-04; 1.30E02, 2.56E-02, and 8.17E-05, 2.20E-05 for children and 1.77E-04, 6.70E05; 8.14E-05, 3.14E-05; 8.37E-03, 1.65E-02, and 6.08E-05, 1.64E-05 for adults, respectively. Carcinogenic risk values for children were higher than adults. The contribution order of CR of each metal to the overall CR values in AS, AD, wheat and maize was 74.7% (Ni) > 25.3% (Cr); 74.4% (Ni) > 25.6% (Cr); 66.4% (Cr) > 33.6% (Ni) and 78.8% (Ni) > 21.2% (Cr) for children and 72.6% (Ni) > 27.4% (Cr); 72.2% (Ni) > 27.8% (Cr); 66.4% (Cr) > 33.6% (Ni) and 78.8% (Ni) > 21.2% (Cr) for adults, respectively. The majority of the CR lay between 1 × 10−5 and 1 × 10−4; only observed high risk levels that exceeded 1 × 10−4 in wheat samples for Ni and Cr, and in AS samples for Ni. Fig. 6 shows that the cumulative CR values of Ni and Cr have exceeded incremental lifetime of 1 × 10−6. Thus, the possibilities of having cancer in the long term are evident for children and adults. The CR obtained for adults was all within the acceptable range (except for Ni in AS, and Ni and Cr in wheat), therefore, it may conclude that there would not occur serious long-term health impacts for adults with respect to Ni and Cr in AD and maize samples, and to Cr in AS samples. In contrast, for children, the total carcinogenic risks (CRs) of Ni and Cr
concentration of Zn in AS, AD and food crops (wheat and maize). The HI values of these HMs in AS and AD was about 9 times and in food crops about 1.3 ~ 1.5 times higher for children compared to adults suggesting that children have much more chance for non-carcinogenic risk in Kermanshah province than adults. The high non-carcinogenic risk of children is mostly due to their pica behavior and hand or finger sucking (Wei et al., 2015; Zhao et al., 2014). The HQs and HIs for all HMs are lower than the safe level (1), indicating low detrimental health risk to children and adults due to heavy metal exposure. The results reflected that exposure to HMs in AS, AD and food crops solely would not cause serious health impacts in Kermanshah province. However, the calculated risk is affected by a high degree of uncertainty. On the other hand, the adverse effects of HMs accumulations in human body for a long time are not considered here. 3.3.2. Carcinogenic risk To assess carcinogenic risk (CR) of Ni and Cr, appropriate SF values were taken from RAIS (2017) and OEHHA (2017). The CR levels of Ni and Cr in AS, AD and food crops in Kermanshah province are listed in Table 3. The CR of Ni and Cr was calculated in AS and AD samples through the ingestion and inhalation, and in food crops 161
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1.80E-03 1.60E-03
8.00E-04
AD Children
AS Adult
7.00E-04
AD Adult
6.00E-04
Cumulative CR
Cumulative CR
1.40E-03
AS Children
1.20E-03 1.00E-03 8.00E-04 6.00E-04 4.00E-04
5.00E-04 4.00E-04 3.00E-04 2.00E-04 1.00E-04
2.00E-04 0.00E+00
0.00E+00
Ni 3.00E-02
Ni
Wheat Children
9.00E-05
Wheat Adult
8.00E-05
Cr Maize Children Maize Adult
7.00E-05
Cumulative CR
Cumulative CR
2.50E-02
Cr
2.00E-02 1.50E-02 1.00E-02 5.00E-03
6.00E-05 5.00E-05 4.00E-05 3.00E-05 2.00E-05 1.00E-05 0.00E+00
0.00E+00
Ni
Ni
Cr
Cr
Fig. 6. Total cancer risk (CR) values for carcinogenic health risks for adults and children involving Kermanshah province agricultural soil (AS), atmospheric dust (AD) and food crops (Wheat and Maize).
of this study would facilitate the decision-makers to manage contaminated AS, AD and food crops, and minimize health risks to province inhabitants and also could serve as a useful case study for the assessment of health risks posed by urban environment in other provinces or countries.
(except for Ni and Cr in maize) were higher than the threshold value (1 × 10−4), highlighting that children may suffer more potentially carcinogenic risks in their daily life via unconscious ingestion pathways. Moreover, the health risk posed by heavy metals via ingestion is higher than that by inhalation for both adults and children. Carcinogenic risks of Ni and Cr for both children and decreased in this order: wheat > AS > AD > maize. On the other hand, CRs of Ni for both children and adults in AS, AD and maize was more than Cr (except via wheat). From the results, we also can conclude that the ingestion of wheat was the most important exposure pathway for children and adults and could have more potential to threaten human health compared to AS, AD and maize. According to the current results, Ni and Cr should be paid more attention for the potential occurrence of carcinogenic risk to threaten human health in the study area. However, further studies are needed to explain the higher CR caused by Ni and Cr in this region.
4. Conclusion The concentrations, pollution levels, and health risks of HMs (Zn, Cu, Ni and Cr) in AS, AD and food crops from Kermanshah province were studied. The obtained results show that mean contents of all studied elements in AS and AD samples exceed background values, indicating that the pollution may come from anthropogenic sources. Compared with the IEQS guidelines for agricultural soil quality of Iran, AS and AD of Kermanshah province have elevated concentrations of Ni. The Ni should be paid more attention. Statistical descriptions of the contents indicate that pollution sources of the HMs in the AS and AD of Kermanshah province for Zn and Cu are due to man-made sources, while Ni and Cr probably have mixed sources of natural and anthropogenic origins in the AS (with less traces of anthropogenic influence) and AD (with less traces of natural influence). The Igeo values reveals that Ni in AS and AD were moderately to heavily contaminated. The results of risk analysis suggest that ingestion of food crops especially wheat is the main pathway for entering the metals to human body and threaten their health. Both the HQ values and the HI value for all studied metals are far lower than the safe level (= 1) for children and adults, indicating there is no non-carcinogenic risk from these metals. The carcinogenic risk values of Ni and Cr for children and adults were above the threshold value (1 × 10−6). On the other hand, children are likely under a higher health risk than adults, especially where the carcinogenic risk is higher than 1 × 10−4, indicating that children may be facing the threat of serious carcinogenic risk over a lifetime.
3.3.3. Uncertainties It is considered to be most accurate and reliable to use the bio-accessible concentrations of elements to determine health risks (Oomen et al., 2002). However, the calculated risk of both non-carcinogenic and carcinogenic of metals via AS, AD and food crops exposure pathways was influenced by several other uncertainty factors (Qing et al., 2015). In this study local parameters used as much as possible, but in some cases, there was not any local data or information, then we had to use the international data bases such as US EPA exposure handbook. The other source of uncertainty is that other elements (e.g., As, Pb, Cd, and Sr) and other exposure pathways (e.g., water or contaminated food) were not considered in this study. Despite the uncertainties involved, the model proved to be a robust tool for assessing human health risks in recognizing the dangerous metals and identifying the exposure pathways of most concern (Wei et al., 2015; Wang et al., 2016). The findings 162
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These findings indicate that more consideration ought to be paid to HM contamination of AS, AD and food crops in Kermanshah province.
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