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Impact of the uncontrolled leakage of leachate from a municipal solid waste landfill on soil in a cultivated-calcareous environment
Waste Management 82 (2018) 51–61
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Impact of the uncontrolled leakage of leachate from a municipal solid waste landfill on soil in a cultivated-calcareous environment Salar Rezapour a,⇑, A. Samadi a, Ioannis K. Kalavrouziotis b, N. Ghaemian c a
Soil Science Department, Urmia University, P.O. Box 165, Urmia 57134, Islamic Republic of Iran School of Science and Technology, Hellenic Open Univ., Tsamadou 13-15 and Saint Andrea, 262 22 Patras, Greece c West Azarbaijan Agricultural Researches Center and Natural Resources, Urmia, Islamic Republic of Iran b
a r t i c l e
i n f o
Article history: Received 29 January 2018 Revised 29 August 2018 Accepted 9 October 2018
Keywords: Leachate Heavy metal Calcareous Potential risk Hazard index
a b s t r a c t The heavy metal pollution generated by landfill leachate becomes increasingly concerning due to its potential to impact human health through the food chain. In the present study, the accumulation and potential health risk of heavy metals (Zn, Cu, Cd, Pb, and Ni) were investigated in a calcareous soil wheat system affected by an uncontrolled landfill leachate. The results showed soils were significantly enriched by both the available and total fractions of the metals in the sequences of Zn > Pb > Ni > Cd > Cu and Cd > Zn > Ni > Pb > Cu, respectively. Nevertheless, only the Cd content exceeded the standard levels. For the various population groups, the mean hazard quotient (HQ) was lower than the unity, implying a lack of non-carcinogenic health risk for the local residents, while the average hazard index (HI) was 2.3 and 1.1 for people aged 0–5 and 6–18 years, respectively, illustrating a moderate non-carcinogenic health risk for the two groups. Cd and Pb contributed the most to HI, followed by Cu, Zn, and Ni. In addition, the carcinogenic health risk of Cd, ranging from 1 105 to 1 106, showed a low potential risk in the different population groups exposed to wheat grains and decreased in the sequence of adult > population 6–18 years > population 0–5 years. The findings of the study, which can be used in regions under similar environmental conditions, provide a valuable benchmark for the design of appropriate strategies to manage these agroecosystems by both local and national managers of such macrosystems. Ó 2018 Elsevier Ltd. All rights reserved.
1. Introduction Globally, the proper management of municipal solid waste (MSW) is a serious challenge in many countries characterized as industrialized and developing regions, which can pose risks to the water-soil-plant-animal-human system. In general, MSW as a waste type, includes plastic, food waste, inorganic salts, glass, paper, building and electronic wastes, metals, and organic fractions and leads to pollution in soil and water mainly through leachates. The leachates are generated when MSW comes in contact with water that infiltrates through a landfill. Leachate is a complex mixture that is composed of various pollutants such as heavy metals, soluble organic and inorganic compounds, nutrients, and suspended particles. Leakage of leachate can cause pollution of groundwater, surface waters, agriculture and natural ecosystems, especially when the leachate is released in an uncontrolled manner (Samadder et al., 2017; Adamcová et al., 2017). A complex mixture ⇑ Corresponding author. E-mail address: [email protected] (S. Rezapour). https://doi.org/10.1016/j.wasman.2018.10.013 0956-053X/Ó 2018 Elsevier Ltd. All rights reserved.
emerging from the bottom of the MSW involves a combination of various pollutants particularly heavy metals, soluble organic and inorganic compounds, nutrients, and suspended particles (Mavakala et al., 2016; Naveen et al., 2017; Arunbabu et al., 2017). Such leachate can effect significant changes in soil attributes after it enters into the soil. The amount of leachate produced also depends on the compaction of the waste, climate and landfill cover at closed landfills. Previous studies associated with landfills without treatment systems showed that the movement of landfill leachate on the soil surface resulted in alterations in the various physicochemical and biological processes of the soil, which eventually affects the level of soil pollution (Samadder et al., 2017). The quantity and quality of leachate are influenced by various factors such as the composition of the waste, the biochemical processes that occur in the degradation stages of the waste, the amount of moisture, and the local parameters (Arunbabu et al., 2017; Ma et al., 2018). The problem of MSW is more serious in developing countries such as Iran, where MSW disposal is primarily conducted using landfills/dumping yards and landfills that lack leachate collection
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and treatment systems. In Iran, as in many nations, the production of MSW has developed in parallel with rapid population growth, as well as industrial, commercial and urban expansion. Such aspects, which have significantly progressed in recent decades, lead to the generation of several environmental problems affecting the soil, air, surface, and groundwater. In addition, the management systems of urban and industrial waste are limited, and landfills considered to be disposal sites, are situated in public spaces, agricultural lands, and urban rivers and are without treatment. Considering the different types of soil contamination, heavy metals are highlighted more and more seriously as one of the most challenging environmental problems due to their bioaccumulation, toxicity, non-biodegradability and persistence (Alloway, 2012). The accumulation of heavy metals in soils, which is mainly caused by anthropogenic activities, can pose a potential hazard to food safety and human health in the water-soil-plant-animal-human system. Such risks result in the fact that soil heavy metals and their enrichment under the influence of various sources have caused widespread concerns throughout the world over time. There are several studies that deal with these problems. For example, Ma et al. (2018) found that the soils around an MSW site were moderately polluted by Cu, Pb, Zn, and Hg and heavily polluted by As and Cd in North China. Similarly, the significant impact of MSW with heavy metal pollution (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) on human health was reported in the soils surrounding an MSW site by Rimmer et al. (2006) in Newcastle. Therefore, to protect and improve the soil-crop ecosystem, it is necessary to identify the pollution characteristics of heavy metals in the soils contaminated by leachate. Particularly, understanding the exposure risks of heavy metals in these soils and apportioning their sources are (i) the basic preconditions for soil pollution prevention, control, and reduction of metal inputs to soils (Chen et al., 2015); (ii) the basic precondition for preparing information on the significance and extent of soil metal contamination from different sources; and (iii) most importantly, provide appropriate data for making decisions regarding remediation of contaminated soils. Furthermore, the concentration, distribution, and toxicity of heavy metals in the soil-crop system affected by uncontrolled leachate are rarely assessed. Accordingly, the impact of landfill leachate on soil attributes in terms of heavy metals accumulation was investigated in a cultivated region in northwest Iran, where dumping a large amount of MSW generates a huge amount of leachate. The specific aims of this work were the following: (i) to compare the available and total fractions of Zn, Cu, Ca, Pb, and Ni in the sites contaminated by leachate and the adjoining non-contaminated sites, (ii) to describe the effects of landfill leachate on the enrichment of selected heavy metals in soil and wheat grains growing on the sites contaminated by leachate, and (iii) to analyses the health risks associated with heavy metals to the local consumers of the wheat grain.
2. Methods 2.1. Site characteristics and soil sampling The study landfill site is located approximately 20 km from Miandoab City in western Azerbaijan Province, which is located in north-western Iran (Fig. 1). The population of the city (Miandoab region) is approximately 280,000, and the studied area is the most important area of wheat production for the local residents, where 100,000 tons/year of wheat are produced (MJA, 2017). This landfill site has been used as an uncontrolled open system without any engineering operations on the flat area and or the surrounding farmland. The site has received the municipal solid and liquid wastes generated from commercial activities, hospitals, urban
municipal, energy generation residues, and industry belonging to Miandoab City. Unfortunately, there are no reports and records clarifying the amount of waste received over the years from the region. After interviews with local farmers and landowners, however, we estimate that the site received over 50 tons of waste every day for over 15 years. At this site, waste has accumulated to a height of 10–15 m and is burned weekly. Then, the leachate generated from the burnt waste (with a length of 1.2 km) flows into the cropland around the site of an area of approximately 10 ha. The lack of any barrier system or a leachate collection system in the landfill studied the resulted in release and transport of its leachate into the surrounding crop land. Consequently, farmers around the area demanded that the landfill site be closed immediately because of damage to their fields. Relevant selected chemical compositions of the investigated leachate are shown in Table 1. The climate of the region is typically characterized by dryhot summers and cold winters; the mean annual precipitation is approximately 320 mm, occurring mostly in autumn and winter, and the mean annual temperature is 13 °C. In general, the groundwater level was present at depths of 5 to 7 m from the soil surface for periods ranging from 1 to 12 months of the year at all of the sites. The region often has a groundwater table of less than 5 m during the wet season, but the groundwater table drops to approximately more than 7 m from the surface during the dry season. The major crop cultivated in the region is winter wheat (Triticum aestivum L.), which is grown from November to July and has a growth period approximately about 230 days. During the field studies, eight soil profiles from the leachateinfluenced soils (four profiles) and the control soils (four profiles) were dug. The soils were described, and sampled along a transect with four experimental sites in August 2016. At each experimental site, two paired soil profiles (involving soil under the influence of the leachate and the adjacent control soil) were identified with similar slope, aspect, drainage conditions, and parent materials. Each profile was considered the central point, and surface soil samples were collected around this central point. Accordingly, four points were sampled within a radius of 5–10 m of the central point from 0 to 30 cm in depth, in triplicate. Soil samples were air-dried, crushed, passed through a 2-mm mesh, and were placed in zipsealed plastic bags prior to analysis. The soil profiles characterized by a high level of calcium carbonate (a range of 10–31%) were classified as Calcisols based on the WRB system (IUSS Working Group WRB, 2014). 2.2. Procedures of laboratory analysis The physicochemical attributes of all soil samples [particle-size distribution (hydrometer methods), pH (1:2.5 soil-0.01 M CaCl2), electrical conductivity (saturation extract), organic carbon (wet oxidation method), cation exchange capacity (sodium acetate method), and calcium carbonate equivalent (acid neutralization method) were determined using standard procedures (Klute and Page, 1996). The available fraction of Zn, Cu, Cd, Pb, and Ni was extracted from 10 g of soil mixed with 20 cm3 DTPA (diethylene triaminepentaacetic acid) solution (Lindsay and Norvell, 1978). To determine the total fraction of heavy metals, the simple method proposed by Sposito et al. (1982) was used, which identifies the total HNO3-extractable fraction in soils. The intention of this procedure is to establish a simple reference method for the determination of total heavy metals in different soils. This method is considered adequate by many researchers from different regions of the world and can provide important information about the risk potential of soil heavy metals (e.g., Olsen et al. (1994); Zeng-Yei et al. (2002); Safari et al. (2015); Rezapour and Moazzeni (2016)). According to the method, 10 cm3 of concentrated HNO3
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Fig. 1. Location of the study region (P1L, . . ., the soil under influence of leachate; P1C,. . . the adjacent control soils).
were added to 2 g of soil and heated for 15 min at 95 °C, followed by the addition of 2 cm3 deionized water and 3 cm3 of 30% H2O2 (Soon and Abboud, 1993). The metalvalues for both the available and total fractions were determined by an atomic absorption spectrophotometer (Shimadzu AA-6300). The detection limit concentration of the metals was between 0.01 and 0.03 cm3 L1, with wavelengths of 213.9, 324.8, 228.8, 283.3, and 232 for Zn, Cu, Cd, Pb, and Ni, respectively. The standard solution concentrations were 0.5, 1, 1.5, 2, and 2.5 or 4, 6, 8, 10, and 12 for Zn and Cu; and 0.5, 1, 1.5, 2 and 2.5 for Cd, Pb, and Ni. At each site under the influence of the leachate, 50 wheat grain (before harvesting wheat) samples were collected randomly for elemental analysis and risk potential determination. Grain samples were washed with deionized water to remove any existing particles, and oven dried at 65 °C for 24 h. Then, 1.000 g of the dried samples was heated at 500 °C for 12 h, subjected to the effect 2 M HCl, filtered by centrifugation, and analysed as above. All statistical analysis was carried out using the program package SPSS 19 (SPSS INC., Chicago, USA). Comparison of the differences between the values of heavy metals in the soils under the
influence of leachate and the control soil was accomplished with Duncan’s multiple range tests using a paired t-test. 2.3. Soil pollution indices To evaluate the pollution levels of the soils affected by leachate, single factor pollution index (PI), Nemerow pollution index (PIN) or comprehensive pollution index (PIN), and pollution load index (PLI) were estimated (Zhang et al., 2013) as follows:
PI ¼ ðC i =Si Þ
PIN ¼
vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2 u n u 1P u PI þ ½maxðPIÞ2 i n t i¼1
2
where Ci is the measured content of the element i at each sampling point, and Si is the regional background content of the heavy metal i; max (PI) = the maximum amount of the single factor pollution
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Table 1 Selected chemical composition of the investigated leachate in different sites. Parameter
Unit
Mean
SD
Site 1 pH EC OM Zn Cu Cd Pb Ni
– dSm1 % mg kg1 mg kg1 mg kg1 mg kg1 mg kg1
6.6 5.3 20.3 59.3 5.7 0.82 7.8 6.2
0.31 0.7 3.7 6.2 0.52 0.04 1.2 0.73
Site 2 pH EC OM Zn Cu Cd Pb Ni
– dSm1 % mg kg1 mg kg1 mg kg1 mg kg1 mg kg1
6.55 5.1 21.5 58.5 5.5 0.78 8.1 6.4
0.28 0.65 4.2 5.6 0.41 0.03 1.4 0.8
Site 3 pH EC OM Zn Cu Cd Pb Ni
– dSm1 % mg kg1 mg kg1 mg kg1 mg kg1 mg kg1
6.53 6.1 19.2 62.1 5.9 0.91 8.4 6.6
0.35 0.88 4.5 6.7 0.55 0.07 1.7 0.61
Site 4 pH EC OM Zn Cu Cd Pb Ni
– dSm1 % mg kg1 mg kg1 mg kg1 mg kg1 mg kg1
6.65 5.1 22.5 61.6 5.8 0.81 7.9 5.9
0.48 0.73 5.6 6.2 0.51 0.05 1.23 0.59
index, n = number of analysed metals, and i = ith value of the metals. The pollution load index (PLI) (Cabrera et al., 1999)
PLI ¼ ðCF1xCF2xCF3 . . . ::CFnÞ1=n where CF = concentration factor = ms/mr, ms-conc. of metal in soil mg kg1, and mr = metal reference value (mg kg1). PLI value less than 1 suggests a lack of pollution. Other indices that can be used are given by Kalavrouziotis and Koukoulakis (2012) and Kalavrouziotis et al. (2012). These indices have been calibrated by Papaioannou et al. (2017) where critical ranges are given. To estimate the potential health risk of heavy metals for local residents via ingestion of wheat grain, both the non-carcinogenic and carcinogenic effects of the metals were computed for different population groups of the area as follows (US EPA, 2004):
C IR EF ED DIM ¼ BW AT HQ ¼
DIM RfD
ð1Þ
ð2Þ
where HQ is hazard quotient that estimates the non-cancer risk during a lifetime, DIM is the daily intake of metals in mg kg1 day1, C is the metal concentration of wheat grains in mg kg1, IR is the ingestion rate in mg day1, BW is the average of the body weight in kg, EF is the exposure frequency (365 days year1), ED is the exposure duration, AT is the mean exposure time for non-
carcinogenic effects (ED 365 day years1), and RfD is the reference oral dose for each metal. The sum of HQ amounts is expressed as Hazard Index P (HI ¼ i1 HQ Þ indicating the overall potential of non-carcinogenic effects (US EPA, 2004; RAIS, 2017). HQ or HI > 1 represents the adverse health impacts while there is the absence of adverse health impacts when their amounts are 1. Cancer risk (CR) adverts to the potential of the appearance of a kind of cancer over a lifetime due to the exposure to a carcinogenic metal. The CR is estimated using Eq. (3) (RAIS, 2017).
CR ¼ DIM SF
ð3Þ
where SF is the slope factor. The admissible risk level is assumed to be 106 for single element carcinogenic risk, while risks at the level of < 104 are advised to be admissible for multi-element carcinogenic risk (RAIS, 2017). 3. Results and discussion 3.1. General physicochemical attributes The contents of selected physicochemical properties measured in this research are listed in Table 2. The soils in the examined region were loamy clay to clay in texture in both soils under the influence of the leachate (SIL) and control, respectively, with the relative value of clay, silt, and sand in the range of 35–60%, 25– 40%, and 13–25%, respectively. The pH value of the control soils was alkaline (7.5–8), and the control soils were remarkably unaffected by the contribution of leachate even though the mean pH value of the leachate was slightly acidic. This situation is contributable to the specific characteristics of Calcisols, which have a high tendency to resist changes in the pH of the soil solution. The content of EC was observed to be significantly higher in the SIL than in the control soils (a rise of 91–150%), resulting in an increase in EC to above the salinity threshold (4 dS m1) in the majority of the studied soil sites. The major cause behind such a trend can be the high levels of cations and anions as well as the total dissolved solids in the leachate itself as previously reported by other authors (Naveen et al., 2017). Soil organic matter was significantly raised in the SIL, ranging from 75 to 95%, compared to the control field, which could build up a beneficial impact on soil properties (e.g., improve soil physical and fertility attributes and reduce the bioavailability of heavy metals) (Kabata-Pendias, 2010). Presumably, the enhancement was directly generated by the biodegradation processes of composted substances occurring in the municipal solid waste and its leachates (Adamcová et al., 2017). In addition, the incorporation of leachate into soil resulted in an increasing trend in the CEC amounts, which is attributable to organic matter added by the leachate. 3.2. Heavy metals in the soil The concentration of available (DTPA-extractable) and total fractions of all heavy metals in the soils are depicted in Tables 3 and 4. The contents of DTPA-Zn, Cu, Cd, Pb, and Ni in the soils under direct contact with the leachate were found to be: 15–49, 4–13, 0.2–1.1, 2.1–5.2, and 1.3–3.9 mg kg1, respectively. However, for the control soils, the concentration of heavy metals was: 1.4– 7.1, 1.5–5.5, 0.11–0.44, 0.6–2.3, and 0.4–1.7 mg kg1, respectively. Adding the leachate to the soils significantly increased all DTPA extractable–metals more than their corresponding control soils in the order of Zn > Pb > Ni > Cd > Cu. Such a pattern was true for all soil sites, which illustrated that these soils were enriched by the DTPA-fraction of heavy metals under the influence of anthropogenic activities. Even with this redundancy, only Zn and Cd val-
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Table 2 Comparison of the some physicochemical properties in the soils influenced by leachate and the adjacent control soils based on paired t-test (*P < 0.05; **P < 0.01; ***P < 0.001). Parameter
Soil under the influence of leachate
Control soils
Difference (%)
SD
Mean
SD
Mean
Site 1 Sand (%) Silt (%) Clay (%) pH EC(dSm1) CEC(cmolckg1) OM(g kg1) CCE(g kg1)
2.4 9.9 9.9 0.4 0.2 2.1 0.1 10.6
19 30.0 51.0 7.5 3.5 21.9 18.7 185.2
1.6 8.2 3.1 0.1 1.1 3.3 0.5 7.7
20.3 29.7 50.0 7.7 1.87 18.8 16.2 183.1
5.0 1.0 2.0 2.5 87.0** 16.5 15.4 2.0
Site 2 Sand (%) Silt (%) Clay (%) pH EC(dSm1) CEC(cmolckg1) OM(g kg1) CCE(g kg1)
5.0 5.7 6.6 0.28 1.6 3.4 0.7 6.3
21 29.5 49.5 7.4 3.79 24.0 21.8 210.0
5.7 2.3 4.0 0.13 0.31 4.1 0.7 8.9
25.2 26.0 48.8 7.6 1.87 20.1 17.5 202.0
16.7 13.5 1.4 2.6 102.30*** 19.3 24.7* 8.0
Site 3 Sand (%) Silt (%) Clay (%) pH EC(dSm1) CEC(cmolckg1) OM(g kg1) CCE(g kg1)
4.2 7.1 10.7 0.14 2.1 1.1 0.3 8.7
19.0 33.0 48.0 7.3 5.98 18.4 19 162.0
5.4 7.1 12.5 0.1 1.5 2.8 0.2 10.3
22.0 32.5 45.5 7.5 2.8 15.6 15.7 153.0
13.6 15.0 5.5 2.31 113.69*** 17.59 21.0* 6.2
Site 4 Sand (%) Silt (%) Clay (%) pH EC(dSm1) CEC(cmolckg1) OM(g kg1) CCE(g kg1)
6.5 6.4 12.5 0.14 0.3 3.05 0.1 7.6
19.0 29.0 52.0 7.5 3.4 24.6 22.7 210.0
5.2 5.3 10.0 0.2 0.3 7.02 0.6 8.3
22.0 28.0 50.0 7.8 1.65 20.63 18.5 203.0
14.0 3.5 4.0 3.34 106.0*** 19.2 22.3* 6.8
EC, Electrical conductivity; CEC, Cation exchangeable Capacity; OM, Organic Matter; CCE, Calcium Carbonate Equivalent.
ues exceeded the permissible contents (Kabata-Pendias, 2010). The average content of Zn and Cd was 2.5–3.5 and 1.1–1.3 times higher, respectively, compared to their maximum identifiable range, implying that the soils affected by leachate may not be advisable to be used for agricultural production because of possible health and phytotoxic problems generated by these two elements for different crops. The health risk of Zn and Cd with the possibility of phyto-accumulation was recognized by previous studies (KabataPendias, 2010; Naveen et al., 2017). Moreover, the high quantities of Zn and Cd are likely to be relative to the amount of batteries, paints, coloured glass, and inks in paper, which are common in MSW (Mavakala et al., 2016; Swati and Thakur, 2017; Krcˇmar et al., 2018). The concentrations of total Zn, Cu, Cd, Pb, and Ni in soils affected by leachate were found to vary, respectively, as follows: 133–210, 35–67, 3.9–6.9, 54–95, and 48–73 mg kg1. For the control soils, the concentrations were found to be, respectively, as follows: 54–76, 34–54, 1.4–2.3, 29–58, and 23–38 mg kg1 (Table 4). These results are comparable to those of Adamcová et al. (2017) but higher than results reported by Samadder et al. (2017) for the surface soils under the influence of leachate. However, the mean concentration of all the investigated metals of soils affected by leachate was higher than the corresponding amounts measured for the control soils. Along the transect, the concentration of heavy metals varied depending on the site of the soils, which can be described in terms of the quality and quantity of the leachate itself
and the impact of the leachate with its affected soils. Increased concentrations of the metals, on average, follow a declining trend in all soils according to the following order: (180–200%) > Zn (155–164%) > Ni (84–99%) > Pb (62–100%) > Cu (23–32%) after contact with the leachate. However, only Cd values exceeded the threshold concentration, which showed that Cd pollution was occurring in the present study following the entrance of leachate into the agricultural soils. Work carried out by Yusof et al. (2009) and Adamcová et al. (2017), who studied the impact of leachate from uncontrolled landfills on the chemical characteristics of soil, highlighted that soil surrounding landfills was affected by a high level of Cd. 3.3. Soil pollution indices The indices of single pollution (PI), comprehensive pollution (PIN), and pollution load (PLI) were calculated (Table 5 and Fig. 2) for various metals and soil sites to assess the range of contamination of the examined soils after contact with leachate. For different soil sites, the mean PI contents of Cu, Pb, and Ni were 1.25–1.4, 1.3–2, and 1.8–2, respectively, implying low contamination. Nevertheless, the average PI values of Zn (2.5–2.6) and Cd (2.8–3) were higher than 2, suggesting that all soils should be moderately polluted by Zn and Cd. The average PIN values of five metals showed a decreasing order as follows: Cd > Zn > Ni > Pb > Cu, which was an order similar to the order for the PI values. The cal-
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Table 3 Comparison of the average values of the DTPA –fraction of heavy metals (mg kg1) in the soils influenced by leachate and the adjacent control soils based on paired t-test (*P < 0.05; **P < 0.01; ***P < 0.001). Heavy metal
Soil under the influence of leachate
Control soils
Difference (%)
SD
Mean
SD
Mean
Site 1 Zn Cu Cd Pb Ni
3.5 1.8 0.2 0.2 0.1
24.5 7.2 0.65 3.1 2.2
1.1 0.6 0.1 0.12 0.1
3.4 3.6 0.4 1.1 0.9
354.0*** 100.0*** 62.5** 181.8*** 139.1***
Site 2 Zn Cu Cd Pb Ni
4.1 0.95 0.1 0.2 0.2
24.3 6.4 0.59 3.3 2.7
1.3 0.8 0.1 0.1 0.1
5.2 4.3 0.34 1.1 1.4
367.3*** 48.8* 73.5** 200*** 92.9**
Site 3 Zn Cu Cd Pb Ni
2.8 0.75 0.1 0.3 0.13
27.8 5.3 0.54 3.7 2.3
0.8 0.7 0.0 0.1 0.1
5.5 4.2 0.3 1.3 0.98
405.5*** 26.2* 86.2** 184.6*** 134.7***
Site 4 Zn Cu Cd Pb Ni
3.1 1.3 0.1 0.27 0.2
33.8 6.7 0.53 3.3 2.9
0.9 0.8 0.1 0.1 0.1
5.9 4.1 0.26 1.2 1.1
472.9*** 63.4* 103.8*** 175.0*** 163.6***
Table 4 Comparison of the average values of the total fraction of heavy metals (mg kg1) in the soils influenced by leachate and the adjacent control soils based on paired t-test (*P < 0.05; **P < 0.01; ***P < 0.001). Heavy metal
Soil under the influence of leachate
Control soils
Difference (%)
SD
Mean
SD
Mean
Site 1 Zn Cu Cd Pb Ni
42.3 5.8 0.5 6.1 4.1
162.9 58.3 5.2 63.2 57.5
4.8 44.2 0.1 2.1 1.8
63.8 3.6 1.8 38.9 30.5
155.3*** 31.9* 189*** 62.5* 88.5**
Site 2 Zn Cu Cd Pb Ni
38.7 4.6 0.8 9.1 4.6
161.9 55.5 5.1 77.8 59.1
3.7 3.3 0.08 2.4 1.6
61.3 45.1 1.7 38.8 31.2
164*** 23.1* 200*** 100.5*** 89.4**
Site 3 Zn Cu Cd Pb Ni
35.2 4.9 0.8 8.3 5.2
166.1 55.7 5.3 80.4 61.3
5.1 3.5 0.1 2.8 2.3
63.3 45.1 1.9 46.4 30.8
162.4*** 23.5* 178.9*** 73.3** 99.0***
Site 4 Zn Cu Cd Pb Ni
29.7 4.7 0.8 6.7 3.9
164.3 55.6 5.2 66.1 56.4
4.9 3.18 0.1 1.9 2.1
62.6 45.2 1.8 33.6 30.7
162.5*** 24.6* 188.8*** 96.7** 83.7**
culated PIN values for Cu, Pb, and Ni were 1–2 in 100%, 75%, and 25% of the total samples, showing that these samples fall into the slightly polluted class. In contrast, the PIN values for Cd, Zn, Ni, and Pb were 2–3 in 100%, 100%, 75%, and 25% of the total samples, respectively, revealing that these soils fall into the moderately polluted class. As shown in Fig. 2, the mean PLI varied between 1 and 2
at all soil sites, indicating moderate deterioration of soil quality after the entrance of the leachate into the soil. Table 6 shows the correlation coefficients between the heavy metals and various soil attributes (clay, silt, sand, pH, EC, OC, CEC, and CCE). Sand fraction is recorded as negatively correlated with the total fraction of Cu and Zn, while positive correlation
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S. Rezapour et al. / Waste Management 82 (2018) 51–61 Table 5 Interpretation of the single pollution index (PI) in varies soil sites. Heavy metal
Min
Max
Mean
Pollution level
Site 1 Zn Cu Cd Pb Ni
2.4 1.1 2.7 1.1 1.4
2.9 1.4 2.9 1.4 2.7
2.5 1.3 2.8 1.3 1.9
MP LP MP LP LP to MP
Site 2 Zn Cu Cd Pb Ni
2.5 1.18 2.8 1.6 1.7
1.3 3.0 3.1 2.9 2.1
1.25 2.6 3.0 2.1 1.9
LP MP MP to HP LP to MP LP to MP
Site 3 Zn Cu Cd Pb Ni
2.3 1.1 2.4 1.4 1.9
2.9 1.5 3.0 1.9 2.1
2.6 1.3 2.8 1.7 2.0
MP LP MP LP LP to MP
Site 4 Zn Cu Cd Pb Ni
2.4 1.14 2.7 1.9 1.72
2.8 1.7 3.2 2.2 2.1
2.6 1.4 2.9 2 1.84
MP LP MP to HP LP to MP LP to MP
LP, Low pollution (1 < PI 2); MP, Moderate pollution (2 < PI 3), HP, High pollution (PI > 3).
mineralogical composition of the clay fraction of these soils (Rezapour et al., 2009). In the soils from other parts of the world, similar results are found (Sharma et al., 2005; Hooda, 2010). However, there was no correlation between the DTPA fractions of all heavy metals and the clay fraction in these soils. The trend could be corroborated with the high base saturation (Ca, Mg, Na, and K) of soils, which does not allow many preferential exchange sites for metals adsorption (Sharma et al., 2005; Rezapour and Moazzeni). Organic matter was positively correlated with the heavy metals, suggesting a remarkable affinity of these metals for organic compounds and the possibility of formation of metal complexes (Kabata-Pendias, 2010). Positive significant correlations were observed between the elemental pairs [e.g., Zn(t)-Cd(t) (0.81), Zn (t)-Pb(t) (0.49), Cd(t)-Pb (t) (0.47), Cd(t)-Ni (t) (0.49), Zn(a)-Cd(a) (0.42), Cd(a)-Pb(a) (0.27), and Cd(a)-Ni(a) (0.32)] suggesting that the influential factors that contribute-control their source and distribution may be similar (Rezapour et al., 2018). All heavy metals show no correlation with soil pH, probably because of the narrow range of the pH (7.3–7.8) in these soils. 3.4. Heavy metals in wheat grains
Fig. 2. The values of PIN (a) and PLI (b).
was found between the metal and clay fractions. This finding could be due to the residence of these metals in Cu/Zn-containing minerals, mainly illite and chlorite that constitute more than 70% of the
The heavy metal concentrations in wheat grains growing at various soil sites under the influence of leachate are illustrated in Table 6. The accumulation of Zn, Cu, Cd, Pb, and Ni in the wheat grain was: 10–22 mg kg1, 0.9–2.4 mg kg1, 0.03–0.15 mg kg1, 0.11–0.31 mg kg1, and 0.015–0.47 mg kg1, respectively, and the metals followed the sequence of Zn > Cu > Pb > Cd > Ni. Referring to the EPA standards (2012), the average values of all five metals were lower than their maximum allowable ranges (50, 20, 0.1, 0.2, and 0.4 mg kg1 DM, respectively) offering no dramatic concentration of these metals in the wheat grains. On average, the highest and lowest concentrations of most of the heavy metals in wheat grains were recorded at soil site 1 and soil site 3, respectively, implying that there was probably a direct connection between soil sites and uptake of heavy metals by the wheat plants. However, the mean comparison between the metals of the grain samples reflected non-significant differences in most of the heavy metals.
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Table 6 Correlation coefficients of heavy metals and main soil attributes (*P < 0.05; **P < 0.01).
Zn(t) Cu(t) Cd(t) Pb(t) Ni(t) Clay Silt Sand pH EC OC CEC CCE Zn(a) Cu(a) Cd(a) Pb(a) Ni(a)
Zn(t)
Cu(t)
Cd(t)
Pb(t)
Ni(t)
Clay
Silt
Sand
pH
EC
OC
CEC
CCE
Zn(a)
Cu(a)
Cd(a)
Pb(a)
Ni(a)
1.00 0.30* 0.81** 0.49** 0.39* 0.22 0.01 0.12 0.04 0.06 0.28* 0.25 0.32* 0.05 0.01 0.05 0.03 0.03
1.00 0.19 0.17 0.08 0.28* 0.03 0.18 0.01 0.07 0.47** 0.06 0.06 0.06 0.13 0.03 0.07 0.04
1.00 0.47** 0.54** 0.04 0.01 0.08 0.00 0.05 0.23 0.02 0.34* 0.03 0.02 0.02 0.08 0.05
1.00 0.31* 0.03 0.02 0.07 0.01 0.04 0.24 0.01 0.28* 0.00 0.01 0.03 0.01 0.03
1.00 0.06 0.04 0.11 0.05 0.07 0.30* 0.08 0.08 0.01 0.01 0.02 0.03 0.01
1.00 0.62** 0.56** 0.18 0.08 0.26 0.53** 0.44* 0.00 0.02 0.04 0.01 0.03
1.00 0.61** 0.04 0.03 0.02 0.11 0.00 0.01 0.05 0.02 0.00 0.01
1.00 0.15 0.31* 0.31* 0.48** 0.09 0.00 0.00 0.01 0.02 0.01
100 0.33* 0.23 0.19 0.37* 0.01 0.02 0.03 0.01 0.02
1.00 0.27 0.00 0.18 0.00 0.04 0.01 0.03 0.00
1.00 0.46* 0.03 0.19 0.31* 0.10 0.09 0.11
1.00 0.11 0.02 0.01 0.03 0.01 0.04
1.00 0.01 0.07 0.05 0.06 0.01
1.00 0.22 0.42* 0.27* 0.29*
1.00 0.10 0.08 0.11
1.00 0.27* 0.32*
1.00 0.26*
1.00
(t), Total fraction; (a), Available fraction.
The bio-accumulation factor (BAF), referred to as the ratio of the metal concentration in the wheat grain to its concentration in the corresponding soil, was lower than 1 for all heavy metals investigated (Fig. 3), indicating lower accumulation of metals in the wheat grains than the corresponding soils. The average BAF followed the following sequence: Cu (0.24) > Zn (0.22) > Cd (0.11) > Pb (0.04) > Ni (0.007), showing that wheat has a capacity 2, 6, and 32 times stronger to absorb and transfer Cu and Zn from soil to wheat compared to Cd, Pb, and Ni, respectively. Such findings are comparable to those found by Zhang et al. (2017), who calculated that the BAF values of Cu and Zn in wheat grains were significantly higher than the BAF values of Pb, Cd, and Cr. However, the sequence mentioned for BAF is remarkably varied from the sequence established for both total and DTPA fractions of heavy metals in the soil, implying also the different uptake/transfer/accumulation capacity of wheat for the five metals tested. The mean content of Cd in the grain samples is lower than its corresponding EPA value (2012), and the values of its BAF were also far below unity, even though the average concentrations of
this element at all soil sites was 2–3 times more compared to permissible levels, which is possibly attributable to the soil physicochemical properties and the different transformative abilities of Cd in the various parts of the wheat crop. In the investigation conducted, the soils were characterized by heavy texture, moderate alkalinity (7.3–7.5), and high CaCO3 (8–16%), three factors known to be the most important attributes controlling heavy metals in soil (Kabata-Pendias, 2010). Given such soil conditions, the stable and mineral forms of CdCO3, CdO, and Cd(OH)3 are likely to be accumulated, which are generally unavailable to crop uptake (Adriano, 2001). Cd-Zn antagonistic interaction appeareds to be based on the carrier sites in the absorption mechanisms of two metals, and may also affect the concentration of Cd and its translocation from the root to tops (Kabata-Pendias, 2010). Some studies showed that Zn reduces the availability of Cd in the uptake-transport process when the Cd/Zn ratio in crop tissues is limited to 0.01 or less (Adriano, 2001; Kabata-Pendias, 2010). The results of the current study illustrated an average Cd/Zn ratio of 0.003–0.005 for the wheat grown at different soil sites, which is consistent with Adriano (2001) and Avci and Deveci (2013) who reported that the values of the Cd/Zn ratio were below 0.008 and 0.001 for wheat and corn. 3.5. Potential health risk evaluation
Fig. 3. The BCF of the analyzed heavy metals in different soil site.
3.5.1. Non-cancer risk For different the population groups (group A: 0–6 years, group B: 7–18 years, and group C: 19 years as the adult population), the daily intake of metals (DIM) was calculated in wheat grains (Table 7) because wheat is known historically as the main staple food for the Iranian people. The average values of DIM varied from 0.00062 (Cd) to 0.072 mg kg1 d1 (Zn), 0.00029 (Cd) to 0.041 mg kg1 d1 (Zn), and 0.00028 (Cd) to 0.04 mg kg1 d1 (Zn) for groups of A, B, and C, respectively. Zn-DIM was actually the highest for all the population groups, presumably because of the plastic, electronic-waste and car tire decomposition process in the current region. Luo et al. (2011) and Oguri et al. (2017) described electronic-waste as the major source of Zn pollution in agricultural soils and plants. Irrespective of the population group, the DIM values of Zn, Cu, Cd, Pb, and Ni were 11.4–35.7, 7.1–25, 1.3–4.2, i.e., 28–100 times lower, respectively, compared with the relevant daily intake allowed by FAO/HWO (2014). This finding shows that the mean daily dose has no deleterious health effect on the local population regarding individual heavy metals. More-
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S. Rezapour et al. / Waste Management 82 (2018) 51–61 Table 7 The mean and level of Zn, Cu, Cd, Pb, and Ni in the wheat grain (mg kg1). Heavy Metal
Zn Cu Cd Pb Ni
Site 1
Site 2
Site 3
Site 4
Range
Mean
Range
Mean
Range
Mean
Range
Mean
11–25 1.7–2.4 0.06–0.15 0.91–0.31 0.032–0.047
16b 1.9a 0.08a 0.22a 0.035a
10–19 1.1–1.7 0.05–0.12 0.15–0.24 0.022–0.036
15a 1.4bc 0.07a 0.18b 0.025bc
16–27 0.9–1.5 0.03–0.09 0.17–0.27 0.015–0.028
21a 1.2c 0.05b 0.2ab 0.021c
13–22 1.4–2.1 0.05–0.1 0.11–0.19 0.027–0.041
17.2a 1.6b 0.06ab 0.15bc 0.029b
For each row, amounts followed by the same small of lower case are not significantly different by Duncan’s test (P 0.05).
Fig. 4. The HQ values of heavy metal in different soil sites to various population groups exposed to wheat grains.
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over, the average total DIM values of group A were 2.1–2.2 and 2.2–2.25 times higher than the total DIM values of groups of B and C, respectively, probably due to the variations in food habits of the three population groups and the pollution range of the five elements (Zhang et al., 2017). The target hazard quotient (HQ) and hazard index (HI) of the five metals were calculated for the three population groups according to the DIM and the RfD of each element (Fig. 4). The HQ generated by Cd, Pb, and Cu posed relatively greater risks to various population groups than other metals because of their high content in soils or lower RfD values (Chen et al., 2015). The HQ values belonging to all population groups were recorded in the sequence of Cd > Pb > Cu > Zn > Ni when subjected to the grains under soil sites 1, 2, and 3 while the sequence of Cd > Cu > Pb > Zn > Ni occurred for populations subjected to the grains under soil site 4. For each soil site, the highest value of HQ was archived for group A followed by group B and group C, which was a similar trend to those recorded for DIM, implying that different soil sites affected by leachate could exhibit various health impacts for the different population groups. The calculated DIM and HQ values in the current study were comparable with previously reported studies (Oguri et al., 2017). In the case of HI, its values of HI were approximately two times higher in population group A (mean value HI = 2.3) than in population groups B (mean value HI = 2.3) and C (mean value HI = 0.99). Such data illustrate a moderate non-carcinogenic health risk for people aged 0–5 and 6–18 years living in the present region through the consumption of wheat grains. By contrast, local residents aged 19 years characterized by an HI value < 1 could suffer from non-carcinogenic health risk effects originated by heavy metals. For each resident group, Cd and Pb had the highest contribution to the HI followed by Cu, Zn, and Ni, which was 26.2–39.3%, 21.4–32.9%, and 6.5–11% of the total HI for the different soil sites. The major contributors for both HQ and HI were Cd and Pb at the majority of the soil sites. Excessive Cd and Pb intake could have caused some threat to the health of human beings, which can affect the nervous and skeletal systems, bone fractures, pulmonary adenocarcinomas, and enzymatic and immune systems (Chen et al., 2015) (See Fig. 5).
Table 8 The daily intake of metals (DIM) for the wheat grains grown from the leachate – affected soils. Heavy metal
DIM (mg kg1 day1) 0–6 years old
7–18 years old
19 years old
Site 1 Zn Cu Cd Pb Ni Mean
0.072 0.0236 0.0099 0.0027 0.0043 0.1125
0.033 0.011 0.0046 0.0013 0.002 0.0519
0.032 0.011 0.0028 0.0012 0.002 0.049
Site 2 Zn Cu Cd Pb Ni Mean
0.063 0.017 0.0087 0.0022 0.0031 0.094
0.029 0.0081 0.004 0.001 0.0014 0.0435
0.028 0.0078 0.0039 0.001 0.0014 0.0421
Site 3 Zn Cu Cd Pb Ni Mean
0.078 0.0149 0.0062 0.0025 0.0025 0.1041
0.036 0.0069 0.0029 0.0012 0.0012 0.0482
0.035 0.0067 0.0028 0.0011 0.0012 0.0468
Site 4 Zn Cu Cd Pb Ni Mean
0.088 0.021 0.0074 0.0019 0.0036 0.1219
0.041 0.0092 0.0035 0.0009 0.0018 0.0564
0.040 0.0093 0.0034 0.0008 0.0016 0.0551
3.5.2. Carcinogenic risk investigation The carcinogenic risk (CR) was estimated only for Cd, for which the cancer slope factor was available. Significantly, values of CR for three population groups exposed to the wheat grain were lower than the maximum allowable range (1 104) suggesting that Cd did not pose a remarkable cancer risk to the local residents. CR was the highest for the population 19 years of age (8.73 105 ± 8.82 105), followed by 7–18 (1.6 105 ± 1.8 105) and 0–6 years of age (7.99 106 ± 8.2 106). These results implied that potential cancer risk for the population 19 years of age was 11 and 5.5 times higher than those populations 0–6 and 7–18 years of age, respectively. The reason for such results could be attributed to (i) the longer duration of exposure in adults (19 years), and (ii) the various values recorded in the distribution of HQ for the three population groups. As a whole, the carcinogenic risk for Cd varied approximately 1 105 to 1 106 for the different population groups exposed to wheat grains, offering a low potential cancer risk (Rapant et al., 2011) (See Table 8). 4. Conclusions
Fig. 5. The HI values of heavy metal in different soil sites to various population groups exposed to wheat grains.
Based on the findings of the present study, a significant accumulation of the available and total fractions of Zn, Cu, Cd, Pb, and Ni occurred in the leachate-affected soils. However, the mean concentrations of these metals (except for Cd) in the soils and wheat grains grown in these soils were within the allowable levels set by the international regulations for environmental health and foodstuffs. The rank of available-heavy metal concentrations was found to be Zn > Pb > Ni > Cd > Cu in the soil, which varied from the rank established in the wheat grain (Zn > Cu > Pb > Cd > Ni). The different population groups exposed to wheat grains were under a moderate non-carcinogenic risk, mainly because of the
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accumulation of Cd and Pb, and a low potential cancer risk because the ingestion of Cd was low. We believe there is need for new strategies and techniques including, (i) the design of appropriate management of selective collection and recycling of solid wastes (ii) leachate collection and retardation of its movement through the development of new dumping sites with proper foundations, (iii) collection and treatment systems at controlled landfill sites to reduce impacts on the soil-plant-human system so that heavy metal and other pollution exposure scenarios can be prevented, and (iiii) finally, open dumps should be closed and covered to reduce the infiltration of precipitation into a landfill and minimize leachate production. Acknowledgements The authors wish to thank Urmia University, Urmia, I.R. Iran for the financial support in this study. References ˇ , S., Pelcová, P., Elbl, J., Kynicky´, Adamcová, D., Radziemska, M., Ridošková, A., Barton J., Brtnicky´, M., Vaverková, M.D., 2017. Environmental assessment of the effects of a municipal landfill on the content and distribution of heavy metals in Tanacetum vulgare L. Chemosphere 185, 1011–1018. Adriano, D.C., 2001. Trace Elements in Terrestrial Environments Biogeochemistry, Bioavailability, and Risks of Metals. University of Georgia Aitken, SC 29802, USA. Alloway, B.J., 2012. Heavy Metals in Soils. Black Academic, New York. Arunbabu, V., Indu, K.S., Ramasamy, E.V., 2017. Leachate pollution index as an effective tool in determining the phytotoxicity of municipal solid waste leachate. Waste Manage. 68, 329–336. Avci, H., Deveci, T., 2013. Assessment of trace element concentrations in soil and plants from cropland irrigated with wastewater. Ecotoxicol. Environ. Saf. 98, 283–291. Cabrera, F., Clemente, L., Diaz Barrientos, E., Lopez, R., Murillo, J.M., 1999. Heavy metal pollution of soils affected by the Guadiamar toxic flood. Sci. Total Environ. 242, 117–129. Chen, H., Teng, Y., Lu, S., Wang, Y., Wang, J., 2015. Contamination features and health risk of soil heavy metals in China. Sci. Total Environ. 512, 143–153. Hooda, P. (Ed.), 2010. Trace Elements in Soils. John Wiley & Sons. IUSS Working Group. WRB. 2014. World reference base for soil resources. World Soil Resources Report. No. 103. Rome (Italy): FAO. Joint FAO/WHO Food Standards Programme, 2014. Report of the 33rd Session of the Codex Committee on Food Additives and Contaminants. Hague: The Netherlands. Kabata-Pendias, A., 2010. Trace Elements in Soils and Plants. CRC Press, Boca Raton, FL, USA. Kalavrouziotis, I.K., Koukoulakis, P.H., 2012. Soil pollution under the effect of treated municipal wastewater. Environ. Monit. Assess. 184, 6297–6305. Kalavrouziotis, I.K., Koukoulakis, P.H., Ntzala, G., Papadopoulos, A.H., 2012. Proposed indices for assessing soil pollution under the application of sludge. Water. Air. Soil Pollut. 223, 5189–5196. Klute, A., Page, A.L., 1996. Methods of Soil Analysis. In: Klute, A. (Ed.), Part 3, Chemical methods. American Society of Agronomy/Soil Science Society of America, Madison, WI, pp. 417–475. Krcˇmar, D., Tenodi, S., Grba, N., Kerkez, D., Watson, M., Roncˇevic´, S., Dalmacija, B., 2018. Preremedial assessment of the municipal landfill pollution impact on soil and shallow groundwater in Subotica. Serbia. Sci. Total Environ. 615, 1341– 1354. Lindsay, W.L., Norvell, W.A., 1978. Development of a DTPA soil test for zinc, iron, manganese, and copper. Soil Sci. Soc. Am. J. 42, 421–428. Luo, C., Liu, C., Wang, Y., Liu, X., Li, F., Zhang, G., Li, X., 2011. Heavy metal contamination in soils and vegetables near an e-waste processing site, South China. J. Hazard. Mater. 186, 481–490. Oguri, T., Suzuki, G., Matsukami, H., Uchida, N., Tue, N.M., Tuyen, L.H., Viet, P.H., Takahashi, S., Tanabe, S., Takigami, H. 2017. Exposure assessment of heavy metals in an e-waste processing area in northern Vietnam. https://doi.org/10. 1016/j.scitotenv.2017.10.115.
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Impact of the uncontrolled leakage of leachate from a municipal solid waste landfill on soil in a cultivated-calcareous environment Salar Rezapour a,⇑, A. Samadi a, Ioannis K. Kalavrouziotis b, N. Ghaemian c a
Soil Science Department, Urmia University, P.O. Box 165, Urmia 57134, Islamic Republic of Iran School of Science and Technology, Hellenic Open Univ., Tsamadou 13-15 and Saint Andrea, 262 22 Patras, Greece c West Azarbaijan Agricultural Researches Center and Natural Resources, Urmia, Islamic Republic of Iran b
a r t i c l e
i n f o
Article history: Received 29 January 2018 Revised 29 August 2018 Accepted 9 October 2018
Keywords: Leachate Heavy metal Calcareous Potential risk Hazard index
a b s t r a c t The heavy metal pollution generated by landfill leachate becomes increasingly concerning due to its potential to impact human health through the food chain. In the present study, the accumulation and potential health risk of heavy metals (Zn, Cu, Cd, Pb, and Ni) were investigated in a calcareous soil wheat system affected by an uncontrolled landfill leachate. The results showed soils were significantly enriched by both the available and total fractions of the metals in the sequences of Zn > Pb > Ni > Cd > Cu and Cd > Zn > Ni > Pb > Cu, respectively. Nevertheless, only the Cd content exceeded the standard levels. For the various population groups, the mean hazard quotient (HQ) was lower than the unity, implying a lack of non-carcinogenic health risk for the local residents, while the average hazard index (HI) was 2.3 and 1.1 for people aged 0–5 and 6–18 years, respectively, illustrating a moderate non-carcinogenic health risk for the two groups. Cd and Pb contributed the most to HI, followed by Cu, Zn, and Ni. In addition, the carcinogenic health risk of Cd, ranging from 1 105 to 1 106, showed a low potential risk in the different population groups exposed to wheat grains and decreased in the sequence of adult > population 6–18 years > population 0–5 years. The findings of the study, which can be used in regions under similar environmental conditions, provide a valuable benchmark for the design of appropriate strategies to manage these agroecosystems by both local and national managers of such macrosystems. Ó 2018 Elsevier Ltd. All rights reserved.
1. Introduction Globally, the proper management of municipal solid waste (MSW) is a serious challenge in many countries characterized as industrialized and developing regions, which can pose risks to the water-soil-plant-animal-human system. In general, MSW as a waste type, includes plastic, food waste, inorganic salts, glass, paper, building and electronic wastes, metals, and organic fractions and leads to pollution in soil and water mainly through leachates. The leachates are generated when MSW comes in contact with water that infiltrates through a landfill. Leachate is a complex mixture that is composed of various pollutants such as heavy metals, soluble organic and inorganic compounds, nutrients, and suspended particles. Leakage of leachate can cause pollution of groundwater, surface waters, agriculture and natural ecosystems, especially when the leachate is released in an uncontrolled manner (Samadder et al., 2017; Adamcová et al., 2017). A complex mixture ⇑ Corresponding author. E-mail address: [email protected] (S. Rezapour). https://doi.org/10.1016/j.wasman.2018.10.013 0956-053X/Ó 2018 Elsevier Ltd. All rights reserved.
emerging from the bottom of the MSW involves a combination of various pollutants particularly heavy metals, soluble organic and inorganic compounds, nutrients, and suspended particles (Mavakala et al., 2016; Naveen et al., 2017; Arunbabu et al., 2017). Such leachate can effect significant changes in soil attributes after it enters into the soil. The amount of leachate produced also depends on the compaction of the waste, climate and landfill cover at closed landfills. Previous studies associated with landfills without treatment systems showed that the movement of landfill leachate on the soil surface resulted in alterations in the various physicochemical and biological processes of the soil, which eventually affects the level of soil pollution (Samadder et al., 2017). The quantity and quality of leachate are influenced by various factors such as the composition of the waste, the biochemical processes that occur in the degradation stages of the waste, the amount of moisture, and the local parameters (Arunbabu et al., 2017; Ma et al., 2018). The problem of MSW is more serious in developing countries such as Iran, where MSW disposal is primarily conducted using landfills/dumping yards and landfills that lack leachate collection
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and treatment systems. In Iran, as in many nations, the production of MSW has developed in parallel with rapid population growth, as well as industrial, commercial and urban expansion. Such aspects, which have significantly progressed in recent decades, lead to the generation of several environmental problems affecting the soil, air, surface, and groundwater. In addition, the management systems of urban and industrial waste are limited, and landfills considered to be disposal sites, are situated in public spaces, agricultural lands, and urban rivers and are without treatment. Considering the different types of soil contamination, heavy metals are highlighted more and more seriously as one of the most challenging environmental problems due to their bioaccumulation, toxicity, non-biodegradability and persistence (Alloway, 2012). The accumulation of heavy metals in soils, which is mainly caused by anthropogenic activities, can pose a potential hazard to food safety and human health in the water-soil-plant-animal-human system. Such risks result in the fact that soil heavy metals and their enrichment under the influence of various sources have caused widespread concerns throughout the world over time. There are several studies that deal with these problems. For example, Ma et al. (2018) found that the soils around an MSW site were moderately polluted by Cu, Pb, Zn, and Hg and heavily polluted by As and Cd in North China. Similarly, the significant impact of MSW with heavy metal pollution (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) on human health was reported in the soils surrounding an MSW site by Rimmer et al. (2006) in Newcastle. Therefore, to protect and improve the soil-crop ecosystem, it is necessary to identify the pollution characteristics of heavy metals in the soils contaminated by leachate. Particularly, understanding the exposure risks of heavy metals in these soils and apportioning their sources are (i) the basic preconditions for soil pollution prevention, control, and reduction of metal inputs to soils (Chen et al., 2015); (ii) the basic precondition for preparing information on the significance and extent of soil metal contamination from different sources; and (iii) most importantly, provide appropriate data for making decisions regarding remediation of contaminated soils. Furthermore, the concentration, distribution, and toxicity of heavy metals in the soil-crop system affected by uncontrolled leachate are rarely assessed. Accordingly, the impact of landfill leachate on soil attributes in terms of heavy metals accumulation was investigated in a cultivated region in northwest Iran, where dumping a large amount of MSW generates a huge amount of leachate. The specific aims of this work were the following: (i) to compare the available and total fractions of Zn, Cu, Ca, Pb, and Ni in the sites contaminated by leachate and the adjoining non-contaminated sites, (ii) to describe the effects of landfill leachate on the enrichment of selected heavy metals in soil and wheat grains growing on the sites contaminated by leachate, and (iii) to analyses the health risks associated with heavy metals to the local consumers of the wheat grain.
2. Methods 2.1. Site characteristics and soil sampling The study landfill site is located approximately 20 km from Miandoab City in western Azerbaijan Province, which is located in north-western Iran (Fig. 1). The population of the city (Miandoab region) is approximately 280,000, and the studied area is the most important area of wheat production for the local residents, where 100,000 tons/year of wheat are produced (MJA, 2017). This landfill site has been used as an uncontrolled open system without any engineering operations on the flat area and or the surrounding farmland. The site has received the municipal solid and liquid wastes generated from commercial activities, hospitals, urban
municipal, energy generation residues, and industry belonging to Miandoab City. Unfortunately, there are no reports and records clarifying the amount of waste received over the years from the region. After interviews with local farmers and landowners, however, we estimate that the site received over 50 tons of waste every day for over 15 years. At this site, waste has accumulated to a height of 10–15 m and is burned weekly. Then, the leachate generated from the burnt waste (with a length of 1.2 km) flows into the cropland around the site of an area of approximately 10 ha. The lack of any barrier system or a leachate collection system in the landfill studied the resulted in release and transport of its leachate into the surrounding crop land. Consequently, farmers around the area demanded that the landfill site be closed immediately because of damage to their fields. Relevant selected chemical compositions of the investigated leachate are shown in Table 1. The climate of the region is typically characterized by dryhot summers and cold winters; the mean annual precipitation is approximately 320 mm, occurring mostly in autumn and winter, and the mean annual temperature is 13 °C. In general, the groundwater level was present at depths of 5 to 7 m from the soil surface for periods ranging from 1 to 12 months of the year at all of the sites. The region often has a groundwater table of less than 5 m during the wet season, but the groundwater table drops to approximately more than 7 m from the surface during the dry season. The major crop cultivated in the region is winter wheat (Triticum aestivum L.), which is grown from November to July and has a growth period approximately about 230 days. During the field studies, eight soil profiles from the leachateinfluenced soils (four profiles) and the control soils (four profiles) were dug. The soils were described, and sampled along a transect with four experimental sites in August 2016. At each experimental site, two paired soil profiles (involving soil under the influence of the leachate and the adjacent control soil) were identified with similar slope, aspect, drainage conditions, and parent materials. Each profile was considered the central point, and surface soil samples were collected around this central point. Accordingly, four points were sampled within a radius of 5–10 m of the central point from 0 to 30 cm in depth, in triplicate. Soil samples were air-dried, crushed, passed through a 2-mm mesh, and were placed in zipsealed plastic bags prior to analysis. The soil profiles characterized by a high level of calcium carbonate (a range of 10–31%) were classified as Calcisols based on the WRB system (IUSS Working Group WRB, 2014). 2.2. Procedures of laboratory analysis The physicochemical attributes of all soil samples [particle-size distribution (hydrometer methods), pH (1:2.5 soil-0.01 M CaCl2), electrical conductivity (saturation extract), organic carbon (wet oxidation method), cation exchange capacity (sodium acetate method), and calcium carbonate equivalent (acid neutralization method) were determined using standard procedures (Klute and Page, 1996). The available fraction of Zn, Cu, Cd, Pb, and Ni was extracted from 10 g of soil mixed with 20 cm3 DTPA (diethylene triaminepentaacetic acid) solution (Lindsay and Norvell, 1978). To determine the total fraction of heavy metals, the simple method proposed by Sposito et al. (1982) was used, which identifies the total HNO3-extractable fraction in soils. The intention of this procedure is to establish a simple reference method for the determination of total heavy metals in different soils. This method is considered adequate by many researchers from different regions of the world and can provide important information about the risk potential of soil heavy metals (e.g., Olsen et al. (1994); Zeng-Yei et al. (2002); Safari et al. (2015); Rezapour and Moazzeni (2016)). According to the method, 10 cm3 of concentrated HNO3
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Fig. 1. Location of the study region (P1L, . . ., the soil under influence of leachate; P1C,. . . the adjacent control soils).
were added to 2 g of soil and heated for 15 min at 95 °C, followed by the addition of 2 cm3 deionized water and 3 cm3 of 30% H2O2 (Soon and Abboud, 1993). The metalvalues for both the available and total fractions were determined by an atomic absorption spectrophotometer (Shimadzu AA-6300). The detection limit concentration of the metals was between 0.01 and 0.03 cm3 L1, with wavelengths of 213.9, 324.8, 228.8, 283.3, and 232 for Zn, Cu, Cd, Pb, and Ni, respectively. The standard solution concentrations were 0.5, 1, 1.5, 2, and 2.5 or 4, 6, 8, 10, and 12 for Zn and Cu; and 0.5, 1, 1.5, 2 and 2.5 for Cd, Pb, and Ni. At each site under the influence of the leachate, 50 wheat grain (before harvesting wheat) samples were collected randomly for elemental analysis and risk potential determination. Grain samples were washed with deionized water to remove any existing particles, and oven dried at 65 °C for 24 h. Then, 1.000 g of the dried samples was heated at 500 °C for 12 h, subjected to the effect 2 M HCl, filtered by centrifugation, and analysed as above. All statistical analysis was carried out using the program package SPSS 19 (SPSS INC., Chicago, USA). Comparison of the differences between the values of heavy metals in the soils under the
influence of leachate and the control soil was accomplished with Duncan’s multiple range tests using a paired t-test. 2.3. Soil pollution indices To evaluate the pollution levels of the soils affected by leachate, single factor pollution index (PI), Nemerow pollution index (PIN) or comprehensive pollution index (PIN), and pollution load index (PLI) were estimated (Zhang et al., 2013) as follows:
PI ¼ ðC i =Si Þ
PIN ¼
vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2 u n u 1P u PI þ ½maxðPIÞ2 i n t i¼1
2
where Ci is the measured content of the element i at each sampling point, and Si is the regional background content of the heavy metal i; max (PI) = the maximum amount of the single factor pollution
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Table 1 Selected chemical composition of the investigated leachate in different sites. Parameter
Unit
Mean
SD
Site 1 pH EC OM Zn Cu Cd Pb Ni
– dSm1 % mg kg1 mg kg1 mg kg1 mg kg1 mg kg1
6.6 5.3 20.3 59.3 5.7 0.82 7.8 6.2
0.31 0.7 3.7 6.2 0.52 0.04 1.2 0.73
Site 2 pH EC OM Zn Cu Cd Pb Ni
– dSm1 % mg kg1 mg kg1 mg kg1 mg kg1 mg kg1
6.55 5.1 21.5 58.5 5.5 0.78 8.1 6.4
0.28 0.65 4.2 5.6 0.41 0.03 1.4 0.8
Site 3 pH EC OM Zn Cu Cd Pb Ni
– dSm1 % mg kg1 mg kg1 mg kg1 mg kg1 mg kg1
6.53 6.1 19.2 62.1 5.9 0.91 8.4 6.6
0.35 0.88 4.5 6.7 0.55 0.07 1.7 0.61
Site 4 pH EC OM Zn Cu Cd Pb Ni
– dSm1 % mg kg1 mg kg1 mg kg1 mg kg1 mg kg1
6.65 5.1 22.5 61.6 5.8 0.81 7.9 5.9
0.48 0.73 5.6 6.2 0.51 0.05 1.23 0.59
index, n = number of analysed metals, and i = ith value of the metals. The pollution load index (PLI) (Cabrera et al., 1999)
PLI ¼ ðCF1xCF2xCF3 . . . ::CFnÞ1=n where CF = concentration factor = ms/mr, ms-conc. of metal in soil mg kg1, and mr = metal reference value (mg kg1). PLI value less than 1 suggests a lack of pollution. Other indices that can be used are given by Kalavrouziotis and Koukoulakis (2012) and Kalavrouziotis et al. (2012). These indices have been calibrated by Papaioannou et al. (2017) where critical ranges are given. To estimate the potential health risk of heavy metals for local residents via ingestion of wheat grain, both the non-carcinogenic and carcinogenic effects of the metals were computed for different population groups of the area as follows (US EPA, 2004):
C IR EF ED DIM ¼ BW AT HQ ¼
DIM RfD
ð1Þ
ð2Þ
where HQ is hazard quotient that estimates the non-cancer risk during a lifetime, DIM is the daily intake of metals in mg kg1 day1, C is the metal concentration of wheat grains in mg kg1, IR is the ingestion rate in mg day1, BW is the average of the body weight in kg, EF is the exposure frequency (365 days year1), ED is the exposure duration, AT is the mean exposure time for non-
carcinogenic effects (ED 365 day years1), and RfD is the reference oral dose for each metal. The sum of HQ amounts is expressed as Hazard Index P (HI ¼ i1 HQ Þ indicating the overall potential of non-carcinogenic effects (US EPA, 2004; RAIS, 2017). HQ or HI > 1 represents the adverse health impacts while there is the absence of adverse health impacts when their amounts are 1. Cancer risk (CR) adverts to the potential of the appearance of a kind of cancer over a lifetime due to the exposure to a carcinogenic metal. The CR is estimated using Eq. (3) (RAIS, 2017).
CR ¼ DIM SF
ð3Þ
where SF is the slope factor. The admissible risk level is assumed to be 106 for single element carcinogenic risk, while risks at the level of < 104 are advised to be admissible for multi-element carcinogenic risk (RAIS, 2017). 3. Results and discussion 3.1. General physicochemical attributes The contents of selected physicochemical properties measured in this research are listed in Table 2. The soils in the examined region were loamy clay to clay in texture in both soils under the influence of the leachate (SIL) and control, respectively, with the relative value of clay, silt, and sand in the range of 35–60%, 25– 40%, and 13–25%, respectively. The pH value of the control soils was alkaline (7.5–8), and the control soils were remarkably unaffected by the contribution of leachate even though the mean pH value of the leachate was slightly acidic. This situation is contributable to the specific characteristics of Calcisols, which have a high tendency to resist changes in the pH of the soil solution. The content of EC was observed to be significantly higher in the SIL than in the control soils (a rise of 91–150%), resulting in an increase in EC to above the salinity threshold (4 dS m1) in the majority of the studied soil sites. The major cause behind such a trend can be the high levels of cations and anions as well as the total dissolved solids in the leachate itself as previously reported by other authors (Naveen et al., 2017). Soil organic matter was significantly raised in the SIL, ranging from 75 to 95%, compared to the control field, which could build up a beneficial impact on soil properties (e.g., improve soil physical and fertility attributes and reduce the bioavailability of heavy metals) (Kabata-Pendias, 2010). Presumably, the enhancement was directly generated by the biodegradation processes of composted substances occurring in the municipal solid waste and its leachates (Adamcová et al., 2017). In addition, the incorporation of leachate into soil resulted in an increasing trend in the CEC amounts, which is attributable to organic matter added by the leachate. 3.2. Heavy metals in the soil The concentration of available (DTPA-extractable) and total fractions of all heavy metals in the soils are depicted in Tables 3 and 4. The contents of DTPA-Zn, Cu, Cd, Pb, and Ni in the soils under direct contact with the leachate were found to be: 15–49, 4–13, 0.2–1.1, 2.1–5.2, and 1.3–3.9 mg kg1, respectively. However, for the control soils, the concentration of heavy metals was: 1.4– 7.1, 1.5–5.5, 0.11–0.44, 0.6–2.3, and 0.4–1.7 mg kg1, respectively. Adding the leachate to the soils significantly increased all DTPA extractable–metals more than their corresponding control soils in the order of Zn > Pb > Ni > Cd > Cu. Such a pattern was true for all soil sites, which illustrated that these soils were enriched by the DTPA-fraction of heavy metals under the influence of anthropogenic activities. Even with this redundancy, only Zn and Cd val-
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Table 2 Comparison of the some physicochemical properties in the soils influenced by leachate and the adjacent control soils based on paired t-test (*P < 0.05; **P < 0.01; ***P < 0.001). Parameter
Soil under the influence of leachate
Control soils
Difference (%)
SD
Mean
SD
Mean
Site 1 Sand (%) Silt (%) Clay (%) pH EC(dSm1) CEC(cmolckg1) OM(g kg1) CCE(g kg1)
2.4 9.9 9.9 0.4 0.2 2.1 0.1 10.6
19 30.0 51.0 7.5 3.5 21.9 18.7 185.2
1.6 8.2 3.1 0.1 1.1 3.3 0.5 7.7
20.3 29.7 50.0 7.7 1.87 18.8 16.2 183.1
5.0 1.0 2.0 2.5 87.0** 16.5 15.4 2.0
Site 2 Sand (%) Silt (%) Clay (%) pH EC(dSm1) CEC(cmolckg1) OM(g kg1) CCE(g kg1)
5.0 5.7 6.6 0.28 1.6 3.4 0.7 6.3
21 29.5 49.5 7.4 3.79 24.0 21.8 210.0
5.7 2.3 4.0 0.13 0.31 4.1 0.7 8.9
25.2 26.0 48.8 7.6 1.87 20.1 17.5 202.0
16.7 13.5 1.4 2.6 102.30*** 19.3 24.7* 8.0
Site 3 Sand (%) Silt (%) Clay (%) pH EC(dSm1) CEC(cmolckg1) OM(g kg1) CCE(g kg1)
4.2 7.1 10.7 0.14 2.1 1.1 0.3 8.7
19.0 33.0 48.0 7.3 5.98 18.4 19 162.0
5.4 7.1 12.5 0.1 1.5 2.8 0.2 10.3
22.0 32.5 45.5 7.5 2.8 15.6 15.7 153.0
13.6 15.0 5.5 2.31 113.69*** 17.59 21.0* 6.2
Site 4 Sand (%) Silt (%) Clay (%) pH EC(dSm1) CEC(cmolckg1) OM(g kg1) CCE(g kg1)
6.5 6.4 12.5 0.14 0.3 3.05 0.1 7.6
19.0 29.0 52.0 7.5 3.4 24.6 22.7 210.0
5.2 5.3 10.0 0.2 0.3 7.02 0.6 8.3
22.0 28.0 50.0 7.8 1.65 20.63 18.5 203.0
14.0 3.5 4.0 3.34 106.0*** 19.2 22.3* 6.8
EC, Electrical conductivity; CEC, Cation exchangeable Capacity; OM, Organic Matter; CCE, Calcium Carbonate Equivalent.
ues exceeded the permissible contents (Kabata-Pendias, 2010). The average content of Zn and Cd was 2.5–3.5 and 1.1–1.3 times higher, respectively, compared to their maximum identifiable range, implying that the soils affected by leachate may not be advisable to be used for agricultural production because of possible health and phytotoxic problems generated by these two elements for different crops. The health risk of Zn and Cd with the possibility of phyto-accumulation was recognized by previous studies (KabataPendias, 2010; Naveen et al., 2017). Moreover, the high quantities of Zn and Cd are likely to be relative to the amount of batteries, paints, coloured glass, and inks in paper, which are common in MSW (Mavakala et al., 2016; Swati and Thakur, 2017; Krcˇmar et al., 2018). The concentrations of total Zn, Cu, Cd, Pb, and Ni in soils affected by leachate were found to vary, respectively, as follows: 133–210, 35–67, 3.9–6.9, 54–95, and 48–73 mg kg1. For the control soils, the concentrations were found to be, respectively, as follows: 54–76, 34–54, 1.4–2.3, 29–58, and 23–38 mg kg1 (Table 4). These results are comparable to those of Adamcová et al. (2017) but higher than results reported by Samadder et al. (2017) for the surface soils under the influence of leachate. However, the mean concentration of all the investigated metals of soils affected by leachate was higher than the corresponding amounts measured for the control soils. Along the transect, the concentration of heavy metals varied depending on the site of the soils, which can be described in terms of the quality and quantity of the leachate itself
and the impact of the leachate with its affected soils. Increased concentrations of the metals, on average, follow a declining trend in all soils according to the following order: (180–200%) > Zn (155–164%) > Ni (84–99%) > Pb (62–100%) > Cu (23–32%) after contact with the leachate. However, only Cd values exceeded the threshold concentration, which showed that Cd pollution was occurring in the present study following the entrance of leachate into the agricultural soils. Work carried out by Yusof et al. (2009) and Adamcová et al. (2017), who studied the impact of leachate from uncontrolled landfills on the chemical characteristics of soil, highlighted that soil surrounding landfills was affected by a high level of Cd. 3.3. Soil pollution indices The indices of single pollution (PI), comprehensive pollution (PIN), and pollution load (PLI) were calculated (Table 5 and Fig. 2) for various metals and soil sites to assess the range of contamination of the examined soils after contact with leachate. For different soil sites, the mean PI contents of Cu, Pb, and Ni were 1.25–1.4, 1.3–2, and 1.8–2, respectively, implying low contamination. Nevertheless, the average PI values of Zn (2.5–2.6) and Cd (2.8–3) were higher than 2, suggesting that all soils should be moderately polluted by Zn and Cd. The average PIN values of five metals showed a decreasing order as follows: Cd > Zn > Ni > Pb > Cu, which was an order similar to the order for the PI values. The cal-
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Table 3 Comparison of the average values of the DTPA –fraction of heavy metals (mg kg1) in the soils influenced by leachate and the adjacent control soils based on paired t-test (*P < 0.05; **P < 0.01; ***P < 0.001). Heavy metal
Soil under the influence of leachate
Control soils
Difference (%)
SD
Mean
SD
Mean
Site 1 Zn Cu Cd Pb Ni
3.5 1.8 0.2 0.2 0.1
24.5 7.2 0.65 3.1 2.2
1.1 0.6 0.1 0.12 0.1
3.4 3.6 0.4 1.1 0.9
354.0*** 100.0*** 62.5** 181.8*** 139.1***
Site 2 Zn Cu Cd Pb Ni
4.1 0.95 0.1 0.2 0.2
24.3 6.4 0.59 3.3 2.7
1.3 0.8 0.1 0.1 0.1
5.2 4.3 0.34 1.1 1.4
367.3*** 48.8* 73.5** 200*** 92.9**
Site 3 Zn Cu Cd Pb Ni
2.8 0.75 0.1 0.3 0.13
27.8 5.3 0.54 3.7 2.3
0.8 0.7 0.0 0.1 0.1
5.5 4.2 0.3 1.3 0.98
405.5*** 26.2* 86.2** 184.6*** 134.7***
Site 4 Zn Cu Cd Pb Ni
3.1 1.3 0.1 0.27 0.2
33.8 6.7 0.53 3.3 2.9
0.9 0.8 0.1 0.1 0.1
5.9 4.1 0.26 1.2 1.1
472.9*** 63.4* 103.8*** 175.0*** 163.6***
Table 4 Comparison of the average values of the total fraction of heavy metals (mg kg1) in the soils influenced by leachate and the adjacent control soils based on paired t-test (*P < 0.05; **P < 0.01; ***P < 0.001). Heavy metal
Soil under the influence of leachate
Control soils
Difference (%)
SD
Mean
SD
Mean
Site 1 Zn Cu Cd Pb Ni
42.3 5.8 0.5 6.1 4.1
162.9 58.3 5.2 63.2 57.5
4.8 44.2 0.1 2.1 1.8
63.8 3.6 1.8 38.9 30.5
155.3*** 31.9* 189*** 62.5* 88.5**
Site 2 Zn Cu Cd Pb Ni
38.7 4.6 0.8 9.1 4.6
161.9 55.5 5.1 77.8 59.1
3.7 3.3 0.08 2.4 1.6
61.3 45.1 1.7 38.8 31.2
164*** 23.1* 200*** 100.5*** 89.4**
Site 3 Zn Cu Cd Pb Ni
35.2 4.9 0.8 8.3 5.2
166.1 55.7 5.3 80.4 61.3
5.1 3.5 0.1 2.8 2.3
63.3 45.1 1.9 46.4 30.8
162.4*** 23.5* 178.9*** 73.3** 99.0***
Site 4 Zn Cu Cd Pb Ni
29.7 4.7 0.8 6.7 3.9
164.3 55.6 5.2 66.1 56.4
4.9 3.18 0.1 1.9 2.1
62.6 45.2 1.8 33.6 30.7
162.5*** 24.6* 188.8*** 96.7** 83.7**
culated PIN values for Cu, Pb, and Ni were 1–2 in 100%, 75%, and 25% of the total samples, showing that these samples fall into the slightly polluted class. In contrast, the PIN values for Cd, Zn, Ni, and Pb were 2–3 in 100%, 100%, 75%, and 25% of the total samples, respectively, revealing that these soils fall into the moderately polluted class. As shown in Fig. 2, the mean PLI varied between 1 and 2
at all soil sites, indicating moderate deterioration of soil quality after the entrance of the leachate into the soil. Table 6 shows the correlation coefficients between the heavy metals and various soil attributes (clay, silt, sand, pH, EC, OC, CEC, and CCE). Sand fraction is recorded as negatively correlated with the total fraction of Cu and Zn, while positive correlation
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S. Rezapour et al. / Waste Management 82 (2018) 51–61 Table 5 Interpretation of the single pollution index (PI) in varies soil sites. Heavy metal
Min
Max
Mean
Pollution level
Site 1 Zn Cu Cd Pb Ni
2.4 1.1 2.7 1.1 1.4
2.9 1.4 2.9 1.4 2.7
2.5 1.3 2.8 1.3 1.9
MP LP MP LP LP to MP
Site 2 Zn Cu Cd Pb Ni
2.5 1.18 2.8 1.6 1.7
1.3 3.0 3.1 2.9 2.1
1.25 2.6 3.0 2.1 1.9
LP MP MP to HP LP to MP LP to MP
Site 3 Zn Cu Cd Pb Ni
2.3 1.1 2.4 1.4 1.9
2.9 1.5 3.0 1.9 2.1
2.6 1.3 2.8 1.7 2.0
MP LP MP LP LP to MP
Site 4 Zn Cu Cd Pb Ni
2.4 1.14 2.7 1.9 1.72
2.8 1.7 3.2 2.2 2.1
2.6 1.4 2.9 2 1.84
MP LP MP to HP LP to MP LP to MP
LP, Low pollution (1 < PI 2); MP, Moderate pollution (2 < PI 3), HP, High pollution (PI > 3).
mineralogical composition of the clay fraction of these soils (Rezapour et al., 2009). In the soils from other parts of the world, similar results are found (Sharma et al., 2005; Hooda, 2010). However, there was no correlation between the DTPA fractions of all heavy metals and the clay fraction in these soils. The trend could be corroborated with the high base saturation (Ca, Mg, Na, and K) of soils, which does not allow many preferential exchange sites for metals adsorption (Sharma et al., 2005; Rezapour and Moazzeni). Organic matter was positively correlated with the heavy metals, suggesting a remarkable affinity of these metals for organic compounds and the possibility of formation of metal complexes (Kabata-Pendias, 2010). Positive significant correlations were observed between the elemental pairs [e.g., Zn(t)-Cd(t) (0.81), Zn (t)-Pb(t) (0.49), Cd(t)-Pb (t) (0.47), Cd(t)-Ni (t) (0.49), Zn(a)-Cd(a) (0.42), Cd(a)-Pb(a) (0.27), and Cd(a)-Ni(a) (0.32)] suggesting that the influential factors that contribute-control their source and distribution may be similar (Rezapour et al., 2018). All heavy metals show no correlation with soil pH, probably because of the narrow range of the pH (7.3–7.8) in these soils. 3.4. Heavy metals in wheat grains
Fig. 2. The values of PIN (a) and PLI (b).
was found between the metal and clay fractions. This finding could be due to the residence of these metals in Cu/Zn-containing minerals, mainly illite and chlorite that constitute more than 70% of the
The heavy metal concentrations in wheat grains growing at various soil sites under the influence of leachate are illustrated in Table 6. The accumulation of Zn, Cu, Cd, Pb, and Ni in the wheat grain was: 10–22 mg kg1, 0.9–2.4 mg kg1, 0.03–0.15 mg kg1, 0.11–0.31 mg kg1, and 0.015–0.47 mg kg1, respectively, and the metals followed the sequence of Zn > Cu > Pb > Cd > Ni. Referring to the EPA standards (2012), the average values of all five metals were lower than their maximum allowable ranges (50, 20, 0.1, 0.2, and 0.4 mg kg1 DM, respectively) offering no dramatic concentration of these metals in the wheat grains. On average, the highest and lowest concentrations of most of the heavy metals in wheat grains were recorded at soil site 1 and soil site 3, respectively, implying that there was probably a direct connection between soil sites and uptake of heavy metals by the wheat plants. However, the mean comparison between the metals of the grain samples reflected non-significant differences in most of the heavy metals.
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Table 6 Correlation coefficients of heavy metals and main soil attributes (*P < 0.05; **P < 0.01).
Zn(t) Cu(t) Cd(t) Pb(t) Ni(t) Clay Silt Sand pH EC OC CEC CCE Zn(a) Cu(a) Cd(a) Pb(a) Ni(a)
Zn(t)
Cu(t)
Cd(t)
Pb(t)
Ni(t)
Clay
Silt
Sand
pH
EC
OC
CEC
CCE
Zn(a)
Cu(a)
Cd(a)
Pb(a)
Ni(a)
1.00 0.30* 0.81** 0.49** 0.39* 0.22 0.01 0.12 0.04 0.06 0.28* 0.25 0.32* 0.05 0.01 0.05 0.03 0.03
1.00 0.19 0.17 0.08 0.28* 0.03 0.18 0.01 0.07 0.47** 0.06 0.06 0.06 0.13 0.03 0.07 0.04
1.00 0.47** 0.54** 0.04 0.01 0.08 0.00 0.05 0.23 0.02 0.34* 0.03 0.02 0.02 0.08 0.05
1.00 0.31* 0.03 0.02 0.07 0.01 0.04 0.24 0.01 0.28* 0.00 0.01 0.03 0.01 0.03
1.00 0.06 0.04 0.11 0.05 0.07 0.30* 0.08 0.08 0.01 0.01 0.02 0.03 0.01
1.00 0.62** 0.56** 0.18 0.08 0.26 0.53** 0.44* 0.00 0.02 0.04 0.01 0.03
1.00 0.61** 0.04 0.03 0.02 0.11 0.00 0.01 0.05 0.02 0.00 0.01
1.00 0.15 0.31* 0.31* 0.48** 0.09 0.00 0.00 0.01 0.02 0.01
100 0.33* 0.23 0.19 0.37* 0.01 0.02 0.03 0.01 0.02
1.00 0.27 0.00 0.18 0.00 0.04 0.01 0.03 0.00
1.00 0.46* 0.03 0.19 0.31* 0.10 0.09 0.11
1.00 0.11 0.02 0.01 0.03 0.01 0.04
1.00 0.01 0.07 0.05 0.06 0.01
1.00 0.22 0.42* 0.27* 0.29*
1.00 0.10 0.08 0.11
1.00 0.27* 0.32*
1.00 0.26*
1.00
(t), Total fraction; (a), Available fraction.
The bio-accumulation factor (BAF), referred to as the ratio of the metal concentration in the wheat grain to its concentration in the corresponding soil, was lower than 1 for all heavy metals investigated (Fig. 3), indicating lower accumulation of metals in the wheat grains than the corresponding soils. The average BAF followed the following sequence: Cu (0.24) > Zn (0.22) > Cd (0.11) > Pb (0.04) > Ni (0.007), showing that wheat has a capacity 2, 6, and 32 times stronger to absorb and transfer Cu and Zn from soil to wheat compared to Cd, Pb, and Ni, respectively. Such findings are comparable to those found by Zhang et al. (2017), who calculated that the BAF values of Cu and Zn in wheat grains were significantly higher than the BAF values of Pb, Cd, and Cr. However, the sequence mentioned for BAF is remarkably varied from the sequence established for both total and DTPA fractions of heavy metals in the soil, implying also the different uptake/transfer/accumulation capacity of wheat for the five metals tested. The mean content of Cd in the grain samples is lower than its corresponding EPA value (2012), and the values of its BAF were also far below unity, even though the average concentrations of
this element at all soil sites was 2–3 times more compared to permissible levels, which is possibly attributable to the soil physicochemical properties and the different transformative abilities of Cd in the various parts of the wheat crop. In the investigation conducted, the soils were characterized by heavy texture, moderate alkalinity (7.3–7.5), and high CaCO3 (8–16%), three factors known to be the most important attributes controlling heavy metals in soil (Kabata-Pendias, 2010). Given such soil conditions, the stable and mineral forms of CdCO3, CdO, and Cd(OH)3 are likely to be accumulated, which are generally unavailable to crop uptake (Adriano, 2001). Cd-Zn antagonistic interaction appeareds to be based on the carrier sites in the absorption mechanisms of two metals, and may also affect the concentration of Cd and its translocation from the root to tops (Kabata-Pendias, 2010). Some studies showed that Zn reduces the availability of Cd in the uptake-transport process when the Cd/Zn ratio in crop tissues is limited to 0.01 or less (Adriano, 2001; Kabata-Pendias, 2010). The results of the current study illustrated an average Cd/Zn ratio of 0.003–0.005 for the wheat grown at different soil sites, which is consistent with Adriano (2001) and Avci and Deveci (2013) who reported that the values of the Cd/Zn ratio were below 0.008 and 0.001 for wheat and corn. 3.5. Potential health risk evaluation
Fig. 3. The BCF of the analyzed heavy metals in different soil site.
3.5.1. Non-cancer risk For different the population groups (group A: 0–6 years, group B: 7–18 years, and group C: 19 years as the adult population), the daily intake of metals (DIM) was calculated in wheat grains (Table 7) because wheat is known historically as the main staple food for the Iranian people. The average values of DIM varied from 0.00062 (Cd) to 0.072 mg kg1 d1 (Zn), 0.00029 (Cd) to 0.041 mg kg1 d1 (Zn), and 0.00028 (Cd) to 0.04 mg kg1 d1 (Zn) for groups of A, B, and C, respectively. Zn-DIM was actually the highest for all the population groups, presumably because of the plastic, electronic-waste and car tire decomposition process in the current region. Luo et al. (2011) and Oguri et al. (2017) described electronic-waste as the major source of Zn pollution in agricultural soils and plants. Irrespective of the population group, the DIM values of Zn, Cu, Cd, Pb, and Ni were 11.4–35.7, 7.1–25, 1.3–4.2, i.e., 28–100 times lower, respectively, compared with the relevant daily intake allowed by FAO/HWO (2014). This finding shows that the mean daily dose has no deleterious health effect on the local population regarding individual heavy metals. More-
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S. Rezapour et al. / Waste Management 82 (2018) 51–61 Table 7 The mean and level of Zn, Cu, Cd, Pb, and Ni in the wheat grain (mg kg1). Heavy Metal
Zn Cu Cd Pb Ni
Site 1
Site 2
Site 3
Site 4
Range
Mean
Range
Mean
Range
Mean
Range
Mean
11–25 1.7–2.4 0.06–0.15 0.91–0.31 0.032–0.047
16b 1.9a 0.08a 0.22a 0.035a
10–19 1.1–1.7 0.05–0.12 0.15–0.24 0.022–0.036
15a 1.4bc 0.07a 0.18b 0.025bc
16–27 0.9–1.5 0.03–0.09 0.17–0.27 0.015–0.028
21a 1.2c 0.05b 0.2ab 0.021c
13–22 1.4–2.1 0.05–0.1 0.11–0.19 0.027–0.041
17.2a 1.6b 0.06ab 0.15bc 0.029b
For each row, amounts followed by the same small of lower case are not significantly different by Duncan’s test (P 0.05).
Fig. 4. The HQ values of heavy metal in different soil sites to various population groups exposed to wheat grains.
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over, the average total DIM values of group A were 2.1–2.2 and 2.2–2.25 times higher than the total DIM values of groups of B and C, respectively, probably due to the variations in food habits of the three population groups and the pollution range of the five elements (Zhang et al., 2017). The target hazard quotient (HQ) and hazard index (HI) of the five metals were calculated for the three population groups according to the DIM and the RfD of each element (Fig. 4). The HQ generated by Cd, Pb, and Cu posed relatively greater risks to various population groups than other metals because of their high content in soils or lower RfD values (Chen et al., 2015). The HQ values belonging to all population groups were recorded in the sequence of Cd > Pb > Cu > Zn > Ni when subjected to the grains under soil sites 1, 2, and 3 while the sequence of Cd > Cu > Pb > Zn > Ni occurred for populations subjected to the grains under soil site 4. For each soil site, the highest value of HQ was archived for group A followed by group B and group C, which was a similar trend to those recorded for DIM, implying that different soil sites affected by leachate could exhibit various health impacts for the different population groups. The calculated DIM and HQ values in the current study were comparable with previously reported studies (Oguri et al., 2017). In the case of HI, its values of HI were approximately two times higher in population group A (mean value HI = 2.3) than in population groups B (mean value HI = 2.3) and C (mean value HI = 0.99). Such data illustrate a moderate non-carcinogenic health risk for people aged 0–5 and 6–18 years living in the present region through the consumption of wheat grains. By contrast, local residents aged 19 years characterized by an HI value < 1 could suffer from non-carcinogenic health risk effects originated by heavy metals. For each resident group, Cd and Pb had the highest contribution to the HI followed by Cu, Zn, and Ni, which was 26.2–39.3%, 21.4–32.9%, and 6.5–11% of the total HI for the different soil sites. The major contributors for both HQ and HI were Cd and Pb at the majority of the soil sites. Excessive Cd and Pb intake could have caused some threat to the health of human beings, which can affect the nervous and skeletal systems, bone fractures, pulmonary adenocarcinomas, and enzymatic and immune systems (Chen et al., 2015) (See Fig. 5).
Table 8 The daily intake of metals (DIM) for the wheat grains grown from the leachate – affected soils. Heavy metal
DIM (mg kg1 day1) 0–6 years old
7–18 years old
19 years old
Site 1 Zn Cu Cd Pb Ni Mean
0.072 0.0236 0.0099 0.0027 0.0043 0.1125
0.033 0.011 0.0046 0.0013 0.002 0.0519
0.032 0.011 0.0028 0.0012 0.002 0.049
Site 2 Zn Cu Cd Pb Ni Mean
0.063 0.017 0.0087 0.0022 0.0031 0.094
0.029 0.0081 0.004 0.001 0.0014 0.0435
0.028 0.0078 0.0039 0.001 0.0014 0.0421
Site 3 Zn Cu Cd Pb Ni Mean
0.078 0.0149 0.0062 0.0025 0.0025 0.1041
0.036 0.0069 0.0029 0.0012 0.0012 0.0482
0.035 0.0067 0.0028 0.0011 0.0012 0.0468
Site 4 Zn Cu Cd Pb Ni Mean
0.088 0.021 0.0074 0.0019 0.0036 0.1219
0.041 0.0092 0.0035 0.0009 0.0018 0.0564
0.040 0.0093 0.0034 0.0008 0.0016 0.0551
3.5.2. Carcinogenic risk investigation The carcinogenic risk (CR) was estimated only for Cd, for which the cancer slope factor was available. Significantly, values of CR for three population groups exposed to the wheat grain were lower than the maximum allowable range (1 104) suggesting that Cd did not pose a remarkable cancer risk to the local residents. CR was the highest for the population 19 years of age (8.73 105 ± 8.82 105), followed by 7–18 (1.6 105 ± 1.8 105) and 0–6 years of age (7.99 106 ± 8.2 106). These results implied that potential cancer risk for the population 19 years of age was 11 and 5.5 times higher than those populations 0–6 and 7–18 years of age, respectively. The reason for such results could be attributed to (i) the longer duration of exposure in adults (19 years), and (ii) the various values recorded in the distribution of HQ for the three population groups. As a whole, the carcinogenic risk for Cd varied approximately 1 105 to 1 106 for the different population groups exposed to wheat grains, offering a low potential cancer risk (Rapant et al., 2011) (See Table 8). 4. Conclusions
Fig. 5. The HI values of heavy metal in different soil sites to various population groups exposed to wheat grains.
Based on the findings of the present study, a significant accumulation of the available and total fractions of Zn, Cu, Cd, Pb, and Ni occurred in the leachate-affected soils. However, the mean concentrations of these metals (except for Cd) in the soils and wheat grains grown in these soils were within the allowable levels set by the international regulations for environmental health and foodstuffs. The rank of available-heavy metal concentrations was found to be Zn > Pb > Ni > Cd > Cu in the soil, which varied from the rank established in the wheat grain (Zn > Cu > Pb > Cd > Ni). The different population groups exposed to wheat grains were under a moderate non-carcinogenic risk, mainly because of the
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