Heavy metals in urban soils of central Jordan: Should we worry about their environmental risks?

ARTICLE IN PRESS

Environmental Research 97 (2005) 258–273 www.elsevier.com/locate/envres

Heavy metals in urban soils of central Jordan: Should we worry about their environmental risks? K.M. Banata, F.M. Howarib,, A.A. Al-Hamada a

Department of Earth and Environmental Sciences, Yarmouk University, Irbid, Jordan Geology Department, Faculty of Science, UAE University, P.O. Box 17551, Al Ain, UAE

b

Received 23 November 2003; received in revised form 20 June 2004; accepted 7 July 2004 Available online 24 August 2004

Abstract Forty soil samples collected from central Jordan were analyzed by atomic absorption spectrophotometry for Pb, Cd, Zn, Cr, and Hg. The samples were also investigated for mineralogy using X-ray, electron, and optical microscopes. Sequential extraction procedures were used to predict the percentages of the Pb, Zn, Cd, and Cr present in each of the soil geochemical phases. The clay mineral assemblage encountered in the analyzed samples is composed of kaolinite, smectite, illite, and illite/smectite mixed-layer. The nonclay minerals of the sand-sized fraction are composed mainly of quartz and calcite as major minerals with pyroxene, biotite, and feldspars as minor minerals. The enrichment factors of the measured heavy metals Pb, Cd, Zn, Cr, and Hg in the clay fraction (o2 mm) of the collected samples are 3.1, 16.6, 1.5, 0.9, and 4.5, respectively. According to the index of geoaccumulation, the soils of the study area are considered to be moderately contaminated with respect to Cd, uncontaminated to moderately contaminated with respect to Pb, Hg, and Zn, and uncontaminated with respect to Cr. The measured metals correlated positively with the determined physicochemical factors such as pH, clay content, organic matter content, and carbonate content. The relatively high concentrations of Cd, Pb, and Hg in the soils of the study area are related to anthropogenic sources such as cement industry, fertilizers, and vehicle exhausts. It was found that Pb, Zn, and Cr are associated mainly with the residual phases and are relatively immobile. On the other hand Cd is enriched in the carbonate phase of the analyzed soil samples. It is possible to suggest the sequence of mobility for Pb, Zn, Cd, and Cr in the analyzed soil samples as the following: CdbPb4Cr4Zn. r 2004 Elsevier Inc. All rights reserved. Keywords: Heavy metals; Soils; Fractionation; Cement; Jordan; Geochemistry

1. Introduction Soils are usually regarded as the ultimate sink for heavy metals discharged into the environment, yet relatively little is known about the way that heavy metals are bound to soils and the ease with which they may be released. Part of the difficulty lies in the complex nature of soils (e.g., Forstner and Wittman, 1983; Chlopecka et al., 1996; Dang et al., 2002). The concentration of heavy metals in soils can be influenced by variation in their texture, composition, reduction/ Corresponding author.

E-mail address: [email protected] (F.M. Howari). 0013-9351/$ - see front matter r 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.envres.2004.07.002

oxidation reactions, adsorption/desorption, and physical transport or sorting in addition to anthropogenic metal input (e.g., Ahumada et al., 1999; Adriano, 1999; Howari and Banat, 2001). Metal concentrations in time and space and metal bioavailability from soils fluctuate due to the above processes (Forstner and Wittman, 1983; Ahumada et al., 1999; Adriano, 1999; Howari and Banat, 2001; Dang et al., 2002). Researchers have studied metal inputs to soil from and/or around various industrial sources such as mining, smelters, cement factories, etc. (Adejumo, 1994; Stephan et al., 1999; Namasivayan, 1994; Kamon et al., 2000; Ract et al., 2003). Assessment of availability and mobility are required to elucidate the behavior of heavy metals in soils and to

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prevent potential toxic hazards. Trace metals may be distributed among several soil components and may be associated with these components in different ways and strengths (Kersten and Fo¨rstner, 1989; Jesu´s et al., 2003). The possibility of metal remobilization from soil materials will depend on the type of metal linkage to the soil material and the possibilities of transformation in more labile species (Kersten and Fo¨rstner, 1989; Jesu´s et al., 2003). Trace metal speciation studies are important because slight changes in metal availability and in environmental conditions can cause these elements to be toxic to animals and plants. The nature of this association is referred to as speciation. To study trace metal partitioning, different schemes based on application of sequential procedures have been proposed (Tessier et al., 1979; Kersten and Fo¨rstner, 1989, 1995). During the past few years public concerns about the quality of the enormous amount of dust deposits from industrial and cement production activities in central Jordan were on the rise. The dust deposits accumulated on soil, plants, and house roofs is believed to have appreciable concentrations of heavy metals, which could reach human or ecological receptors under certain physicochemical conditions (Adejumo, 1994; Kersten and Fo¨rstner, 1995; Howari and Banat, 2001). The present work examines the distribution of Pb, Cd, Zn, Cr, and Hg as they relate to physicochemical factors believed to affect their mobility such as the pH, total dissolved solids (TDS), total organic matter (TOM), carbonate content (CaCO3), phosphorous content (P2O5), and cation exchange capacity (CEC). Sequential extraction methods (e.g., Tessier et al., 1979; Gleyzes et al., 2002) were also used to assess the mobility of heavy metals in soil of the study area. The study area was located in central Jordan in Fuhis city, southeast from the city of Salt and southwest from the city of Sweileh. The study area is bounded by longitude (351450 –351480 4500 E) and latitude (311590 1800 –32120 3000 N) (Fig. 1). The climate of the study area is that of the eastern Mediterranean region where it is hot and dry in summer and rainy in winter. Average temperatures in the Fuhis–Amman area are 8 1C (46 1F) in January, 16 1C (60 1F) in April, and 28 1C (82 1F) in July. Annual rainfall reaches 200–600 mm in northwestern parts of the country and declines progressively toward the eastern and southern deserts. The rainy season normally extends from late October through March (e.g., Salameh and Bannayan, 1993). The study area is located in the northwest part of the Arabian plate where most of the country is located within the stable shelf part of the plate. Based on its underlying geology, the county can be divided into five regions: (1) limestone with flint in the highlands and interior deserts, (2) sandstone hills in the Rift Margins

259

and Wadi Rum area, (3) ancient basement rocks behind Aqaba, (4) basalt desert in the northeast, and (5) the Rift Valley, forming Jordan’s western borders (Bender, 1968; Abed, 1982; Howari and Banat, 2002). According to Bender (1968), during the late Proterozoic, the area was characterized by Arabian Shield cratonization and island arc accretions which left basement sutures indicating east–west compression. Extensional rift-related tectonics dominated the area during late Precambrian–early Cambrian periods. Passive margin conditions with periods of transgressions and regressions dominated Jordan during the early Paleozoic, whereas active tectonic movements of deep erosion dominated late Paleozoic periods. Upper Ordovician glacial clastics and lower Silurian organic-rich shales were among the most important sediments deposited in this period (Fig. 2). Most Paleozoic basins in Jordan are compartmentalized by Cretaceous–Tertiary wrench faults related to late Cretaceous fragmentation of the Arabian plate. Mesozoic–Cenozoic basins in Jordan are dominantly rift related (Azraq, Safawi, and Northern Highlands). A mid-Tertiary tectonic phase resulted in the opening of the Gulf of Aden and the Red Sea and led to the development of the Dead Sea–Wadi Arab plate boundary that separated the Arabian plate from the African plate from the Levant–Sinai fragment and sutured the Arabian plate to Eurasia (Bender, 1968).

2. Methodology 2.1. Sample collection and preparation Forty soil samples were collected in a grid system around the cement factory in Fuheis from parks, play yards, and residential parts of the investigated area (Fig. 1). The samples were most densely collected near the cement plant and became less densely collected with increasing distance from the cement plant. This scheme was designed to allow a spatial trend of metal variations to be detected. The collected samples were preserved in prewashed polyethylene bags and transported to the laboratory 3–4 h after collection for various analyses. Handling the soil samples followed the 1981 EPA/CE81-1 protocol (Plumb, 1981). The collected samples were dried at 55 1C; after homogenization, wet sieving was carried out using a 63-mm sieve to separate the mud fraction from the sand fraction. Mud was dried at 55 1C to prevent changes and collapse of the clay minerals. Clay was separated from silt by using the pipette method (Folk, 1974; Loring and Rantala, 1992). A computerized sedigraph was used for the determination of the percentage of the silt and the clay fractions in the samples.

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3

1

5

2 6 4

7

14

8 9

11 15

12

10 13

16 Al-Zahwaa Mountain

20

17

19

18

23

22

21

FUHIS

24

25

26

Bakaloria School

Cement Factory 27 28 Um-AliaBasin

32

34

33

35

39 38o

36o

N

LEBANON

SY R I A

Hashemite Palace Study Area

32o

37

36

32o

AMMAN

S A U D I A R A B I A J O R D A N

38 30o 300

m

Aqaba

40

30o 36o

38o

40 km

Fig. 1. Location map of the study area.

2.2. Mineralogical analyses The bioavailability of metals is influenced by soil mineralogy and especially the type of clay minerals present (Forstner and Wittman, 1983). Therefore, a polarized transmission microscope was used to study the nonclay minerals in the sand-sized fraction of 15 samples. A transmission electron microscope (TEM) was used to study the detailed structures and shapes of clay minerals in 20 samples. According to the methods reported by Brown (1961), Muller (1967), Grim (1968), and Carroll (1970), 20 oriented clay samples were prepared for the determination of clay minerals in the clay fraction (o2 mm). The samples were examined as untreated, ethylene glycolated, and heated to 550 1C. The following conditions were considered during their

scanning by the X-ray diffraction technique: 2y , 3–171; X-ray radiation, Cu Ka; generator current, 30 mA; generator voltage, 30 kV; scanning speed, 0.05 cm/min. The nonclay minerals in the mud fraction (o63 mm) were identified in eight selected samples by scanning at 11/min in the range of 2y from 31 to 651. 2.3. Physicochemical characteristics The pH and TDS of the collected soil samples were measured by a calibrated digital pH meter and a digital conductivity meter, respectively (Loring and Rantala, 1992). The percentage of calcium carbonate in the fraction less than 63 mm was measured by using the calcimetry method according to the procedure reported by Loring and Rantala (1992). The percentage of the

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Fig. 2. Geology of the study area and surrounding locations.

organic matter in the soil samples was measured by the titration method which is based on the oxidation of organic matter by potassium dichromate; then titration with ferrous sulfate was conducted until the color flashed to green (e.g., Belcher and Nutten, 1970; Loring and Rantala, 1992). The determination of the percentage of P2O5 was based on the optical density of the prepared solution by using the spectrophotometer at a wavelength of 460 nm. The samples were prepared by adding concentrated HCl, HNO3, and H2SO4, with vandomolybdate at the final stage (Jeffry and Huthchinson, 1981). The CEC was determined by measuring the sodium content after treatment of 5 g taken from the less than 63-pm soil fraction with sodium acetate and ammonium acetate solution (Hesse, 1972). 2.4. Sequential extraction and metal measurements The soil material can be partitioned into specific fractions which can be extracted selectively by using appropriate reagents (Ahumada et al., 1999; Li and Thornton, 2001). In this work a sequential extraction procedure (Tessier et al., 1979) was used to distinguish between exchangeable, carbonate-bound, Fe–Mn-oxi-

des-bound, organic-matter-bound, and residual fractions of Cr, Cd, Pb, and Zn in the mud fraction (o63 mm). The atomic absorption spectrophotometer was used for the determination of Pb, Zn, Cd, and Cr contents in all analyzed soil samples in both the clay fraction (o2 mm) and the mud fraction (63 mm). The fine-grade fractions were used due to their higher surface areas which have positive effects on the amounts of heavy metals that can be bounded at their surfaces (e.g., Forstner and Wittman, 1983). Duplicate samples and triplicate measurements were obtained. The limits of detection at the time of measurement were calculated as the concentration equal to three times the standard deviation (3s) of a series of five measurements of a procedural blank solution, and the values were 0.08, 0.11, 0.61, 0.06, and 0.03 mg g1 for Pb, Cr, Zn, Cd, and Hg, respectively. According to the procedure described by Hesse (1972), a combination of 4 mL of 25% HCl, 4 mL of 25% HNO3, and 2 mL concentrated HF were used for the dissolution of the soil samples. A flameless atomic absorption spectrophotometer was used to determine the Hg in the clay fraction of 19 selected soil samples based on the method reported by Loring and Rantala (1992); those samples were dried at room

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Table 1 Measurements of metal pollution in soils and sediments (Muller, 1969; Ntekim et al., 1993) Index of geoaccumulation

I-geo class

Designation of sediment quality

10–5

6

4–5

5

3–4

4

2–3

3

1–2

2

0–1 0

1 0

Extremely contaminated Strongly/extremely contaminated Strongly contaminated Moderately contaminated Uncontaminated/ moderately contaminated Contaminated Uncontaminated

temperature. The descriptive statistics were obtained by Excel (Microsoft, 2000), and contour maps were generated by Surfer 7.0 from Golden Software. The value of the enrichment factor (EF) was calculated using the formula EF ¼ Cn=Bn; where Cn (sample) is the content of the examined element in the examined environment and Bn (background) is the content of the examined element in the environment. A quantitative measure of the extent of metal pollution in the studied soil was calculated using the geoaccumulation index proposed by Muller (1969). This index (I-geo) of heavy metal is calculated by computing the base 2 logarithm of the measured total concentration of the metal over its background concentration using the mathematical relation (Muller, 1969; Ntekim et al., 1993)

Standard US Department of Agriculture Soil Textural Classification Triangle (Brady and Weil, 2001) (Fig. 3). The soils of the study area are medium- to moderately fine-textured soils and to a lesser extent moderately coarse and fine soils. They can be classified as silty loam to silty clay loam, with a lesser extent of sandy loam, silty clay, and silt. 3.2. Mineralogical analyses Clay minerals. Clay minerals were determined in the clay fractions (o2 mm) of 20 random samples using the X-ray diffraction technique and TEM. Kaolinite was recognized in all analyzed soil samples as a major clay mineral. It is characterized by basal reflection of 7 A˚ in both the untreated and the glycolated samples, which disappears after heating to 550 1C for 2 h (Fig. 4). TEM micrographs show that kaolinite is characterized by pseudohexagonal plate-like morphology generally with a well-formed euhedral crystal shape (Fig. 5). The smectite content has been identified by the basal reflections of 12–13 A˚. Upon glycolation, the d-spacing increases to 16–17 A˚ due to the swelling of this mineral. After heating to 550 1C, the d-spacing decrease to 9.8–l0 A˚ due to the collapse of smectite to illite (Fig. 5). TEM micrographs show the irregular and featherlike appearance of smectite (Fig. 5). Illite was identified by 10-A˚ basal reflections which remained the same after glycolation and heating to 550 1C, with an enhancement in peak intensities due to the collapse of the illite/ smectite mixed-layer and smectite to illite (Fig. 5). The TEM micrograph of illite shows a fibrous characteristic structure (Fig. 5). By heating to 550 1C, the smectite of

CLAY 100%

I-geo ¼ log2 ðCn=1:5BnÞ; where Cn is the measured total concentration of element n in the o63-mm fraction of sediment, Bn is the average (crystal) concentration of element n in the shale (background), and 1.5 is the factor compensating the background data (correction factor) due to lithogenic effects. The heavy metal pollution levels are measured using this index (I-geo), which consists of seven grades: 0–6. The highest grade, 6, reflects a 100-fold metal concentration relative to background values (Table 1).

Clay

Silty clay

Sandy clay Clay loam

Silty clay loam

Sandy clay loam Loam Sandy loam

3. Results and discussion 3.1. Textural analyses Forty soil samples from the study area were subjected to grain size analyses. The results are plotted on a

Loamy Sand sand SAND 100%

Silt loam

Silt SILT 100%

Fig. 3. Textural classification of the collected soil samples (USDA soil textural triangle; Brady and Weil, 2001).

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No. 5

K

263

S

K, kaolinite S, smectite I, illite S Normal (N)

Heated (H)

K

I/S Glaucoated (G)

I

No. 10

K

S

Normal (N)

Heated (H)

K

Glaucoated (G)

S

No. 10 K I

I

Normal (N)

Heated (H)

Fig. 5. Transmission electron micrographs showing pseudohexagonal plate-like morphology of kaolinite, illite, and smectite clay minerals.

K I

Glaucoated (G)

16

14

12

10 2θ

8

6

4

Fig. 4. X-ray diffraction pattern of selected soil samples collected from the study area showing the clay minerals.

Nonclay minerals. A powder X-ray diffraction technique was applied to identify the nonclay minerals in eight random samples of the mud fraction. The identified nonclay minerals in the sand-sized fraction arranged according to their decreasing abundance are quartz, calcite, and to a lesser extent pyroxene, biotite, and feldspar minerals (Fig. 6). Quartz grains are the most common primary mineral in the soils of the study area. These may be derived from the local lithology such as Cretaceous Kurnub sandstone and Cretaceous deposits adjacent to the study area (Abed, 1982; Howari and Banat, 2002). 3.3. Physicochemical characteristics of soils

the mixed-layer collapses to a 10-A˚ d-spacing illite (Fig. 4). Illite/smectite mixed-layers were of low content in the analyzed samples.

The soil samples are slightly alkaline. The pH values display relatively equal distributions in the entire study area, with their highest values in the soil samples

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lithologic units exposed within the study area and belonging to the Jurassic and Upper Cretaceous carbonate rock formations may be partly responsible for the recorded total carbonate content.

C, calcite P, plagioclase A, apatite Q, quartz

CC

C

Q

P C

Q

56

52

AC

A

Q

60

3.4. Distribution of metals

Q P

48

44

40

36

32

P

28

24

20

2θ

Fig. 6. X-ray powder diffraction pattern of nonclay minerals of the sand-sized fraction of soil samples collected from the study area.

collected closer to the cement factory (Fig. 7a). Also, high %TDS values are found close to the cement factory with increasing values toward Amman city (Fig. 7b). In the investigated soils, the organic matter content ranges from 0.3% to 4.9% with a mean value of 2.2%. Fig. 7c indicates that the total organic matter content shows the highest values in the central part of the study area. This distribution pattern of organic matter reflects the variable distribution of vegetation cover in the study area. The percentage of the total phosphate content in the analyzed soil samples range from 0.05% to 2.68%, with a mean of 1.03% (Table 2). An increase of the %P2O5 is recorded in the soil samples collected from the area adjacent to the cement factory (Fig 7e). P2O5 is introduced to the cement to slow its hardening (Soroka, 1979). Another major source of the phosphate in the soils of the study area is the upper Cretaceous phosphate-bearing rocks of north Jordan. Tuff deposits enriched with hydroxyapatite west of the Jordan valley, and the use of phosphate fertilizers in agricultural land are other sources of the P2O5 content in the analyzed samples. The cation exchange capacity of the soil samples range between 53 and 197 meq/100 g with a mean value of 133.4 meq/100 g (Table 2). As shown in Fig. 7f the soil samples collected around the cement factory display the higher CEC values. According to Brady and Weil (2001) the CEC increases with increasing pH and organic matter and calcium contents. This may explain the slight increase of CEC close to the cement factory. The total carbonate content of the analyzed soil samples ranges from 0.22% to 50% with a mean value of 30.1% (Table 2). Soil samples with the highest carbonate content are concentrated in the central part of the study area around the cement factory (Fig. 7d). This can be attributed to the cement industry in which carbonates are used as raw materials and form the major constituents of the emitted dust released to the environment. In addition, certain

The concentrations of the heavy metals Pb, Zn, Cd, and Cr were measured in both the mud fraction (o63 mm) and the clay fraction (o2 mm) to determine the effect of the grain size on the distribution of the heavy metals in the collected soil samples. Since both silt and clay fractions comprise the major carriers for both natural and anthropogenic compounds, different authors have used metal concentration in the clay fraction for assessment of pollution in the sediment and that in the mud fraction for determination of heavy metal phases by the sequential extraction procedure (Tessier et al., 1979; Forstner and Wittman, 1983; Chakrapani and Subramanian, 1993; Szefer Glasby et al., 1995; Zhixun et al., 1997; Gupta and Subramanian, 1998). Consequently, in the present study the clay fraction was used to assess the pollution intensity and the mud fraction to determine the different heavy metal phases. Because of limited resources, Hg was measured in only 19 soil samples in the clay fraction. The reported results reveal that the measured heavy metal concentrations are higher in the clay fraction than in the mud fraction (Tables 3 and 4). On the other hand Spearman correlation coefficient was calculated and indicated that the measured heavy metals were positively correlated with pH (r ¼ 0:91), clay content (r ¼ 0:89), organic matter (r ¼ 0:87), CaCO3 (r ¼ 0:85), and P2O5 (r ¼ 0:68), indicating that those parameters control the distributions of the measured metals. The concentration of Pb in the clay fraction of the analyzed samples ranged from 26 to 98.5 mg kg1with a mean of 62.2 mg kg1 and an EF of 3.1 (Table 3); shale were considered average crystal concentrations after Muller (1969), Ntekim et al. (1993), Forstner and Wittman (1983), and Howari and Banat (2001). High values of Pb are encountered in the samples collected from the northeast of the cement factory toward Amman city (Fig. 8a). The highest concentrations were recorded close to the cement factory. The Pb content is attributed to the cement industry in which the calcination process and production of the clinker require a substantial amount of energy supplied by burning fuel. This process causes the emission of Pb to the environment. The concentrations of Cr in the clay fraction varies from 32 to 156.5 mg kg1 with a mean of 84.4 mg kg1. The EF of Cr is equal to 0.9. The highest concentrations are recorded northwest of the cement factory (sample Nos. 15 and 16). In the cement industry the linings for the rotaries contain Cr, which could be liberated by wear and friction to be a source of Cr in the

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159

N

pH

158

159

265

N

TDS

158

157

157

-

-

Al Zahwaa Mountain

Al Zahwaa Mountain FUHIS

FUHIS

Bakaloria School

Bakaloria School

156

Cement Factory

Cement Factory

156 Um-Alia Basin

Um-Alia Basin

155

155 Hashemite Palace Hashemite Palace

154

154

(a) 21.5 22 22.5 23 23.5 24 24.5 25 25.5 26

(b)

159

159

%TOM

158

21.5 22 22.5 23 23.5 24 24.5 25 25.5 26

%CaCO3

158

157

157

-

Al-Zahwaa Mountain

Al Zahwaa Mountain FUHIS

FUHIS Bakaloria School

Bakaloria School

156

Cement Factory

156 Um-Alia Basin

Cement Factory

Um-Alia Basin

155

155 Hashemite Palace

Hashemite Palace

154

154

(c) 21.5 22 22.5 23 23.5 24 24.5 25 25.5 26

(d)

21.5 22 22.5 23 23.5 24 24.5 25 25.5 26

159

159

CEC(meq)%

% P2O5

158

158

157

157

Al-Zahwaa Mountain

AlZahwaa Mountain FUHIS

FUHIS Bakaloria School Cement Factory

156

Bakaloria School

Um-AliaBasin

Um-Alia Basin

155

155 Hashemite Palace

154

(e)

Cement Factory

156

Hashemite Palace

154

21.5 22 22.5 23 23.5 24 24.5 25 25.5 26

(f)

21.5 22 22.5 23 23.5 24 24.5 25 25.5 26

Fig. 7. Geochemical map of pH, total dissolved solids (%TDS), total organic matter (%TOM), % CaCO3, % P2O5, and cation exchange capacity (CEC in meq/100 g) measured in soil samples of the study area.

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Table 2 Values of pH, %CaCO3, %TDS, %P2O5, %TOM, and CEC (meq/100 g) and their associated descriptive statistics Sample no.

pH

% CaCO3

%TDS

%P2O5

%TOM

CEC (meq/100 g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 Mean Standard deviation Kurtosis Skewness Minimum Maximum

7.55 7.78 7.68 7.76 7.87 7.83 7.72 7.91 7.69 7.81 7.86 7.57 7.73 7.69 7.56 7.92 7.9 7.9 7.96 7.92 7.8 7.96 7.96 7.85 7.31 7.7 7.83 7.88 7.94 7.87 7.96 7.85 7.81 7.89 7.94 7.74 7.87 7.79 7.72 7.36 7.79 0.15 3.035 1.61 7.31 7.96

27.61 12.83 3.48 8.48 14.35 31.09 0.87 4.57 27.61 43.48 62.39 26.09 68.91 1.96 0.54 0.22 4.57 36.3 21.09 36.96 80 18.91 5.22 0.33 72.61 49.35 20.54 55 66.3 20.87 21.07 62.17 0.43 2.28 63.48 64.35 22.17 62.83 40.43 43.91 30.20 25.25 1.20 0.41 0.22 80

6.66 6.72 7.42 7.1 7.17 18.43 7.04 5.82 8.19 8.06 6.65 7.49 8.89 7.23 8.77 5.76 9.39 6.98 7.74 6.85 8.38 12.29 7.17 5.57 9.98 17.91 11.71 8.26 9.09 8.83 8.51 6.4 9.86 8.51 7.68 11.33 6.85 10.43 6.53 6.22 8.54 2.77 6.04 2.28 5.57 18.43

1.86 1.81 1.87 1.06 0.49 1.49 0.75 0.75 0.74 0.62 2.42 0.31 10.6 2.88 1.43 0.49 0.93 0.87 1.37 0.19 2.36 0.37 2.44 0.06 0.73 1.06 0.05 0.12 0.17 0.56 1.49 0.25 1.24 0.47 1.18 0.99 0.87 0.83 0.83 0.86 1.23 1.69 25.85 4.70 0.05 10.6

3.43 4.94 2.17 1.35 2.79 2.6 2.87 0.38 1.61 2.19 0.3 3.18 1.98 1.19 1.97 1.97 1.04 2.86 1 2.48 0.93 4.22 1.9 0.99 0.77 1.47 3.89 2.87 4.65 2.1 3.72 1.45 2.02 1.05 1.54 0.34 1.47 1.01 4.88 3.14 2.13 1.24 0.14 0.71 0.3 4.94

141 175 124 149 179 113 165 165 125 123 73 151 84 197 178 132 166 127 158 177 53 160 153 170 79 116 137 83 93 126 113 110 144 100 70 191 120 151 104 105 131.76 36.54 0.76 0.20 53 197

investigated soils. In line with the current findings, Dwaikat et al. (2002) found that dust to the west of Amman derives from the Fuhis cement factory because most of the prevailing winds are from the west. The average concentration of Cd in the clay fraction of the analyzed samples is 4.9 mg kg1 with an EF of 16.6, a minimum value of 3.0 mg kg1, and a maximum value of 10 mg kg1 (Table 3). The air emission from cement kilns and the use of phosphatic fertilizers around the investigated area are possible sources of Cd. The concentrations of Zn in the clay fractions of the analyzed samples vary between 50 and 500 mg kg1 with

a mean of 146 mg kg1. The soils are enriched by 1.5 EF. The Zn content increases toward the west, where a marked increase of Zn concentration is recorded near a waste dump (sample No. 27) in a form of anomaly (Fig. 8d). The average Zn content is similar to the average background value in shale, which indicates that Zn is derived from lithogenic sources. The mean concentration values of Hg in the clay fraction of the analyzed samples are 1.8 mg kg1, with a concentration ranging from 0.6 to 3.0 mg kg1. The EF of Hg in the investigated soils is 4.5. Hg content shows a nearly constant concentration in the analyzed soil

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Table 3 Concentrations of Pb, Cr, Zn, Cd and Hg in clay fractions of the investigated soil and their associated descriptive statistics Sample no.

Pb (mg kg1)

Cr (mg kg1)

Zn (mg kg1)

Cd (mg kg1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 LOD (mg g1) Mean Standard deviation Kurtosis Skewness Minimum Maximum

68 65.5 49.5 56 93.5 37 78 58 72 26 46 53.5 38 67.5 71 67.5 71 65 61.5 42 63 68 54 39.5 80.5 63 98.5 55 53.5 70 72.5 71 63.5 62.5 71.5 62 84 38 68 65 0.08 62.17 15.28 0.413 -0.097 26 98.5

101 94.5 77.5 94 81.5 85.5 97.5 83.5 80.5 95.5 63.5 37 84 103 154 156.5 88 76.5 79.5 87.5 32 81 90 81.5 90.5 66 95 70 52.5 85 74 80 106.5 91 69 67 99.5 56 89.5 78 0.11 83.93 23.25 3.76 0.95 32 156.5

150.5 196 109.5 130.5 134 132.5 132 133 131 130 89.5 81 11.5 163 245.5 186.5 156 150.5 133 124.5 62.5 138.5 125.5 129 140 554.5 96 117 116 133.5 125 155 153 118.5 96.5 196 178.5 136.5 114 120 0.61 146.94 77.99 21.06 3.9574 11.5 554.5

5 6.5 5 4.5 3.5 4 6 5 4.5 3.5 5.5 5 4.5 4 10 9.5 8 4 5 5 5 4 4 3 4 4.5 6 3.5 4 5 6 4 5 5.5 6 3 4 5 5 4.5 0.06 4.98 1.50 3.99 1.80 3 10

samples (Fig. 8c). However, considerable concentrations are recorded around the cement factory near Jabal AlZahua in Fuhis (sample Nos. 11, 21, and 23). Hg is found in both stack and fugitive emissions in cement factories (Soroka, 1979; Lea and Hewlett, 1997); the use of commercial fertilizers and pesticides in the nearby agricultural farms could be other potential sources of Hg in the investigated soils (Forstner and Wittman, 1983; Olaf et al., 2000; Howari and Banat, 2001). It has become obvious that the concentrations of metals are

Hg (mg kg1)

2.24

1.58 1.65 3.05 2.28 0.95

1.09

2.07 2.8

1.02 1.05

1.02 1.05 2.31 0.7

0.6 1.82 2.21

1.93 0.03 1.81 0.72 0.97 0.28 0.6 3.05

highest around the cement factory and this location would pose relative elevated risks to human or ecological receptors. 3.5. Indices of geoaccumulation The geoaccumulation indices of Pb, Cr, Cd, Zn, and Hg were 0.32, o0, 2, 0.01, and 0.42, respectively (Table 4). This indicates that the soils are classified as uncontaminated to moderately contaminated with Pb,

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1 2 1 1 0 0.32 1.04 0.48 0.01 o0 3.1 16.6 4.5 1.5 0.9 60.2 3.25 1.25 143.9 82.45 20 0.3 0.4 95 90 Pb Cd Hg Zn Cr

62.17 4.98 1.81 146.94 83.93

Pollution intensity I-geo grade I-geo value Enrichment factor Average in mud fraction Average in clay fraction Average shale value Heavy metal

Table 4 Average, background, enrichment factor, calculated I-geo index, and grade of pollution intensity of heavy metals in the analyzed samples

Uncontaminated to moderately contaminated Moderately contaminated Uncontaminated to moderately contaminated Uncontaminated to moderately contaminated Uncontaminated

K.M. Banat et al. / Environmental Research 97 (2005) 258–273

268

uncontaminated with Cr, moderately contaminated with Cd, uncontaminated to moderately contaminated with Zn, and uncontaminated to moderately contaminated with Hg. 3.6. Heavy metals affinity for geochemical phases Studies on the distribution of trace metals in sediments and other media are of great importance in the context of environmental pollution (Karczewska, 1996; Lee and Patrick, 1997; Li and Thornton, 2001; Li and Liu, 2001). Within biogeochemical cycles, an important step is the speciation of metals causing accumulation and/or release by various processes, which depends on the physico-chemical conditions of the depositional environment (Lee and Patrick, 1997; Kabata–Pendias and Pendias, 2000; Dang et al., 2002). Chemical analytical methods have been developed to better estimate the fraction of metal that is available for uptake by a receptor. Sequential extraction or leaching schemes have been used extensively to partially characterize the phase associations of metals in soils and sediments to identify the fractions of total metal that are or could become bioavailable (Tessier et al., 1979; Zalidis et al., 1999). Fig. 9 and Tables 5 and 6 summarize the results of the sequential extraction techniques. The exchangeable fraction is considered to be the most mobile and bioavailable phase present in the soils and sediments (Tessier et al., 1979; Ahumada et al., 1999; Howari and Banat, 2001). The exchangeable fraction in the analyzed soil samples is able to retain heavy metals in the order Cd (17.65%)bPb (10.93%)bCr (2.18%)4Zn (1.16%) (Fig. 9). The carbonate phase is considered the most active and bioavailable part of the metal after the exchangeable phase (Tessier et al., 1979; Howari and Banat, 2001). Cd bound to carbonates is enriched in the soil samples of the study area in comparison to Pb, Cr, and Zn in the same soil samples. The carbonate fraction in the analyzed soil samples is able to retain heavy metals in the order Cd (33.29%)bPb (16.23%)bZn (4.90%)4Cr (1.26%) (Fig. 9). Iron and manganese oxides exist as nodules, concretions, cement between particles, or simply coating on particles. Those oxides are excellent scavengers for trace metals and can be mobilized under reducing and acid conditions (Tessier et al., 1979; Szefer Glasby et al., 1995; Howari and Banat, 2001; Dang et al., 2002). Fe–Mn oxides retain heavy metals in the soils of the study area in the order Cd (16.63%)4Zn (15.80%)bPb (9.19%)4Cr (2.73%) (Fig. 9). The organic phase is a relatively stable phase in nature, but it can be mobilized under strong oxidizing conditions due to organic matter degradation, leading to a release of the soluble metal (Tessier et al., 1979). This fraction is able to retain heavy metals in the order Zn(9.09%)4Cr(6.65%)4

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159

159

Pb

158

269

Cr

158

157

157 Al-Zahwaa Mountain

AlZahwaa Mountain

FUHIS

FUHIS

Bakaloria School

Bakaloria School

156

156

Cement Factory

Um-Alia Basin

Um-Alia Basin

155

155

Hashemite Palace

Hashemite Palace

154

(a)

Cement Factory

21.5

22

22.5

23

23.5

24

24.5

154

25

25.5

(b)

26

21.5

22

22.5

23

23.5

24

24.5

25

25.5

26

159 159

Hg

Zn

158 158

Al-Zahwaa Mountain

157

FUHIS

Bakalori School

Cement Factory

156

Al-Zahwaa Mountain

157 FUHIS

Bakaloria School Cement Factory

156

Um-Alia Basin

Um-Alia Basin

155

155 Hashemite Palace

Hashemite Palace

154

(c)

154

22.5

23

23.5

24

24.5

25

25.5

26

(d)

21.5

22

22.5

23

23.5

24

24.5

25

25.5

26

1

Fig. 8. Geochemical maps of Pb, Cr, Hg, and Zn concentrations (mg kg ) of clay fraction of soil samples from the study area.

Fig. 9. Selected heavy metal percentages in different geochemical phases (fractions) of the investigated soils.

Pb(5.83%)4Cd(3.69%) (Fig. 9). The residual solid should contain mainly primary and secondary minerals, which may hold trace metals within their crystal structure. Metals present in this fraction are a measure of the degree of environmental pollution: the higher the metals present in this fraction the lower the degree of pollution (Forstner and Wittman, 1983; Howari and Banat, 2001; Ahumada et al., 1999; Dang et al., 2002). The heavy metals bound to the residual fraction are in the order Cr(86.85%)bZn(69.04%)4Pb(57.82%)bCd(28.74%). The affinity of those metals in the investigated soils toward the different geochemical phases are in the following order: Pb, residualbcarbonate4exchangeable4Fe–Mn oxides4organic matter; Cd, carbonate4

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Table 5 Sequential extraction results of percentages of Cr and Cd in the exchangeable, carbonate, Fe-Mn oxide, organic matter, and residual phases Serial no.

Sample no.

Exchangeable phase/Cr

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Mean Standard deviation Skewness Minimum Maximum

33 34 16 26 13 14 40 19 10 24 6 21 1 9 18 3 27 39 32 29 20.05263 11.6832 0.109684 1 40

Serial no.

Sample no.

Exchangeable phase/Cd

Carbonate phase/ Cd

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Mean Standard deviation Skewness Minimum Maximum

33 34 16 26 13 14 40 19 10 24 6 21 1 9 18 3 27 39 32 29 20.05 11.68 0.10 1 40

24.5 19.44 30.05 16.26 15.95 17.77 17.86 15.3 11.44 17.6 13.99 12.5 19.54 19.75 10.46 19.73 23.38 15.66 14.38 12.59 17.03 4.56 1.194 10.46 30.05

42.5 36.51 23.71 34.6 35.79 34.15 42.86 32.74 33.21 34.8 34.45 31.07 29.89 25.29 29.41 29.59 25.92 36.55 35.53 32.37 32.54 4.57 0.084 23.71 42.86

1.78 0.89 2.58 2.06 2.83 1.47 1.59 1.71 2.61 2.1 2.45 1.7 2.29 2.48 2.12 1.69 2.16 1.79 2.76 4.92 2.221053 0.821211 1.864706 0.89 4.92

Carbonate phase/ Cr 1.84 0.86 1.34 2 1.05 1.09 1.19 1.34 0.96 0.2 0.83 1.49 1.46 0.78 0.96 0.92 1.58 1.2 1.98 2.09 1.227368 0.472509 0.144285 0.2 2.09

residualbexchangeable4Fe–Mn oxides4organic matter; Zn, residualdFe–Mn oxides4organic matter4 carbonate4exchangeable; and Cr, residual4organic matter4Fe–Mn oxides4exchangeable4carbonate. Based on this, the bioavailabilty of metals in the soil samples of the

Fe–Mn oxide phase/Cr

Organic matter phase/Cr

Residual phase/Cr

7.67 0.93 12.29 0.61 6.56 7.46 6.03 4.49 6.58 6.36 3.37 4.13 9.08 4.67 6.91 6.62 8.67 6.36 9.65 11.97 6.46 3.11445 0.005855 0.61 12.29

85.52 96.09 83.43 87.49 85.04 88.32 88.9 90 86.62 88.26 90.04 88.47 85.71 89.71 88.16 89.05 84.59 89.4 77.26 74.93 86.91947 4.675559 1.08863 74.93 96.09

Fe–Mn oxide phase/Cd

Organic matter phase/Cd

Residual phase/Cd

1 6.35 18.19 24.22 22.57 6.27 19.64 13.88 20.66 8 15.64 26.79 15.23 12.93 12.42 15.65 22.54 21.29 24.32 20.14 17.19 6.129 0.416 6.27 26.79

0 3.57 12.52 5.19 1.95 2.44 3.57 2.85 1.48 3.6 3.7 1.43 8.05 0 1.63 6.8 4.23 2.41 1.37 2.16 3.62 2.90 1.84 0 12.52

32 34.13 15.53 19.72 23.74 39.37 16.07 35.23 33.21 36 29.22 28.21 27.29 17.82 46.08 28.23 23.94 24.1 27.39 32.73 28.31 8.09 0.25 15.53 46.08

3.19 1.24 0.37 1.16 4.52 1.66 2.28 2.46 3.68 1.32 2.81 4.2 1.45 2.06 1.86 1.71 2.99 1.28 8.35 6.09 2.71 1.955874 1.64089 0.37 8.35

study area is as follows: CdbPb4Cr4Zn. Future tasks would be to develop comprehensive screening-level benchmarks for ecological risk assessment of contaminated soils for central Jordan and to analyze metal contents in biological samples.

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Table 6 Sequential extraction results of percentages of Zn, and Pb in the exchangeable, carbonate, Fe-Mn oxide, organic matter and residual phase Serial no.

Sample no.

Exchangeable phase/Zn

Carbonate phase/ Zn

Fe–Mn oxide phase/Zn

Organic matter phase/Zn

Residual phase/Zn

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Mean Standard deviation Skewness Minimum Maximum

33 34 16 26 13 14 40 19 10 24 6 21 1 9 18 3 27 39 32 29 20.05 11.68 0.109 1 40

0.83 0.47 1.19 1.33 0.76 0.68 1.17 0.83 1.26 0.68 1.26 1.95 1.4 2.07 0.49 0 1.71 2.06 1.31 1.8 1.18 0.58 0.14 0 2.07

4.17 3.64 4.17 3.23 5.59 3.42 3.97 3.33 3.77 2.15 4.55 6.67 3.85 4.61 0.91 3.86 21.57 4.8 3.17 6.61 4.94 4.24 3.63 0.91 21.57

8.13 31.96 11.73 11.81 31.04 5.34 8.88 10.32 10.06 45.93 8.59 16.94 11.56 12.21 7.69 6.12 16.92 21.61 18.47 20.72 16.20 10.43 1.59 5.34 45.93

3.13 13.64 12.33 19.24 7.38 3.42 5.37 2.99 3.77 2.71 4.79 5.83 8.06 5.76 37.71 4.46 22.05 7.72 5.78 5.41 9.39 8.70 2.29 2.71 37.71

83.75 50.28 70.58 64.38 55.22 87.12 80.61 82.53 81.13 48.53 80.81 68.61 75.13 75.35 53.18 85.35 37.74 63.81 71.27 65.47 68.21 13.96 0.60 37.74 87.12

Serial no.

Sample no.

Exchangeable phase/Pb

Carbonate phase/ Pb

Fe–Mn oxide phase/Pb

Organic matter phase/Pb

Residual phase/Pb

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Mean Standard deviation Skewness Minimum Maximum

33 34 16 26 13 14 40 19 10 24 6 21 1 9 18 3 27 39 32 29 20.05 11.68 0.109 1 40

15.27 10.23 17.3 10.28 8.82 8.32 10.94 11.45 9.16 10.37 12.65 9.12 11.38 14.79 10.16 14.21 9.89 12.84 6.35 5.16 10.70 2.85 0.35 5.16 17.3

19.66 20 21.84 18.45 17.62 14.06 17.54 16.75 13.28 16.98 16.92 16.83 16.83 17.83 15.18 16.48 12.92 18.17 8.82 8.47 16.05 3.35 -0.95 8.47 21.84

4.89 4.04 2.12 11.81 16.79 1.13 10.46 10.46 9.51 11.12 1.61 14.21 18.8 8.94 11.86 7.01 4.65 17.87 11.42 8.09 9.57 5.26 0.01 1.13 18.8

5.38 3.77 13.26 11.95 2.64 3.93 2.83 3 4.81 8.85 6.2 2.6 3.05 4.14 3.53 6.28 20.89 6.06 2.42 0.99 5.85 4.86 2.00 0.99 20.89

54.8 61.96 45.48 47.51 54.13 72.56 58.22 59.28 61.63 62.19 50.01 52.63 59.8 51.37 64.12 58.38 38.42 51.51 74.32 78.01 57.96 10.03 0.25 38.42 78.01

4. Conclusions The soils of the urban areas of central Jordan can be classified as silty loam to silty clay loam, with a lesser extent of sandy loam and silty clay. The clay mineral

assemblage encountered is composed of kaolinite, smectite, illite, and illite/smectite mixed-layer. The nonclay minerals consist of quartz and calcite as major minerals, with pyroxene, biotite, and feldspars as minor minerals. The data indicate that this area has been

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affected by human activity, in particular the cement industry, leading to a high accumulation of heavy metals compared with the natural background levels. The EFs of the measured heavy metals Pb, Cd, Zn, Cr, and Hg in the clay fraction (o2 mm) of the collected samples are 3.1, 16.6, 1.5, 0.9, and 4.5, respectively. The distribution of those metals in the soils of Fuhis city indicated that the cement industry together with the agricultural fertilizers and vehicle exhausts were mainly responsible for metal pollution. The data indicated higher concentrations of metals in the fine-grained soils due to the increase in the surface area and surface properties of clay minerals. The geoaccumulation (I-geo) values obtained from this study for the measured metals in the soils indicate that the soils are classified as uncontaminated to moderately contaminated with Pb, uncontaminated with Cr, moderately contaminated with Cd, uncontaminated to moderately contaminated with Zn, and uncontaminated to moderately contaminated with Hg. The study found that Pb, Zn, and Cr are mainly associated with the residual phase which retains those metals in the order Cr(86.85%)bZn(69.04%)4 Pb(57.82%)bCd(28.74%). Thus those metals are relatively immobile.

Acknowledgments We express our thanks to the head, staff, and technical personnel of the Department of Earth and Environmental Sciences/Jordan and to Mr. Hamdi Kandeel from UAE University for his technical assistance in preparing the figures.

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Further reading Turekian, K.K., Wedepohl, K.H., 1961. Distribution of the elements in some major units of the Earth’s crust. Geol. Soc. Am. Bull. 72, 175–192.