Open Journal of Soil Science, 2012, 2, 123-132
http://dx.doi.org/10.4236/ojss.2012.22018 Published Online June 2012 (http://www.SciRP.org/journal/ojss)
123
Concentration, Distribution and Comparison of Total
and Bioavailable Heavy Metals in Top Soils of Bonab
District in Zanjan Province
Abdolhossein H. Parizanganeh1*, Vahid Bijnavand1, Abasali A. Zamani2, Ali Hajabolfath3
1Department of Environmental Sciences, Faculty of Science, Zanjan University, Zanjan, Iran; 2Department of Analytical Chemistry,
Faculty of Science, Zanjan University, Zanjan, Iran; 3Department of Geology, Faculty of Science, Zanjan University, Zanjan, Iran.
Received October 8th, 2011; revised November 10th, 2011; accepted December 28th, 2011
ABSTRACT
Heavy metal contamination of soils is a widespread problem in Zanjan province located in North West Iran due to
natural pedo geochemical background and anthropogenic sources. The province is highly polluted by some heavy met-
als due to the presence of mineral resources notably Lead and Zinc, their improper utilization, and also the development
of a number of related industries. Bonab district was selected for detail study and the objectives of the study were set to
evaluate the total as well as bioavailable fraction of heavy metals in surficial soils within the studied area. 72 soil sam-
ples were collected and analyzed for heavy metal contamination by Atomic Absorption Spectrometry (AAS). The ob-
tained results when compared with WHO and USEPA standards show a very high concentration of some toxic metals.
Soils were basically polluted by Pb, Zn, Cu, and Cd. Bioavailable fraction of studied metals were also measured with
formation of metal complex with Diethylene tri amine penta acetic acid (DTPA) agent. To find the share of the anthro-
pogenic sources in the contamination of soils, the Enrichment factor (EF) and Geological Accumulation Index were
measured and the distribution maps were drawn using Arc GIS (9.3). Highest concentrations of some toxic metals were
found as isolated patches around the Bonab Industrial Town as well as within and around the most populated areas of
the district notably Zanjan city indicating its anthropogenic origin.
Keywords: Soil Pollution; Pedogeochemical; Anthropogenic; Heavy Metals; Zanjan-Iran
1. Introduction
Heavy metal contamination of soils is widespread and
there is a risk of transfer of toxic and available metals to
human, animals, and agricultural crops [1]. Heavy metals
are natural constituents of the Earth crust. A number of
these elements are biologically essential at trace levels
and play an important role in human health [2]. The po-
tential risk for the environment and population due to soil
heavy metals arising from metallic mining has been well
described [3]. Heavy metals can induce toxicity in wild-
life if the soil level reaches critical values; also plant ac-
cumulation in above-ground tissues can result in an in-
crease of metal accumulation in top-soil, via leaf deposi-
tion, or can create an exposure pathway for metal intro-
duction into the food chain [4]. In contrast with soils in
agricultural areas, soils in urban environment, particu-
larly in parks and gardens, have a direct influence on
public health not related with production of food. This is
due to that they come easily in contact with humans and
are transferred to them, either as suspended dust or by
direct contact [5]. Two main sources of heavy metals in
soils can be considered: 1) the natural pedo-geochemical
background, which represents the heavy metal concen-
tration inherited from the parent rock [6] and 2) anthro-
pogenic contamination, which can be directed via wastes,
animal manure [7], compost [8], sewage sludge [9], or
diffuse via aerosol deposition [10]
Angoran area of Zanjan province located in North
West of Iran has a large metalliferous site and has been
considered as a traditional mining region since antiquity.
There are still large reserves of lead (Pb) and zinc (Zn) in
the area. Both mines and smelting units in the province
present a risk of contamination of soils, plants, surface
and ground water by dissemination of the particles car-
rying metals by wind action and/or by runoff from the
tailings. Heavy metal contamination in Zanjan province
has also been previously reported in the vicinity of Lead
and Zinc mining and smelting sites [11,12]. The total
heavy metal contents can indicate the extent of contami-
nation, but is not usually an accurate indication of the
*Corresponding author.

Concentration, Distribution and Comparison of Total and Bioavailable Heavy Metals in Top Soils of
Bonab District in Zanjan Province
124
phyto-toxicity; so many latest studies investigated the
heavy metal fractions of mine soils [13] and evaluated
the phyto-toxic risk for human receptors. However, the
determination of heavy metal fractions is a more com-
plex task than the determination of the total contents of
heavy metals [14]. The main purpose of this research is
the measurement of the quantity of heavy metals existing
in top soils of the study area, the determination of the
rate of the bioavailable elements in top soil is also one of
the pillars of this research, since this part aside from pol-
luted or unpolluted the soils, show the absorption ability
of the plants.
2. Materials and Methods
2.1. The Study Site
In this study the Bonab district located near the city of
Zanjan was selected for detailed study. Soil samples were
collected from the studied area during second week of
October 2010 (Figure 1).
2.2. Sample Collection
Seventy two soil samples were collected through system-
atic random sampling (top 0 - 30 cm soil layer). The
study area was divided into a 4*4 km grid and samples
were collected from every corner of the grid. Based on
the information gathered through field trips and taking
into account the type of landuse and population concen-
tration, the numbers of samples were increased by subdi-
viding the grid in selected locations (2.2 km grid).
Soil samples were collect from the surface of the soil
(0 - 30 cm deep) and preserved by using the methods of
soil analysis [15]. From each sampling points, four soil
samples were gathered and mixed properly to obtain a
composite sample mixture. The soil sampling spots were
cleared of debris before sampling. Each composite soil
samples were placed in cellophane bags labeled then
taken to the laboratory for pre-treatment and analysis.
The sampling tools, were washed with soap and rinsed
with distilled water after each sampling [16].
2.3. Soil Analysis
In the laboratory, bulk soil samples were spread on trays
and were air dried at ambient conditions for two weeks.
The samples were then grounded by mortar and pestle,
sieved through a 2 mm mesh, and oven-dried at 50˚C for
about 48 hours. The samples were then stored in poly-
ethylene bags and re-homogenized before being used.
The soil samples were digested using the 11466 ISO
standard methods (the aqua regia digestion method) [17].
3 g of soil was placed in a 100 ml round bottom flask
with 21 ml of concentrated HCl (35%) and 7 ml concen-
trated HNO3 (65%). The solution was kept at room tem-
perature overnight before a water condenser was attached
and the solution heated to boiling point for 2 hours.
Added 25 ml water to the condenser before filtration of
the mixture through using a Whatman (No. 42) filter. The
filtered residue was rinsed twice with 5 ml of water and
the solution was made up to 100 ml. The bioavailable
content of metals were determined using Lindsey method
(Lindsay, 1978), 10 g of soil was added in 20 mL mix-
ture of 0.005 mol·L−1 DTPA and 0.01 mol·L−1 CaCl2 and
0.01 mol·L−1 triethylamine (pH 7.3), shaken for 2 h and
then filtered through using a Whatman (No. 42) filter.
Figure 1. Location map of the studied area indicating sampling points.

Concentration, Distribution and Comparison of Total and Bioavailable Heavy Metals in Top Soils of
Bonab District in Zanjan Province
125
The metals (Zn, Pb, Cu, Fe, Ni, Co and Cd,) in the soil
extracts were analyzed by Atomic Absorption Spectro-
metry (AAS). Three analytical replicates were measured
for each sample. Data with replicates were presented as
mean-standard error and difference test was made using
SPSS 14 software. The pH and EC (solid: distilled water
= 1:5) of the soil samples were also measured by with pH
and EC meters (Metrohm, Germany). Finally, using the
geostatistical methods with Arc GIS (9.3) the heavy me-
tal distribution maps were drawn.
3. Results and Discussion
Total Heavy Metal in Soils
Comparing the results with standard range, shows that
the concentrations of heavy metals Pb, Zn, Cu, Cd in the
studied area are higher than standards. Summary statis-
tics for the analyzed elements in all the studied samples
are presented in Table 1. Though, Cadmium has the low-
est mean concentration (1.49 mg/kg), it is well above the
maximum permissible limits given by all existing stan-
dards (Table 2). While the highest contents are for Fe
(66933.7 mg/kg), Pb, Zn, and Cd are also much higher
than standards and do not relate to the pedo geochemical
sources. These points out that Zinc industry are most
possibly the major anthropogenic source for the enrich-
ment of these heavy metals in the top soil. The extremely
high metal levels in tailings made them a potentially
hazardous source of soil contamination. Soil pH aver-
aged 7.78 (from 7.16 to 8.08) indicating a neutral to al-
kaline nature. Electrical conductivity (EC) in the samples
is quite variable ranging from 248 to 1721 µs·cm–1.
The concentration of the studied metals are in the or-
der of Fe > Zn > Cu > Pb > Ni > Co > Cd.
The bioavailable heavy metals [19] content in soil
samples are less than total metal content. With increasing
total heavy metal content in soils, the bioavalaible con-
tent of metals are also increase and there are a significant
correlation between them, (Table 3).
Figure 2 shows the concentration and distribution of
each metal within the studied area. Zinc concentration
(Figure 2(a)) is very high in Bonab industrial town and
its damping site located in the center of the studied area,
indicating its anthropogenic source. Lead is also found in
some localized areas with extremely high concentrations
among them the Bonab industrial town and its damping
area and can be related to Zanjan Zinc and Lead smelting
plant. Lead is also found in high concentration in Zanjan
city area which is mainly due to traffic and use of leaded
gasoline and also may by air borne (Figure 2(b)).
Table1. The nature of the soil samples and total metal concentrations in the top soil (mg·kg–1).
pH EC (µs·cm–1) Pb Zn Cd Cu Co Ni Fe
Avg. 7.80 491.1 58.18 299.31 1.4 67.68 18.53 28.11 66933.7
Max. 8.08 1721.0 615.3 13461.67 5.6 3106.6 41.97 69.20 157916.7
Min. 7.16 248.0 14.33 25.10 0.3 0.83 8.53 1.07 30950.0
Median 7.80 425.0 38.16 93.96 1. 3 20.65 18.87 25.85 61583.3
STDEV 0.17 251.9 91.42 1574.91 0.7 346.51 4.92 14.35 23102.9
Table 2. Metal concentrations were compared with existing standard (mg·kg–1) [18].
Standard Pb Zn Cd Cu Co Ni Fe
USEPA1 10 NR - 30 8 40 NR
GLC2 20 NR - NR NR 20 NR
WHO 20 50 0.3 4 19 68 47200
Average in the study area 58.18 299.311.4 67.68 18.53 28.11 66933.70
1United State Environmental Protection Agency; 2Great London Council.
Table 3. Bioavailable heavy metal content in the top soil (mg·kg–1).
Pb Zn Cd Cu Co Ni Fe
Avg. 4.68 2.00 0.15 1.92 0.32 0.59 6.88
Max. 71.00 10.50 1.04 13.30 1.01 2.57 38.2
Min 0.06 0.07 0.05 0.14 0.09 0.08 1.68
Median 2.80 1.21 0.10 1.48 0.26 0.49 5.47
STDEV 8.77 2.23 0.16 1.48 0.20 0.42 5.39

Concentration, Distribution and Comparison of Total and Bioavailable Heavy Metals in Top Soils of
Bonab District in Zanjan Province
126
Figure 2. Concentration & distribution of (a) Zn; (b) Pb; (c) Co; (d) Cu; (e) Cd; (f) Fe; (g) Ni.

Concentration, Distribution and Comparison of Total and Bioavailable Heavy Metals in Top Soils of
Bonab District in Zanjan Province
127
Significant correlation between concentration of Cu,
Co, and Fe in the north east of the studied area (Figures
2(c), (d) and (f)) are mainly natural pedo-geochemical
background and maybe related to the Zaker (Fe) mining
area .
Nickel is also found in high concentration in south east
of the area its high concentration may be related to agri-
cultural fertilizer used in the cultivated lands in this part
of the studied area (Figure 2(g)).
4. Enrichment Factor (EF)
A common approach to estimate how much the sediment
is impacted (naturally and anthropogenically) with heavy
metal is to calculate the Enrichment Factor (EF) for me-
tal concentrations above un-contaminated background
levels [20]. Pollution will be measured as the amount or
ratio of the sample metal enrichment above the concen-
tration present in the reference station or material [21,22].
The EF method normalizes the measured heavy metal
content with respect to a samples reference such as Fe,
Al or Zn [21]. The EF of a heavy metal in sediment can
be calculated with the following formula [20]:
metal normalizer
metal controlnormalizercontrol
CC
EF= CC
where Cmetal and Cnormalizer are the concentrations of heavy
metal and normalizer in sediment and in unpolluted soil.
Enrichment factor (EF) can be used to differentiate be-
tween the metals originating from anthropogenic activi-
ties and those from natural procedure, and to assess the
degree of anthropogenic influence. Five contamination
categories are recognized on the basis of the enrichment
factor as follows: [23].
EF < 2 is deficiency to minimal enrichment,
EF 2 - 5 is moderate enrichment,
EF 5 - 20 is significant enrichment,
EF 20 - 40 is very high enrichment,
EF > 40 is extremely high enrichment.
As the EF values increase, the contributions of the an-
thropogenic origins also show an increase [22]. Figure 3
shows the EF for heavy metals Cd (a), Pb (b), Cu (c), Co
(d), Zn (e), and Ni (f) in the study area.
5. Index of Geo-accumulation
Index of Geo-accumulation (Igeo) has been used widely
to evaluate the degree of metal contamination or pollu-
tion in terrestrial, aquatic and marine environment. The
Igeo of a metal in sediment can be calculated with the
fallowing formula [21]:
 metalmetal Control
Igeo log2C1.5C
where Cmetal is the concentration of the heavy metal in the
enriched sample and Cmetal(control) is the concentration of
the metal in the unpolluted or control sample. The factor
1.5 is introduced to minimize the effect of the possible
variations in the background or control values which may
be attributed to lithogenic variations in the sediment [21].
The degree of metal pollution is assessed in terms of
seven contamination classes based on the increasing nu-
merical value of the index as follows: [20].
Igeo < 0 = means unpolluted
0 ≤ Igeo < 1 means unpolluted to moderately polluted,
1 ≤ Igeo < 2 means moderately polluted,
2 ≤ Igeo < 3 means moderately to strongly polluted,
3 ≤ Igeo < 4 means strongly polluted,
4 ≤ Igeo < 5 means strongly to very strongly polluted,
Igeo ≥ 5 means very strongly polluted.
Figure 4 shows the Index of Geo-accumulation for
heavy metals Pb (a), Co (b), Cu (c), Fe (d), Zn (e), Cd (f)
and Ni (g) in the studied area.
6. Conclusions
72 soil samples were analyzed to determine the concen-
tration and distribution of heavy metals (Cd, Pb, Ni, Cu,
Co, Fe and Zn) in top soils of Bonab district in Zanjan-
Iran. Determination of bioavailability of heavy metal in
soils with DTPA method has been shown that by increas-
ing total amount of heavy metals in soil, the bioavailable
content of heavy metal also will show an increased. The
dispersion maps provided for lead shows that the most
concentration of lead is near the industries specially near
Iran Lead and Zinc Factory and also observed in the
Zanjan City so it is possible to conclude that the concen-
tration of lead in the soils of study area is related to in-
dustries on the other hand the pollution is because of
human activities.
According to the dispersion maps provided for nickel
and landuse map of study area it was observed that the
concentration of nickel has a direct relationship with
landuse in study area as such as the most concentration
of nickel existed in the agricultural lands confirm of the
study area which it is due to the over use of chemical
fertilizer in this area.
For Cd and Zn the maximum concentration observed
near the Iran Lead and Zinc Factory and industrial areas
but for the Fe, Cu, and Co heavy metals obviously ob-
served that the concentration of this metals in top soils is
just related to the structural geology and the rock kinds
of the study area as it was observed that the average of
Fe, Pb, Zn, Cu, and Cd in sequence in top soils are
66933.70, 58.18, 299.31, 67.68, 1.49 mg · k g –1 and the
average of this metals according to the WHO standard in
sequence are 47,200, 20, 50, 45, 0.3 mg·kg–1. This means
that the study area is polluted by these heavy metals. For
Co and Ni, the average concentrations in sequence are

Concentration, Distribution and Comparison of Total and Bioavailable Heavy Metals in Top Soils of
Bonab District in Zanjan Province
128

Concentration, Distribution and Comparison of Total and Bioavailable Heavy Metals in Top Soils of
Bonab District in Zanjan Province
129
Figure 3. Enrichment Factor (EF) for heavy metals Cd (a), Pb (b), Cu (c), Co (d), Zn (e), and Ni (f) in the study area.

Concentration, Distribution and Comparison of Total and Bioavailable Heavy Metals in Top Soils of
Bonab District in Zanjan Province
130

Concentration, Distribution and Comparison of Total and Bioavailable Heavy Metals in Top Soils of
Bonab District in Zanjan Province
131
Figure 4. Index of Geo-accumulation for heavy metals Pb (a), Co (b), Cu(c), Fe (d), Zn (e), Cd (f) and Ni (g) in the study area.
28.11 and 18.53 mg·kg–1 and the WHO standards for
these metals are 68 and 19 mg·kg–1 respectively.
The percentage of bioavilable metals to the total con-
centration of them for each studied metal are Fe 0.01%,
Cd 10.06%, Co 1.72%, Ni 2.04%, Cu 2.83%, Zn, 0.66%
and Pb 8.04%.
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