Geochemistry of Urban Soils in the Masjed-i-Soleiman (MIS) City, Khuzestan Province, Iran: Environmental Marks
The aim of this study was to assess and evaluation of
the amount and severity of heavy metal contamination of residential areas
soils of the Masjed-i-Soleiman (MIS) City, which located on a wide oil
field (Masjed-i-Soleiman (MIS) oil field) with abundant springs. The present
degree and spatial distribution of heavy metal concentrations in 25 topsoil
samples in the Masjed-i-Soleiman (MIS) were examined. Analytical determinations
were performed by XRF. Six metals, namely Co, Cr, Cu, Ni, Pb and Zn were
considered. The abundance of heavy metals measured in these soils decreases
as follows: Ni>Zn>Cr>Cu>Pb>Co. The major sources for Pb,
Cu, Zn and Cr contamination in Masjed-i-Soleiman (MIS) City are most possibly
emissions from vehicles and air conditioning coolants and Ni contamination
is hydrocarbon seepage. Total concentrations of Cr, Cu, Ni and Zn in some
soils exceed the background values. Direct ingestion of soil by children
and inhalation of contaminated windblown dust may contribute largely to
the accumulation of heavy metal in human.
Soil pollution of cities that located on oil fields is a major environmental
problem. The Masjed-i-Soleiman (MIS) is a City in Northeast Khuzestan
Province, Southwestern of Iran, located on Masjed-i-Soleiman (MIS) oil
field, which has many petroleum seepages and springs (asphalt, oil and
gas) with 14 active oil and gas wells. Continuous exploit of crude oil
and there are many hydrocarbon springs together in city with use of vehicles
leads to an increased pollution of soil and air and thus a growing risk
for heavy metal uptake by human. Heavy metals are extremely persistent
in the environment; they are non-biodegradable and non-thermo degradable
and thus readily accumulate to toxic levels.
Several researchers have indicated the need for a better understanding of urban
soil pollution (De Kimple and Morel, 2000; Manta
et al., 2002) and indeed, increasing research has focused on heavy
metals in urban soils (Kelly et al., 1996; Chen
et al., 1997; Mielke and Reagan, 1998). Heavy
metals in urban soils may come from various human activities, such as industrial
and energy production, construction, vehicle exhaust, as well as coal and fuel
combustion (Wong and Mak, 1997; Martin
et al., 1998; Li et al., 2001). These
activities send heavy metals into the air and the metals subsequently are deposited
into urban soil as the metal containing dust falls. Atmospheric deposition reflected
by high heavy metal concentrations in urban dust (Li et
al., 2001) is one of the main sources of heavy metal accumulation in
urban soils. Key heavy metals are thus; Pb from leaded gasoline, Cu, Zn and
Cd from car components, tire abrasion, lubricants and industrial and incinerator
emissions (Markus and McBratney, 1996; Thornton,
1991; Wilcke et al., 1998) and Cr from air
conditioning coolants. Sakagami et al. (1982) reported
that there was a close relationship between heavy metal concentrations in soils
and those in the dust falls. Heavy metals in the soils can also generate airborne
particles and dusts, which may affect the air environmental quality (Chen
et al., 1997; Bandhu et al., 2000;
Cyrys et al., 2003; Gray et
Urban soils especially that in residential areas which is not used for food
crops, may also have a direct influence on public health since it can be easily
transferred into human bodies (De Miguel et al., 1997;
Madrid et al., 2002). In particular, the ingestion
of dust and soil has been widely regarded as one of the key pathways by which
children are exposed to the heavy metals and metalloids from paint, leaded gasoline,
vehicles and local industry (Meyer et al., 1999;
Rasmussen et al., 2001). Contaminated soil can
be ingested directly by (Moller et al., 2005)
playing children. Most of the metals ingested by humans are excreted and only
small proportions are actually retained in the body tissues (Cameron
et al., 1997). Depending on duration and frequency of a potential
ingestion of soil, especially at polluted sites, the uptake of heavy metals
with soil can, however, result in serious health risks. Children at the age
between 1 and 8 are of specific concern for this pathway. The frequency of a
potential uptake varies for different regions depending on the climatic conditions
and cultural habits.
A further direct pathway of heavy metal uptake is inhalation. Especially
under the dry conditions found in Masjed-i-Soleiman (MIS) City with a
higher presents of dust in the urban atmosphere. This pathway can be important,
especially in summer-time. Therefore, the objective of the study were
to verify the concentrations and spatial distribution of heavy metals
(Co, Cr, Cu, Ni, Pb and Zn), to assess the heavy metal contamination in
the soils of the Masjed-i-Soleiman (MIS) City and to identify the risk
of heavy metal uptake by the population.
MATERIALS AND METHODS
Masjed-i-Soleiman (MIS) City, located in the Southwest of Iran, it
was a developed city during the oil exploration in the Middle East and
is an ancient city on history of Iran and less than 300 thousand urban
residents. Masjed-i-Soleiman (MIS) first city in Middle East in which
first oil well exploited petroleum, about 100 years ago. Nowadays, there
are more than 300 petroleum wells (oil and gas) in the suburbs, 14 of
them are exploiting. Also, in study area, there are approximately 17 main
area of seepages and springs of petroleum (Fig. 1).
The 7 area of them investigated in this study, which located in residential
The average precipitation is about 372 mm year-1. The main potential
evaporation is more than 1000 mm year-1. The soils in the study area
are almost deep, textured, with poorly drained, moderately alkaline pH, low
CaCO3 concentrations less than 35%, a very high electrical conductivity
(EC; Table 1). Pattern and density of the vegetation in the
study area are scattered and characterized by seasonal changes and raining.
Almost all known human activities and industries are related to petroleum industrial
in the Masjed-i-Soleiman (MIS) City. The texture of the soils is shown in Fig.
2. The cluster of points shows that the soil texture regularly classified
on sandy clay loam (Brady and Weil, 2001), which the average
ratio sand over clay is approximately 3.
|| Soil properties of the samples (0-25 cm, n = 25)
||Location of the study area, oil and gas indications
and sampling points
|| Ternary diagram of soil texture: each point represents
the value of the three size of grains for each soil sample (fine fraction
In summer 2007, 25 topsoil samples (0-25 cm depth) were sampled in the study
area (Fig. 1). Topsoil samples were sampled from residential
area, around active oil wells and hydrocarbon seepage area. Soil samples were
air dried, crushed and passed through 2 mm mesh sieve and stored at ambient
temperature before analysis of soil properties and concentrations of heavy metals.
Twenty-five samples of urban soil were analyzed for major and trace elements
by XRF (Philips PW2400, equipped with a Rh-tube) using fused borate glass beads
at the Binalood Kansaran laboratory, Pardis Science and Technology Park, Tehran,
Iran. The detection limit for the major oxides is about 0.01 wt.% but it varies
for trace elements (in ppm): Nb (1); Th and Rb (2); Y and Ni (3); Cr, V and
Zr (4); Sr (5) and Ba (10). The particle size distribution was determined by
hydrometer (Richards, 1954). Cation exchange capacity was
measured according to Richards (1954). Calcium carbonate
was measured volumetrically using the Scheibler apparatus and Hg-manometer.
Electrical conductivity was determined in the saturation extract and pH in H2O
1:5 (w/v) by electrode, following Jackson (1958).
RESULTS AND DISCUSSION
Heavy Metal Concentrations
There is no information available on typical background values for Iranian
soils or heavy metal concentrations in soils of other cities of the Iran. So,
the data were compared with available background values (median) of European
soils (Utermann et al., 2004), threshold values provided by Eikmann
and Kloke (1993) and Kloke (1993) and heavy metal concentrations established
in soils of cities from other regions. The median Cr, Cu and Ni concentrations
are located at the upper range of background values, while the Pb and Zn concentrations
are located at lower end. In all of the soils samples, the contents of Cr, Cu
and Ni exceed the threshold values for multifunctional land use (Eikmann
and Kloke, 1993). In all of the samples Ni exceed slightly the to lerable
values of soil for agricultural use (Kloke, 1993). In 83% of the topsoils samples
the Cu concentration exceeds the threshold of natural background in China (NEPAC,
1995). In 32% of soil samples collected the Ni concentration and all of them,
exceeds the world range in non-polluted (Kabata-Pendias and
Pendias, 1992) and standard value (Rademacher, 2003;
Table 2), respectively. The threshold values may not be directly
transferable to Iranian soils, but give a first idea of their heavy metal status.
Taking into account the high metal binding capacity of the soils the elevated
heavy metal values in some points of study area do not represent an immediate
risk for grown agricultural production in residential area.
Comparing the results with results from other cities, especially old and developed
cities like London (Culbard et al., 1991
) and Palermo (Manta et
) these cities show higher concentrations of heavy metals in
their topsoils. Similar results with comparable or lower heavy metal concentrations
were found for younger cities like Bangkok (Wilcke et al.,
) or Hong Kong (Li et al., 2001
) and old
cities but non- industrialized like Damascus (Moller et
). Li et al. (2001)
important relation between the Cu, Pb and Zn concentrations in the urban park
soils and the age of the parks. Though Masjed-i-Soleiman (MIS) is one of the small
cities of the Iran, there is petroleum industrial, load traffic and high temperate
weather thus pollution took place at a relatively upper stage compared to other
industrialized cities. Therefore, the today`s comparatively k- high concentrations
of heavy metals in the soils in Masjed-i-Soleiman (MIS) could be the result of
the relationship between major accumulation rates in minor time.
Though, it should be mentioned that in this study only residential soils
with a sampling depth of 0-25 cm were collected, while in the other studies
soils from 0-5 or 0-10 cm with different land use were collected. Also,
different extraction methods were used (Table 2).
|| Range and median of heavy metal contents in topsoils
of the several cities and literature data for comparison
Thus, relative dilution, diverging extraction efficiency depending on
the extraction method used, as well as sampling of soils in more areas
next to streets and seepage areas may be an additional reason for major
concentrations of heavy metals in soils of study area.
aCulbard et al. (1991): Garden
soils and in brackets public garden soils (0 â€“ 5 cm, n = 654 (35); concentrated
HNO3 and HClO4)).
bLu (1993): Surface soils (0- 5 cm, n = 977; powder
cManta et al. (2002): Topsoils
(0-10 cm, n = 50; powder X-ray diffraction).
dMoller et al. (2005): Topsoils
(0-25 cm, n = 5 1, aqua regia extraction).
eWilcke et al. (1998): Topsoils
(0-5 cm, n = 30; sequential extraction.
fUtermann et al. (2004): Range of heavy metal
background values (medians) of European soils from calcareous rocks and
clayey materials (aqua regia extraction).
gEikmann and Kloke (1993): Limit values
based on aqua regia extraction for multiple land use (Germany).
hKloke (1993): Tolerable aqua regia extractable metal
values for arable land (Germany).
INational Environmental Protection Agency of China
jKabata-Pendias and Pendias (1992).
kFrom European norms (Rademacher, UN/ECE; 2003).
Cobalt concentration in the soils did not differ in the soils of across of
study area. So, suggesting that concentration of Co in the soils is conquered
by the parent material, as anthropogenic emissions of this heavy metal is relatively
rare especially for Co. Cu, Pb and Zn are a group of heavy metals which are
commonly found to be anthropogenic enriched in the topsoils of urban environments
(Moller et al., 2005; Culbard
et al., 1991; Lux, 1986; Manta
et al., 2002). Cr and especially Ni are high in topsoils of Masjed-i-Soleiman
(MIS) City. This reflects anthropogenic and geogenic (hydrocarbon) sources.
Spatial Distribution of Pb, Cu and Zn
The three metals show similar spatial distributions within the study area
which is in agreement with a similar study of Kelly et
al. (1996) and Moller et al. ( 2005) for
urban soils in Britain and Damascus in Syria. The distributions of these metals
clearly reveal polluted area with increased values. The soils within the city
of Masjed-i-Soleiman (MIS) show significantly increased concentrations compared
to the rest of the soils studied in around of city. Li et
al. (2001) found higher Zn concentrations in the street dust of Hong
Kong compared to a similar study in London (Thornton, 1991).
He stated that based on the high temperatures in the tropical environment abrasion
of car tires would be increased, as Zn is used as a vulcanization agent in vehicle
tires. Cu is often a component in car lubricants, while leaded gasoline, in
Iran used up to now, is the major source for Pb in the urban environment. This
point out that traffic is most possibly the major source for the enrichment
of these heavy metals in the topsoils of Masjed-i-Soleiman (MIS) City.
Spatial Distribution of Cr
The spatial distribution of Cr differs considerably from those of
Pb, Cu and Zn. In the through topsoil of Masjed-i-Soleiman (MIS) the significantly
increased Cr concentrations were found. Seem one of Cr polluter sources
in study area, there is in air conditioning coolants. Though, there is
high temperature weather in Masjed-i-Soleiman (MIS) in during year (almost
10 months), use continuous by air condition almost in all houses, cause
increasing concentration of Cr in air and soil.
Spatial Distribution of Ni
The distribution of Ni clearly reveals polluted areas with increased
values. The soils within the hydrocarbon seepage areas show increased
concentrations compared to the rest of the soils studied in Masjed- Suleiman
City. Note to be Ni in petroleum, to be hydrocarbon springs within the
Masjed-i-Soleiman (MIS) City, caused transfer Ni from petroleum to soil.
Heavy Metal Uptake
The soil properties found in the study area like moderate alkaline
pH, low clay and CaCO3 content do not indicate a significant
bioavailability and mobility of heavy metals, as well as the translocation
of contaminants through mobile colloids in these soils. About the health
risks of the inhabitants other pathways of heavy metal uptake like direct
ingestion and inhalation of dust may be more important. For the area near
by the hydrocarbon seepage areas and springs, the Ni concentration in
the soil is obviously over threshold values for the ingestion pathway
at playground. Surely, the area is not considered to be a playground;
however, many children are playing near the polluted areas. Also, the
residues from the petroleum wells emissions contain Ni, which have a high
potential by inhalation to contribute largely to these metals together
with Zn and Cu accumulation in humans, especially during the summer month
where the dispersal of dust in the ambiance is very high.
||The abundance of heavy metals measured in topsoils decreases as
follows: Ni>Zn>Cr >Cu>Pb>Co
||The results show the anthropogenic impact on Cu and Zn concentrations
in the topsoils of the Masjed-i-Soleiman (MIS) City
||The highest value of Ni can be established in the Masjed-i-Soleiman
(MIS) Masjed-i-Soleiman (MIS) City, nearby hydrocarbon seepages and
||Traffic in Masjed-i-Soleiman (MIS) as a major pollution source has
a high potential for the decrease of Cu and Zn pollution in the future
||The Cr pollution found in through the topsoils and Ni pollution
found near hydrocarbon seepages and springs are potentially serious
even taking into account the immobility of Cr in soil
||With regards to health risks, bioavailability and mobility of heavy
metals can be stated to be of minor significant in these soils. Other
pathways like inhalation of dust and direct ingestion seem to be more
important for the heavy metal uptake by the population of Masjed-i-Soleiman
The first author want to acknowledge the financial support of the Islamic
Azad University, Masjed-i-Soleiman (MIS) Branch to the project distribution
of heavy metals in urban soils of Masjed-i-Soleiman (MIS) under contract
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