HEAVY METAL CONTAMINATION AND ACCUMULATION IN SOIL AND WILD PLANT SPECIES FROM INDUSTRIAL AREA OF ISLAMABAD, PAKISTAN
ABSTRACT This study was designed to assess total contents of 6 toxic metals viz., Pb, Cu, Zn, Co, Ni, and Cr in the soil and plant samples of 16 plant species collected from industrial zone of Islamabad, Pakistan. The concentration, transfer and accumulation of metals from soil to roots and shoots was evaluated in terms of Biological Concentration Factor (BCF), Translocation Factor (TF) and Bioaccumulation Coefficient (BAC). Total metal concentrations of Pb, Zn, Cu, Co, Ni, and Cr in soils varied between 2.0-29.0, 61.9-172.6, 8.9 to 357.4, 7.3-24.7, 41.4-59.3, and 40.2-927.2 mg/kg. Total metal concentrations pattern in roots were: Cu>Cr>Zn>Ni>Pb>Co. Grasses showed relatively higher total Zn concentration. Accumulation of Cu was highest in shoots followed by Zn, Cr, Pb, Co and Ni. None of plant species were identified as hyperaccumulator; however, based on BCFs, TFs, and BACs values, most of the studied species have potential for phytostabilization and phytoextraction. Parthenium hysterophoirus L., and Amaranthus viridis L., is suggested for phytoextraction of Pb and Ni, whereas, Partulaca oleracea L., Brachiaria reptans (L.) Gard. & Hubb., Solanum nigrum L., and Xanthium stromarium L., for phytostabilization of soils contaminated with Pb and Cu.
- SourceAvailable from: Jabbar Kadhium Kassim[Show abstract] [Hide abstract]
ABSTRACT: Metal rich soils derived mainlyfrom ultramafic (i.e. serpentinitic soils) are wide spread over Penjwin (Mlakawa) area. Three serpentinitic (S1, S2, S3) with one non-serpentinitic soils (S4) were used and these soils contain high concentrations of heavy metals such as Ni, Cr, Co and Mn. Results showed that total metal concentration ranged between 192.0 -1714.8 mg kg -1 , 289.0 -1264.2 mg kg -1 , 128.8-177.6 mg kg -1 and 4125-4795 mg kg -1 respectively, while after harvesting plants (wheat and grass) in the biological pots (CRD) experiment. The concentration of the total and potentially available metals Ni, Cr, Co and Mn decreased in the grass and wheat soil pots. But The CaCl 2 -extractable and water –soluble metals increased in soils after harvesting the wheat and grass except for Co which decreased. In wheat and grass plants (wheat Triticum aestivum and canarygrass Phalaris canariensis), the uptake of Ni and Cr metals for soil S1 were above the normal range and the values were 14.47 mg Ni pot -1 and 6.6 mg Cr pot -1 . The concentrations of both Ni and Cr metals were found to be at the toxic level. While Ni in other soil samples was observed within the normal range and tolerance limits, but Cr, in the other soil samples, was above the tolerance level and was slightly less than toxic level. Wheat could take up highest amounts of toxic metals when grown in serpentine soils. The study showed that none of plants (wheat and grass) were identified as hyperaccumulator.
Dataset: 315 pdf
Pak. J. Bot., 42(1): 291-301, 2010.
HEAVY METAL CONTAMINATION AND ACCUMULATION IN
SOIL AND WILD PLANT SPECIES FROM INDUSTRIAL
AREA OF ISLAMABAD, PAKISTAN
RIFFAT NASEEM MALIK1, SYED ZAHOOR HUSAIN1 AND ISHFAQ NAZIR1
1Environmental Biology Laboratory,
Department of Plant Sciences, Quaid-i-Azam University, Islamabad, Pakistan.
This study was designed to assess total contents of 6 toxic metals viz., Pb, Cu, Zn, Co, Ni, and
Cr in the soil and plant samples of 16 plant species collected from industrial zone of Islamabad,
Pakistan. The concentration, transfer and accumulation of metals from soil to roots and shoots was
evaluated in terms of Biological Concentration Factor (BCF), Translocation Factor (TF) and
Bioaccumulation Coefficient (BAC). Total metal concentrations of Pb, Zn, Cu, Co, Ni, and Cr in
soils varied between 2.0-29.0, 61.9-172.6, 8.9 to 357.4, 7.3-24.7, 41.4-59.3, and 40.2-927.2 mg/kg.
Total metal concentrations pattern in roots were: Cu>Cr>Zn>Ni>Pb>Co. Grasses showed relatively
higher total Zn concentration. Accumulation of Cu was highest in shoots followed by Zn, Cr, Pb,
Co and Ni. None of plant species were identified as hyperaccumulator; however, based on BCFs,
TFs, and BACs values, most of the studied species have potential for phytostabilization and
phytoextraction. Parthenium hysterophoirus L., and Amaranthus viridis L., is suggested for
phytoextraction of Pb and Ni, whereas, Partulaca oleracea L., Brachiaria reptans (L.) Gard. &
Hubb., Solanum nigrum L., and Xanthium stromarium L., for phytostabilization of soils
contaminated with Pb and Cu.
Phytoremediation is one of the promising methods for reclamation of soils
contaminated with toxic metals by using hyperaccumulator plants (Baker et al., 2000;
Ghosh & Singh, 2005; La’zaro et al., 2006). More than 400 plant species belonging to 45
plant families have been identified and reported from temperate to tropical regions with
the ability to tolerate and hyperaccumulate trace elements (Baker & Brooks, 1989). These
plants have been considered suitable for soil stabilization and extraction of heavy metals
(Madejon et al., 2002). Hyperaccumulator plants can play a key role in the fate of the
pollutants of contaminated matrixes via their root systems.
The use of plant species to decontaminate and remediate polluted soils with heavy
metals is non-existence in Pakistan. Transfer of toxic elements from soils to plants in
industrial areas is of great concern (Malik & Hussain 2006). To our knowledge there has
not been any study that has identified heavy metal accumulator or tolerant plant species
from contaminated soils. In this study, 16 plant species belonging to 11 families were
investigated for metals such as lead, zinc, nickel, copper, cobalt and chromium from
industrial zone of Islamabad. The aim of the present study was to assess the total metal
concentration of selected metals in the soils and plant samples. Species which have the
potential for phytoremediation process such as phytostabilization and phytoextraction
were also identified.
RIFFAT NASEEM MALIK ET AL.,
Fig. 1. Location of study showing study site.
Materials and Methods
Industrial zone of Islamabad city, the capital of Pakistan was established in 1963 and
lies between 33°-28' and 33°-58' north latitude and 72°–48' and 73°–22' east longitude at
an elevation of 480-550m (a.s.l). It houses more than 200 different industrial units which
spreads over 625 acres of land. Plants growing in the nearby zone of industrial areas
along various industrial units exhibiting increased concentrations of heavy metals,
serving in many cases as biomonitors/accumulators of pollution load. Six sites were
selected for the collection of plant and soil samples (Fig. 1).
Plant species collected were the most common/dominant species at these sites. A total
of 16 species such as Amaranthus viridis L., Brachiaria reptans (L.) Gard. & Hubb.,
Cannabis sativa L., Cenchrus pennisetiformis Hochst. and Steud. ex Steud., Chenopodium
album L., Cynodon dactylon (L.) Pers., Cyprus rotundus L., Dactyloctenium aegyptium (L.)
P. Beauv., Elusine indica (L.) Gaerth., Ipomoea hederacea Jacq., Malvastrum
coromandelianum (Linn.) Garcke., Parthenium hysterophoirus L., Partulaca oleracea L.,
Ricinus communis L., Solanum nigrum L., and Xanthium stromarium L., were collected in
August and September in 2006. A total of 6-10 plant samples including roots, stems and
leaves of each species were collected from each site and mixed to form a composite sample,
placed in labelled bags and transported to Environmental Biology Laboratory for further
analysis. Before analysis, from each plant roots and mixture of stems and leaves were
carefully removed and washed (for 2-3 minutes approximately) with tap water and with
deionized water (Behropur B25) to remove any soil and surface dust. Plant samples were
dried at room temperature for two weeks, pulverized and passed through 2mm stainless
steel sieve. Soil samples (3–5 replicates), at 0–20 cm depth from rhizosphere of each plant,
HEAVY METAL IN SOIL AND WILD PLANT FROM INDUSTRIAL AREA
were taken from each site from where plant sample was rooted. Soil samples (a composite
mixture) were air dried at room temperature for two weeks, crushed and pulverised to pass
through 2-mm sieve. For each soil sample, soil pH, TDS, EC, texture and heavy metals viz.,
Pb, Cu, Zn, Co, Ni and Cr were measured. Soil pH was determined using portable pH meter
(Thermo Orien 240A) in a 1:2.5 soil–water suspension. Total Dissolved Solids and EC was
measured using conductivity meter (Hi 8033 Hanna Hungry). The proportion of percent
sand, silt and clay of the soil samples were calculated to determine soil textural class using
Bouycous hydrometer method. Acid digests of each soil sample were prepared using
USEPA 3051A (1998) method. Digestion of soil samples were carried out by nitric acid
(69% purity) and hydrochloric acid (28% purity). Soil sample measuring 0.5g (10: 3v/v)
and 2 g (10:3-5, v/v) of plant sample was digested in a mixture of concentrated nitric acid
and hydrochloric acid for 30 minutes using Microwave Accelerated Reaction System
(MARS, CEM®). Soil and plant sample digests were used to measure total concentration of
Pb, Cu, Zn, Co, Ni and Cr using a Fast Sequential Atomic Absorption Spectrometer (Varian
240AA FS). Standard Reference Material (SRM) of National Institute and Technology
(NIST, 2709 San Joaquin Soil and 1547Peach leaves) and internal reference materials were
used for precision, quality assurance and control (QA/QC) for selected metal
measurements. Average values of three replicates were taken for each determination. The
precision of analytical procedures was expressed as Relative Standard Deviation (RSD)
which ranged from 5-10% and was calculated from the standard deviation divided by the
mean. The recovery rates of studied metals were within 90±10%. Chemicals, stock
solutions and reagents were obtained from Sigma/Fluka/Merck and were of analytical
grade. All glassware before use were washed with distilled water, soaked in nitric acid
(30%) overnight, rinsed in deionized water and air-dried.
Biological Concentration Factor (BCF) was calculated as metal concentration ratio
of plant roots to soil given in equation 1 (Yoon et al., 2006). Translocation Factor (TF)
was described as ratio of heavy metals in plant shoot to that in plant root given in
equation 2 (Cui et al., 2007; Li et al., 2007). Biological Accumulation Coefficient (BAC)
was calculated as ratio of heavy metal in shoots to that in soil given in equation 3 (Li et
al., 2007; Cui et al., 2007).
Site 1 was sandy loam with pH of 8.4, EC of 1.8 mS/cm and TDS 120 ppm. Soil of
three sites viz., 2, 5 and 6 was loamy sand and was a dominant soil texture class with pH
varied from 7.8-8.5, EC ranged between 0.11-0.12 mS/cm and TDS varied between 70-80
ppm. Sites 3 and 4 were characterised by sandy clay loam, the second dominant soil texture
class with average pH of 8.45, EC 0.09 mS/cm and TDS 60 ppm. Higher concentration of
Zn was found at site 4 followed by site 3 and site 1. Maximum contents of Cr was present at
site 1 which was 927.2 (mg/kg) and minimum concentration was observed at site 5 (40.24
mg/kg). Total Pb concentration varied from 2.0–29.0 (mg/kg) whereas Co contents ranged
) 1 ( BCF
) 2 ( TF
) 3 (
RIFFAT NASEEM MALIK ET AL.,
from 7.26-24.73 (mg/kg) at site 2 and 3 respectively. Total concentration of Cu was found
between 8.88-357.40 mg/kg at site 3 and 2. Maximum total content of Ni was recorded at
site 2 (57.5 mg/kg) and minimum at site 4 (41.4 mg/kg).
Total concentration of selected metals in plants roots and shoots is given in Table 1.
In plant roots, the Cu total concentration was highest in C. pennisetiformis (416.9 mg/kg)
and lowest in D. aegyptium (7.5 mg/kg). In general total Cu concentrations in all plant
samples were greater in roots than shoots. Total Pb concentration in roots ranged between
1.0 mg/kg and 43.0 mg/kg in P. hysterophoirus and A. viridis whereas Zn total
concentration varied between 18.5 mg/kg in M. coromandelianum and 135.1 mg/kg in A.
viridis. Among plant species with higher Zn concentration, grasses showed relatively
higher contents. Highest concentration was found in E. indica (117.9 mg/kg) followed by
C. pennisetiformis (113.7 mg/kg), D. aegyptium (112.2 mg/kg) and C. dactylon (52.2 mg/
kg), respectively. Total Co contents in roots varied between 7.1 mg/kg in E. indica and
39.5 mg/kg in P. oleracea. Similarly, C. rotundus also had higher concentration of Co in
roots. Cr concentration varied between 8.8 mg/kg in A. viridis and 184.3 mg/kg in C.
pennisetiformis. In addition to C. pennisetiformis, R. communis also contained higher
concentration of Cr.
The results indicated that accumulation of Pb, Cu, Zn, Ni, Co and Cr in none of the
shoots of the plant species studied was more than 1000 mg/kg, however, it varied greatly
among plants species and from different sites. Total Cu concentration in shoots varied
significantly between plant species. Minimum contents were found in C. rotundus (3.4
mg/kg) and maximum in P. oleracea (171.8 mg/kg). Total Zn contents ranged between
17.3 mg/kg and 135.3 mg/kg in M. coromandelianum and A. viridis, respectively whereas
S. nigrum and P. oleracea had minimum of 11.0 mg/kg and C. dactylon had maximum of
41.0 mg/kg of Pb concentration in their shoots. Total concentration of Ni, Co and Cr
ranged between 6.2-18.3 mg/kg, 9.5–24.6 mg/kg and 2.1–76.9 mg/kg, respectively.
Most of plant species had BCF or TF>1, although the concentration of heavy metals
remained below 1000 mg/kg. In general, BCF values of Cu and Pb was highest as
compared to other metals (Table 2). The BCF values of P. oleracea, S. nigrum and X.
stromarium was highest for Cu (25.4, 14.8 and 14.2) and B. reptans for Pb (18.5). A.
viridis, C. sativa, C. album, C. dactylon, D. aegyptium, M. coromandelianum had BCF>1
for Pb and I. hederacea, P. oleracea, and X. stromarium had BCF >1 only for Cu. C.
rotundus had BCF>1 for Zn and Pb (1.2 and 2.5). B. reptans, C. pennisetiformis, E.
indica and S. nigrum had BCF>1 for three heavy metals (Pb, Cu and Zn). B. reptans had
BCF values of 1.3, 2.2 and 18.5 for Cu, Zn and Pb, C. pennisetiformis had BCF values of
1.0, 1.2, and 1.3 for Zn, Cu and Pb, and S. nigrum had BCF values of 1.0, 1.7 and 14.8.
None of plant species had BCF >1 for Ni, Cu and Cr, respectively.
Among the plant species screened for Pb, Cu, Zn, Ni, Co and Cr, most of the species
were efficient to take up and translocate more that one heavy metal from roots to shoots
(Table 2). Variations between TF values were found (Table 2). The highest TF value was
found for P. hysterophoirus and A. viridis were 23.0 for Pb and 20.7 for Ni. P.
hysterophoirus was efficient in translocateing metals such as Pb, Cu, Ni, Zn, Cr, and Cu
from roots to shoots at site 1 and 2. P. oleracea had translocated metals such as Pb, Zn,
Ni, and Co. A. viridis showed TF>1 for Pb, Zn, Ni, Co and Cr. Plant species such as B.
reptans, C. sativa, C. pennisetiformis, C. album, I. hederacea, M. coromandelianum and
R. communis and X. stromarium showed TF>1 for Zn and Cr, Pb and Zn, Pb and Co, Zn
and Co, Pb and Ni, Co and Cr, and Pb and Ni respectively. C. dactylon, C. rotundus, D.
aegyptium, E. indica and S. nigrum also showed TF>1 for one metal (Table 2).
HEAVY METAL IN SOIL AND WILD PLANT FROM INDUSTRIAL AREA
RIFFAT NASEEM MALIK ET AL.,
HEAVY METAL IN SOIL AND WILD PLANT FROM INDUSTRIAL AREA
Table 2 indicated the all plant species screened for total metal concentration showed
value of BAF>1 for one or more heavy metals except Ni and Cr where it varied between
0.11-0.40 and 0.02-0.56. Six species such as A. viridis, C. pennisetiformis, M.
coromandelianum, P. hysterophoirus, P. oleracea and R. communis had BAC>3. BAC
values for Pb and Co was >1 for most of species whereas the BAC values of two species
such as B. reptans and E. indica were >1 for Zn which were 2.2 and 1.2 respectively.
Highest BAC value of Pb was found for B. reptans (14.0) and C. dactylon (4.6). P.
oleracea showed highest BAC value for Cu. BAC value for Co was highest for M.
Accumulation of selected metals varied greatly among plants species and uptake of
an element by a plant is primarily dependent on the plant species, its inherent controls,
and the soil quality (Chunilall et al., 2005). Large number of factors control metal
accumulation and bioavailability associated with soil and climatic conditions, plant
genotype and agronomic management, including: active/passive transfer processes,
sequestration and speciation, redox states, the type of plant root system and the response
of plants to elements in relation to seasonal cycles (Kabata-Pendias & Pendias, 1984).
Structure of the sediment has also been considered very important that affect the extent of
the metals taken up by the plants. Clay particles also play an important role in availability
of the metals. Metal solubility in soils is predominantly controlled by pH, amount of
metals cations exchange capacity, organic carbon content and oxidation state of the
system (Ghosh & Singh, 2005). The results indicated that soils of study area were sandy
clay loam, loamy sand and sandy loam and were basic in nature with pH greater than 7.5
with low EC and TDS. Higher pH values may result in greater retention of metals and
their lower solubility in the soils of study area. High soil pH can stabilize soil toxic
elements, resulting in decreased leaching effects of the soils toxic elements. Moreover,
toxic elements may also become stabilized due to high soil pH which may result in less
element concentrations in the soil solution. This may restrain the absorbability of the
elements from the soil solution and translocation into plant tissues (Liu et al., 2005).
The results showed that most of plant species accumulated higher concentration of
Pb, Cu and Zn than normal limits in shoots. The normal level in shoots of plants for Pb,
Cu and Zn as given by Zu et al., (2004) are 5, 10 and 100 mg/kg. Zn, Cu and Co are
essential to plant growth and needed in small (micro) quantities, however, their excessive
concentration in plant tissues may cause toxic symptoms. Cu concentration >40 mg/kg of
dry matter could induce toxicity in plants and cause toxic effects in animals (i.e. sheep)
feeding on them (Annenkov, 1982). These nutrients are vital physiologically and are
important constituents of enzymes thus critical for number of plant functions and health.
The availability of micronutrients to plants is dependent on many soil characteristics. Soil
pH plays important role in micronutrients availability to the plants which is greatly
reduced at higher pH. Thus, higher values of pH in this study played an essential role in
availability of micronutrients to plants. Total concentration of Cu in shoots of A. viridis,
C. sativa, C. pennisetiformis, E. indica, I. hederacea, M. coromandelianum, P.
hysterophoirus, P. oleracea, R. communis, S. nigrum and X. stromarium was greater than
normal limit. Cui et al., (2007) reported total concentration of 101.9 mg/kg and 97.0
mg/kg of Pb, 104.7 mg/ kg, 154.9 mg/kg of Zn and 27.7 mg/kg and 28.1 mg/kg of Cu in
roots and shoots of Chenopodium accuminatum Willd. In the present study, total
RIFFAT NASEEM MALIK ET AL.,
concentration of Cu in shoots and roots and of C. album were 5.1 mg/kg and 13.9 mg/kg
which were lower in comparison to study of Cui et al., (2007) in C. accuminatum.
Similarly, the total concentration of Pb and Zn in shoots and roots of C. album was also
less than Cu concentration in shoots and roots of C. accuminatum (Cui et al., 2007).
Plants varied widely in their tolerance and toxicity to Cu which may cause chlorosis. The
availability of Cu+2 in soil is generally linked with soil pH, texture, and interactions with
other nutrients. Increased soil pH may also reduce the availability of Cu+2 to plants
through increased adsorption at cation exchange sites. Leached podzolic sands and
calcareous sands tend to have lower levels of Cu+2. In the present study, total Pb
concentration in shoots of all plant species was well above normal limit of 5 mg/kg and
ranged between 11.0 to 39.0 mg/kg thus could have toxic effects on photosynthetic
activity of plants. Total of Zn content in B. reptans also exceeded normal level of Zn in
shoots. In non-tolerant plants, Zn toxicity is apparent in soils with high Zn content which
could effect inhibition of root elongation and chlorosis of young leaves. Soil pH, soil
organic matter and soil hydrology primarily govern the availability of Zn+2. High pH may
result in Zn precipitation as ZnFe2O4 or ZnSiO4 which become unavailable for plant
uptake. Soil organic matter can either increase or decrease the availability of Zn+2 by
binding it or increasing its mobility. Presence of plant species in the study area with high
level of Cu, Zn and Pb in shoots above the normal limits suggested their adaptation to
contaminated soils and possibly has developed mechanism for metal detoxification
(Ghosh & Singh, 2005).
TF, BCF and BAC values >1 had been used to evaluate the potential of plant species
for phytoextraction and phytostabilization (Yoon et al., 2006; Li et al., 2007). The results
indicated that P. hysterophoirus and A. viridis had highest TF values for Pb (23.0) and Ni
(20.7). High root to shoot translocation of these metals indicated that these plants have
vital characteristics to be used in phyto-extraction of these metals as indicated by Ghosh
& Singh (2005) and La´zaro et al., (2006). Plant species with slow plant growth, shallow
root system and small biomass production are not generally preferred for
phytoremediation. These two species had high biomass and based on high TF values
could have enormous potential to be used for phyto-extraction of Pb and Ni than other
species which also showed TF>1 for different metals. A sequence of decreasing TF
values: Pb>Ni>Co>Cr>Zn and >Cu was found for plant species. It is easy for plants
species with TF>1 to translocate metals from roots to shoots than those which restrict
metals in their roots. High metal accumulation may be attributed to well develop
detoxification mechanism based on sequestration of heavy metal ions in vacuoles, by
binding them on appropriate ligands such as organic acids, proteins and peptides in the
presence of enzymes that can function at high level of metalicions (Cui et al., 2007) and
metal exclusion strategies of plant species (Ghosh & Singh, 2005). Plant species with
high TF values were considered suitable for phytoextraction generally requires
translocation of heavy metals in easily harvestable plant parts i.e. shoots (Yoon et al.,
2006). According to Ghosh & Singh (2005) phyto-extraction is a process to remove the
contamination from soil without destroying soil structure and fertility. The results
highlighted that number of plant species had TF>1 for Pb and Ni in comparison to other
metals in particular Cu which was only accumulated in P. hysterophoirus with TF value
of 1.9. The results showed that it was easy for P. hysterophoirus and P. oleracea to
translocate five (Pb, Cu, Zn, Ni and Cr) and four (Pb, Zn, Ni and Co) metals from roots to
shoots. TF value for C. album varied between 1.0-1.3 for Pb, Zn and Co. The TF values
for C. album were lower (>1) for Cu compared to TF value for Cu of C. accuminatum
HEAVY METAL IN SOIL AND WILD PLANT FROM INDUSTRIAL AREA
which was >1 (Cui et al., 2007). B. reptans (Zn and Cr), C. sativa (Pb and Zn), C.
pennisetiformis (Pb and Co), I. hederacea (Pb and Ni), M. coromandelianum (Co and Cr)
and R. communis (Pb and Ni) had TF values >1 for two heavy metals. Cui et al., (2007)
found TF values >1 of Zn for S. nigrum whereas in the present study TF value was 0.4
which was lower than values indicated by Cui et al., (2007). Similarly, Li et al., (2007)
reported TF values <1 for Solanum bigeminatum. Cui et al., (2007) considered C.
accuminatum as an appropriate species for Cu, Cd and S. nigrum for Zn and Cd
extraction to remediate polluted soils. The species which have ability of to tolerate and
accumulate heavy metals may be useful for phyto-stabilization and phyto-extraction
(Yoon et al., 2006). However, based on the present results S. nigrum is not suitable for
phytoextraction as it has TF<1 whereas C. album can be considered for phytoextraction
for Pb, Zn and Co. Although, Del-Río-Celestino et al., (2006) considered C. album
suitable for phytoextraction of Pb contaminated soils based on TF values. TF value of Ni
for S. nigrum was >1 indicating its potential for phytoextraction.
Phyto-stabilisation is a process which depends on roots ability to limit the
contaminant mobility and bio-availability in the soils which occurs through the sorption,
precipitation, complexation or metal valance reduction (Ghosh & Singh, 2005). Heavy
metals tolerant species with high BCF and low TF can be used for phyto-stabilisation of
contaminated soils. Species such as B. reptans, S. nigrum P. oleracea and X. stromarium
showed very high BCF values (18.5 for Pb, 14.8, 25.4 for Cu; 14.2 for Cu) indicating that
these species retains metals in their roots and limit metal mobility from roots to shoots
once absorbed by roots of plants (Cui et al., 2007). The elevated concentration of heavy
metals in roots and low translocation in above ground parts indicated their suitability for
phyto-stabilisation. The results indicated that a total of 12 species with BCF>1 and TF<1
may be useful for phyto-stabilisation of one, two or three metals contaminated sites of the
study area. These species included B. reptans, E. indica, and S.nigrum with BCF >1 and
TF<1 for Pb, Cu and Zn. C. pennisetiformis, and C. rotundus with BCF >1 and TF<1 for
Zn and Cu and Pb and Zn. A. viridis, C. sativa, C. album, D. aegyptium and M.
coromandelianum with BCF >1 and TF<1 for Pb and I. hederacea, P. oleracea and X.
stromarium with BCF>1 and TF<1 for Cu respectively.
Bioaccumulation factor (BAC) of studied plant species were highest for Pb, followed
by Cu, Zn, and Co. Fifteen species showed BAC values >1 for one, two or three metals
viz., Pb, Cu, Zn and Co. Based on higher BAC values, B. reptans and E. indica was most
efficient in accumulating three metals viz., Pb, Zn and Co. P. oleracea, X. stromarium
and I. hederacea had potential to accumulate Pb and Cu whereas A. viridis (site 2), B.
reptans (site 1), P. hysterophoirus, C. pennisetiformis (site 1), C. album and C. rotundus
(Pb and Co). Plant species such as A. viridis at site 1 (Co), C. pennisetiformis at site 2
(Co), P. hysterophoirus at site 2 (Co), C. dactylon (Pb), D. aegyptium (Pb), M.
coromandelianum (Co), R. communis (Co) and S. nigrum (Cu) have the ability to
accumulate only one metal. Wei et al., (2006) reported S. nigrum as hyper-accumulator
of Cd. In the present study, the BAC value of S. nigrum was 2.5 for Cu indicated its
potential for accumulation of Cu. The BAC of C. dactylon was very high for Pb (BAC =
4.6) and based on Pb tolerance this species can be used for phytoremediation processes.
There are many reports about C. dactylon where it has been identified to accumulate
heavy metal in shoots. For example, Shu et al., (2000) have considered C. dactylon
suitable for reclamation of Pb/Zn mine wastelands. Similarly, Archer & Caldwell (2004)
also found C. dactylon as an accumulator of Pb, Cu, and Cd and considered this species
suitable for phytostabilization. Low growth habit makes it ideal for providing a dense mat
RIFFAT NASEEM MALIK ET AL.,
on the soil surface which can prevent erosion and at the same time remove heavy metals
from the soil. It spreads by both tillering and seedling which makes its establishment easy
(Archer & Caldwell, 2004). The results of this study also highlighted that grasses such as
C. dactylon, C. pennisetiformis, B. reptans and E. indica had higher BAC values
compared to other plant species. Grasses have been more preferable in use for phyto-
accumulation than shrubs or trees because of high growth rate, more adaptability to stress
environment and high biomass.
In general the results indicated that none of the plant species were identified as
hyperaccumulator because all species accumulated Pb, Cu, Zn, Ni, Co and Cr less than
1000 mg/kg (Baker & Brooks, 1989). However, based on BCFs, TFs, and BAC values
plant species were identified which have the potential for phytostabilization and
phytoextraction. B. reptans, S. nigrum P. oleracea and X. stromarium had very high BCF
values and could be useful for phytostabilization of soils contaminated with Cu and Pb.
Most of the species were efficient to take up and translocate more than one metal from
roots to shoots. Based on highest TF value P. hysterophoirus and A. viridis can be used
for phytoextraction of Pb and Ni. The results also find P. hysterophoirus the most
efficient species in translocateing Pb, Cu, Ni, Zn, Cr, and Cu from roots to shoots at site 1
and 2. The results highlighted that grasses such as B. reptans, C. dactylon, and C.
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(Received for publication 15 July 2008)