Research Journal of Environmental and Earth Sciences 4(4): 413-418, 2012
ISSN: 2041-0492
© Maxwell Scientific Organization, 2012
Submitted: December 10, 2011
Accepted: January 31, 2012
Published: April 15, 2012
Comparative Effects of Abelmoschus esculentus (L) Moench (Okro) and
Corchorus olitorius L (Jew Mallow) on Soil Contaminated
with Mixture of Petroleum Products
Kelechi L. Njoku, Bola O. Oboh, Modupe O. Akinola and Arinola O. Ajasa
Department of Cell Biology and Genetics, University of Lagos, Akoka Lagos, Nigeria
Abstract: The comparative effects of Abelmoschus esculentus and Corchorus olitorius on soil contaminated
with mixture of petroleum products were evaluated in this study. The pH, moisture, organic matter, microbial
population and total petroleum hydrocarbon of the soils at the beginning and the end of the study were
evaluated. Growth of A. esculentus led to loss of more TPH from the soil than the growth of C. olitorius. The
growth of A. esculentus increased soil alkalinity and the soil moisture content more than that of C. olitorius.
More bacteria and fungi were isolated from soil that had A. esculentus than from soil that had C. olitorius.
Significant differences were noticed between the impacts of A. esculentus and that of C. olitorius on the soil
contaminated with mixture of petroleum (p<0.05, p<0.01, p<0.001). The findings in this study show that
A. esculentus has better ability to remediate petroleum contaminated soils than C. olitorius. Since both crops
are easily propagated and readily grow in most soils, they can be very useful in combating the problems
associated with contamination of soil with petroleum products.
Key words: Abelmoschus esculentus, contamination, Corchorus olitorius, petroleum mixture, remediation
INTRODUCTION
The application of plants for remediation
(phytoremediation) of soils contaminated with petroleum
hydrocarbons is one of the promising cost and
environmental effective approaches to remediation (Diab,
2008). Phytoremediation has been found to be a feasible
method for improving petroleum contaminated soils
(Abedi-Koupai et al., 2007). Some plants have been
shown to have the ability to remediate petroleum
hydrocarbon contaminated soils. Issoufi et al. (2006)
reported that Zea mays and Glycine max have the
potential to enhance remediation of petroleum polluted
soils. Njoku (2008) and Njoku et al. (2009) showed that
Glycine max has the potential of remediating crude oil.
Other plants like ryegrass, alfalfa, reedgrass, barley,
sedge, oat, redclover, clover, fababean, etc have been
reported to remediate soils polluted with oil.
Most plants that have been used to remediate areas
polluted with oil are weeds with little or no economic
values. However to improve the economic benefit of
phytoremediation, useful crops need to be tried for their
remediation potentials (Njoku, 2008). The objectives of
this study is to evaluate the potential of two vegetable
crops; Abelmoschus esculentus (okra) and Cochorus
olitorius (Jew’s mallow) to clean soil contaminated with
mixture of gasoline, diesel and spent oil. Although no
report has shown that either of the crops has the potential
to clean up polluted soils, A. esculentus has been observed
to show no visible injury due to their growth in soils
contaminated with heavy metals (Sharma and Agrawal,
2010). Adenipekun et al. (2009) also reported that
Petroleum products are some of the most widely used
chemicals (Sarkar et al., 2005) which because of their
wide usage, can easily spill, leak or be discharged to the
environment. According to Adedokun and Ataga (2007),
the leakage, discharge and spillage of petroleum products
lead to the pollution of terrestrial and aquatic
environments. It has been known that soil contamination
by petroleum products is one of the world’s most common
environmental problems (USEPA, 2000). The presence of
petroleum products in the environment poses danger to
the growth of plants and the well being of animals
resident or dependent on the environment. Several
researchers have shown that the individual petroleum
products have effects on the growth and performance of
plants (Odjegba and Sadiq, 2002; Adenipekun et al.,
2008; Ogbo, 2009).
There is the need to reclaim soils polluted with
petroleum products. Hitherto remediation of soil polluted
with petroleum products has involved physical, chemical
and biological processes (Ebuehi et al., 2005; Sarkar et
al., 2005). However, because of the expensive nature of
the physical and chemical methods (Chekol et al., 2004;
Escalante-Espinosa et al., 2005), the use of biological
process for remediation is being evaluated. In the
biological process of remediation, plant, animal and/or
microbial activities are used. It involves treatment or
breakdown of wastes contaminants into non-toxic forms
(Riser-Roberts, 1998) using biological processes.
Corresponding Author: Kelechi L. Njoku, Department of Cell Biology and Genetics, University of Lagos, Akoka Lagos, Nigeria
413
Res. J. Environ. Earth. Sci., 4(4): 413-418, 2012
A. esculentus tolerates contamination of soil with spent oil
up to a certain level. In addition, Oyedele et al. (2006)
reported that C. olitorius has the potential to
decontaminate soils contaminated with heavy metals.
Because of these potentials to tolerate and decontaminate
soils with spent oil contamination and soils with heavy
metals pollution, it is important to try their potentials in
decontaminating soils contaminated with mixture of
petroleum products. Also since in the developing
countries like Nigeria citing of mechanic workshops
where these products are used is not usually far from
homes and gardens, it will be good to try the potentials of
crops commonly found in gardens to remediate
contamination due to petroleum mixture. The information
obtained will not only help to restore contaminated soil
but will also boost the data bank of phytoremediating
plants and help to manage oil contaminated environment.
shaker for 30 min. The supernatant was filtered through
whatman filter paper into a beaker of known weight. The
solvent was carefully evaporated using hot plate as was
described by Okolo et al. (2005) after which the final
weight of the beaker was determined. The difference
between the initial and final weights of the beaker was
taken to be the amount of TPH in the soil (1 g). The
difference between the initial and final amounts of TPH
in the soils was taken be the amount of the TPH lost from
the soil and the percentage TPH loss was determined as:
Initial TPH-Final TPH/Initial TPH ×100
The pH of the soil was determined using modified
form of the method described by Eckert and Sims (1995)
using 1:1 soil to water ratio. The method described by
Schneekloth et al. (2002) was used to determine the
moisture content of soil by weighing soil dried at 105±5oC
for 24 h. The soil organic matter content was determined
as described by Krishna (2008) using muffle furnace at
440oC to burn oven dried soil for 24 h.
The bacterial and fungal loads of the soils were
determined using the plate count method with minimal
salt medium as was described by Zuberer (1994) and
Pepper (1995). 1 drop of 10G3 serially diluted soil solution
was incubated for 3 and 5 days for bacteria and fungi
respectively after which the colony forming units were
counted.
MATERIALS AND METHODS
The gasoline and diesel fuel used in this study were
obtained from fuel station (AP fuel station, University of
Lagos, Nigeria) while the spent oil was obtained from a
mechanic workshop beside the fuel station. The petroleum
products were mixed in a ratio of 1:1:1. The seeds of the
crops were obtained from gene bank section of National
Institute for Horticulture (NIHORT) Ibadan, Nigeria
through random selection of the seeds. The soil used was
a sandy loam soil (with 0.6% organic carbon content)
obtained from the biological garden of the University
of Lagos.
The soil was sieved through 5 mm sieve to remove
debris and large particles. The sieved soil was used to fill
thirty six 10 L pots (34 cm in diameter) up to threequarter full (5 kg of soil). Each pot was perforated at the
base to aid water drainage. The soils in the different pots
were contaminated with different volumes of the
petroleum mixture equivalent to 1, 2, 3 and 4% of the
soils (w/w). The different volumes of the petroleum
mixture in the soil served as the treatments. The pots were
then divided into three groups; one group without plant,
one group planted with A. esculentus and the other group
planted with C. olitorius. Each treatment in each group
was replicated three times (i.e. three pots with equal
volume of petroleum represented one treatment)
RESULTS AND DISCUSSION
The total petroleum hydrocarbon: More Total
Petroleum Hydrocarbon (TPH) was lost from the soils
with plants than from soils without plants (Fig. 1). Growth
of A. esculentus led to greater loss of total petroleum
hydrocarbon from the soil than the growth of C. olitorius.
The difference in the loss from the soils with different
plants indicate that A. esculentus has greater efficiency in
remediating soils polluted with petroleum mixture than
C. olitorius This could be as a result of the difference in
the nature of the plants or their ability to influence
rhizosphere effect.
This data shows that both plants have the ability to
remediate soils polluted with different petroleum mixture.
It is similar to the reports of earlier researchers on the
ability of plants to facilitate loss of TPH from the soil
(Lee and Banks, 1993; Schwab and Banks, 1994; Merkl
et al., 2005; Diab, 2008; Njoku et al., 2009). The
mechanism used by the A. esculentus and C. olitorius for
the remediation of the petroleum in this study could be
one or a combination of the several mechanisms known to
be used by plants in the remediation of pollutants. In most
cases, the plants enhance the activities of petroleum
degrading microbes by producing beneficial environments
for the microbial growth and/or enhance their activities.
Plants are known to produce exudates which contain
Sampling: The soil samples were collected from each pot
before the seeds were sown (initial) and after the growth
of the crops (final). The soil samples from the buckets that
had crops were collected from the root region and a little
distance away (about 5 cm) from the root region. The
soils collected from each pot at each time of sampling
were composited and were analysed for the pH, moisture,
organic matter content, microbial load and total petroleum
hydrocarbon content.
Analytical: The total petroleum hydrocarbon content of
the soils was extracted with n-hexane using mechanical
414
Res. J. Environ. Earth. Sci., 4(4): 413-418, 2012
Amount of TPH lost (%)
150
Table 2: The amount of moisture (%) contained in the soils planted
with A. esculentus and C. olitorius. Values are means of three
replicate treatments±standard error moisture
Oil, no plant
A. esculentus
C. olitorius
1% initial
2.430±0.452
2.420±0.225
2.177±0.218
1% final
16.470±0.035
14.827±0.958
8.437±1.811c2
2% initial
2.370±0.023
2.177±0.015
2.227±0.193
2% final
19.383±2.356
16.777±1.526
10.307±1.708
3% initial
2.197±0.033
1.987±0.096
5.673±3.289
3% final
17.617±0.234
18.513±0.458
17.610±0.227
4% initial
1.937±0.249
2.600±0.139
2.367±0.035
4% final
18.750±0.350
17.140±0.488
13.307±1.407a
Letters in superscript show significant difference between the soil at the
beginning and at the end of the study (a: 0.05; b: 0.01; c: 0.001);
asterisks show significant difference between soil without plant and soil
with plants (*: 0.05; **: 0.01; ***: 0.001)
Oil on plant
A. esculentus
C. olitorius
100
50
4%
3%
2%
1%
0
Fig. 1: Percentage Total Petroleum Hydrocarbon (TPH) lost
from soils contaminated with mixture of spent oil, diesel
and gasoline as a result of growth of A. esculentus and
C. olitorius
soils to be more alkaline than the growth of C. olitorius.
This could be due to certain factors like the nature of root
exudates released by the plants. The nature and products
of decomposed leaves from different plants can also affect
the acidity of the soil as some leaves may have products
that are more acidic than the others. The difference in the
acidity of the soil due to the growth of the two plants can
also alter the soil chemistry and soil binding capacities.
These findings partly agree with the findings of
Njoku et al. (2009) who reported that the growth of
G. max led to rise in the soil pH of crude oil contaminated
soil. The higher pH of the soils with the crops than the
soil without plant may mean that more bacteria would
thrive in such soils better than in the soils without plants.
Song et al. (1986) and Phung (1988) suggested that
bacteria thrive well in neutral soils than in acid soil.
Therefore the soils planted with the crops being less
acidic than those without plants would support more
bacterial growth than soils without plants.
Table 1: pH of the contaminated soils without plants, with A. esculentus
and with C. olitorius. Values are means of three replicate
treatments±standard error
Oil, no plant
A. esculentus
C. olilthorius
1% initial
6.030±0.092
6.053±0.055
6.200±0.220
6.540±0.021*b
6.823±0.101c
1% final
6.963±0.023c
2% initial
5.370±0.136
5.543±0.143
5.450±0.064
6.547±0.023c
6.447±0.113c
2% final
6.613±0.055c
3% initial
5.187±0.069
5.507±0.110
5.283±0.035
6.847±0.027c
6.690±0.069c
3% final
6.510±0.046c
4% initial
5.650±0.072
5.480±0.176
5.417±0.260
6.890±0.040c
6.507±0.043c
4% final
6.740±0.045c
Letters in superscript show significant difference between the soil at the
beginning and at the end of the study (a: 0.05; b: 0.01; c: 0.001);
asterisks show significant difference between soil without plant and soil
with plants (*: 0.05; **: 0.01; ***: 0.001)
nutrients that microbes use to grow. Also plant roots help
to increase water and air penetration into soil. These
increase the microbial and degradation activities in the
soil. The effects of plant roots on the dissipation of
organic pollutants has been attributed mainly to increased
microbial numbers and selection of specialized microbial
communities in the rhizosphere (Schnoor, 1997;
Vecchioli, 1990), but also to improved physical and
chemical soil conditions, supply of root exudates for
cometabolic processes (Yateem et al., 2000) and
increased humidification and absorption of pollutants
increasing their bioavailability (Yoshitomi and Shann,
2001). The greater loss of the TPH in the vegetated soils
than in the non-vegetated soil indicated that the crops
used in this study can be used to facilitate petroleum
remediation from soil.
Soil moisture: The growth of the plants encouraged
greater loss of water from the vegetated soils than in the
non vegetated soils (Table 2). This could be due to
transpiration through the leaves and greater drainage of
water because of the roots penetrating and loosening the
soil thereby creating pores in the soil which encourage
drainage. As was noted by Njoku et al. (2009), growth of
plant roots helps to create pores in the soil and thereby
enhance water penetration and infiltration in soils polluted
with oil. From the observation made in this study it can be
deduced that growth of A. esculentus and C.olitorius will
assist to increase water permeability in soils and reduce
artificial drought caused by oil pollution (Hutchinson
et al., 2001; Andrade et al., 2004).
The pH: The pH of the soils at the beginning of the study
was significantly lower than the pH of the soils at the end
of the study for the different treatments Table 1. In the 3
and 4% treated soils, the growth of the plants increased
the pH of the soil contaminated with different levels of
the petroleum mixture. The growth of A. esculentus in the
soil contaminated with 2-4% petroleum mixture made the
Soil organic matter content: The organic matter content
of the contaminated soil that had A. esculentus,
C. olitorius and the contaminated soil without plant is
shown in Table 3. The growth of A. esculentus
significantly reduced the organic matter content of the soil
treated with the different levels of the petroleum mixture.
415
Res. J. Environ. Earth. Sci., 4(4): 413-418, 2012
Table 3: The amount of organic matter (%) contained in the soils
planted with A. esculentus and C. olitorius. Values are means
of three replicate treatments±standard error
Oil, no plant
A. esculentus
C. oilthorius
1% initial
3.847±0.075
3.640±0.026
1.913±0.042***
1% final
3.593±0.092
2.713±0.374***c 1.730±0.042***
2% initial
2.407±0.067
2.457±0.082
1.990±0.032
2% final
2.333±0.073
2.007±0.141a
1.743±0.024**
3% initial
2.567±0.071
2.470±0.047
2.867±0.0702
c
3% final
2.677±0.178
1.513±0.035
2.220±0.021c
4% initial
2.990±0.082
2.850±0.081
3.157±0.090
2.430±0.087a
2.747±0.027a
4% final
1.790±0.234c
Letters in superscript show significant difference between the soil at the
beginning and at the end of the study (a: 0.05; b: 0.01; c: 0.001);
asterisks show significant difference between soil without plant and soil
with plants (*: 0.05; **: 0.01; ***: 0.001); figures in superscript show
significant difference between soil with different plants (1: 0.0; 2: 0.01;
3: 0.001)
microbes in vegetated soils than in non-vegetated soil
(Kirk et al., 2005; Njoku, 2008). This could be because of
the exudates and root debris from the plants’ roots which
would have favoured microbial growth in the soils.
According to Liljeroth and Baath (1998), microbial
proliferation in the rhizosphere occurs in response to the
input of organic compounds exuded by the roots. The
presence of microbes has been associated with enhanced
remediation of pollutants and researchers have reported
that bacteria play a significant role in the degradation of
crude oil (Atlas and Bartha, 1977; Amund and Igiri, 1990;
Frick et al., 1999; Van Hamme et al., 2003). It can be
implied that the higher microbial load in the vegetated in
this work soil indicates that more degradation of the
TPH occurred in the vegetated soil than in the nonvegetated soil.
Before the growth of the plants in the contaminated
soils, the number of fungi in the soils was more the
number of bacteria. However, with the growth of the
plants, the number of bacteria became more than that of
the fungi (Table 4). This could be attributed to the acidic
conditions of the soils before and after the growth of the
plants. As was noted by Song et al. (1986) and Phung
(1988), bacteria thrive better in neutral to alkaline soils
more than in acidic soils. Since the soils at the beginning
of the study had lower pH than those at the end of the
study more bacteria is therefore expected in the soils at
the end of the study hence more abundance of bacteria at
the end of the study than fungi.
The growth of A. esculentus in the 1 and 2% treated
soil encouraged more bacterial growth than the growth of
C. olitorius. More fungal growth was noticed in soils that
A. esculentus grew on them than in soils that had
C. olitorius grown on them in the 1 and 2% treated soil.
The reverse was the case in the 3 and 4% treated soil. The
differential effect of the plants on the microbial load of
the soil is similar what Kirk et al. (2005) reported on the
effects of ryegrass and alfalfa on the microbial load of
soil. Norino (2004) reported differential influence of
The growth of C. olitorius only led to significant
reduction of the organic matter content of soil treated with
3 and 4% of petroleum mixture. The reduced organic
matter content of the vegetated soil when compared with
that in the non-vegetated soil is similar to the observations
made by Ayotamuno et al. (2004). This could be as a
result of organic matter removal by plants.
The soil treated with 1, 2 and 3% petroleum mixture
that had A. esculentus grown accumulated more organic
matter than those that had C. olitorius grown on them.
However, the reverse was the case in the soils that had 4%
treatment with the soil that had C. olitorius having
significantly higher organic matter than that having
A. esculentus (p<0.01). The level of root activities affects
the binding properties and ability of the soil. It is also
known that higher abilities in plants increase the organic
matter accumulation. The difference in the organic matter
levels in the soils with the different plants could be
attributed to the impact of their roots on the soil.
The microbial population: Generally, more bacteria and
fungi occurred in the soils that had the crops than in the
non-vegetated soils (Table 4). These findings are
similar to those of earlier researchers who reported more
Table 4: The microbial load (x 104 cfu/g) of the contaminated soils without plant, with A. esculentus and with C. olitorius. Values are means±standard
error of three replicate treatments
Oil, no plant
Oil, no plant
A. esculentus
A. esculentus
C. olitorius
C. olitorius
(bacteria)
(fungi)
(bacteria)
(fungi)
(bacteria)
(fungi)
1% initial
64.333±11.566
98.000±4.726
84.333±4.910
104.333±5.239
76.667±14.380
95.333±8.647
1% final
91.000±24.007
135.667±40.925
164.333±26.340
134.333±24.039
111.333±10.837
84.333±18.095
2% initial
88.333±2.333
115.667±4.372
92.000±3.215
125.667±4.372
94.000±4.041
120.333±3.844
200.000±48.693+
159.000±20.526
2% final
90.000±3.512
106.667±14.678
209.000±39.107+++ 160.333±13.968
3% initial
124.000±4.041
143.667±4.117
145.333±9.939
153.333±6.173
98.000±9.539
131.000±10.817
3% final
175.000±16.258
155.000±30.567
163.333±255.182
161.667±17.629
219.667±18.315
160.000±23.502
4% initial
153.000±8.083
214.000±8.145
160.000±23.544
215.000±11.930
158.333±26.984
181.333±12.785
4% final
170.667±34.479
157.667±31.136
177.667±5.239
179.333±33.844
247.667±16.455
240.333±23.730+
Letters in superscript show significant difference between the soil at the beginning and at the end of the study (a: 0.05; b: 0.01; c: 0.001); Asterisks
show significant difference between soil without plant and soil with plants (*: 0.05; **: 0.01; ***: 0.001); Figures in significant difference between
soil with different plants (1: 0.05; 2: 0.01; 3: 0.001); + signs in superscript show significant difference between soil without plant and soil with plants
but with same microbe (+: 0.05; ++: 0.01; +++: 0.001)
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maize and oat on the microbial levels in a crude oil
polluted. Such difference was attributed by the
researchers to mean that maize provided more stimulatory
influence on the microbial community of the polluted soil
than oat. This could imply that different plants have
different ability to enhance microbial load in the soil and
that A. esculentus has more stimulatory influence on
microbial growth than C. olitorius. This may be attributed
to the different abilities of different plants to impact the
soil as Abdel-Rahim et al. (1983) had earlier noted that
the influence microorganisms varies with plant age as
well as plant type.
CONCLUSION
The findings of this study show that both crops can
grow in soil contaminated with mixture of spent oil, petrol
and diesel. The results also show that both crops have
positive impacts on the pH, moisture, organic matter
content and microbial load of soils polluted with mixtures
petroleum products and reduce the amount of total
petroleum hydrocarbon in the soil. This means that both
crops can be used to restore petroleum contaminated soils
around mechanic workshops especially in the rural areas
where such workshops are cited in open spaces. The
higher loss of TPH from the soils as a result of the growth
of A. esculentus than in the case of C. olitorius indicates
that A. esculentus has better impact on petroleum polluted
soil than C. olitorius. This implies that A. esculentus has
better potentials to remediate petroleum polluted soils
than C. olitorius. However, the crops should be analysed
for their potentials to accumulate petroleum hydrocarbon
before using them for food to avoid the indirect poisoning
of consumers that will feed on the crops after using them
for remediation of petroleum polluted soil.
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