25 Advances in Environmental Biology, 2(1): 25-30, 2008 ISSN 1995-0756

25
Advances in Environmental Biology, 2(1): 25-30, 2008
ISSN 1995-0756
© 2008, American-Eurasian Network for Scientific Information
This is a refereed journal and all articles are professionally screened and reviewed
O RIGINAL A RTICLE
Determination of Lead, Cadmium and Chromium in the Tissue of an Economically
Important Plant Grown Around a Textile Industry at Ibeshe, Ikorodu Area of Lagos
State, Nigeria
Akinola, M.O., Njoku, K.L. and Ekeifo, B.E.
Environmental Biology, Laboratory, Department of Cell Biology & Genetics, University of Lagos, Akoka,
Lagos, Nigeria.
Akinola, M.O., Njoku, K.L. and Ekeifo, B.E.,: Determination of Lead, Cadmium and Chromium in
the Tissue of an Economically Important Plant Grown Around a T extile Industry at Ibeshe, Ikorodu
Area of Lagos State, Nigeria, Adv. Environ. Biol., 2(1): 25-30, 2008
ABSTRACT
Dietary exposure to heavy metals has been identified as a risk to human health through the consumption
of vegetable crops. The levels of Lead (Pb), Cadmium (Cd) and Chromium (Cr) in the tissue of Talinum
triangulare, an economic plant grown around a textile industry in Ikorudu area of Lagos State was carried out
in this study. Two soil and plant samples each were collected from four different points. Three of the points
were around the textile industry while the fourth was from a non-industrial area. The soil and plant samples
were analyzed for Pb, Cd and Cr using Atomic Absorption Spectrophotometry (AAS). The levels of Pb
(10.89±4.69) and Cd (0.81±0.01) in soil from the industrial area were higher than the non-industrial area (Pb)
2.33±0.01 and (Cd) 0.65±0.08 at P<0.05. The same trend was recorded for the plant samples from the
industrial and non-industrial area. These results suggest that contamination is due to industrial activities. This
study further confirms the increased danger of growing vegetables around industries and if it is allowed to
continue may lead to health hazard on part of consumers of the crop on the long term. This calls for proper
monitoring and enforcement of industrial regulations by regulatory agencies.
Key words:
Introduction
Pollution is correlated with the degree of
industrialization and the intensity of chemical usage.
Past and present industrial activities have often
resulted in the pollution of underlying soils
where
these
activities
take place, either by
leaching of water from landfills or direct discharge
of industrial wastewater into soil[6]. These industrial
wastewaters are produced mainly and in large
quantities by textile industries[11], due to the
nature
of their operations, which require high
volume of water that eventually results in high
wastewater generation. The most common toxic
soil pollutants include heavy metals and their
compounds, organic chemicals, oils, tars and
pesticides[20]. Soil pollution by heavy metals such
as mercury, cadmium, chromium and lead are of
great concern to public health[12]. The source of
heavy metal in plant is the environment in which
they grow and their growth medium (soil) from
which heavy metals are then taken up by roots or
foliage of plants[19]. Plants growing in polluted
environment can accumulate heavy metals at high
concentration causing serious risk to human health
when consumed [4 ,2 3 ,6 ]. Moreover, heavy metals are
dangerous because they tend to bioaccumulate in
plants and animals thereby causing deleterious
effects, bioconcentrate in the food chain or attack
specific organs in the body[8].
Corresponding Author
Akinola, M. O., Environmental Biology, Laboratory, Department of Cell Biology &
Genetics, University of Lagos, Akoka, Lagos, Nigeria
Email: [email protected]
Adv. Environ. Biol., 2(1): 25-30, 2008
26
Ingesting large amount of heavy metal like
chromium, cadmium and lead can cause reduced
litter size and weight, liver and kidney damage[7].
Cadmium can also accumulate in kidney where it
damages filtering and causes excretion of essential
proteins and sugar from the body[7]. In herbaceous
plants, roots and leaves retain higher metal
concentration of heavy metal than stems and
fruits[19]. Therefore, there is need to know the
concentration of heavy metals in crops particularly
leafy
vegetables
which
are
consumed
by
humans. Over time, the soils within the vicinity
of a textile industry in Ikorodu area of Lagos
State in Nigeria have been used by residents for
the cultivation of vegetables. This is probably
due to the high volume of wastewater generated from
the industry, which serves as a means of irrigation
for their vegetable gardens. This is because the
vegetable growers believe wastewaters from
industries contain a lot of nutrients that can support
and promote a high yield of vegetables. Talinum
triangulare is an herbaceous perennial plant which is
an all season vegetable and it is extensively grown
in Nigeria. It serves as a nutritious source of food
for both man and livestock because it contains
vitamins A, C and mineral like calcium. Though it is
consumed most times without consideration of its
medicinal values, Talinum triangulare is medicinal
and can be used for the treatment of diuretic and
stomach problems[22] .
In this study, Talinum triangulare which is the
dominant leafy vegetable in the gardens around the
textile industry was used to determine the level of
heavy metal pollution that might have been caused
by the operations of the textile industry.
the point was designated as D. A map of the
different sampling points is shown in Figure 1.
M aterials and methods
Soil and plant samples were digested before
analysis to reduce organic matter interference and
allow for the conversion of the metal into a form
that can be analyzed by the Atomic Absorption
Spectrophotometer (AAS).
The sampling was done around the surrounding
of United Nigeria Textile PLC (UNT), which is
located in Ibeshe town near Ikorodu, Lagos state.
The textile industry occupies a large expanse of land
in the vicinity while banks and residential houses
occupy the neighboring land. T he industry is located
along a major express road. Very tall palm trees and
vegetable gardens abound within the surrounding of
this industry. The industry produces large amount of
wastewater and this water flows through the soil to
the surrounding gardens.
Description of sampling points
Three different points (A, B and C) 50 M around
the textile industry were sampled for soil and plant
while the fourth sampling point is located in a nonindustrial area about 500 M away from the industry.
The samples from this point served as control and
Collection of plant and soil samples
Two soil and plant samples each were collected
from points A, B, C and D. Plant samples were
collected carefully using hand trowel to dig the soil
around the plant and the plants were pulled out
carefully, ensuring that no part of the root was lost.
The different plant samples were kept in different
polythene bags and properly labeled.
Soil samples were collected from the same point
where the plant samples were uprooted. The soil
samples were collected to a depth of 15cm using a
soil auger. The soil samples were kept in polythene
bags and labeled to avoid a mix-up of the different
soil samples. The plant and soil samples were
brought to the Environmental Biology laboratory and
kept in the fridge prior to analysis for heavy metals.
Sample preparation
Each plant sample was separated into leaves,
roots, and stems and then dried at 50ºC for 8 hours
using an oven. The dried plant samples were milled
using a laboratory blender and kept for digestion.
Unwanted materials such as stones, leaves and
debris were removed from the soil samples by handpicking. The soil sample was further broken down
into finer particles using a laboratory mortar and
pestle. The soil samples were dried for 8 hours at
80ºC using an oven.
Sample digestion
Plant sample digestion
Plant samples were digested following the
method of Allen et al., 3g of the milled plant sample
were weighed into a conical flask using a digital
weighing balance. 3 ml of 60% hydrochloric acid
and 10 ml of 70% nitric acid were added to the
weighed milled plant sample. The conical flask was
then placed on a laboratory hot plate for digestion
until the white fume evolving from the conical flask
turned brown. The digest was allowed to cool and
then filtered through a W hatman’s filter paper,
leaving a whitish residue. The filtrate was then made
up to 50 ml using distilled water and kept for
further analysis.
Adv. Environ. Biol., 2(1): 25-30, 2008
27
Fig. 1: IKOROUDUL LAGA SHOW ING SAMPLING PONITS.
Soil sample digestion
The same procedure for the digestion of plant
sample was used according to the method of
Allen et al.
Determination of Heavy Metals in the Digested
Samples using
Atomic Absorption Spectrometer
(AAS)
The digested plant and soil sample were analyzed
for lead (Pb), cadmium (Cd) and chromium (Cr)
using Atomic Absorption Spectrometer (AAS).
The readings were taken from the equipment and
the results were converted to actual concentration of
metals in the samples using the equation;
Sample weight refers to the weight of the sample
used. After which the mean of the heavy metal
concentrations in soils from the industrial and nonindustrial sites were then calculated.
The Multiplication Coefficient (M C) or
Bioconcentration Factor (BCF) according to Joonki et
al, was also calculated using the equation:
Concentration of R (µg/g)
Concentration in S (µg/g)
W here concentration of heavy metal in R is the
concentration of heavy metal in the roots and
concentration of heavy metal in S is the
concentration of heavy metal in soil.
Determination of Soil pH
Concentration µg/g =
Calibration reading x
Extract volume
Sample weight
W here calibration reading is the value of the
reading obtained from the AAS equipment
Extract volume is the final volume of the digest used
for spectrometric analysis
The soil pH was determined following the
method of Eckerts and Sims. The soil samples were
first air-dried and 5 g of the air-dried soil was mixed
with 5 ml of distilled water and stirred. T he mixture
was allowed to stand for thirty minutes to allow it
to settle. The slurry was decanted into a test tube.
Adv. Environ. Biol., 2(1): 25-30, 2008
The electrode of a pH meter was put into the slurry
and the pH read off.
Results and discussion
Results
The results of the chemical analysis of lead (Pb),
cadmium (Cd), and chromium (Cr) in soil and plant
samples collected are presented in Table 1. The pH
of soils from both industrial (5.92±0.02) and
non-industrial (6.02±0.01) areas are slightly acidic.
The concentrations of lead, cadmium and chromium
are higher in soil samples obtained from the textile
industry area when compared with those obtained
from the non-industrial area. Lead and cadmium
concentrations of the soil from the industrial area
were significantly higher than those of the nonindustrial area (Table 1). But generally the
concentrations of the three heavy metals are low as
it has been previously reported for soils in
Nigeria[3,4]. Table 2 shows the concentrations of
the heavy metals in the tissue of the plant.
The concentrations of the heavy metals in the plant
tissue were higher in the industrial area than the nonindustrial area however chromium was not detected
in the tissue of plants from non-industrial area. The
concentrations of the three heavy metals in plant
tissues from the industrial area were also higher than
from non-industrial area at P<0.05 (Table 2).
Table 3 shows the rate at which the roots of T.
triangulare bi-accumulates these heavy metals as
shown by the Multiplication Coefficient (MC) or
Bio-concentration Factor (BCF). The soils of both
industrial and non-industrial areas have more of the
heavy metals than the roots of the vegetable except
for cadmium concentration in the roots of vegetables
from the industrial area. The MC or BCF for Pb and
Cr in both study areas are less than one, while that
for Cd in the industrial area is greater than one, with
MC or B CF value of Cd from the industrial area
being the highest. Generally, these MC/BCF values
are low because of low levels of the heavy metals in
the roots (Table 3).
Discussion
The concentration of Pb, Cd and Cr in the soil
was higher in soil samples from the industrial site
compared with the non-industrial site. There is no
doubt that heavy metals are present in soil naturally
and non-degradable, and can be accumulated in the
plant tissues[3,17] as shown by the concentrations of
heavy metals obtained in soils from non-industrial
site, but their concentrations can be increased by
industrial activities[20]. In this case, chemicals such
as dyes and other finishes used on the fabrics can
lead to an increase in the concentration of heavy
28
metals in the soils. T his is similar to the observation
of Abdulkaaheem and Singh[1] in which heavy
metals like Cd, Cr, Cu, Pb and Zn in soil and plants
samples around tannery and textile industries
decreased as the distance from point of effluent
diacharge increased. Fakayode and Onianwa[10]
made similar observation noting that plant and soil
samples from industrial sites contain more heavy
metals than those from non-industrial sites. Moreover,
direct and indirect discharges of industrial effluents,
dumping of metallic products and atmospheric
deposit can lead to high levels of heavy metals in
soils and water bodies[2]. The high levels of heavy
metals in the shoots of T. triangulare obtained in this
study are similar to those observed by Akinola and
Njoku[4]. This observation calls for caution because
it is the shoot portion of this popular pot herb that is
consumed by the people. Heavy metals are known to
be biomagnified in the tissues of the consumers
along the foodchain. Moreover, the short foodchain
between plant and man as an herbivore makes the
efficiency of transfer from plant to man very
high[18]. H ence the level of heavy metals in man
can easily increase. It is opined that cultivation of
vegetables around industrial areas should be
minimized and discouraged as much as possible.
This is because of its implication to human health.
For instance, lead has been found to be toxic to the
red blood cell, kidney, nervous and reproductive
systems[21]. Excess of cadmium has been reported to
cause renal tubular dysfunction accompanied by
o s te o m a l a c i a ( b o n e s o f t e n in g ) a n d o t h e r
complications which can lead to death[14]. Although
the levels of the heavy metals in the tissue of T.
triangulare in this study were less than the values
recommended as the minimum intake values.
However, continuous consumption of the vegetable
from this site is not advisable. The quantity of the
vegetable which is usually consumed is a lot more
than the small quantity which is used for analysis of
heavy metal concentrations. This implies that the
heavy metal levels can be more in the quantity of the
vegetable consumed. Furthermore, heavy metals are
known to bio-accumulate in the tissue of organisms
at higher trophic levels, so continuous consumption
of the vegetable may lead to increase in the levels in
humans. It has been noted that more heavy metals
are absorbed by plants when pH is as low as 2-3[9].
So the pH of near neutral recorded for the soils
could be the cause of low uptake of Pb and Cr by
the vegetable[15] thereby leaving a higher
concentration of the two heavy metals in the soil
than the concentration in the root. A high pH value
has been found to cause immobilization of heavy
metals in the soil[16]. This can further explain the
low concentrations of these metals in the roots of the
crops. But these concentrations become magnified as
they move up from the roots to the shoot portion of
Adv. Environ. Biol., 2(1): 25-30, 2008
29
Table 1: M ean concentration of heavy m etals Lead, Cadm ium and Chrom ium (µg/g) in soil sam ples.
Sam pling Points
Soil pH
Lead (Pb)
Cadm ium (Cd)
Textile industry area
5.92±0.02
10.89± 4.69
0.81± 0.01
N on-industrial area
6.02±0.01
2.33± 0.01
0.65± 0.08
Chrom ium (Cr)
12.50 ±3.18
12.48 ±1.21
Table 2: M ean concentrations of heavy m etals (µg/g) in tissues of T. triangulare.
H eavy M etal
Plant tissues
Sam pling Site
------------------------------------------------------------------------------------Industrial area
N on-industrial area
Lead
Root
0.71±0.59
0.60±0.25
Stem
0.23±0.19
0.16±0.01
Leave
0.86±0.68
0.74±0.56
Cadm ium
Root
1.22±0.32
0.63±0.05
Stem
1.21±0.40
0.73±0.05
Leave
1.25±0.37
0.86±0.06
Chrom ium
Root
1.51±0.37
ND
Stem
2.78±0.48
ND
Leave
65.60±39.74
1.21±0.12
N D – N ot D etected
The concentration of heavy m etals in soils in relation to its concentrations in plant roots as show n by the m ultiplication
coefficient/bio-concentration factor (M C/BCF).
Sam pling Site
Lead
Cadm ium
Chrom ium
Industrial area
Root
0.71±0.59
1.22±0.32
1.51±0.37
Soil
10.89±4.69
0.81±0.01
12.50±3.18
M C/BCF
0.07
1.51
0.12
N on-industrial area
Root
0.60±0.25
0.63±0.05
ND
Soil
2.33±0.01
0.65±0.08
12.48±1.21
M C/BCF
0.26
0.97
0
N D – N ot D etected
Table 3:
the crops. This also explains the generally low
magnification coefficients/bioconcentration factors
(M C/BCF) recorded in this study.
7.
8.
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