Journal of Research in Biology
Heavy metal accumulation by Amaranthus hybridus L. grown on
waste dumpsites in South-Eastern Nigeria.
Keywords:
Heavy metal, Amaranthus hybridus, accumulation, pollution, Safety risk.
ABSTRACT:
The accumulation of some heavy metals by Amaranthus hybridus grown on two waste dump sites within Abakaliki metropolis, South-Eastern Nigeria was studied using atomic absorption spectrophotometer. The results indicate that Cd, Cu and Pb in the two dump sites were above the stipulated standard, while Zn was within the stipulated standard in the soil. The two dumpsites had high level of Pb in the plant leaves; in Site 2, Cu and Zn showed the highest value while Zn in site 2 has the lowest value. Although all the values obtained in the leaves of Amaranthus hybridus were within recommended limits, but it may be dangerous to consume Amaranthus hybridus grown on dump sites since it can accumulate most of these toxic metals. The BCF value was >2 for Pb and Cd in site 1 while in site 2 the BCF value was >2 for Pb, Cu, Zn and Cd, showing that Amaranthus hybridus can tolerate and sequester these metals from soil and translocate them to the shoots. The TLF in Amaranthus hybridus indicate the following: in Iyiudele stream (Site 1) the rate of Cd and Zn in Amaranthus hybridus up take is >1 and in site 2 the rate of Pb, Cd, Cu, and Zn up take in Amaranthus hybridus were >1. The results obtained from this study showed that heavy metals in soils at the waste dump sites ended up in the studied plant, Amaranthus hybridus, cultivated on such land. Therefore farmers should be discouraged from cultivating their crops on these waste dump sites.
809-817 | JRB | 2013 | Vol 3 | No 2
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Authors:
Uka UN1, Chukwuka KS2, 3 and Okorie N1.
Institution:
1.Department of Applied Biology, Ebonyi State University, Abakaliki-Nigeria.
2. Department of Botany, University of Ibadan, Ibadan-Nigeria.
3. Department of Plant Science and Biotechnology, Abia State University, Uturu-Nigeria.
Corresponding author:
Chukwuka KS.
Email:
kanayodrchukwuka97@gmail.com
Web Address:
http://jresearchbiology.com/documents/RA0298.pdf.
Dates:
Received: 31 Oct 2012 Accepted: 14 Nov 2012 Published: 22 Feb 2013
Article Citation:
Uka UN, Chukwuka KS and Okorie N.
Heavy metal accumulation by Amaranthus hybridus L . grown on
Waste dumpsites in South-Eastern Nigeria.
Journal of Research in Biology (2013) 3(2): 809-817
Journal of Research in Biology
An International Scientific Research Journal
Original Research
INTRODUCTION
Vegetables constitute important functional food components by contributing protein, vitamins, iron and calcium which have marked health effects in all organisms (Arai, 2002). Vegetables, especially leafy vegetables, grown in heavy metal contaminated soils, accumulate higher amounts of metals than those grown in uncontaminated soils (Al Jassir et al., 2005). Heavy metals are important contaminants and are found in the surface and tissues of vegetables in environments with such contaminants. The quest for urbanisation and industrialization has resulted to the contamination of soil and metal accumulation in soils and crops, resulting to metal contamination exceeding the maximum permissible level. Plant species have a variety of capacities in removing and accumulating heavy metals, so there are reports indicating that some species may accumulate specific heavy metals, causing serious health risk to human health when plant based food stuff are consumed (Wenzel and Jackwer, 1999).
Odai et al., (2008) studied the concentration levels of heavy metals in vegetables grown on urban waste dump sites. This study was carried out on three waste dump sites in Kumasi where vegetables cultivation (cabbage, lettuce and spring onions) are practiced. Crops and soil samples were collected and analyzed for the presence of four heavy metals: Cadmium, lead, copper and zinc. The levels of the two most toxic heavy metals were far higher in the vegetables than the WHO/FAO recommended values and the transfer factors of these two metals were also the highest suggesting that consumption of vegetables grown on such sites could be dangerous to human health. Chove et al., (2006) carried out a study to determine the levels of two heavy metals, Lead (Pb) and Copper (Cu), in two popular leafy vegetables grown around Morogoro Municipality in Tanzania. Vegetable samples of Pumpkin leaves (Cucurbita moschata) and Chinese cabbage (Brassica chinensis) were collected from three sites and analyzed for the concentrations of the two metals using an Atomic Absorption Spectrophotometer. The results showed that levels of Lead and Copper in the two vegetables were found to be below the maximum permissible levels recommended by FAO/WHO for the two metals in the vegetables.
In Abakaliki, South-eastern Nigeria, there is an indiscriminate and inappropriate waste disposal. This implies that the concentration of heavy metals in both plant and soil is expected to be high. In this study, Amaranthus hybridus was chosen for phytoremediation study as well as heavy metal contamination because it is a vegetable crop, rich in proteins, vitamins and minerals. Its yield, ability to grow in hot weather conditions, high nutritive value and their pleasant taste and the fact that they grow all year round, makes it a popular vegetable. (Grubben, 1976). This study was undertaken to determine:
MATERIALS AND METHODS
The study was carried out during the month of October, 2011 which is part of the rainy season in the area under investigation. Samples of Amaranthus hybridus and soils were collected from 2 dump sites located at Iyiudele street and Abakaliki-Enugu Expressway located within Abakaliki Urban, Ebonyi State. Ebonyi State lies within the Cross River plain, approximately between 7°30’ N and 8°30’ N latitude and 5°40’E and 6°45’E longitude (Nnamani et al, 2009). A total of 12 plants and soil samples were collected from the two dump sites (six per
dump site). The plants were washed with tap water to remove sand from the leaves, stem and roots. The plants were put into separate polythene bags, labelled and taken to the laboratory. In the laboratory the plants were further washed with distilled water.
Identification of plants
The selected plant was collected in triplicate. The identification and taxonomic characterization was performed at the herbarium facility of the Ebonyi State University, Abakaliki through botanical keys where the vouchers were deposited.
Sample preparation and analysis
The plants were separated into leaves, stem and root and air dried for 21 days to remove moisture. Soil samples were air dried for 21 days, then sieved through 2 mm mesh. 0.5 g dried, grinded and sieved plant and soil samples were analysed according to methods of Umoren and Onianwa (2005). Concentrations of Pb, Cu, Zn and Cd were determined using atomic absorption spectrophotometer model sp-9 (Pye Unicam). The mean values of three determinations per composite sample were recorded.
The Bioconcentration Factor (BCF) of metals was used to determine the quantity of heavy metals that were absorbed by the plant from the soil (Ghosh and Singh, 2005a) and is calculated using the formula:
BCF = Metal Concentration in whole plant
Concentration of metal in soil
To evaluate the potential of plants for phytoextraction the translocation factor (TF) was used, according to Marchiol et al., (2000) and is calculated as follows:
TF = Metal Concentration (Stem + leaves)
Metal concentration (roots)
RESULTS
The mean concentration of the four heavy metals (Pb, Cu, Zn and Cd) in soil samples from the waste dump sites in Abakaliki Urban are presented in Table 1. The mean concentration of Pb ranged from 0.07±0.01 in site 2 to 0.12±0.01 Mg/g in site 1 (Table 1and Fig 1). Mean concentration of Cu ranged from 0.06± 0.01 Mg/g in site 2 to 0.24±0.01 Mg/g in site 1. These differences were significant (P<0.05). The mean concentration of Zn (0.01±0.00) in both sites were similar, while the highest mean concentration of Cd (0.08±0.01) was found in
site 2 compared to ‘site 1’ (0.05± 0.01). However, the differences were not significant (P >0.05).
The comparison of the maximum levels of the various heavy metals in the dump site soil from site 1 and site 2 to acceptable standards is as shown in Table 2. Cd, Cu and Pb were above the stipulated standard. Zn was within the acceptable standard.
The accumulation of metals in the Amaranthus hybridus parts from Iyiudele stream were varied with Pb ranging from 0.01 mg/g- root, 0.33 mg/g- stem and 0.5 mg/g leaf, Cu ranged from 0.12 mg/g-root,0.07 mg/g stem and leaf (not detected); Zn ranging from 0.01 mg/g for leaf, while it was detected in root and stem. Cd ranged from 0.02 mg/g for root, 0.43 mg/g for stem, while in leaf it was not detected (Figure 1, Table 2). The concentration of Pb in leaf and stem in site 1 were above the WHO/FAO limit for vegetables, while Cu and Zn were within the acceptable standard. Cd concentration in stem was also above WHO/FAO Limit. Amaranthus hybridus from old Kpirikpiri ranged as follows: Pb-0.2 mg/g for root,0.04 for stem and 0.6 mg/g for leaf. Cu ranged from 0.08 mg/g-root, 0.05 mg/g-stem, 0.08 mg/g for leaf. Zn ranging from 0.03 mg/g-root, 0.04 mg/g-stem and 0.09mg/g leaf and Cd ranging from 0.05 mg/g- root, 0.38 mg/g- stem and 0.15 mg/g - leaf (Figure 1, Table 2). Pb concentration in leaf at site 2 was above the recommended dietary allowance. The concentration of Cd in stem was above the WHO/FAO allowance.
Determination of the movement of metals from soil to plant
The Bioconcentration factor (BCF) represented in Table 4 showed the ability of Amarathus hybridus to extract heavy metals from the soil. BCF Value at the site 1 was highest for Cd followed by Pb, Zn and Cu. At site 2, the BCF index was highest for Zn followed by Pb, Cd and Cu.
Translocation Factor
Metals that are accumulated by plants and mostly stored in the roots of plants are indicated by TF values <1. Values >1 indicate translocation to the aerial parts of plant. These are represented in Table 5. Values <1 were found for Cu and Zn in site 1, while values >1 were found for Pb and Cd in site 1. TF values were >1 in site 2.
DISCUSSIONS
A study of Pb, Cu, Zn and Cd in soils and naturally growing Amaranthus hybridus from selected waste dump sites in Abakaliki urban was carried out. The results show that Cd, Cu and Pb concentration in the soil from the studied sites were above the stipulated standard, while zinc was within the acceptable standard (Table 2). The high levels of heavy metals in the dump site could be attributed to huge amount of waste products disposed of at the dump site (Ebong et al., 2007). The high levels of these metals present the sites as potentially hazardous and highly inimical to the food chain and biological life and a clean environment. Al Jassir et al., (2005) reported that leafy vegetables grown in heavy metals contaminated soils, accumulate higher amount of metals than those grown in uncontaminated soils because of the fact that they absorb these metals through their leaves.
Pb is a chemical pollutant in the environment and an element that is toxic to plants. (Sasmaz et al., 2008). Kabata-Pendias and Pendias (2001) reported that Pb contents of plants grown in uncontaminated areas varied between 0.05 and 3.0 mg/kg. Carranza- Alvarez et al., (2008) also reported that Pb concentration ranged from 10 to 25 Mg/kg. In this study, Pb accumulation was higher in the leaves of Amaranthus hybridus in the two sites. According to Zurera-Cosano et al., (1989), vegetables take up metals by absorbing them from contaminated as well as from deposits on different parts of vegetables exposed to the air from polluted environment.
The ranges of Cu obtained in all the plant parts in both dump sites are lower than 11.50±2.16, 2.50, 0.923 mg kg-1 as reported in different types of vegetables by Farooq et al., (2008). In site 1 there was no trace of
Cu in the leaf of Amaranthus hybridus, it could be that the metal is within the root and stem, thus it has not been translocated to the leaf. Despites the presence of Cu in the other parts of Amaranthus hybridus, it was within the recommended limit.
In site 1 there were no trace of Zn in the root and stem but present in the leaf with low value, the absence of Zn in the root and stem of Amaranthus hybridus in site 1 may be that it has been volatilized or that it is not essential for plant growth, the presence of Zn in the leaf may be due to emissions from the environment. In site 2, there were presence of Zn in the root, stem and leaf of Amaranthus hybridus although the leaf had higher heavy metal but they were all within recommended standard. However, since the leaf of this vegetable is the edible part, continuous intake of this vegetable from the dump sites may be toxic and lethal to the health of the consumers.
The ranges of Cd obtained from Amaranthus hybridus in Site 1 are, root 0.02±0.01, stem, 0.43±0.01 and leaf was below detection limit. Cd in the stem of Amaranthus hybridus in site 1 was higher when compared to the ranges of Cd obtained from other vegetables as reported by Maleki and Zarasvard (2008) but lower than 0.667-0.933 as reported in other vegetables (Abdullahi et al., 2009). However, the level of Cd in the stem is within the recommended limit.
Comparing the two dump sites, stem had a higher heavy metal, it could be that Amaranthus hybridus had taken these metals up and stored mostly in the stem. The BCF signifies the amount of heavy metals in the soil that ended up in the vegetable crop. The BCF values were >2 for Pb and Cd at site 1 whereas in site 2 BCF values was >2 for Pb, Cu, Zn and Cd. This implies that the degree of transportability of these metals is site dependent and could be due to different forms in which these metal ions are available at these sites. These results enable us to conclude that Amaranthus hybridus can tolerate and sequester these metals from the soil and translocate it to the shoots, thus making Amaranthus hybridus cultivated
on these waste dump sites unfit for human consumption.
The translocation factor can be used to estimate plants potential for phytoremediation purposes. Metals that are accumulated by plants and mostly stored in the roots of plants are indicated by TLF values greater than 1. The translocation ability of Amaranthus hybridus for these heavy metals were in these order Pb (83) >Cd (21.50), while in site 2, Cd (10.60) >Zn (4.33) >Pb (3.20) >Cu (1.63). This is an indication of efficient way of transportation of these metals from root and its accumulation in shoot. Baker (1981) and Zu et al., (2005) reported that TLFs higher than 1.0 were determined in metal accumulator species, whereas TLFs was typically lower than 1.0 in metal excluder species. The TLFs higher than 1.0 indicated an efficient ability to transport metal from root to leaf, most likely due to efficient metal transporter system of plants (Zhao et al., 2002), and probably sequestration of metals in leaf vacuoles and apoplast (Lasat et al., 2002). The vacuole is generally considered to be the main storage site for metals in yeast and plant cells, and there is evidence that phytochelatin-metal complexes are pumped into the vacuole (Gratăo et al., 2005). It was reported that plants also have the ability to hyperaccumulate various heavy metals by the action of phytochelatins and metallothioneins, forming complexes with heavy metals and translocate them into vacuoles (Suresh and Ravishankar, 2004).
The results obtained from this study have shown that heavy metals in soils at the waste dump sites ended up in the studied plant, Amaranthus hybridus, cultivated on such land. The Four heavy metals Lead, Cadmium, Copper and Zinc were present in the studied sites. The concentration of lead and Cadmium that ended up in this vegetable far exceeded the WHO/FAO dietary allowance. Therefore farmers should be discouraged from cultivating their crops on these waste dump sites.
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Marchiol L, Assolari S, Sacco P and Zerbi G. 2004. Phytoextraction of heavy metals by canola (Brassica napus) and radish (Raphanus sativus) grown on multicontaminated soil. Environmental Pollution, 132:21-27.
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Odai SNE, Mensah D. Sipitey, Ryo S and Awuah E. 2008. Heavy metals uptake by vegetables cultivated on urban waste dumpsites. Case study of Kumasi, Ghana. Res. J. Environ. Toxicol., 2:92-99.
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Uka et al., 2013
810 Journal of Research in Biology (2013) 3(2): 809-817
Uka et al., 2013
Sample Location |
Pb |
Cu |
Zn |
Cd |
Site 1 |
0.12±0.01 |
0.24±0.01 |
0.01±0.00 |
0.05±0.01 |
Site 2 |
0.07±0.01 |
0.06±0.01 |
0.01±0.00 |
0.08±0.01 |
Table 1 Heavy metal variations (Mg/g) in soil sample from
some waste dumpsites in Abakaliki Urban.
Journal of Research in Biology (2013) 3(2): 809-817 811
Site 1
Site 2
Figure 1 Concentration of metals in soil samples from the waste dump soil samples
Concentration Mg/Kg
Concentration Mg/Kg
812 Journal of Research in Biology (2013) 3(2): 809-817
Uka et al., 2013
|
|
Site 1 |
Site 2 |
||||
Metal/Plant Part |
Root |
Stem |
Leaf |
Root |
Stem |
Leaf |
*WHO/FAO |
Pb |
0.01±0.00 |
0.33±0.08 |
0.5±0.11 |
0.2±0.06 |
0.04±0.01 |
0.6± 0.12 |
0.30 |
Cu |
0.12±0.01 |
0.07±0.01 |
ND |
0.08±0.01 |
0.05±0.01 |
0.08±0.02 |
73.30 |
Zn |
ND |
ND |
0.01±0.00 |
0.03±0.01 |
0.04±0.01 |
0.09±0.01 |
99.40 |
Cd |
0.02±0.01 |
0.43±0.01 |
ND |
0.05±0.01 |
0.38±0.01 |
0.15±0.01 |
0.20 |
WHO/FAO = Guideline for heavy metal concentration in leafy vegetables
Table 2 Heavy metal contamination of Amaranthus hybridus (Plant parts) (Mg/kg)
at waste dumpsites in Abakaliki Urban.
Figure 2 Comparison of metal content in soil from the study sites
Pb Concentration Mg/Kg
Cu Concentration Mg/Kg
Zn Concentration Mg/Kg
Cd Concentration Mg/Kg
Uka et al., 2013
Journal of Research in Biology (2013) 3(2): 809-817 813
This Study |
Maximum Standards |
|
Pb |
0.13 |
0.0066 |
Cu |
0.26 |
0.0066 |
Zn |
0.02 |
0.05 |
Cd |
0.08 |
0.07 |
Table 2 Mean concentration (Mg/g) found in the dumpsite soil and maximum permissible
metal content in soil
Source: Kabata-Pendias and Pendias 1992;
Figure 3 Heavy metal content (Pb,Cu, Zn and Cd ) of Amaranthus hybridus at the study sites
Concentration Mg/Kg
Concentration Mg/Kg
814 Journal of Research in Biology (2013) 3(2): 809-817
Uka et al., 2013
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Figure 4 Mean concentration of Pb,Cu,Zn and Cd in roots, stem and leaf of
Amaranthus hybridus from the two respective sites
Pb Concentration in root, stem and
leaf Mg/Kg
Cu Concentration in root, stem and
leaf Mg/Kg
Zn Concentration in root, stem and
leaf Mg/Kg
Cd Concentration in root, stem and
leaf Mg/Kg
Uka et al., 2013
Journal of Research in Biology (2013) 3(2): 809-817 815
Translocation Factor |
||
|
Site 1 |
Site 2 |
Pb |
83* |
3.20* |
Cu |
0.53 |
1.63* |
Zn |
0.01 |
4.33* |
Cd |
21.50 |
10.60* |
Values > 1 are regarded as high values
Table 5 Translocation factor of the studied heavy metals at the dumpsite soil in Abakaliki Urban
Bioconcentration Factor |
||
|
Site 1 |
Site 2 |
Pb |
7 |
12 |
Cu |
0.8 |
3.5 |
Zn |
1 |
16 |
Cd |
9 |
7.3 |
Table 4 Bioconcentration factor (BCF) of each metal at the dumpsite soil in Abakaliki Urban
BCF values > 2 will be regarded as high values
816 Journal of Research in Biology (2013) 3(2): 809-817
Uka et al., 2013
Uka et al., 2013
Journal of Research in Biology (2013) 3(2): 809-817 817
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