Lead and Cadmium Phytoremediation Potentials of ...

Sciknow Publications Ltd.

NE 2014, 2(3):33-38 DOI: 10.12966/ne.11.01.2014

Natural Environment ©Attribution 3.0 Unported (CC BY 3.0)

Lead and Cadmium Phytoremediation Potentials of Plants from Four Lead Smelting Slags Contaminated Sites Ibigbami Olayinka Abidemi1, 2,*, Ogundiran Mary Bosede2 and Osibanjo Oladele2 1

Department of Chemistry, Ekiti State University, P.M.B 5363, Ado- Ekiti, Nigeria Analytical/Environmental Unit, Department of Chemistry, University of Ibadan, Nigeria

2

*Corresponding author (Email: [email protected])

Abstract - The study considered the potentials of plants grown on four lead smelting contaminated sites in Ibadan as heavy metals accumulator. Twenty six plants and associated soils were collected and analysed for Pb and Cd concentrations. Accumulation of Pb and Cd from soil to roots and shoots was evaluated in terms of enrichment coefficient and translocation factor. Concentrations of Pb and Cd in soil ranged from 230-18500 and ND – 162mgkg-1. Lead and Cd amounts in shoots varied from 124 to 8390 and 0.50 to 36.6mgkg-1. A few of the plants samples were identified as potential heavy metal accumulators. Gomphrena celosioides, Cleome viscosa, Andropogon gayanus, Urena lobata and Capsicum frutescens accumulated Cd appreciably and are therefore proposed for consideration to remediate soils polluted with Cd. Gomphrena celosioides, Andropogon tectorum, Eleusine indica, Urena lobata and Sporobolus pyramidalis accumulated Pb substantially and as such suggested for study on phytoremediation of Pb polluted soils. Keywords - Heavy metals, Hyperaccumulator, Enrichment coefficient, Translocation factor

1. Introduction Heavy metal contamination of soil is inimical to ecosystem. When heavy metals are present above acceptable limits in the environment they can contaminate the surrounding soil, surface and ground waters and in effect may become toxic to living organisms. Plant growth may be adversely affected by metals in soil or concentrate in leaf, stems or roots where they can be subsequently transferred to both lower and higher animals. In humans, following exposure to high levels, heavy metal toxicity has been associated with various physiological disturbances. For example, Pb toxicity is been linked to various reproductive effects, developmental delay and mental retardation in children [1]. Thus, there is global concern on remediation of heavy metal polluted sites. Phytoremediation is one of the promising methods for reclamation of soils contaminated with toxic metals by using hyperaccumulator plants [2]. It involves the use of plant species to decontaminate and remediate heavy metal polluted soils. Phytoremediation which is also called green remediation, agro remediation, butano-remediation, uses vegetation and associated microbiota, soil amendments and agronomic techniques to remove, contain or render the heavy metals harmless in the soil [3, 4, 5]. Phytoremediation of heavy metal from environment involves such techniques as, phytoextraction, phytofiltration, phytovolatilization, phytostabilization [6, 7, 8, 9, 10, 11, 12, 13]. Phytoextraction is defined as the use of

plants to remove metals from soil and to transport and concentrate them in above ground biomass. Phytofiltration entails the use of plant root or seedlings to absorb or adsorb pollutants, many metals from groundwater and aqueous waste streams rather than the remediation of polluted soils. Phytovolatilization use plants to turn volatile chemical species of soil metals and phytostabilisation, use plants to minimize metal mobility in contaminated soil through accumulation by roots or precipitation within the rhizophere. Over four hundreds plants have been identified and reported as hyper accumulators [14, 15, 12]. These plants have been considered suitable for soil stabilization and extraction of heavy metals [16]. Metal concentration in the shoots of hyper accumulators normally exceeds those in roots, and it has been suggested that metal hyper accumulation has the ecological role of providing protection against fungal and insect attack [6]. Among plants that have been identified as Pb and Cd hyperaccumulators are Armeria maritime, Thlaspi caerulescens, Cardaminopsis halleri. Most of these plants are non-destructive to the environment and does not involve waiting for new plant communities to recolonise the site. The enrichment coefficient and translocation factor have been used to demonstrate the ability of plants to accumulate heavy metal [17]. The enrichment coefficient (shoot/soil quotients) of the plants was calculated by dividing the concentration of the heavy metal in the shoot by the concentration in the soil while translocation factor (shoot/root quotients)

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were calculated by dividing the heavy metal concentrations in shoot by that of the root [17]. Four important factors have been used to identify plants as a hyper accumulator. (i) Plant species whose shoots contain >100mgkg ˉ¹ Cd; 1000 mgkgˉ¹ Ni, Co, Pb, Cr and Cu; 10,000 mgkgˉ¹ Zn and Mn [14, 18] are said to be hyperaccumulators. (ii) concentration of heavy metals in shoots is 10-500 times as much as those in normal plant, Pb (5mgkgˉ¹), Cd (1mgkgˉ¹), Zn (100 mgkgˉ¹) [19] (iii) metal concentration in shoots is invariably greater than that of roots [20, 18] and (iv) enrichment coefficient is ˃ 1 [ 21, 22]. In Nigeria, particularly in Ibadan, a few sites had been used as dumpsites for secondary lead smelting slag. The aim of this study therefore was to investigate Pb and Cd accumulation potentials of plants that grow naturally on these sites with the view of using them for future cleanup of the sites

2. Materials and Methods 2.1. Site Description Samples used in this study were collected from four lead smelting slag contaminated sites in Ibadan, Nigeria (Fig. 1). The sites contained slags dumped by lead acid battery manufacturing companies. Dumping started around 1990s where slags from lead smelting operations were dumped on these sites. 2.2. Sampling Samples of plant and soil were randomly collected from the sites. Maximum sampling depth of 20cm, rooting zone was applied. Twenty six (26) plant samples and the soils on which they grew were collected. The sampled plant species grew very well and were dominant in the dumpsites vicinities. The choice of plant species collected was based on the availability of the plant at the point of collection. Samples identification was done in the herbarium of the Department Botany, University of Ibadan, Nigeria.

Figure 1. Map of Lagelu local government showing the sampling site

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2.3. Soil pre-treatment and analysis The soil samples were air dried at room temperature for 2 weeks, crushed with porcelain mortar and pestle and sieved through ˃ 2mm nylon sieve. Composite soil samples were taken to determine the soil pH, CEC, particle size distribution and Organic matter. The pH of the sieved soil samples in water was determined by the method of Hendershotz et al. [23], the soil particle size was determined by hydrometer method described by Shedrick & Wang, [24], while wet oxidation method of Walkley and Black described by Schulte [25] was used to determine the organic carbon content from which organic matter content was calculated and the N.P.K determined (AOAC) [26]. One gramme of soil sample was digested using 10 mL of 2 M HNO3 [1]. The total concentration of Pb and Cd were determined by Atomic absorption spectrophotometric method. Standard solutions were included for quality assurance and control.

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2.4. Plant pre-treatment and analysis Plant samples were thoroughly washed with running tap water to remove adhered soil particles. The shoot and root tissues were then separated, air-dried and oven dried at 700 C to constant weight. The dried samples were ground with porcelain mortar and pestle into powders, sieved to < 2mm size. 1 g of < 2mm fraction plant samples was ignited in a muffle furnace for 6 hrs at a temperature between 450C – 5000C. The ashed samples were allowed to cool and then subjected to dissolution with 10 m.L of 2 M HNO3 [27]. The concentrations of Pb and Cd in plant digests were determined using AAS.

3. Results and Discussion 3.1. Soil Characteristics and metal concentrations Table 1 presents the physico-chemical characteristics of the soil from the four sampling sites. Soils from the studied area showed variation in pH.

Table 1. Analytical parameters of composite soil samples from the four contaminated Sites Parameter pH Organic matter (%) CEC (meq/100g) Clay % Silt % Sand % N (mgkg-1) P (mgkg-1) K(mgkg-1)

Site 1 6.20 0.87 2.88 5.40 40.8 53.8 600 13.5 130

The pH ranged between 5.00 and 8.40. The soil in site 2 was moderately alkaline while the soils from sites 1, 2 and 3 were slightly acidic. The pH values for these three sites imply bioavailability of metals in soil solution may be enhanced [28, 29]. Organic matter ranged from 0.87 to 1.47%, the low organic matter could be attributed to sparse vegetation in the vicinity of the slag. Cation exchange capacity (CEC) ranged from 2.74- to 3.23me/100g. The CEC of the soil was highest at site 4 which may be due to high clay content. Results from site 4 showed high clay content of 21.6% when compared with other sampling sites. Soil samples with clay minerals

Site 2 8.40 1.47 2.74 7.70 18.9 73.4 980 22.8 130

Site 3 5.60 1.09 2.83 1.80 14.6 83.6 756 24.5 120

Site 4 5.00 1.19 3.23 21.6 18.2 60.2 810 13.0 130

have strong tendency to absorb chemical species in soil. The clay minerals may also effectively immobilise dissolved chemicals or species in soil. For the particle size analysis, the percentage of clay, silt and sand ranged from 1.8 to 21.6 %, 14.6 to 40.8 % and 53.8 to 83.6 %. The result showed similar trend as percentage of sand was found higher than silt and clay in the samples. The presence or absence of soil micro nutrients and macronutrients determine the viability of plants on a particular soil. The N, P and K concentration ranged from 600 to 980, 13.0 to 24.5, and 120 to130 mgkg-1.

Table 2. Soil and plants Pb concentrations (mgkg-1), concentration times level, enrichment coefficient and translocation factor Site

Plant Species

Site 1

Azadirachta indica Azadirachta indica Cleome viscosa Dactyloctenium aegyptium Cynodon dactylon Azadirachta indica Gomphrena celosioides Digitaria horizontalis Andropogon tectorum

Site 2

Soil mg/kg 800 1800 18500 12500 6250 2040 16600 2840 2840

Root mg/kg 500 890 6710 3300 3880 2470 4200 2940 3790

Shoot mg/kg 250 520 2540 2180 1190 540 8390 610 5660

Conc. Times level 50 104 508 436 238 108 1678 122 1132

Enrichment Coefficient 0.31 0.29 0.14 0.17 0.19 0.26 0.51 0.21 1.99

Translocation factor 0.50 0.58 0.38 0.66 0.31 0.22 2.00 0.21 1.49

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Site 3

Site 4

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Sporobolus pyramidalis Andropogon gayanus Psidium guajava Psidium guajava Gomphrena celosioides Imperata cylindrica Blighia sapida Eleusine indica Cyperus eresctus Parquetina nigrescens Amaranthus viridis Ageratum conyzoides Urena lobata Gomphrena celosioides Chromolaena odorata Triumfetta cordifolia Capsicum frutescens

16000 10800 960 1510 610 960 970 7820 6080 3160 2310 1600 1420 5410 4130 4140 430

5590 7300 540 860 350 810 490 1860 3520 6390 1600 1040 1460 3810 2810 1900 590

5890 3580 230 300 520 750 820 3680 1750 2100 850 450 1550 5160 3180 880 120S

1178 716 46 60 104 150 164 736 350 420 170 90 310 1032 636 176 24

0.37 0.33 0.24 0.20 0.85 0.78 0.85 0.47 0.29 0.66 0.37 0.28 1.09 0.95 0.77 0.21 0.28

1.05 0.49 0.43 0.35 1.49 0.93 1.67 1.98 0.50 0.33 0.53 0.43 1.06 1.35 1.43 0.46 0.20

Plant Pb concentration from non-polluted environment is Pb 5 mgkg-1 [19]. Table 3. Soil and plants Cd concentrations (mgkg-1), concentration times level, enrichment coefficient and translocation factor Site

Plant Species

Soil mg/kg

Root mg/kg

Site 1

Shoot mg/kg

Conc. level

Times

Enrichment Coefficient

Azadirachta indica ND 0.30 1.75 2 ND Azadirachta indica 1.10 0.58 1.70 2 1.55 Cleome viscosa 162 30.1 36.6 37 0.23 Dactyloctenium aegyptium 30.1 6.18 2.38 2 0.08 Cynodon dactylon 72.3 0.95 8.63 9 0.12 Azadirachta indica 21.1 0.30 3.25 3 0.15 Gomphrena celosioides 8.30 6.10 1.70 2 0.20 Digitaria horizontalis 4.10 0.90 0.50 1 0.12 Site 2 Andropogon tectorum 21.3 2.95 5.43 5 0.25 Sporobolus pyramidalis 10.9 2.38 4.83 5 0.44 Andropogon gayanus 37.0 5.13 19.5 20 0.53 Psidium guajava 64.7 3.22 0.53 1 0.008 Psidium guajava 63.4 2.68 1.05 1 0.02 Site 3 Gomphrena celosioides 0.60 6.45 17.5 18 29.2 Imperata cylindrica 0.40 0.78 1.18 2 2.95 Blighia sapida 17.6 2.58 0.73 1 0.04 Eleusine indica 0.81 1.48 1.23 1 1.52 Cyperus eresctus 66.2 11.2 0.75 1 0.01 Parquetina nigrescens 40.6 5.18 1.93 2 0.05 Site 4 Amaranthus viridis 6.70 0.90 1.13 1 0.17 Agerantum conyzoides 124 15.9 2.25 2 0.02 Urena lobata 82.3 4.58 11.8 12 0.14 Gomphrena celosioides 7.10 14.0 10.8 11 1.52 Chromolaena odorata 27.9 3.43 0.90 1 0.03 Triumfetta cordifolia 33.2 4.40 1.83 2 0.06 Capsicum frutescens 98.4 0.40 17.7 18 0.18 Plant Cd concentration from non-polluted environment is Cd 1 mgkg-1 [19], Detection limit of Cd is 0.01 mg/L

3.2. Heavy metal accumulation by the plant species Table 2 shows the concentrations of Pb in soil, root and shoot of the plant, Pb shoots concentration time levels compared to plants from non-polluted environment, enrichment coefficient and translocation factor. The concentration of Pb in the soil from site 1, 2, 3 and 4 ranged from 800 to 18500, 960 to 16000, 960 to 7820 and 430 to 5410mgkg-1, respectively. The results showed gross contamination of the sites with lead when compared with normal range of 2- 300 mg/kg of Pb in uncontaminated soil [1]. The soil samples also contained high level of Cd, ranging from ND – 98.4mgkg-1 compared with

Translocation factor 5.83 2.93 1.22 0.39 9.08 10.8 0.28 0.56 1.84 2.03 3.80 0.16 0.39 2.71 1.51 0.28 0.83 0.07 0.37 1.26 0.14 2.58 0.77 0.26 0.42 44.3

0.01-2.7 mg/kg which is the normal range of Cd in uncontaminated soils. Most of the plants showed high level of Pb in shoots. The concentration of lead in shoot from site 1, 2, 3 and 4 ranged from 250 to 8390, 230 to 5890, 520 to 3680 and 120 to 5160 mgkg-1 while the concentration of root ranged from 500 to 6710, 540 to 7300, 490 to 6390, 590 to 3810 mgkg -1, respectively. The variation in the levels of Pb and Cd concentration in the plants could be as a result of the waste dumped at different times, composition of the waste and the ability of the plant to tolerate and accumulate heavy metals. The levels of Pb and Cd in plants from these contaminated sites were very high as compared to concentration from non

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polluted environment Pb 5 mgkg-1 and Cd 1 mgkg-1 [19]. For enrichment coefficient of Pb, only Andropogon tectorum in site 2 showed enrichment coefficient (EC) > 1, this showed that Pb move easily in Andropogon tectorum than other plant species. The lowest EC was found in Urena lobata. Gomphrena celosioides, Andropogon tectorum, Sporobolus pyramidalis, Blighia sapida, Eleusine indica, Urena lobata, Chromolaena odorata showed transloction factor TF > 1, which illustrates that the translocation of Pb, was higher from the roots to the shoots. Gomphrena celosioides from sites I, 2 and 4 showed TF > 1. Plants with TF values greater than 1 are reported to show very efficient ability to transport metals from roots to shoots [30] and probably sequestration of metals in leaf vacuoles and apoplast [15]. Azadirachta indica, Cleome viscosa, Dactyloctenium aegyptium, Cynodon dactylon, Digitaria horizontalis, Andropogon gayanus, psidium guajava, Imperata cylindrical, Cyperus eresctus, Parquetina nigrescens, Amaranthus viridis, Agerantum conyzoides, Triumfetta cordifolia, Capsicum frutescens showed TF < 1. Three Azadirachta indica and two Psidium guajava from site 1 and 2 showed similar behaviour by having TF < 1. Hyperaccumulators have been defined as plant species whose shoots contain >1000mgkg-1 of Pb [18]. Cleome viscosa, Dactyloctenium aegyptium, Cynodon dactylon, Gomphrena celosioides, Andropogon tectorum, Sporobolus pyramidalis, Andropogon gayanus, Eleusine indica, Cyperus eresctus, Parquetina nigrescens, Urena lobata, Chromolaena odorata had over 1000 mgkg-1 of Pb in their shoots. Another important parameter used in identifying hyperaccumulator as reported by Baker and Walker [20] and Baker et al. [18] is when the metal concentration in shoots is invariably greater than that in the root. Gomphrena celosioides, Andopogon tectorum, Blighia sapida, Eleusine indica, Urena lobata and Chromolaena odorata all showed greater than 1000mg/kg Pb in their shoots. Furthermore, considering the concentration time level where the concentration of heavy metals in shoots is 10-500 times as much as those in normal plant, all the plant sampled showed concentration time level of over 10 for Pb accumulation. Whereas 30.7% of the plants accumulated over 500 times amount of Pb. The concentrations of Cd in soil root and shoot of the plant, Cd shoots concentration time levels compared to plants from non-polluted environment, enrichment coefficients and translocation factors are presented in Table 3. Six of the samples analysed had concentrations > 10 mgkg-1 Cd in there shoots while twenty samples had > 10 mgkg-1 in shoots. The concentration of Cd in shoots from sites 1, 2 , 3 and 4 ranged from 0.50 to 36.6, 0.53 to 5.43, 0.73 to 17.5, 0.90 to 17.7 mgkg-1. Many of the plants analysed for Cd indicated greater amount in shoots than roots. Azadirachta indica, Cleome viscosa, Cynodon dactylon, Angropogon tectorum, Sporobolus pyramidalis, Andropogon gayamus, Gomphrena celosioidies, Imperata cylindrica, Urena lobata and Capsicum frutescens showed considerable level of Cd in shoots compared with Cd concentration in their roots. Gomphrena celosioides met the last three conditions as potential Cd hyperaccumulators. Cleome viscosa, Urena

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lobata and Capsicum frutescens met the second and third condition as potential Cd hyperaccumulators where the concentration of Cd in shoots are 10 times that of normal plant and where Cd concentration in shoot are invariably greater than that in roots.

4. Conclusion The study was conducted to identify potential Pb and Cd accumulators that can be used to clean up lead slag contaminated sites. The study showed that the concentrations of Pb in the studied sites are much higher than its concentrations in normal soils. Some of the plants investigated were identified as potential Pb and Cd hyperaccumulators based on the literature conditions for selecting plants as an hyperaccumulator. Gomphrena celosioides, Andropogon tectorum, Eleusine indica, Urena lobata and Sporobolus pyramidalis accumulated Pb substantially and as such suggested for study on phytoremediation of Pb polluted soils. Gomphrena celosioides, Cleome viscosa, Andropogon gayanus, Urena lobata and Capsicum frutescens accumulated Cd appreciably and are therefore proposed for consideration to remediate soils polluted with Cd.

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