CHOWDHURY, M.T.A., NESA, L., KASHEM, M.A. and HUQ, S.M. ...

80 

S.M. Imamul Huq et al. / Pedologist (2010) 80-95 

Assessment of the Phytoavailability of Cd, Pb and Zn using 

Various Extraction Procedures 

M.T.A. CHOWDHURY 1 , L. NESA 1 , M.A. KASHEM 2 and S.M. Imamul HUQ* ,1 

1 

Bangladesh-Australia Centre for Environmental Research (BACER-DU), University of Dhaka, Dhaka1000, Bangladesh 

2 

Department of Soil Science, Chittagong University, Chittagong, Bangladesh 

Keywords: Heavy metal, phytoavailability, single extraction, sequential extraction, correlation 

Abstract 

The phytoavailability of cadmium (Cd), lead (Pb) and Zinc (Zn) in soils from Bangladesh was assessed. The uptake 

by Ipomea aquatica and Oryza sativa was measured and a range of extractants tested on soils and plant tissue samples. 

Extractants tested were distilled H 2 

O, 1 M NH 4 

Cl, 0.01 M CaCl 2 

, 0.005 M diethylenetriamine pentaacetic acid (DTPA), 0.1 M 

ethylenediamine tetraacetic acid (EDTA), 0.1 M HCl and 1 M HCl. The extractability of metals varied depending on the metal 

species, the crop and the extractant used. The best extractant was 1 M HCl, which extracted the highest amount of heavy 

metals and correlated most strongly with plant uptake measures. The use of 1 M HCl is therefore recommended for first-level 

screening of soil contaminated with heavy metals, followed by 0.1 M HCl as the second best choice if only one extractant is 

to be used. Regardless of the soils and the extractants used, the relative extractability was higher for Pb compared with Cd 

and Zn. Sequential extraction showed that Cd was associated mostly with the 1 M NH 4 

Cl extractable fraction, while Pb and 

Zn were associated with the 0.005 M DTPA, 0.1 M EDTA, 0.1 M HCl and 1 M HCl fractions in most cases. The fractions of 

metals extracted varied widely using the sequential extraction procedure compared to single extractions for all soil types. 

1. Introduction 

Heavy metal contamination of the Bangladesh 

environment, particularly the soil, has not yet reached a 

level for concern. However, heavy metal contamination of 

arable soils through industrial activities is likely to reach 

alarming levels in the near future. Industrial waste has 

been found to increase the heavy metal load in surrounding 

agricultural soils (Joardar et al., 2005). These metals are 

taken up by plants and from here enter into the food chain 

where they may cause health hazards (Imamul Huq et al., 

2000). 

Chemical extraction procedures enable the prediction 

of changes in heavy metal mobility or bioavailability in 

soils (Kashem et al., 2007). In order to understand the 

chemistry of heavy metals in their interactions with other 

soil components, such as clay minerals, organic matter 

and the soil solution, or to assess their mobility and 

retention as well as their availability to plants, the usual 

approach is to use selective chemical extraction (Ure, 

1996). Single and sequential extraction methods have 

been used in the study of nutrient element deficiency in 

agricultural crops and animals as well as in environmental 

pollution analysis (Kashem et al., 2007). The ultimate goal 

of such studies has been to see whether different pools of 

elements in soil are obtained using different extractants, 

both in single and sequential extraction. These properties 

could be linked to phytoavailability, phytoremediation 

and/or soil reclamation. However, data on plant uptake 

and the pool of elements extracted using different 

extractants are lacking. The present study aims to assess 

the phytoavailability of heavy metals in soils varying in 

*Corresponding author: Imamul Huq, E-mail: imamhuq@hotmail.com, Tel: +880-18-1922-7377, Fax: +88-861-5583 

Received 18 January 2010; accepted 28 March 2010

S.M. Imamul Huq et al.: Phytoavailability of Cd, Pb and Zn 

81 

their degree of contamination and using various extraction 

procedures. 

2. Materials and Methods 

Sampling site: Three sampling sites were selected 

for the study. Surface soils (0–150 mm) from two sites 

suspected to be contaminated and one site with no 

known source of industrial contamination were used. 

The suspected contaminated soils (steel mill and textile 

mill soils) were collected from the Sonargaon industrial 

area of Narayanganj district (23°39.051’ N, 90°34.919’ E 

and 23°39.065’ N, 90°34.903’ E) and the apparently noncontaminated 

soil was collected from an agricultural land 

located in Dhamrai, Dhaka (23°54.749’ N, 90°10.842’ E) 

(Figure 1). A sample of Dhamrai soil artificially spiked 

(as described below) was also included in the study. The 

soils were designated NC (apparently non-contaminated, 

Dhamrai series), SM (steel mill soil, Sonatala series), TM 

(textile mill soil, Shilmandi series) and Sp (spiked soil, 

Dhamrai series). 

Soil collection and sample preparation: The collected 

soil samples were dried in air for 3 days (at ~35°C) by 

spreading in a thin layer on a clean piece of paper after 

being transported to the laboratory. Visible roots and debris 

were removed from the samples and discarded. To hasten 

the drying process, the samples were exposed to sunlight. 

After air-drying, a portion of the sample containing the 

larger aggregates was ground by gently crushing with a 

wooden hammer. Ground samples were passed through a 

2 mm stainless steal sieve. The sieved samples were then 

mixed thoroughly and stored in labeled plastic containers 

until required for various physical analyses. Another 

portion of the soil samples (2-mm sieved) were further 

ground and passed through a 0.5-mm sieve. The sieved 

sample were mixed thoroughly and stored as above until 

required for chemical and physicochemical analyses. The 

bulk soil samples collected for pot experiments were airdried, 

cleared of debris and crushed to reduce the size 

of large clods. The crushed soil samples were screened 

through a 5-mm sieve. 

phytoavailability of heavy metals in soil and their 

extractability by different extractants, a pot culture 

experiment was performed using four categories of soils: 

NC, SM, TM and Sp. Two crop species were used: an 

upland crop, Ipomoea aquatica, which is a leafy-vegetable 

plant commonly known as “kalmi sak”; and a lowland 

crop, rice (Oryza sativa; BRRI dhan-29 variety). Upland 

and submerged conditions were used for growing kalmi 

and rice, respectively. All experiments were performed in 

triplicate, as follows: 

• 12 pots (2×2×3) for the two suspected contaminated 

soils (each soil with two plant species); 

• 6 pots (2×3) for the non-contaminated soil (with two 

plant species), representing the control; and 

• 6 pots (2×3) containing the spiked soils (with two plant 

species). 

Therefore, a total of 24 pots were used in this pot 

experiment; 12 pots were used for kalmi and 12 pots for 

rice plants. 

Pot preparation: Earthen pots (5 kg and 7 kg) with 

no hole at the bottom were used. Air-dried 5-mm sieved 

soil samples amounting to 4 kg and 5 kg were placed in 

each of the earthen pots used to grow kalmi and rice, 

respectively. 

Soil spiking: To prepare the spiked soil, noncontaminated 

(Dhamrai soil) soil was used. Solutions 

of heavy metals (Cd, Pb and Zn) at concentrations one 

and a half times that of the standard background levels 

of the corresponding heavy metal in soil were used. The 

metal salts used were Cd(NO 3 

) 2 

・4H 2 

O, Pb(NO 3 

) 2 

and 

ZnSO 4 

・7H 2 

O. The amounts of the heavy metal salts 

for three replicate pots were calculated. Solutions were 

made separately using 300 ml distilled water and mixed 

uniformly with the soils adding 100 ml of each solution 

to the pots. The spiked pots were allowed to stand for 2 

weeks before plantation. The same spiking procedure was 

used for an additional pot that was used to measure the 

amount of the elements two weeks after spiking. This 

measure was the background value for the spiked soils. 

The spiking rates are presented in the Table 1. 

Pot culture experiment: In order to study the 

Sowing of plants: Kalmi seeds were obtained from a

82 


Figure 1 GPS-GIS based location map of the contaminated and non-contaminated soil sampling sites.


83 

Table 1 Spiking rates of corresponding heavy metals. 

Element 

local market and rice seedlings (BRRI dhan-29) were 

collected from a farmer’s field. Ten kalmi seeds were 

sown in each pot and allowed to germinate. After 12 days 

the seeds began to germinate. After germination, 4–7 

seedlings were kept in each pot and allowed to grow. For 

the rice pots, soil was puddled and nine rice seedlings 

were randomly transplanted to each pot and allowed to 

grow. All pots were placed in a net-house in a randomized 

arrangement. 

Standard background value* 

(mg/kg) 

Plant culture: Plants were watered with tap water 

twice daily, in the morning and afternoon due to the 

heavy sunshine and warm weather. Sometimes, pots were 

watered less frequently when the soil was saturated with 

rainwater. A blanket application of urea fertilizer was made 

to the soils of rice pots after transplantation of seedlings. 

Intercultural operations were carried out whenever 

necessary. Weeds were removed manually. Positions of 

the pots were changed every alternate day to allow equal 

exposure of each pot to sunlight. Adequate plant protection 

measures were taken during the growing period. During 

the cultivation, different parameters such as growth and 

the appearance of any symptoms were noted. 

Collection and processing of plant samples: At 

harvest, the plants and soils were collected individually 

and processed and prepared for chemical analysis. 

Spiking rate 

(mg/kg) 

Cadmium (Cd)

84 


Table 2 Summary of the extraction methods used in this study. 

Extractant Ratio (w/v) / Time / Temperature Pool Reference 

Distilled H 2 

O 1:10, 1 h, room temp. Water soluble - 

1 M NH 4 

Cl 1:6, 16 h, room temp. Neutral salt soluble/exchangeable Krishnamurti et al. (1995) 

0.01 M CaCl 2 

1:5, 16 h, room temp. Neutral salt soluble/ exchangeable Ahnstrom and Parker (1999) 

0.005 M DTPA 1:2, 2 h, room temp. Chelating extractable Lindsay and Norvell (1978) 

0.1 M EDTA 1:2, 2 h, room temp. Chelating extractable Lindsay and Norvell (1978) 

0.1 M HCl 1:10, 0.5 h, room temp. Weak acid extractable CSTPA (1980) 

1 M HCl 1:33.3, 2 h, room temp. Weak acid extractable ANZECC and ARMCANZ (2000) 

Sequential extraction: For the sequential extraction 

procedure (SEP), 10 g soil (2-mm sieved fraction) was 

placed in a 50 mL polycarbonate centrifuge tube and the 

extractions were performed sequentially in the order of 

strength of the extractants (distilled H 2 

O < 1 M NH 4 

Cl 

< 0.01 M CaCl 2 

< 0.005 M DTPA (diethylenetriamine 

pentaacetic acid) < 0.1 M EDTA (ethylenediamine 

tetraacetic acid) < 0.1 M HCl < 1 M HCl) at a ratio of 

1:2 and following the duration given in the Table 2. 

Extractions were performed in triplicate for each sample. 

All the extracts were centrifuged for 5 minutes at 2000 

rpm. After each extraction procedure, the supernatants 

were filtered. 

Data analysis: The results were statistically evaluated 

using Pearson correlation coefficients and descriptive 

statistics were performed with Microsoft Excel and 

Minitab (Minitab, Inc.). 

3. Results and Discussion 

Soil Properties 

The selected soils were analyzed to ascertain the 

levels of nutrients as well as other elements present (Table 

Table 3 Physical, chemical and physicochemical properties of the soils. 

Soil property NC soil SM soil TM soil Sp soil 

pH 7.26 4.57 5.61 7.33 

% Sand 11.6 2.1 14.9 11.6 

% Silt 41.8 61.6 64.4 41.8 

% Clay 46.6 36.3 20.7 46.6 

Textural class Silty clay Silty clay loam Silt loam Silty clay 

Available P (mg/kg) 4.67 1.72 6.85 4. 56 

Available K (mg/kg) 33.43 57.38 43.37 37.51 

Total N (%) 0.17 0.10 0.20 0.18 

Total P (%) 0.07 0.04 0.06 0.06 

Total K (%) 0.18 0.14 0.13 0.17 

Total S (%) 0.03 0.03 0.02 0.05 

OC (%) 0.34 0.42 0.48 0.42 

OM (%) 0.59 0.72 0.82 0.73 

Total Cd (mg/kg) 0.931 0.895 0.906 2.885 

Total Pb (mg/kg) 27.95 26.28 19.26 81.48 

Total Zn (mg/kg) 95.47 490.9 70.24 236.5 

NC, Apparently Non-contaminated; SM, Steel Mill; TM, Textile Mill; Sp, Spiked; OC, Organic carbon; 

OM, Organic matter.


85 

3). Soil pH ranged from 4.4 to 5.8 in the contaminated 

soils. These lower pH values may be attributed to acid 

effluent coming from nearby industrial operations as well 

as high organic content. 

Metal Extractability 

Among the seven extractants used, 1 M HCl extracted 

the highest proportion of Cd (70.91–98.60%), Pb (104.5– 

122.1%) and Zn (28.2–60.30%) from the soils (Table 4a, b 

and c). Regardless of the soils and extractants, the relative 

metal extractability was observed to be in the order: 

Pb>Cd>Zn. Evidently, 1 M HCl was the most efficient 

agent for extracting Pb (112%), followed by Cd (86%) and 

Zn (41%) from the soils. There was a wide difference in 

metal extractability between 0.1 M HCl and 1 M HCl 

extractants (Cd, 23.76–62.43%; Pb, 38.06–63.94%; Zn, 

42.7–64.34%). The amount of Cd and Pb extracted by H 2 

O 

in the suspected contaminated soils (SM and TM) varied 

from 15% to 22.23% and 15.95% to 21.26%, respectively. 

CaCl 2 

extracted a relatively smaller amount (4.45–18.82%) 

Table 4a Concentration of Cd in the soils after individual extractions (mg/kg) and percent of 

total in parentheses. 

Extractant 

Range 

(min. to max.) 

Cadmium (Cd) 

SD 

% of total 


Mean (%) 

Apparently non-contaminated soil 

H 2 

O 0.172–0.173 0 18.48–18.59 0.172 (18.48) 

1 M NH 4 

Cl 0.180–0.198 ± 0.01 19.34–21.27 0.192 (20.59) 

0.01 M CaCl 2 

0.121–0.130 ± 0.005 12.95–13.97 0.126 (13.54) 

0.005 M DTPA 0.064–0.069 ± 0.003 6.86–7.41 0.067 (7.21) 

0.1 M EDTA 0.135–0.143 ± 0.004 14.53–15.37 0.139 (14.98) 

0.1 M HCl 0.299–0.320 ± 0.01 32.13–34.38 0.307 (32.95) 

1 M HCl 0.660–0.737 ± 0.04 70.91–79.15 0.701 (75.33) 

Total 0.913–0.946 ± 0.02 — 0.931 

Steel mill soil 

H 2 

O 0.157–0.199 ± 0.02 17.54–22.23 0.184 (20.52) 

1 M NH 4 

Cl 0.154–0.174 ± 0.01 17.16–19.44 0.165 (18.43) 

0.01 M CaCl 2 

0.154–0.169 ± 0.008 17.20–18.82 0.160 (17.85) 

0.005 M DTPA 0.061–0.070 ± 0.005 6.81–7.86 0.066 (7.32) 

0.1 M EDTA 0.076–0.123 ± 0.03 8.47–13.72 0.106 (11.81) 

0.1 M HCl 0.245–0.270 ± 0.01 27.37–30.16 0.258 (28.78) 

1 M HCl 0.680–0.693 ± 0.007 75.95–77.44 0.686 (76.57) 

Total 0.812–1.025 ± 0.11 — 0.895 

Textile mill soil 

H 2 

O 0.136–0.155 ± 0.01 15.01–17.11 0.143 (15.78) 

1 M NH 4 

Cl 0.335–0.428 ± 0.05 37.02–47.22 0.373 (41.17) 

0.01 M CaCl 2 

0.122–0.138 ± 0.01 13.47–15.18 0.132 (14.55) 

0.005 M DTPA 0.221–0.266 ± 0.03 24.42–29.32 0.237 (26.11) 

0.1 M EDTA 0.219–0.346 ± 0.07 24.22–38.15 0.266 (29.39) 

0.1 M HCl 0.494–0.630 ± 0.07 54.53–69.54 0.545 (60.15) 

1 M HCl 0.867–0.893 ± 0.01 95.66–98.6 0.878 (96.88) 

Total 0.869–0.925 ± 0.03 — 0.906 

Spiked soil 

H 2 

O 0.135–0.175 ± 0.02 4.68–6.07 0.149 (5.18) 

1 M NH 4 

Cl 1.468–1.811 ± 0.18 50.89–62.78 1.602 (55.53) 

0.01 M CaCl 2 

0.129–0.147 ± 0.01 4.45–5.09 0.138 (4.77) 

0.005 M DTPA 1.130–1.149 ± 0.01 39.17–39.82 1.137 (39.41) 

0.1 M EDTA 1.759–1.810 ± 0.03 60.97–62.72 1.780 (61.70) 

0.1 M HCl 2.137–2.037 ± 0.05 70.60–74.07 2.099 (72.75) 

1 M HCl 2.743–2.763 ± 0.01 95.08–95.77 2.753 (95.43) 

Total 2.809–2.974 ± 0.08 — 2.885

86 


of total Cd than NH 4 

Cl (17.16–62.78%) from the soils. The 

chloride salts (NH 4 

Cl and CaCl 2 

) were found to be weak 

extractants for Pb (up to 17.93%). The efficiency of Zn 

extraction with H 2 

O, NH 4 

Cl and CaCl 2 

was not consistent 

and was therefore found to be unsatisfactory. EDTA was 

a better extractant than DTPA for the metals. DTPA 

extracts metals that are thought to represent the plantavailable 

fractions (Lindsay and Norvell, 1978; Mellum 

et al., 1998; Kashem et al., 2007). DTPA and EDTA form 

soluble complexes with metals, reducing their activity 

in the soil solution; therefore, ions desorbed from the 

surface enter into the extraction solution. It is clear that 

HCl is a better extractant for the metals though the 1M 

concentration performed better than the 0.1 M HCl. The 

extractability, in general, of the metals with different 

extractants was in the order: 1 M HCl > 0.1 M HCl > 0.1 

M EDTA > DTPA > 1 M NH 4 

Cl > H 2 

O > 0.01 M CaCl 2 

. 

It is therefore apparent from these results that 1 M HCl 

is the best choice for metal extraction from soil and could 

be recommended for future use in the extraction of heavy 

Table 4b Concentration of Pb in the soils after individual extractions (mg/kg) and percent of total 

in parentheses. 

Extractant 

Range 


Lead (Pb) 

SD 

% of total 


Mean (%) 


H 2 

O 2.892–3.27 ± 0.19 10.35–11.7 3.072 (10.99) 

1 M NH 4 

Cl 2.119–2.299 ± 0.10 7.58–8.23 2.229 (7.98) 

0.01 M CaCl 2 

2.107–2.736 ± 0.32 7.54–9.79 2.386 (8.54) 

0.005 M DTPA 2.366–2.477 ± 0.06 8.46–8.86 2.412 (8.63) 

0.1 M EDTA 4.983–6.537 ± 0.78 17.83–23.39 5.800 (20.75) 

0.1 M HCl 11.13–11.90 ± 0.42 39.83–42.59 11.43 (40.88) 

1 M HCl 29.22–30.97 ± 0.88 104.5–110.8 30.05 (107.53) 

Total 27.48–28.79 ± 0.73 — 27.95 


H 2 

O 4.191–5.04 ± 0.48 15.95–19.18 4.492 (17.09) 

1 M NH 4 

Cl 4.341–4.711 ± 0.19 16.52–17.93 4.550 (17.32) 

0.01 M CaCl 2 

2.995–3.621 ± 0.33 11.40–13.78 3.256 (12.39) 

0.005 M DTPA 1.823–1.951 ± 0.07 6.94–7.43 1.881 (7.16) 

0.1 M EDTA 5.190–5.373 ± 0.09 19.75–20.45 5.285 (20.11) 

0.1 M HCl 10.93–12.47 ± 0.86 41.99–47.47 11.48 (43.68) 

1 M HCl 30.30–32.07 ± 0.89 115.3–122.1 31.18 (118.76) 

Total 25.64–26.85 ± 0.61 — 26.28 


H 2 

O 3.364–4.095 ± 0.40 17.47–21.26 3.824 (19.86) 

1 M NH 4 

Cl 1.895–2.317 ± 0.23 9.84–12.03 2.055 (10.67) 

0.01 M CaCl 2 

2.258–2.780 ± 0.26 11.72–14.43 2.508 (13.02) 

0.005 M DTPA 1.800–1.880 ± 0.05 9.35–9.76 1.854 (9.62) 

0.1 M EDTA 2.136–4.820 ± 1.54 11.09–25.03 3.045 (15.81) 

0.1 M HCl 9.396–9.623 ± 0.12 48.79–49.97 9.536 (49.51) 

1 M HCl 21.53–22.54 ± 0.53 111.8–117.0 21.94 (113.94) 

Total 18.96–19.67 ± 0.37 — 19.26 

Spiked soil 

H 2 

O 3.713–4.197 ± 0.25 4.56–5.15 3.981 (4.89) 

1 M NH 4 

Cl 2.719–3.638 ± 0.46 3.34–4.47 3.178 (3.90) 

0.01 M CaCl 2 

2.363–2.907 ± 0.27 2.90–3.57 2.626 (3.22) 

0.005 M DTPA 26.60–28.86 ± 1.13 32.64–35.42 27.75 (34.05) 

0.1 M EDTA 65.90–67.50 ± 0.80 80.88–82.84 66.67 (81.82) 

0.1 M HCl 53.56–55.21 ± 0.83 65.73–67.76 54.34 (66.69) 

1 M HCl 86.46–90.39 ± 2.16 106.1–110.9 88.94 (109.16) 

Total 81.00–82.26 ± 0.68 — 81.48


87 

Table 4c Concentration of Zn in the soils after individual extractions (mg/kg) and percent 

of total in parentheses. 

Extractant 

Range 


Zinc (Zn) 

SD 

% of Total 


Mean (%) 


H 2 

O BDL BDL BDL BDL 

1 M NH 4 

Cl BDL BDL BDL BDL 

0.01 M CaCl 2 

BDL BDL BDL BDL 

0.005 M DTPA 1.014–1.128 ± 0.06 1.06–1.18 1.078 (1.13) 

0.1 M EDTA 3.572–3.752 ± 0.10 3.74–3.93 3.685 (3.86) 

0.1 M HCl 9.399–10.00 ± 0.25 9.84–10.5 9.718 (10.18) 

1 M HCl 26.92–27.16 ± 0.40 28.2–29.0 27.26 (28.55) 

Total 91.81–98.96 ± 3.58 — 95.47 


H 2 

O 12.87–13.89 ± 0.51 2.62–2.83 13.40 (2.73) 

1 M NH 4 

Cl 40.64–43.92 ± 1.71 8.28–8.95 41.99 (8.56) 

0.01 M CaCl 2 

36.13–36.74 ± 0.31 7.36–7.48 36.41 (7.42) 

0.005 M DTPA 90.85–110.1 ± 9.65 18.5–22.4 100.9 (20.55) 

0.1 M EDTA 19.52–19.98 ± 0.24 3.98–4.07 19.79 (4.03) 

0.1 M HCl 96.29–96.77 ± 0.26 19.6–19.7 96.58 (19.67) 

1 M HCl 185.9–191.7 ± 2.90 37.9–39.1 188.6 (38.42) 

Total 420.6–547.6 ± 64.6 — 490.9 


H 2 

O 0.177–0.602 ± 0.22 0.25–0.86 0.367 (0.52) 

1 M NH 4 

Cl 1.484–1.936 ± 0.24 2.11–2.76 1.674 (2.38) 

0.01 M CaCl 2 

BDL BDL BDL BDL 

0.005 M DTPA 2.801–2.876 ± 0.04 3.99–4.09 2.848 (4.05) 

0.1 M EDTA 2.818–4.094 ± 0.68 4.01–5.83 3.322 (4.73) 

0.1 M HCl 10.15–11.37 ± 0.64 14.5–16.2 10.87 (15.47) 

1 M HCl 26.88–27.83 ± 0.54 38.3–39.6 27.21 (38.74) 

Total 69.16–72.13 ± 1.64 — 70.24 

Spiked soil 

H 2 

O 0.295–0.363 ± 0.03 0.12–0.15 0.327 (0.14) 

1 M NH 4 

Cl 2.245–5.990 ± 1.89 0.95–2.53 3.968 (1.68) 

0.01 M CaCl 2 

BDL – 0.075 ± 0.31 BDL – 0.03 0.075 (0.03) 

0.005 M DTPA 17.63–18.09 ± 0.23 7.46–7.65 17.87 (7.56) 

0.1 M EDTA 19.02–19.62 ± 0.31 8.04–8.30 19.37 (8.19) 

0.1 M HCl 78.21–79.05 ± 0.48 33.1–33.4 78.76 (33.31) 

1 M HCl 132.0–142.7 ± 5.34 58.2–60.3 137.4 (58.12) 

Total 213.8–252.6 ± 20.2 — 236.5 

BDL = Below Detection Limit. 

metals such as Cd, Pb and Zn. 

Extent of Soil Contamination 

The apparently non-contaminated soil (NC soil, 

Dhamrai series) contained relatively higher amounts of 

Cd, Pb and Zn than the suspected contaminated soils (SM 

or TM soils). However, the levels of most of the heavy 

metals in all soils were within the tolerable limit (Kloke, 

1980). The higher values for the elements in the NC soil 

were perhaps due to the sampling site of the Dhamrai soil 

being adjacent to the Dhaka–Manikganj highway. Levels 

of Pb, Cd and Zn have previously been reported to be high 

in soils along the highways due to automobile exhaust 

(Imamul Huq et al., 1999). 

The extent of contamination due to heavy metal 

deposition in the soils studied here was compared with 

the values of Kashem and Singh (1999) for different 

industrial sites in Bangladesh. In this previous study,

88 


background concentrations were found to be 0.01–0.2 mg 

kg −1 for Cd, 12–20 mg kg −1 for Pb, and 68 mg kg −1 for Zn. 

The total heavy metal content of the soil samples (Tables 

4a, b and c) showed a wide variation in values ranging from 

levels similar to background to a level reflective of severe 

contamination. The tolerable and in excess of tolerable 

levels were also calculated on the basis of information 

published by Kloke (1980), where maximum tolerable 

concentrations were defined as 3, 100 and 300 mg kg −1 

for Cd, Pb and Zn, respectively. Cd, Pb and Zn contents 

were found to be at a tolerable level (


89 

Figure 2 Mean proportion of Cd in each of the single extractants (SE) compared with the corresponding fraction 

in the sequential extraction procedure (SEP) for NC, SM, TM and Sp soils. 

Figure 3 Mean proportion of Pb in each of the single extractants (SE) compared with the corresponding fraction 

in the sequential extraction procedure (SEP) for NC, SM, TM and Sp soils.

90 


Figure 4 Mean proportion of Zn in each of the single extractants (SE) compared with the corresponding fraction 

in the sequential extraction procedure (SEP) for NC, SM, TM and Sp soils. 

Figure 5 Content of Cd (a), Pb (b) and Zn (c) in the edible parts of kalmi and rice.


91 

Cd content in the rice plants and the Pb and Zn contents in 

both plant species exceeded the toxic levels. 

However, of the two suspected contaminated soils 

from the steel mill and textile mill areas, the concentrations 

of the metal elements in the plants were found much higher 

in the steel mill soil. This may be due to the fact that the 

metals were in a more labile state than those in the TM 

soil. The TM soil would have been contaminated primarily 

with cellulosic organic waste, with the metals bound to 

these organic materials rendering them less mobile for 

plant uptake. Elevated levels of Cd, Pb and Zn in plants 

near metal smelters have previously been demonstrated 

in other investigations (Cox and Hutchinson, 1980; Farago 

and O’Connell, 1983; Hogan and Wottom, 1984; Kashem 

and Singh, 1999). 

Uptake of Heavy Metals by Plants 

The uptake of Cd, Pb and Zn by the kalmi and rice 

plants was calculated by multiplying the concentration of 

the metal elements in the dry matter with the total dry 

matter produced. The results are expressed as µg per pot 

for Cd uptake and mg per pot for Pb and Zn uptake. The 

maximum uptake of Cd in kalmi was found in the SM soil: 

22.07 µg/pot, with 10.24% in the roots and 89.76% in the 

edible parts. In the case of rice, highest Cd levels were in 

plants grown in the Sp soil (123.48 µg/pot), with the major 

portion taken up by the grains (up to 70.3% of total uptake) 

in all soil types (Figure 6). 

The maximum uptake of Pb by the roots (0.039 mg/ 

pot) and edible parts (0.017 mg/pot) of kalmi was observed 

in the SM soil (Figure 7a). These values represented 

70.38% (by roots) and 29.62% (by shoots and leaves) of 

the total Pb accumulation in kalmi. The level of Pb uptake 

by rice plants was in the order: SM soil > Sp soil > TM 

soil > NC soil (Figure 7b). 

Zn uptake by kalmi and rice was also observed 

to be highest in the SM soil (2.31 and 19.59 mg/pot, 

respectively), followed by TM, Sp and NC soils. Similar 

Zn uptake was found in the NC and Sp soils (Figure 8). A 

relatively higher amount of Zn was taken up by the rice 

Figure 6 Uptake of Cd by kalmi (a) and rice (b) plants. 

Figure 7 Uptake of Pb by kalmi (a) and rice (b) plants.

92 


Figure 8 Uptake of Zn by kalmi (a) and rice (b) plants. 

straw in all soils. 

Interrelationships among Soil Parameters 

A significant positive correlation (r = 0.56–0.99; p 


93 

Table 8 Correlation coefficients between extracted metal elements and their corresponding plant 

contents irrespective of soil types. 

Metal 

element 

Cd 

Pb 

Extractant 

Single extraction 

Kalmi 

(total plant) 

Rice 

(grain) 

Sequential extraction 

Kalmi 

(total plant) 

Rice 

(grain) 

H 2 

O 0.51 –0.29 –0.17 –0.39 

1 M NH 4 

Cl 0.29 0.89 a 0.38 0.90 a 

0.01 M CaCl 2 

0.66 a –0.14 0.53 0.84 a 

0.005 M DTPA 0.30 0.87 a 0.35 0.90 a 

0.1 M EDTA 0.32 0.89 a 0.39 0.85 a 

0.1 M HCl 0.29 0.87 a 0.37 0.88 a 

1 M HCl 0.33 0.88 a 0.14 0.80 a 

Total 0.37 0.88 a 

H 2 

O 0.71 a 0.59 b 0.24 0.39 

1 M NH 4 

Cl 0.94 a 0.51 0.70 a 0.25 

0.01 M CaCl 2 

0.79 a 0.55 b –0.40 –0.56 b 

0.005 M DTPA 0.26 0.36 0.27 0.37 

0.1 M EDTA 0.28 0.37 0.28 0.36 

0.1 M HCl 0.28 0.36 0.22 0.36 

1 M HCl 0.32 0.36 0.43 0.36 

Total 0.29 0.34 

H 2 

O 0.99 a 0.38 0.93 a 0.27 

1 M NH 4 

Cl 0.99 a 0.37 0.99 a 0.35 

0.01 M CaCl 2 

0.99 a 0.35 0.99 a 0.39 

Zn 

0.005 M DTPA 0.99 a 0.36 0.40 0.18 

0.1 M EDTA 0.61 b 0.22 –0.03 0.05 

0.1 M HCl 0.71 a 0.26 0.04 0.07 

1 M HCl 0.78 a 0.27 0.52 0.24 

Total 0.92 a 0.25 

a 

denotes significance at p

94 


Figure 9 Concentrations in soils before and after harvest for Cd (a), Pb (b) and Zn (c). 

Conclusion 

The results of the present study suggest that 

agricultural soils of Bangladesh in the vicinity of different 

industrial areas are at risk of heavy metal contamination/ 

pollution. The concentration of Cd, Pb and Zn in the soils 

and the plant tissues and a strong correlation among the 

extractable metal fractions and metals content in plants 

indicate the phytoavailability of the heavy metals. However, 

the assessment of the phytoavailability of the elements 

considered in this study was found to be dependent on 

the method of extraction, the crop and metal species, as 

well as the soil type. The present study indicates that a 

mild extractant such as 1 M HCl can be used to assess the 

phytoavailability of the heavy metals Cd, Pb and Zn. 

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CHOWDHURY, M.T.A., NESA, L., KASHEM, M.A. and HUQ, S.M. ...

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