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Phytoremediation of chromium contamination using Azadirachta indica
Kannan.V and Kanimozhi. M
Centre for Advanced Studies in Botany,
University of Madras,
Guindy campus, Chennai. 600 025.


Leather industry is one of the important industries in India as it earns a high proportion of foreign exchange. It is also the major reason for the environmental influx of chromium(Cr). The effluent and sludge disposed from these industries into rivers and onto land has led to extensive degradation of productive land (Ramasamy, 1997). Cleaning up of the Cr contaminated sites is a challenging task. Phytoremediation involves the use of plants to remove toxic substances from the environment. The use of plants has been investigated for a wide variety of chemical substances, including metal and organic contaminants, in various media, most commonly soil and water. It is an emerging technology that can be considered for remediation of contaminated sites because of its cost effectiveness, aesthetic advantages, and longterm applicability. Though many small herbs have been successfully proved to accumulating heavy metal ions like chromium, the burden of harvesting and disposing the one season plants poses greater difficulty in applying the bioremediation. Hence large plants with long period of life and soil covering and transpiration potentials could be the best choice. On this basis an attempt has been made to use Azadirachta indica with economic timber value, applying hydroponic studies, pot culture and by field experiments for the remediation of chromium contamination.


Chromium concentrations were selected based on previous hydroponic studies of annual plants (Shanker et al., 2004). Chromium was used at levels such as 10, 25, 50, 100, 150mM in the experiments. Soil amended with various levels of tannery sludge (10%, 20%, 40%, 60%, 80% and 100% were prepared and filled in to the pots and pot with only garden soil served as control. All the experiments were repeated twice. Based on these results, field trials were conducted to evaluate the metal accumulation.

Measurement of chromium content (mg Kg-1) was made on plant parts according to Jones et al. (1991).

Results and discussion

Plants have the genetic potential to clean up soil contaminated with toxic metals. Some plants can take up, translocate, and tolerate increased levels of certain heavy metals that would be toxic to any other known organisms. Identification of metal hyperaccumulator species has been an impetus for Phytoremediation research. In the present study, a significantly high accumulation of heavy metals was found in various parts of the Azadirachta indica,grown on hydroponic and tannery sludge amended soil. It was observed that under normal control conditions, the concentration of Cr in various parts of the plant was < 1 mg/Kg dry weight (DW) of plant tissues. The accumulation of hexavalent Cr in hydroponics experiment of Azadirachta indica was found maximum in shoots followed by roots and leaves which increased with increase in chromium amendments (Fig.1). Of the total amount of chromium accumulated by Azadirachta indica 95.16% was in the shoots and 4.63% in roots. However, chromium accumulation in the leaf was quiet low or very negligible when compared to stem and roots(Fig.2). Presence of Cr in the external environment does not lead to any changes in the growth and development pattern of the plants at the initial low concentrations (Table1). While, Hasselgren (1999) found stem biomass production of three willow clones was enhanced by sludge application rate; it also led to more uniform growth and a greater shoot number than in control plants. But Sinapsis alba showed reduction in plant height at 200 – 400 mg chromium per kilogram soil (Hanus and Tomas, 1993).

In pot studies also the test plant accumulated higher amount of chromium in the stem followed by roots and leaves; but the chromium accumulation in the shoot was over 2 and 28 fold when compared to the root and leaf respectively (Table2). The accumulation of Cr increased with increase in sludge amendments and exposure periods as observed by Hasselgren (1999). Whereas, Huffman and Allaway (1973) have reported as much as 98% chromium accumulation in the roots of bean plants.

The reason for the high accumulation in roots of the plants could be because chromium is immobilized in the vacuoles of the root cells (Shanker et al., 2004). Khan (2000) further reported the potential of mycorhiza in protecting tree species Populus euroamericana, Acacia arabica and Dalbergia sisso against the harmful effects of chromium contaminated tannery effluent polluted soil.

In the field experiment, the test plant also showed higher accumulation of Cr in stem tissues. Thus Azadirachta indica was not only able to tolerate very high concentrations of chromium but also showed appreciable growth over control plants (Fig.3). Similar results have been recorded in 16 Salix clones grown in a field trial (Watson, 2002; Pulford et al., 2002). Therefore, Azardirachta indica could be potentially exploited in phyto remediation practices like soil reclamation, phyto extraction of metals like Cr from tannery effluent amended soil.

Table : 1 Growth parameters of Azadirachta indica as influenced by Cr(VI) in nutrient medium after 120 h of treatment.




Cr (VI)
(10 µM)
Cr (VI)
(25 µM)
Cr (VI)
(50 µM)
Cr (VI)
(100 µM)

Cr (VI)
(150 µM)

Shoot length (cm)

9.48 ±0.6
9.12 ±0.1
8.42 ±0.6
7.63 ±0.3
6.91 ±0.5

6.75 ±0.6


Root length (cm)


6.97 ±0.1


4.06 ±0.4


4.29 ±0.2


3.87 ±0.1


3.98 ±0.2


3.06 ±0.4


Total leaf area


16.3 ±2.1
16.7 ±0.9
15.6 ±1.1
14.68 ±1.9
14.7 ±2.3

13.73 ±2.3


Shoot( dry weight


0.028 ±0.003
0.028 ±0.006
0.029 ±0.006



0.024 ±0.004


0.015 ±0.006

0.012 ±0.006


Root( dry weight(g))


0.099 ±0.009


0.056 ±0.018


0.052 ±0.018


0.045 ±0.07


0.043 ±0.018


0.041 ±0.018

Table: 2 Accumulation of Cr * in A. indica treated with tannery sludge in pot experiment.

Plant parts



Tannery sludge ( % )












48.43 ± 0.90
71.43 ± 0.95
94.26 ± 0.86
110.40 ± 0.72
253.03 ± 1.35
341.66 ± 1.60



242.13 ± 1.55

451.43 ± 1.25
597.93 ± 0.47
785.26 ± 1.27
896.36 ± 2.85
1021 ± 2.25




17.03 ± 1.15
21.93 ± 0.41
25.50 ± 0.72
29.16 ± 1.30
35.00 ± 1.50
36.66 ± 0.85

*mg/Kg tissue (DW)

Table: 3 Accumulation of Cr (VI) in different parts of A. indica in field experiment.

Plant – parts
Cr mg/Kg (DW)



16.3 ± 0.02


5.2 ± 0.02




471.5 ± 0.16

Fig. 1. Azadirachta indica grown at various concentrations of chromium (VI).

Fig. 2. Accumulation of Chromium (VI) in different parts of A.indica.

Fig.3. Growth of Azadirachta indica plants in tannery sludge amended soil


Hasselgren K. 1999. Utilisation of sewage sludge in short-rotation energy forestry: a pilot study. Waste Manage Res;17:251–62. India. Fourth international conference on the biogeochemistry of trace elements.

Jones,B., Wolf,B., Mills,H.A., 1991. Plant analysis handbook: a practical sampling, preparation, Analysis and Interpretation Guide. Micro-Macro International, Athens, GA. University of California, Berkeley, USA. June 23-26, pp 771-772.

Khan AG, Kuek C, Chaudhry TM, Khoo CS and Hayes WJ. 2000. Role of plants, mycorrhizae and phytochelators in heavy metal contaminated land remediation. Chemosphere;41:197–207.

Pulford ID, Riddell-Black D and Stewart C. 2002. Heavy metal uptake by willow clones from sewage sludge-treated soil: the potential for phytoremediation. Int. J. Phytoremediation;4:59–72.

Ramasamy, K. 1997. Tannery effluent related pollution on land and water ecosytems in Raskin, I. and B.D. Ensley (Eds.), 2000. Phytoremediation of Toxic Metals: Using Plants to Clean up the Environment, John Wiley, New York.

Shanker A. K, Djanaguiraman, M., Sudhagar, R., Chandrashekar, C.N and Pathmanabhan G. 2004. Differential antioxidative response of ascorbate glutathione pathway enzymes and metabolites to chromium speciation stress in green gram (Vigna radiata (L) R Wilczek, cv CO 4) roots. Plant Sci , 166:1035– 43.

Watson C, Pulford ID and Riddell-Black D. 1999. Heavy metal toxicity responses of two willow (Salix) varieties grown hydroponically: development of a tolerance screening test. Environ Geochem Health;21:359– 64.

Watson, C. 2002. The phytoremediation potential of Salix: studies of the interaction of heavy metals and willows. PhD thesis, University of Glasgow.

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