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262 PLANT SOIL EN VIRON., 54, 2008 (6): 262–270
Pollution of environment by toxic metals arises as
a result of various industrial activities and has turned
these metal ions into major health issue (Waisberg
et al. 2003). Although several adverse effects of
the toxic metals have been known for a long time,
exposure to heavy metals continues, and is even
increasing in some parts of the world, in particular
in less developed countries. Heavy metal pollution
is also a multi-element problem in many areas (An
et al. 2004). Under these circumstances, synergistic
and antagonistic interactions may be important, and
predicted impact based on individual effects of each
metal species is likely to be erroneous (Ting et al.
1991). There is therefore a clear need to understand
the interactive effects produced by combinations
of metal ions at different concentrations.
Of all toxic heavy metals, cadmium (Cd) ranks
the highest in terms of damage to plant growth
and human health. Moreover, its uptake and ac-
cumulation in plants poses a serious health thread
to humans via the food chain (Shah and Dube y
1998). The presence of excessive amounts of Cd
in soil commonly elicits many stress symptoms
in plants, such as reduction of growth, especially
root growth, disturbances in mineral nutrition and
carbohydrate metabolism (Moya et al. 1993), and
may thus strongly reduce biomass production.
Lead (Pb) is one of the most abundant toxic
metal in the earth crust. Exposure to lead in the
environmental and occupational settings contin-
ues to be a serious public health problem (WHO
1995). Elevated Pb in soils may compromise soil
productivity and even a very low concentration can
inhibit some vital plant processes, such as photo-
synthesis, mitosis and water absorption with toxic
symptoms of dark leaves, wilting of older leaves,
stunted foliage and brown short roots (Mohan
and Hosetti 1997, Patra et al. 2004).
More recently, the use of plants in metal extrac-
tion (phytoremediation) appeared as a promising
alternative in the removal of heavy metal excess
from soil and water (Glass 2000). Ting et al. (1991)
showed the uptake of cadmium and zinc by alga
Chl o rella v ulgaris. Lemna minor w a s used to
reclaim the lead contaminated water (Rahmani
and Sternberg 1999). Prasad et al. (2001) also
showed the bioaccumul ation o f c admiu m and
copper by Lemna trisulca.
Effect of cadmium and lead on growth, biochemical
parameters and uptake in Lemna polyrrhiza L.
R. John1, P. Ahmad2, K. Gadgil1, S. Sharma2
1Centre for Energy Studies, Indian Institute of Technology Delhi, New Delhi, India
2Biochemistry Laboratory, CRDT, Indian Institute of Technology Delhi, New Delhi, India
ABSTRACT
Aquatic plants are known to accumulate heavy metals. In this study, Duckweed plants (Lemna polyrrhiza L.) were
exposed to different concentrations of Cd and Pb. Various physio-biochemical parameters (fresh weight, chlo-
rophyll content, soluble protein, soluble sugars, proline content and metal absorption) were studied. At lower metal
concentrations, an increase in proline, protein and sugar was observed but at higher concentrations (above 30 mg/l)
their decrease was noticed. Uptake of the metals was concentration and time dependent. Treatment with 1, 10 and
20 mg/l of Cd and Pb showed synergistic relation while 30 and 40 mg/l treatments showed antagonistic relation
during the metal uptake. e results suggest that the L. polyrrhiza can be effectively used as a phytoremediator for
wastewater polluted with more than one heavy metal at moderate concentrations.
Keywords: absorption; biochemical parameters; heavy metal; Lemna polyrrhiza L.; phytoremediation
Supported by the Council for Scientific and Industrial Research, New Delhi, India.
PLANT SOIL EN VIRON., 54, 2008 (6): 262–270 263
Duckweed (family Lemnacea) is a small, fragile,
free-floating a q u atic plant that flour i she s in
quiescent, shallow water bodies (Rahmani and
Ster nberg 1999). Due to its special features, it
is used as a t est organism fo r aq u atic studi e s
and for wa s t ew a t e r t reatm e n t . Cons t r ucte d
wetlands/phytoremediation claim to be low-cost,
low-technology system able to treat a variety of
wastewaters. In the present study, the effect of Cd
and Pb on L. polyrrhiza was examined by exposing
the aquatic plant separately to e ach of the two
metal species and then to combination of the
two at various concentrations. Effects on biomass
growth, biochemical parameters (chlorophyll a,
total soluble sugar, soluble protein, and proline
content) an d bio acc umulat ion of heavy me tals
were studied.
MATERIAL AND METHODS
Duckweed p l a nts , obtaine d from oxidation
pon d at Wazir abad on the outskirts of Delhi ,
identified as Lemna polyrrhiza, w ere k e p t in
a water tank (containing tap water and compost),
and maintained as stock in Micro model, Indian
Institute of Technology, New Delhi, India.
The plants were ta ken out o f the sto ck tank
and expose d to different concentrations of Cd
(CdSO4.7H 2O) and Pb (C2H3O2)2.3H 2O i.e.,
1.0 mg/l, 10 mg/l, 20 mg/l, 30 mg/l and 40 mg/l
and different concentrations of Pb (C2H3O2)2
.3H2O i.e., 1 mg/l, 10 mg/l, 20 mg/l, 30 mg/l and
40 mg/l separately as well as in combination
(1 mg/l Cd + 1 mg/l Pb, 10 mg/l Cd + 10 mg/l Pb,
20 mg/l Cd + 20 mg/l Pb, 30 mg/l Cd + 30 mg/l Pb,
40 mg/l Cd + 40 mg/l Pb). The experiments were
conducted in pl astic tubs with three replic ates
for each treatment. Initially in each tub 5.0 mg of
biomass was added. Comparisons of metal-exposed
plants were made with untreated (control) plants.
The dat a p ertai ning to plant g rowth ( bioma ss
yield), chlorophyll, soluble protein, total soluble
sugar, proline content and metal accumulation
were obtained after 6, 12, 18, 24 and 30 days after
treatment. All the chemicals used were of analytical
grade reagent (Merck, India).
Determination of chlorophyll. Chlorophyll
content was determined by the method of Hiscox
and Israelstam (1979). Fresh leaves (100 mg) were
kept in the extraction reagent, dimethylsulphooxide
(DMSO). The tubes were kept in the oven at 65°C
for 40 min. 1 ml aliquot was mixed with 2 ml
DMSO and vortexed. Absorbance was determined
photometrically at 480, 510, 645, 663 nm (Beckman
640 D, USA) using DMSO for a blank.
Protein estimation. Proteins were estimated
by the method of Bradford (1976). Fresh leaves
(0.5 g) were homogenized in 1 ml phosphate buffer
(pH 7.0). The crude homogenate was centrifuged
at 5000 × g for 10 min. Half ml of freshly prepared
trichloroacetic acid (TCA) was added and centrifuged
at 8000 × g for 15 min. The debris was dissolved in
1 ml of 0.1N NaOH and 5 ml Bradford reagent was
added. Absorbance was recorded photometrically
at 595 nm (Beckman 640 D, USA) using bovine
serum albumin as a standard.
Estimation of proline. Proline concentration
was determined using the method of Bates et al.
(1973). Fresh leaves (300 mg) were homogenized
in 10 ml of 30% aqueous sulphosalicylic acid. The
homogenate was centrifuged at 9000 × g for 15 min.
A 2 ml aliquot of the supernatant was mixed with
an equal volume of acetic acid and acid ninhydrin
(1.25 g ninhydrin in 30 ml acetic acid and 20 ml
of 6N H3PO4) and incubated for 1 h at 100°C. The
reaction was terminated in an ice bath and extracted
with 4 ml of toluene. The extract was vortexed for
20 s and the chromatophore-containing toluene was
aspirated from the aqueous phase and absorbance
determined photometrically at 520 nm (Beckman
640 D, USA) using toluene for a blank.
Estimation of soluble sugars. Sugar was esti-
mated by the method of Dey (1990). Leaves (0.5 g)
were extracted twice with hot 90% ethanol. The
ethanol extracts were then combined. The final
volume of the pooled extract was made to 25 ml
with double distilled water. A suitable aliquot
was taken from the extract and 1 ml 5% phenol
and 5 ml concentrated sulphuric acid were added.
Final volume of this solution was made to 10 ml by
adding double distilled water. Absorbance of this
solution was measured at 485 nm using a UV-Vis
spectrophotometer.
Estimation of Cd and Pb accumulation. Tissue
concentrations of nutrient elements were measured
in the solution after wet digestion (HNO3:HClO4,
10:1, v/v, mixture) of the oven-dried plant material.
The Cd and Pb contents in the solution were
estimated employing a Perkin-Elmer (Analyst
Mo del 300) ato mic absor p t i o n spec t rome ter
equipped with an air-acetylene flame atomizer.
The heavy metal content was expressed as mg/g dw
of the sample.
Statistical data. Data was subjected to analysis
of variance (ANOVA) by Agries programme and
Microsoft Excel for Standard Error.
264 PLANT SOIL EN VIRON., 54, 2008 (6): 262–270
RESULTS AND DISC USSION
Fresh weight
The results pertai ning to effect of dif ferent
concentrations of heavy meals on biomass yield
of Lemna polyrrhiza are depicted in Tables 1 and 2.
It was observed that 1 mg/l of Cd and 1 mg/l of Pb
increased growth at the end of 30 days to 13% and
28% of the control, respectively. The concentration
of 30 and 40 mg/l of Cd and Pb proved to be toxic,
affecting the plant growth severely. Fresh weight
after 30 days dec rease d fro m 35. 30 g to 0.55 g
and 1.22 g with 40 mg/l of Cd and 40 mg/l of Pb,
respectively.
The most common effect of Cd toxicity in plants
is stunted growth, leaf chlorosis and alteration
in the activity of many key enzymes of various
metabolic pathways (Arduini et al. 1996). In our
study, varied concentrations of Cd and Pb affected
fresh weight of L. polyrrhiza. The reduction in the
growth in L. polyrrhiza could be also due to the
suppression of the elongation growth rate of cells,
because of an irreversible inhibition exerted by Cd
on the proton pump responsible for the process
(Aidid and Okamoto 1993). Parameters such as
fresh weight of shoot as well as root length were
used as useful indicators of metal toxicity in plants.
In our study, Cd stress showed a higher decline in
these parameters as compared to Pb.
Chlorophyll content
It w a s obse r ved that 1 mg/ l of each Cd and
Pb used individually marginally increased the
chlorophyll (chl a, chl b and total chlorophyll).
The prolonged exposure to high concentration of
Cd (40 mg/l) reduced chl a significantly to about
82% of the control, and Pb showed the decline of
77% of the control after 30 days (Figure 1).
Similarly, chl b decreased from 0.36 to 0.01 and
0.04 mg/g fw after 24 days of exposure to 40 mg/l
of Cd and 40 mg/l of Pb, respectively (Figure 2).
Table. 1. Effect of different concentrations of Cd on the fresh weight (g) of Lemna polyrrhiz a. Values are means
of ± SE (n = 3)
Cd (ppm) Number of days
6 12 18 24 30
Control 7.52 ± 0.04 9.52 ± 0.07 12.54 ± 0.09 20.93 ± 0.05 35.30 ± 0.02
1 7.61 ± 0.03 10.89 ± 0.02 15.32 ± 0.10 25.9 ± 0.07 39.98 ± 0.02
10 6.87 ± 0.09 8.35 ± 0.02 9.61 ± 0.07 13.66 ± 0.04 17.01 ± 0.04
20 5.10 ± 0.08 4.71 ± 0.03 4.24 ± 0.07 3.25 ± 0.05 3.21 ± 0.02
30 4.21 ± 0.06 3.95 ± 0.04 2.5 ± 0.07 2.1 ± 0.03 1.24 ± 0.09
40 3.5 ± 0.03 2.21 ± 0.06 1.51 ± 0.06 0.98 ± 0.98 0.55 ± 0.03
CD at 5% 1.43 1.65 2.77 3.21 4.64
Table. 2. Effect of different concentrations of Pb on the fresh weight (g) of Lemna poly rrhiza . Values are means
of ± SE (n = 3)
Pb (ppm) Number of days
6 12 18 24 30
Control 7.52 ± 0.04 9.52 ± 0.07 12.54 ± 0.09 20.93 ± 0.05 35.30 ± 0.02
1 7.88 ± 0.03 13.64 ± 0.05 20.32 ± 0.06 30.87 ± 0.02 45.32 ± 0.08
10 7.32 ± 0.06 9.43 ± 0.03 11.32 ± 0.11 20.1 ± 0.09 33.56 ± 0.02
20 6.86 ± 0.05 10.22 ± 0.04 14.8 ± 0.09 17.32 ± 0.07 18.44 ± 0.08
30 6.43 ± 0.03 6.23 ± 0.11 5.55 ± 0.09 5.03 ± 0.04 4.65 ± 0.07
40 4.32 ± 0.08 3.23 ± 0.03 2.34 ± 0.10 2.21 ± 0.06 1.22 ± 0.04
CD at 5% 1.21 2.64 3.23 5.73 8.74
PLANT SOIL EN VIRON., 54, 2008 (6): 262–270 265
10 mg/l of Cd and Pb concentrations decreased
the total chlorophyll with time (Figure 3).
Various abiotic stresses decrease the chlorophyll
content in plants (Ahmad et al. 2007). Several
reports show chlorophyll biosynthesis inhibition
by metals in higher plants (Prasad and Prasad
1987). The decline in chlorophyll content in plants
expos e d to Cd 2+ and Pb2 + stres s is believe d to
be due to: (a) inhibition of important enzymes,
such as δ-aminolevulinic acid dehydratase (ALA-
dehydratase) and protochlorophyllide reductase
(Van Assche and Clijsters 1990) associated with
chlorophyll biosynthesis; (b) impairment in the
supply of Mg2+ and Fe2+ required for the synthesis
of chlorophylls ; (c) Zn2 + deficiency resulting in
inhibition of enzymes, such as carbonic anhydrase
(Van Assche and Clijsters 1990); (d) the replacement
of Mg2+ ions associated with the tetrapyrrole ring
0
0.2
0.4
0.6
0.8
6�days 12�days 18�days 24�days 30�days
Chlorophyll�a�(mg/g�fw)
0�ppm 1�ppm 10�ppm
20�ppm 30�ppm 40�ppm
0
0.2
0.4
0.6
0.8
6�days 12�days 18�days 24�days 30�days
Chlorophyll�a�(mg/g�fw)
0�ppm 1�ppm 10�ppm
20�ppm 30�ppm 40�ppm
Figure 1. Effect of different concentrations of Cd (A), Pb (B) on chlorophyll a of Lemna polyrrhiza. Values are
means ± SE (n = 3)
0
0.1
0.2
0.3
0.4
0.5
6�days 12�days 18�days 24�days 30�days
Chlorophyll�b�(mg/g�fw)
0�ppm 1�ppm 10�ppm
20�ppm 30�ppm 40�ppm
0
0.1
0.2
0.3
0.4
0.5
6�days 12�days 18�days 24�days 30�days
Chlorophyll�b�(mg/g�fw)
0�ppm 1�ppm 10�ppm
20�ppm 30�ppm 40�ppm
Figure 2. Effect of different concentrations of Cd (A), Pb (B) on chlorophyll b of Lemna polyrrhiza. Values are
means ± SE (n = 3)
Figure 3. Effect of different concentrations of Cd (A), Pb (B) on total chlorophyll of Lemna polyrrhiza. Values
are means ± SE (n = 3)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
6�days 12�days 18�days 24�days 30�days
Total�chlorophyll�(mg/g�fw)
0�ppm 1�ppm 10�ppm
20�ppm 30�ppm 40�ppm
0
0.2
0.4
0.6
0.8
1
1.2
1.4
6�days 12�days 18�days 24�days 30�days
Total�chlorophyll�(mg/g�fw)
0�ppm 1�ppm 10�ppm
20�ppm 30�ppm 40�ppm
A
A
A
B
B
B
266 PLANT SOIL EN VIRON., 54, 2008 (6): 262–270
of chlorophyll molecule. Our results of decrease in
chlorophyll content corroborated with the findings
of Siedlecka and Krupa (1996) who also found
a decrease in chlorophyll content with heavy metal
stress in Ze a mays and Acer rubrum. The lo ss
in chlorophyll content can consequently lead to
disruption of photosynthetic machinery.
Soluble protein content
Cd treatment (20 mg/l) declined the soluble
protein in L . pol y r rhiza to 52% and 70% after
24 days and 30 days, respectively, while 30 mg/l of
Cd proved to be significantly more toxic decreasing
the value to about 76% of the control after 24 days
(Figure 4A). Cd showed much more toxic effects
as compared to Pb. The exposure to 30 mg/l Pb
led to the decline of 62% and 72.8% after 24 days
and 30 days, respectively (Figure 4B).
Abiotic stress may inhibit a synthesis of some
proteins and promote others (Ericson and Alfinito
1984) with a general trend of decline in the overall
content. Our studies coincide with Costa and
Sp i tz ( 1 9 97) w h o a l s o reporte d a de c rea se i n
soluble protein content under heavy metal stress
in Lupinus albus. Mohan and Hosetti (1997) found
more pronounced decrease in the protein content
with Cd as compared to Pb treatment in L. minor.
The decrease in protein content in L. polyrrhiza
may be caused by enhanced protein degradation
process as a result of increased protease activity
(Palma et al. 2002) that is found to increase under
stress conditions. It is also likely that these heav y
metals may have induced lipid peroxidation in
L. polyrrhiza and fragmentation of proteins due
to toxic effects of reactive oxygen species led to
reduced protein content (Davies et al. 1987).
Proline content
Maximum proline accumulation of 5.6 fold was
observed with 20 mg/l Cd 24 days (Figure 5A) but
30 mg/l of Cd declined the proline to about 25%
of the control, while in the case of Pb (30 mg/l)
the maximum accumulation of proline was found
5.1 fold after 30 days (Figure 5B).
Proline, an amino acid, is well known to get
accumulated in wide variety of organisms ranging
Figure 4. Effect of different concentrations of Cd (A), Pb (B) on soluble protein content (µg/g f w) of Lemna
polyrrhiza. Values are means ± SE (n = 3)
0
10
20
30
40
50
6�days 12�days 18�days 24�days 30�days
Protein�content�(mg/g�fw)
0�ppm 1�ppm 10�ppm
20�ppm 30�ppm 40�ppm
0
10
20
30
40
50
6�days 12�days 18�days 24�days 30�days
Protein�content�(mg/g�fw)
0�ppm 1�ppm 10�ppm
20�ppm 30�ppm 40�ppm
Figure 5. Effect of different concentrations of Cd (A), Pb (B) on proline content (µg/g fw) of Lemna polyrrhiza.
Values are means ± SE (n = 3)
0
10
20
30
40
50
6days 12days 18days 24days 30days
Prolinecontent(g/gfw)
0ppm 1ppm 10ppm
20ppm 30ppm 40ppm
0
10
20
30
40
50
6days 12days 18days 24days 30days
Prolinecontent(g/gfw)
0ppm 1ppm 10ppm
20ppm 30ppm 40ppm
A
A
B
B
PLANT SOIL EN VIRON., 54, 2008 (6): 262–270 267
from bac teria to higher plants on exposure to
abiotic stress (Saradhi et al. 1993, Ahmad et al.
2006). Proline accumulation in shoots of Brassica
juncea, Triticum aestivum and Vigna radiata in
response to cadmium toxicity was demonstrated
by Dhir et al. (2004) but they found that proline
accumu latio n decreased with the exp o sure to
cadmium in hydrophytes (Ceratophyllum, Wolffia,
and Hy drilla). It has been often suggested that
proline accumulation may contribute to osmotic
adjustment at the cellular level (Perez-Alfocea
et al. 1993) and stabilizes the structure of
macromolecules and organelles. Proline also acts as
a major reservoir of energy and nitrogen, which can
be used in resuming the growth (Chandrashekhar
and Sandhyarani 1996) after the stress removal.
Soluble sugar content
The results related to the soluble sugar content
are depicted in Tables 3 and 4, which revealed
that lower concentrations of Cd and Pb increased
the soluble sugar content; however, higher
concentrations of 40 mg/l of Cd and Pd showed
a decrease of 74.7 and 73.8% in soluble sugar
content after 30 days, respectively.
The total carbohydrates got inhibited if
Cd concentration is more than 5 mg/kg soil (Saleh
and Al-Garni 2006). Our results corroborate with
the findings of Ahmad et al. (2006) who found
that an increase in soluble sugars at low con-
centrations of salt stress and decrease at higher
concentrations in Pisum sativum. The decrease
in total sugar content of stressed leaves probably
corresponde d w ith the photosyntheti c inhibi-
tion or stimulation of res piratio n rate. Hi gher
starch accumulation in damaged leaves of Tilia
argentea and Quercus cerris may re sult both in
the higher resistance of their photosynthetic ap-
paratus (Prokopiev 1978) and low starch export
from the mesophyll. The negative effect of heav y
metals on carbon metabolism is a result of their
possible interaction with the reactive centre of
ribulosebisphosphate carboxylase (Stiborova et.
al. 1987).
Table 3. Effect of different concentrations of Cd on soluble sugars (mg/g fw). Values are means ± SE (n = 3)
Cd (ppm) Number of days
6 12 18 24 30
Control 32.44 ± 4.2 33.32 ± 5.1 33.54 ± 5.5 33.88 ± 5.4 34.01 ± 5.7
1 33.56 ± 4.8 34.76 ± 4.9 35.29 ± 5.1 37.25 ± 5.7 39.44 ± 6.2
10 33.11 ± 3.9 32.17 ± 4.7 33.12 ± 5.1 33.55 ± 5.3 34.36 ± 4.8
20 29.32 ± 3.7 27.43 ± 4.6 25.21 ± 3.8 22.11 ± 3.3 20.12 ± 2.9
30 22.43 ± 3.7 20.11 ± 3.5 18.67 ± 3.5 15.66 ± 2.6 11.01 ± 1.9
40 18.13 ± 2.8 16.47 ± 2.5 13.36 ± 2.2 11.59 ± 1.4 8.12 ± 1.1
CD at 5% 7.32 7.11 6.84 5.88 4.32
Table 4. Effect of different concentrations of Pb on soluble sugars (µg/g fw). Values are means ± SE (n = 3)
Pb (ppm) Number of days
6 12 18 24 30
Control 32.44 ± 4.2 33.32 ± 5.1 33.54 ± 5.5 33.88 ± 5.4 34.01 ± 5.7
1 33.12 ± 3.8 34.06 ± 4.5 35.35 ± 4.7 36.22 ± 5.3 37.09 ± 5.3
10 33.05 ± 3.1 33.89 ± 3.4 34.12 ± 2.9 36.01 ± 2.9 36.55 ± 2.5
20 32.5 ± 4.7 31.12 ± 3.3 31.55 ± 3.0 32.61 ± 2.8 31.32 ± 2.1
30 29.3 ± 1.4 28.4 ± 2.7 27.37 ± 2.5 26.52 ± 1.5 25.61 ± 1.2
40 25.3 ± 3.1 20.6 ± 2.4 17.53 ± 1.9 15.41 ± 1.2 10.05 ± 1.0
CD at 5% 7.71 6.52 5.11 4.31 4.12
268 PLANT SOIL EN VIRON., 54, 2008 (6): 262–270
Absorption of Cd and Pb
Lemna polyrrhiza absorbed less Cd as compared
to Pb. The concentrations of Cd and Pb were
0.42 and 0.81 µg/g dw, respectively (Figure 6). The
rate of accumulation of Cd and Pb was higher at
lower concentrations. Among different heavy metal
treatments, almost linear uptake was observed for
10 mg/l Cd while in the case of Pb linear uptake took
place for 10 and 20 mg/l Pb (Figure 6). For lower
concentrations, i.e. 10 and 20 mg/l, the uptake was
concentration and time dependent. However, at
higher concentrations (30 and 40 mg/l) the uptake
of both metals was lower and at the end of 30 days
the absorption was almost stagnant at 40 mg/l due
to the toxicity caused to the plant (Figure 6).
Duckweed (L. minor) was found to be an efficient
hyperaccumulator of heav y metals and to exhibit
mortality at higher concentrations of metals.
Rahmani and Sternberg (1999) observed the
complete die-off in L. minor at high doses of Pb.
Wojcik et al. (2005) found higher metal accumulation
in roots than in shoots of hydroponically grown
Thlaspi caerulescens. Some literature data show
a higher Cd accumulation in shoots than in roots
(Roosens et al. 2003) as well, although other authors
reporte d a higher Cd co ntent in ro ots tha n in
shoots. Our studies corroborate with Brennan and
Shelley (1999) who found higher accumulation of
Pb in the roots than shoots of maize.
The bioaccumulation of single metal is known
to be inf luenced by the presence of other metals,
resulting in inhibited or enhanced bioaccumulation
of one metal in the mixture (An et al. 2004). Several
studies reported that the presence of one metal
influenced the uptake of another metal (Peralta-
Figure 6. Absorption of Cd and Pb by Lemna polyrrhiza
from individual metal solutions. Values are means
± SE (n = 3)
0
10
20
30
40
50
60
6 12 18 24 30 6 12 18 24 30
Days
Pbcontent(g/gdw)
0
10
20
30
40
50
60
Cdcontent(g/gdw)
1ppm 10ppm 20ppm
30ppm 40ppm
Videa et al. 2002). Our studies show a higher
accumulation of Cd than Pb, which confirms the
results of An et al. (2004) who observed lesser
uptake of Cd in the shoots of Cucumis sativus in
presence of Pb.
In conclusion, our results indicate that the
exposition of Lemna p olyr r h i za to d i fferent
concentrations of Cd and Pb results in an increase
in growth, pigment content, proline, protein and
sugar content at lower concentration; at higher
co n c e ntrations t h eir decrease w as ob s e r ved.
Cd effect was more significant than that of P b
in hampering plant growth and development.
Cd was accumulated more than Pb by L. polyrrhiza.
Phytoremediation may contribute in the treatment
of various sites contaminated with heavy metals/
toxic metals. L. polyrrhiza can be used to reclaim
the water bodies polluted with heavy metals.
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Received on February 18, 2008
Corresponding author:
Riffat John, Ph.D., Indian Institute of Technology Delhi, Centre for Energy Studies, Hauz Khas, New Delhi 110016,
India
phone: + 911 126 591 116, e-mal: riffat_dusc@rediffmail.com
