According to Sinha et al., (2004) the plants act both
as “accumulators” and “excluders”. Accumulators
survive despite concentrating contaminants in their
aerial tissues. They biodegrade or biotransform the
contaminants into inert forms in their tissues. The
excluders restrict contaminant uptake into their
biomass. Plants to be used for phytoextraction
should have: (a) tolerance to high concentrations
metals, (b) high metal-accumulation capability, (c)
heavy biomass, (d) ability to grow fast and a (e)
profuse root system. The success of phytoextraction
depends especially on the plant’s ability (a) to
accumulate biomass rapidly, and (b) to store large
quantities of the uptaken metals in the shoot tissue
(Blaylock et al., 1997; McGrath, 1998; Blaylock and
Huang, 2000). Pb is not an essential nutrient for
plants, majority of lead is easily taken up by plants
from the soil and accumulated in root while only a
small fraction was translocated upward to the
shoots (Patra et al., 2004). Pb affects several
metabolic activities in different cell compartments.
The effect of Pb depends on concentration, type of
soil, soil properties and plant species. Pb toxicity
leads to decreases germination per cent, length and
dry mass of root and shoots (Munzuroglu and Geckil,
2002), disturbed mineral nutrition (Paivoke, 2002),
reduction in cell division (Eun et al., 2000).
Nickel has been classified among the essential micro
nutrients and remains associated with some metalloenzymes, but Ni is toxic at elevated concentrations
in plants (Srivastava et al., 2005). In plants Ni is
responsible for chlorosis, yellowing and necrosis of
leaves, deformation of plant parts, stunted growth
and generation of free radicals (Halliwell and
Gutteridge, 1999). In the environment, Ni is found
primarily combined with oxygen (oxides) or sulphur
(sulfides) (Ministry of the Environment, 2001). The
present study used Catharanthus roseus a nonedible plant for phytoremediation of Nickel and Lead
from the contaminated soils.
Phytoremediation is currently divided into the
following areas: (1) phytoextraction use
hyperaccumulators to remove metals or organics
from soil by concentrating them in above soil tissue,
(2) phytodegradation use of plants and their
associated microorganisms to degrade organic
pollutants, (3) rhizofiltration use of plant roots to
absorb and adsorb pollutants, mainly toxic heavy
metals, from water and aqueous waste streams, (4)
phytostabilization use plants to reduce the
bioavailability of pollutants in the environment, and
(5) phytovolatilization use plants to volatilize
pollutants and remove them from air. Based on the
phytoremediation techniques listed above, we can
see that plants have abilities of cleaning waste
elements in different ways, and phytoaccumulation
is the most widely studied topic. Plants that can
grow on metalliferous soils without suffering
phytotoxic effects and accumulate extraordinarily
high amounts of heavy metals in the aerial organs are described as hyperaccumulators. To date, there
are more than 450 hyperaccumulation species,
accounting only for less than 0.2% of all known
species. (Rascioa and Navari-Izzo, 2011).
2.0 Materials and methods:
2.1: Experimental plant description:
Catharanthus roseus (Periwinkle) is a species of
Catharanthus genus and Apocynaceae family native
to Madagascar. Synonyms include Vinca rosea (the
basionym), Ammocallis rosea, and Lochnera rosea;
other English names occasionally used include Cape
Periwinkle, Rose Periwinkle, Rosy Periwinkle, and
"Old-maid". It is also widely cultivated and is
naturalized in subtropical and tropical areas of the
world. As an ornamental plant, it is appreciated for
its hardiness in dry and nutritionally deficient
conditions, popular in subtropical gardens where
temperatures never fall below 5°C to 7°C, and as a
warm-season bedding plant in temperate gardens. It
is noted for its long flowering period, throughout the
year in tropical conditions, and from spring to late
autumn, in warm temperate climates. Full sun and
well-drained soil are preferred. Numerous cultivars
have been selected, for variation in flower colour
(white, mauve, peach, scarlet and reddish-orange),
and also for tolerance of cooler growing conditions
in temperate regions. Notable cultivars include
'Albus' (white flowers), 'Grape Cooler' (rose-pink;
cool-tolerant), the Ocellatus Group (various colours),
and 'Peppermint Cooler' (white with a red centre;
cool-tolerant). (Huxley, 1992). It is an evergreen subshrub or herbaceous plant. The flowers are white to
dark pink with a darker red centre. The fruit is a pair
of follicles 2–4 cm long and 3 mm broad. As an
ornamental plant, it is appreciated for its hardiness
in dry and nutritionally deficient conditions, popular
in subtropical gardens. It is noted for its long
flowering period, throughout the year in tropical
conditions. Numerous cultivars have been selected,
for variation in flower colour (white, mauve, peach,
scarlet and reddish-orange), and also for tolerance of
cooler growing conditions in temperate regions.
(Gamble, 2008).
Photo: Photograph of Catharanthus roseus, the
experimental plant
2.2: Sample collection and metal analysis:
Catharanthus roseus plants were grown in pots
filled with garden soil. The seedlings were collected
from the uncontaminated soils. All the selected
seedlings were of uniform size and free of any
disease symptoms. Nickel and Lead were selected
for the study , the uptake was estimated in root,
stem and leaves for every 20 days for a total period
of 60 days. In addition a set of control blank
experimental pots was also maintained. The metal
solutions prepared by dissolving in distilled water to
prepare stock solution of 1000 ppm for each metal.
The calibration curves for each metal were also
prepared. A blank reading was taken to incorporate
necessary correction factor. The heavy metal
solutions of 5mg/L was prepared from the stock and
administered to the plants and care was taken to
avoid leaching of water from the pots. The metal
uptake was estimated once in every 20 days. The
sample plants were removed from the pots and
washed under a stream of water and then with
distilled water. The collected plants were air dried,
then placed in a dehydrator for 2-3 days and then
oven dried for four hours at 100 ºc. The dried
samples of the plant were powdered and stored in
polyethylene bags. The powdered samples were
subjected to acid digestion. 1gm of the powdered
plant material were weighed in separate digestion
flasks and digested with HNO3 and HCl in the ratio of
3:1. The digestion on hot plate at 110ºc for 3-4 hours
or continued till a clean solution was obtained. After
filtering with Whatman No. 42 filter paper the filtrate was analyzed for the metal contents in AAS.
(Simarzdu 6800).
3.0 Results and Discussion
In the present investigation, Catharanthus roseus
plant accumulated both the metals. By 20th day Lead
content was high in roots and low in leaves. While in
stem it was 67.31 mg/kg biomass. There was no
change in lead accumulation in leaf after 40th day.
Stem concentration increased to 68.09 mg/kg and
root concentration was increased to 88.74 mg/kg
biomass much change observed in the roots (Table
1). In the 60th day only minimum change was
observed in leaf, stem and root. Finally, after the
total experimental period it was concluded that root
accumulation was higher compared to stem and
leaves.
Summarize the above information and write a main point