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Over time, man has battled with the extreme consequences of environmental
contamination of heavy metals particularly lead (Seregin et al., 2004). This
poses a serious environmental concern as Heavy metals cannot be destroyed
by degradation (Lanza, 2008). More to this environmental problem is the high
cost of treatment by conventional methods. Phytoremediation overtime has
provided a cost-effective alternative to high-energy and high-cost
conventional methods. It is considered to be a “Green Revolution” in the field
of innovative cleanup technologies (Epstein, 2009). Phytoremediation is a
bioremediation techniques which involves the use of plants to remediate
environmental media, this techniques is being pursued as a new approach for
the cleanup of contaminated soils and waters, including groundwater.
Phytoremediation uses plants to clean up contaminated soil and groundwater,
taking advantage of plants’ natural abilities to take up, accumulate, and/or
degrade constituents of their soil and water environments.
This “Plant-assisted bioremediation technique”, involves the interaction of
plant roots and the microorganisms associated with these root systems to 
2
remediate soils containing elevated concentrations of metallic compounds
(Epstein, 2009). These techniques provides cost-effective methods of
remediating soils and groundwater contaminated with metals, radionuclides,
and various types of organics, with fewer secondary wastes and less
environmental impact than would be generated using traditional remediation
methods (Bazzaz et al., 2005).
All plants extract necessary nutrients, including metals, from their soil and
water environments. Some plants, called hyper-accumulators, have the ability
to store large amounts of metals, even some metals that do not appear to be
required for plant functioning. In addition, plants can take up various
chemicals compounds from environmental media and degrade or otherwise
process them for use in their physiological processes. Phytoremediation
technologies are in the early stages of development, with laboratory research
and field trials being conducted to determine processes and more refined
methods (Lanza, 2008). Additional research, including genetic engineering, is
being conducted to improve the natural capabilities of plants to perform
remediation functions and to investigate other plants with potential
phytoremediation applications.
3
Human activities constitute one of the major means of introducing heavy
metals into the soil. (Seregin et al., 2004), reported that controlled and
uncontrolled disposal of wastes, accidental and process spillage, mining and
smelting of metalliferous ores and sewage sludge application to agricultural
soils are responsible for the migration of contaminants into the soil. Other
sources of anthropogenic metal contamination include electroplating, gas
exhaust, energy and fuel production as well as the application of fertilizer and
industrial manufacturing (Sharma and Dubey, 2005).
Nigeria’s quest to develop has necessitated the massive building of
industries by private entrepreneurs and multinational conglomerates. Land
as a resource is suddenly becoming scarce and one of the reasons is that the
Governments at the Federal, State and Local levels take up lots of land for
infrastructure. Small and medium scale industrialists are also in the land
acquisition and farmers are not left out. (Lombi et al., 2009), reported that
undisturbed and pristine arable lands are hard to come by in Nigeria, such
that abandoned mine fields, dump sites and most available plots are being
cultivated to meet the ever increasing demand for food. (Lanza, 2008),
reported that one of the consequences of using dumpsites and exposing the
‘clean’ soil in the unpopulated areas to external nutrient sources such as
fertilizer and sewage sludge is the incidence of pollution by heavy metals. 
4
Excessive metal concentrations in contaminated soils can result in decreased
soil microbial activity, soil fertility and yield losses (Lanza, 2008). Unlike
many organic contaminants, most metals cannot be eliminated from the
environment by physico-chemical. They do not degrade and are persistent in
the environment (Bouchier, 2003), though it may however be possible to
reduce the toxicity by influencing their speciation (Memon et al., 2007). In
soil these pollutants (metal concentrations) might accumulate in plants to
unacceptable levels, causing reduction in crop yields and toxic effects in soil
microorganisms.
(Seregin et al., 2004), reported that physico-chemical technologies for soil
remediation render the land useless as a medium for plant growth because the
technique removes all the biological activities including useful microbes such
as nitrogen fixing bacteria, mycorrhizal-fungi and the fauna thus decreasing
biodiversity. Lombi et al. (2009) reported that traditional solutions such as
disposal of contaminated soil in landfills presently account for a large
proportion of the remediation operations. It becomes imperative that new
technologies based on environmentally friendly and low-cost processes be
employed.
5
A promising cost-effective plant-based technology for the cleanup of heavy
metal pollution is phytoremediation. Lombi et al. (2009) stated that this
technology has attracted attention in recent years because of the low cost of
implementation and is particularly attractive in the tropics, where normal
climatic conditions favour plant growth and microbial activity.
1.2 Aim and Objectives
Aim
The aim of this work was to remove lead from lead-polluted soil through
phytoremediation using Peperomia pellucida herb
Objective
To achieve this aim the following objective were focused on:
1. To contaminate a certain amount of soil with known concentration of lead
2. To cultivate P. pellucida in the polluted soil
3. To determine the concentration of lead in the soil sample
4. To determine the concentration of lead in the plant.
1.3 Method
This study employs the phytoextraction technique, a type of
phytoremediation method, also referred to as phytoaccumulation, this 
6
involves plant roots taking up and translocating contaminants in the soil to
other parts of the plant. (Memon et al., 2007).
1.4 The scope of study
This work entails the following:
1. Collection of top soil in a wet area and analysis lead concentration in the
soil.
2. Pollution of soil with lead compound and left overnight to acclimatize.
3. Cultivation of the herb in the polluted soil for eight weeks.
4. Analysis of the lead concentration in soil and herb at interval of a week
using atomic absorption spectroscope 
7
2. CHAPTER TWO
2.1 Literature review
Phytoremediation is the direct use of living plants for remediation of
contaminated soil, sludge, sediments, and ground water through contaminant
removal, degradation, or containment. Growing and, in some cases,
harvesting plants on a contaminated site as a remediation method is an
aesthetically pleasing, solar-energy driven, passive technique that can be used
to clean up sites with shallow, low to moderate levels of contamination. This
technique can be used along with or, in some cases, in place of mechanical
cleanup methods. Phytoremediation can be used to clean up metals,
pesticides, solvents, explosives, crude oil, polycyclic aromatic hydrocarbons,
and landfill leachates (Lestan and Helena, 2012).
Phytoremediation has been studied extensively in research and small-scale
demonstrations, but full scale applications are currently limited in number.
Further development and research of the mechanisms described below likely
will lead to wider acceptance and use of phytoremediation (Epstein, 2009).
Phytoremediation is a general term for several ways in which plants are used
to remediate sites by removing pollutants from soil and water. Plants can 
8
degrade organic pollutants or contain and stabilize metal contaminants by
acting as filters or traps. Some of the methods that are being tested are
described below (Lestan et al., 2012).
Phytoextraction
Phytoextraction, also called phytoaccumulation, refers to the uptake and
translocation of metal contaminants in the soil by plant roots into the
aboveground portions of the plants. Certain plants called hyperaccumulators
absorb unusually large amounts of metals in comparison to other plants. One
or a combination of these plants is selected and planted at a site based on the
type of metals present and other site conditions. After the plants have been
allowed to grow for several weeks or months, they are harvested and either
incinerated or composted to recycle the metals (Bouchier, 2003). This
procedure may be repeated as necessary to bring soil contaminant levels down
to allowable limits. If plants are incinerated, the ash must be disposed of in a
hazardous waste landfill, but the volume of ash will be less than 10% of the
volume that would be created if the contaminated soil itself were dug up for
treatment.
Rhizofiltration
Rhizofiltration is the adsorption or precipitation onto plant roots or absorption
into the roots of contaminants that are in solution surrounding the root zone. 
9
The plants to be used for cleanup are raised in greenhouses with their roots in
water rather than in soil (Godbold and Kettner, 1997). To acclimate the plants
once a large root system has been developed, contaminated water is collected
from a waste site and brought to the plants where it is substituted for their
water source (Bouchier, 2003). The plants are then planted in the
contaminated area where the roots take up the water and the contaminants
along with it. As the roots become saturated with contaminants, they are
harvested and either incinerated or composted to recycle the contaminants.
Phytostabilization
Phytostabilization is the use of certain plant species to immobilize
contaminants in the soil and ground water through absorption and
accumulation by roots, viii adsorption onto roots, or precipitation within the
root zone. This process reduces the mobility of the contaminant and prevents
migration to the ground water or air, and it reduces bioavailability for entry
into the food chain (Lanza, 2008). This technique can be used to reestablish a
vegetative cover at sites where natural vegetation is lacking due to high metal
concentrations in surface soils or physical disturbances to surficial materials.
Metal-tolerant species can be used to restore vegetation to the sites, thereby
decreasing the potential migration of contamination through wind erosion, 
10
transport of exposed surface soils, and leaching of soil contamination to
ground water.
Phytodegradation
Phytodegradation, also called phytotransformation, is the breakdown of
contaminants taken up by plants through metabolic processes within the plant,
or the breakdown of contaminants external to the plant through the effect of
compounds (such as enzymes) produced by the plants. Pollutants are
degraded, incorporated into the plant tissues, and used as nutrients.
Rhizodegradation
Rhizodegradation, also called enhanced rhizosphere biodegradation,
phytostimulation, or plant-assisted bioremediation/degradation, is the
breakdown of contaminants in the soil through microbial activity that is
enhanced by the presence of the rhizosphere and is a much slower process
than phytodegradation. Microorganisms (yeast, fungi, or bacteria) consume
and digest organic substances for nutrition and energy. Certain
microorganisms can digest organic substances such as fuels or solvents that
are hazardous to humans and break them down into harmless products through
biodegradation (Bouchier, 2003).
Natural substances released by the plant roots sugars, alcohols, and acids
contain organic carbon that provides food for soil microorganisms, and the 
11
additional nutrients enhance their activity (Lanza, 2008). Biodegradation is
also aided by the way plants loosen the soil and transport water to the area.
Phytovolatilization
Phytovolatilization is the uptake and transpiration of a contaminant by a plant,
with release of the contaminant or a modified form of the contaminant to the
atmosphere from the plant. Phytovolatilization occurs as growing trees and
other plants take up water and the organic contaminants. Some of these
contaminants can pass through the plants to the leaves and volatilize into the
atmosphere at comparatively low concentrations.
A significant advantage of phytoremediation is that a variety of
chemical compounds both organic and inorganic are amenable to the
phytoremediation process. Phytoremediation can be used either as an in situ
or ex situ application. In situ applications are frequently considered because
minimizes disturbance of the soil and surrounding environment and reduce
the spread of contamination via air and waterborne wastes. Another advantage
of phytoremediation is that it is a green technology and when properly
implemented is both environmentally friendly and aesthetically pleasing to
the public.
Phytoremediation does not require expensive equipment or highly-specialized
personnel, and it is relatively easy to implement. It is capable of permanently 
12
treating a wide range of contaminants in a wide range of environments.
However, the greatest advantage of phytoremediation is its low cost compared
to conventional clean-up technologies. For example, the cost of cleaning up
one acre of sandy loam soil with a contamination depth of 50 cm with plants
was estimated at $60,000 to $100,000 compared to $400,000 for the
conventional excavation and disposal method (Bazzaz et al., 2005).
2.2 Advantages of phytoremediation
It is capable of treating sites affected by radiological and chemical
contamination:
• Trials have shown that key radionuclides such as Sr-90, Cs-137, and isotopes
of U and Pu are amenable to phytoremediation (Xiong, 2007).
• The technique is also capable of targeting heavy metals and a number of
chemicals in the event that a mixture of contaminants are available.
It is an environmentally beneficial technique:
• Improves soil quality (physical and chemical) for future use.
• Improves biodiversity by encouraging the development of local
ecosystems.
• Reduces soil erosion and the potential for contamination spread.
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• Results in minimal disruption to the local environment, by avoiding the use
of intrusive techniques or potentially harmful chemicals.
• Secondary waste generation is minimized, as harvested biomass can be
thermally treated.
It is cost effective:
• It utilizes standard, off-the-shelf agricultural equipment.
• It is a passive technique that requires minimal effort following plant
establishment.
It is flexible:
• Can be deployed in both terrestrial and aquatic environments (e.g. pontoons,
reed beds).
• Can be deployed in-situ or ex-situ in a more controlled environment.
• Can be used in conjunction with engineered remediation techniques, on its
own, or as a polishing step.
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2.3 Disadvantages of Phytoremediation?
It is unpredictable
• Plants may not establish.
• Transfer factors are not well defined.
• Efficacy is highly dependent on a number of factors (e.g. species selected,
soil chemistry, etc.)
• Could result in contamination transfer along food chains.
It can take a while!
• Numerous growing seasons may be required to achieve the desired level of
decontamination.
• Poor environmental conditions may slow down normal metabolic processes
and therefore the ability to interact with contamination.
• It is unlikely to be suitable for areas with high levels of contamination that
require urgent attention.
However, there are mitigation measures that can be used to enhance the
effectiveness of the technique:
• Introduce already established plants to a site, rather than sowing seeds.
• Use soil amendments such as chelators or acids to increase contaminant
availability.
15
• Target sites that have no immediate value due to the contamination present
(e.g. facilities that are entering a care and maintenance phase).
• Use containment structures such as tents to control the environment (e.g.
temperature, light, water availability, etc.) and reduce the risk of predation.
2.4 Peperomia pellucida
Peperomia pellucida also known as shiny bush or silver bush belonging to
the genus of the pepper family (Piperaceae) comprising some 1,600 species
of tropical and subtropical fleshy herbs, annuals as well as perennials. Some
are epiphytic (growing on the branches of trees). The leaves, sometimes
attractively coloured with veins or spots, are oval, thick, fleshy, and smoothedged. The thick stalk of the leaf is in some species attached to the centre of
the underside of the leaf (Brooks, 2009). Flowers are minute and densely
packed on a slender spike, which is likely to be curved.
Peperomia pellucida is an herbaceous plant found in many African, South
American and Asian countries. The species develops during rainy periods
(often in the spring) and thrives in loose, humid soils under the shade of trees.
It grows in moist habitat and is found throughout the major parts of southern
Nigeria. Whole plant or parts of plant are used for different purposes. Despite 
16
its wide range of folk medicinal uses, there is very little scientific
documentation available on its biological activities as well as its chemical
constituents (Burzynski, 2001).
2.5 Botanical description of Peperomia pellucida
Peperomia pellucida is an annular herb with fibrous roots; translucent pale
green stems which are erect or ascending, usually 15-45 cm long, internodes
usually 3-8 cm long, glabrous and the leaves are medium green on upper
surface, lower surface whitish green, thinly fleshy, drying papery, broadly
ovate, 1.5-4 cm long, 1-3.3 cm wide, palmately 3-nerved or 5-nerved,
glabrous, apex acuminate, base subcordate to truncate, petioles 0.5-2cm long,
glabrous. One to several spikes are available, terminal and axillary or leafopposed, filiform, ca. 3-6 cm long, the rachis ca. 0.4-0.6 mm in diameter,
glabrous, flowers well-spaced, peduncles ca. 0.6-1 cm long, glabrous; ovary
ovoid; stigmas terminal and also fruits were subglobose, ca. 0.5 mm long,
longitudinally ridged, apex beaked (Lombi et al., 2009).
2.6 Phytoconstituents
The plant Peperomia pellucida was found to have variety of chemical
constituents. Phytochemical screening revealed the presence of alkaloids,
cardenolides, saponins and tannins, while anthraquinones was observed to be 
17
absent. Stem also contain alkaloid, tannins, flavanoids and steriods, except
saponins. The roots of Peperomia pellucida also had shown the presence of
alkaloid, tannins, steroids and carbohydrates etc. The essential oils of the plant
were found primarily in medical literature. One study identified 71
compounds from the essential oils of 10 Piperaceae species. Sesquiterpenes
appear to be the major chemical constituents in the essential oils. Carotol
(13.41%) was the major hydroxylated sesquiterpene in a chemical analysis of
Peperomia pellucida. Flavonoids, phytosterols, arylpropanoids (eg, apiols),
substituted styrenes, and pellucidin A have been isolated. Other compounds,
like the peperomins, have cytotoxic or anticancer activity in vitro. Isolated
flavonoids include acacetin, apigenin, isovitexin, and pellucidatin. Isolated
phytosterols include campesterol and stigmasterol (Memon et al., 2007).
Observations from scientific studies has proven that peperomia pellucida has
the ability to sprout and grow in metal laden soils. The plants has a high
tolerance for metal pollution in soil and is a candidate for remediation
strategies and management for heavy metals contaminated soils (Sharma and
Dubey, 2005).
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2.7 Lead
Lead (Pb) is a bluish-grey metal that occurs naturally in minute amounts
within the Earth’s crust. It has also been referred to as plumbum, lead metal,
and pigment metal.
Frequent use in many industrial processes is the main reason for lead
contamination of the environment (Huang and Cunningham, 2000). There are
a variety of industrial processes that involve the use of lead such as mining,
smelting, manufacture of pesticides and fertilizers, dumping of municipal
sewage and the burning of fossil fuels that contain a lead additive. Many
commercial products and materials also contain lead including paints, ceramic
glazes, television glass, ammunition, batteries, medical equipment (i.e., x-ray
shields, fetal monitors), and electrical equipment. The uses of lead for roofing
and the production of ammunition has increased from previous years. Lead
battery recycling sites, of which 29 have been labeled Superfund sites, and
manufacturers use more than 80% of the lead produced (Seregin et al., 2004). 
19
2.8 Health Effects of lead
Lead has been listed as a potential carcinogen, inhalation and ingestion are the
two main routes of exposure, and the effects from both are the same. Lead
(Pb) accumulates in the body organs (i.e., brain), which may lead to poisoning
(plumbism) or even death. The gastrointestinal tract, kidneys, and central
nervous system are also affected by the presence of lead. Children exposed to
lead are at risk for impaired development, lower IQ, shortened attention span,
hyperactivity, and mental deterioration, with children under the age of six
being at a more substantial risk. Adults usually experience decreased reaction
time, loss of memory, nausea, insomnia, anorexia, and weakness of the joints
when exposed to lead (Xiong, 2000).
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3. CHAPTER THREE
3.1 Materials and methods
3.2 Materials
TABLE 3. 1: LIST OF MATERIALS
S/N Materials Source Physical and Chemical
Properties
1 Lead(II)
nitrate
(Pb(NO3)2
Chemical engineering
laboratory, University
of Benin
Molecular weight: 331.2g/mol
Colour: white crystals
Odour: odourless
Solubility: soluble in water
2 Nitric acid
HNO3
Chemical engineering
laboratory, University
of Benin
Molecular weight: 63.01g/mol
Colour: colorless
Odour: acrid, suffocatin
Solubility: soluble in water
3 De-ionized
water
Chemistry laboratory,
University of Benin
Appearance: colourless
Odour: odourless 
21
Table 3.2: List of Equipment and Apparatus 1
S/N Equipment/Apparatus Operational characteristics
1 Atomic adsorption spectroscopy
(AAS)
Wavelength range: 185-900nm.
Focal Length : 400mm
2 Muffle furnace Model: OPTIMA OS-752
Revolution per minute: 120rpm
3 Weighing balance Model: METTLER PM4800
Sensitivity: 0.001g
4 Oven Model: SHASHIO-3500
Heating capacity: 2500C
22
Table 3.3 Glassware 1
Apparatus Operational characteristics
Beaker 50ml, 250ml, 500ml
Conical flask 500ml capacity
Funnels 20ml
Standard flask 25ml, 500ml, 1000ml standard
Measuring cylinder 50ml capacity
Desiccator 250cm3
Crucibles Porcelain crucibles
Sample bottles (plastic) 25ml 
23
3.3 METHOD
This experiment was conducted within the period of eight weeks of plant
growth and soil treatment in a lead contaminated soil. The sample contained
10kg of soil with 500ppm of lead contamination with the plant weighing 700g,
was cultivated under shady environment (but exposed enough to receive
sunlight) during the period of experiment. Water was sprinkled on the plant
regularly in a succession of two days interval. With a careful and notable
observation of the plant (Flathman and Lanza, 2008).
3.4 Plant and soil collection/preparation
The herb peperomia pellucida were collected from the premises of the
Faculty of Agricultural Science, University of Benin. The plants were
collected by uprooting it together with the soil, and was conveyed in
polyethylene bags to the site for transplanting.
The soil was collected from the top 12 inches of the marsh area at the
Department of Chemical Engineering University of Benin, it was weighed and
stored in the sample bowl. Both the plant and the soil were then taken to the
laboratory for further preparation (Flathman and Lanza, 2008).
24
3.5 On site preparation.
The soil was air dried for a period of two weeks, this was done in order to
reduce the moisture content and organic matter present in the soil. A sample
of the soil was sent to the laboratory for further analysis. The soil on the roots
of the collected plants were washed off, weighed with a balance and taken to
the laboratory for further preparation.
3.6 Preparation of lead solution
To prepare 500ppm of lead, 0.799g of Pb(NO3)2 was dissolved in a 1liter of
distilled water. (See appendix II for the calculation).
3.7 Soil contamination
Five kilograms of the air-dry soil was placed into the bowl (previously washed
clean with distilled and deionized water). Lead in the form of lead salt
(PbNO3)2 was then added to the soil to achieve the 500ppm level of leadcontamination. The amount of (PbNO3)2 added was 0.799g (PbNO3)2 for 500
ppm contamination. The soil and (PbNO3)2 were stirred and mixed with
deionized water to bring the soils to saturation. After the soil and (PbNO3)2
were mixed, another 5kg of the air dried soil was added to the mixture to bring
the total soil mass to 10kg. The soil was brought to saturation again. . The 
25
mixture was allowed to sit for a day in darkness to allow for the soil solution
and (PbNO3)2 to come to equilibrium (Brooks, 2009).
3.8 Plant propagation and growth period
The peperomia pellucida herb was introduced into the contaminated soil
samples, and water of about 1 liter was sprinkled on the plants and the buckets
were placed at the base of a tree to shade the plant from direct contact with
the sun but exposed enough to receive the necessary amount of sun light
needed for propagation.
 As the peperomia pellucida grew in size, it remained partially shaded
from direct sunlight throughout the duration of the experiment, the plants/ soil
were regularly watered (every two days interval) as needed to keep them
inundated with approximately 20ml to 50ml of water. The watering continued
for the entire 8 weeks of growth.
At week six, the primary vegetative shoots of the regrowth treatment
were collected by cutting the shoots 3.5 cm above the surface of the soil. The
harvested shoots were taken to the laboratory for analysis of lead content
After 8 weeks of growth, all of the shoots were harvested.
26
3.9 Sample extraction
The vegetative shoots and roots were extracted, by gently uprooting the plant
by the shoot and placed in brown paper bags rinsed and allowed to air dry for
2 to 3 hours (Meagher, 2010).
While the soil samples were extracted with the aid of a spade placed into
sealable plastic sample bags for soil-lead analysis.
3.10 Plant and soil samples pretreatment
Plant samples collected from the experiment site were washed under running
tap water to remove adhered soils. The samples were dried in an oven for 48
h at 80oC (Meagher, 2010). The dried samples were ground using agate mortar
and pestle, sieved to 2mm and transferred to polyethylene bags for storage
until later analysis. The soil samples were air-dried at room temperature for
two weeks, mechanically ground and sieved to 2 mm diameter size.
3.11 Lead in soil
The 2 mm fraction soil samples were digested to determine the maximal
environmentally available heavy metals. This was done using 2 M HNO3 in
centrifuge tubes which were placed in boiling water in a 1 L beaker on a hot
plate for 2 hours and shaken at 20 min intervals. The digested samples were 
27
filtered into 25mL standard. The filtrates were diluted to the marks on the
flasks with deionized water and stored in polyethylene tubes prior to
instrumental analysis (Meagher, 2010).
3.12 Lead in Plant
The roots and shoots of the plants were analyzed together for heavy metal
content. 1 g of 2 mm fraction plant samples was weighed into porcelain
crucibles and was ignited in a muffle furnace for 6 h at a temperature between
450 - 500oC. Grey white ash was obtained at the completion of the ashing.
The ash samples were allowed to cool and then 10 mL of 2 M HNO3 was
added to each sample (Flathman and Lanza, 2008). The solution was
evaporated to near dryness on a hot plate and the cooled residues were redissolved in 10 mL 2 M HNO3. The solutions were then filtered into 25 mL
volumetric flasks. Both the crucible and the filter paper were washed into the
flasks, made up with deionized water and then stored in polyethylene tubes
for instrumental analysis (Blaylock et al., 2007). Atomic absorption
spectrophotometer Buck Scientific 200 was used to analyze soil and plant
digests for lead.
28
4. CHAPTER FOUR
4.1 Result and discussion
4.2 Result
Table 4.1 : Result from the analysis of lead in soil and plant using Atomic
absorption spectrophotometer lead (AAS)
Weeks Pb2+ in soil (mg/kg) Pb2+ in Plant (mg/kg)
0. 63.86 0.46
1. 50.70 13.62
2. 43.10 15.00
3. 40.14 19.80
4. 35.56 24.73
5. 33.92 24.09
6. 29.29 23.78
7. 25.24 22.29
8. 20.02 21.20
29
Figure 4.1: chart showing the accumulation of lead from soil by plant
0
10
20
30
40
50
60
1 2 3 4 5 6 7 8
Period of cultivation in weeks
SOIL
PLANT
Concentration of lead (mg/kg)
30
Figure 4.2: Rate of phytoremediation
0
10
20
30
40
50
60
1
2
3
4
5
6
7
8
CONCENTRATION OF LEAD (MG/KG)
Period of cultivation in weeks
soil
plant
31
4.3 Discussion
4.4 Sample analysis
The lead accumulation was analyzed in the laboratory using the atomic
assumption spectroscopy (AAS) weekly, the lead concentration was reported
in mg/kg dry tissue for both the plant and soil (see table 4.1). The actual
milligram of lead uptake was analyzed to determined feasibility of the
remediation. A reasonable amount of the Lead concentration of was absorbed
by the plant out of the contaminated soil.
4.5 Plant observation
During the period of cultivation, the only visual sign of plant stress was
reduced growth in the plants apparently due to the 500 ppm lead present in
the soil. Browning and death of shoot tips and yellowing of the margins was
noticed (see Figure 3 and 4). The tip death in plant was suspected to have
been caused by the salt effect and heavy-metal uptake from the lead complex.
Peperomia pellucida demonstrated its tolerance to lead-contaminated soil, in
that the plant survived and significantly treated the lead contaminated soil
within the period of 8 weeks. From the result one could ascertain that the plant
might have reached hyperaccumulator status. 
32
4.6 Accumulation of lead by Peperomia pellucida
In the uptake and translocation of sufficient quantities of lead to enhance
effective phytoremediation system for lead-contaminated soil using P.
pellucida, the plants was cultivated under shady environment. However, as
presented in the literature review, there are several aspects that are very
promising for lead phytoremediation using P. pellucida herb in a natural
setting, as it can proliferate rapidly, yielding in multiple harvest within a short
period of time as opposed to one harvest per year as in the case of some other
hyperaccumulating plants (Lee and Bukaveckas, 2002). The remediation time
required for a lead phytoremediation approach with this herb could be
theoretically reduced seasonally (Bouchier, 2003). During the course of
remediation the herb approached hyperaccumulator status and accumulated
significantly greater quantities as well as higher concentrations of lead. The
herb proved to have high tolerance to increased levels of lead contamination.
In the eighth weeks of growth the plant grown in the 500 ppm contaminated
soils were approaching the same height as the herb grown without lead
contamination (control sample). Peperomia pellucida have a strong tolerance
for many heavy metal contaminants and this study corroborates previous
reports of the herb’s tolerance to lead (Bontidean et al., 2003).
33
5. CHAPTER FIVE
5.1 Conclusion and Recommendation
5.2 Conclusion
This phytoremediation approach carried out by growing peperomia pellucida
herb in lead-contaminated soil have been seen in similar studies conducted
hydroponically by (Epstein, 2009) as a chemically enhanced leadphytoremediation approach. A number of different laboratory and field
studies have been conducted focusing on the phytoremediation of lead (Pb).
The results have been very promising, although further research and
understanding of the process is still required.
Phytoremediation is considered to be an innovative technology and hopefully
by increasing our knowledge and understanding of this intricate clean up
method, it will provide as a cost-effective, environmentally friendly
alternative to conventional cleanup methods.
Peperomia pellucida may be considered a weed in many places, but it is a
promising lead-phytoremediation candidate that is likely to find a home in
the world of phytoremediation of heavy metals in soil.
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5.3 Recommendation
 Phytoremediation using Peperomia pellucida is a potential remediation
strategy that can be used to decontaminate soils contaminated with lead
pollutants. Research related to this relatively new technology needs to
be promoted and emphasized and expanded and developed, since it is
of a relatively low cost.
 This technology can be enhanced and applied to remediate shallow soil,
ground water and surface water bodies.
 Aged soils are more difficult to phytoremediate than freshly
contaminated ones. Therefore it is recommended that phytoremediation
is done quickly on soils freshly contaminated than aged ones.
 Research needs to be developed on optimizing crop management
practices that can maximize the cleanup potential of remediative plants,
such as sowing practices and seedbed conditions, irrigation, crop
rotations, crop cycle duration, harvesting schedule and methods,
 The effects on metal uptake of all these aspects must be tested in the
field under different site-specific conditions and on multi-contaminated
soil.
35
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