ABSTRACT
Contamination of existing and potential agricultural lands is a major problem associated with
the processing and distribution of crude and refined petroleum products in many oil producing
countries like Nigeria. Hydrocarbon contaminants in soil are potentially phytotoxic to plants and
can interfere with plant establishment and growth as well as other potential land uses.
Pollution control strategies involving physico-chemical methods are usually expensive and have
often aggravated the problem rather than eliminate it. Phytoremediation is recently being
favoured as a good option for the remediation of polluted sites and has proven to be a better
alternative; hence there is the need to identify various plants especially native ones with
potential for the phytoremediation of petroleum-polluted soils. The objectives of this study
were to plant Kenaf (Hibiscus cannabinus L.) in a three media of simulated diesel polluted soil
samples – soil amended with compost (Sample A), soil amended with fertilizer (Sample B) and
unamended soil (Sample C); monitor the rate of reduction of TPH in the soil samples; determine
pollutant concentrations in the plant parts and; and to identify the medium most suitable for
the effective breakdown of hydrocarbons in the contaminated soils. From an initial TPH
concentration of 32387.68 ± 15.70 mg/kg, a Total Petroleum Hydrocarbon (TPH) reduction of
68.14 % was recorded in sample A while a reduction in TPH of 65.13 and 12.12 % were recorded
in soil samples B and C respectively after 15 weeks of planting. Analysis of variance (ANOVA)
carried out showed a significant different (P<0.05) in the TPH in the soil samples A (10319.53 ±
284.25 mg/kg), B (11293.85 ± 446.75 mg/kg) and C (28462.77 ± 90.95mg/kg) after 15 weeks of
planting. Predictive models were developed using regression analysis to predict the TPH
reduction in the three soil samples with time. A strong negative correlation (P<0.05) were
observed (R2 for sample A = 0.9687, R2 for sample B = 0.9614 and R2 for sample C = 0.8600).
Analysis of contaminant accumulation in the plant parts revealed that 405.45 ± 4.59, 126.85 ±
3.15 and 273.39 ± 4.32 mg/kg were recorded in the root, stem and leaf parts respectively. The
results showed that a total of 57.44, 17.97 and 38.76 % of the contaminant were stored in the
root, stem and leaf of Kenaf (Hibiscus cannabinus L.) plant. Generally, the plant showed no
adverse growth effect, hence presents itself as a good candidate for phytoremediation of diesel
contaminated soil samples amended with compost and fertilizer.
TABLE OF CONTENTS
ACKNOWLEDGEMENT ……………………………………………………………………………………………………………. iii
TABLE OF CONTENTS……………………………………………………………………………………………………………… vi
LIST OF FIGURES ………………………………………………………………………………………………………………….. viii
LIST OF TABLES……………………………………………………………………………………………………………………… ix
ABSTRACT …………………………………………………………………………………………………………………………….. x
CHAPTER 1 ………………………………………………………………………………………………………………………….. 11
1.0 INTRODUCTION …………………………………………………………………………………………………………. 11
1.1 Problem Statement ………………………………………………………………………………………………… 13
1.2 Objectives of the Study …………………………………………………………………………………………… 13
1.3 Project Justification ………………………………………………………………………………………………… 14
1.4 Scope of the Study ………………………………………………………………………………………………….. 15
CHAPTER 2 ………………………………………………………………………………………………………………………….. 16
2.0 LITERATURE REVIEW ………………………………………………………………………………………………….. 16
2.1 Oil, Petroleum Hydrocarbons and their Effects on Soil …………………………………………………. 16
2.2 Methods of Remediation of Oil-Contaminated Soils ……………………………………………………. 18
2.2.1 Physical and chemical remediation …………………………………………………………………….. 18
2.2.2 Biological remediation ……………………………………………………………………………………… 18
2.3 Bioremediation of Organic Polluted Soil …………………………………………………………………….. 19
2.4 Phytoremediation: A Plant-Assisted Bioremediation Mechanism ………………………………….. 21
2.4.1 Mechanisms of hydrocarbon phytoremediation …………………………………………………… 22
2.4.1.1 Phytostabilisation ……………………………………………………………………………………………. 23
2.4.1.2 Phytodegradation ……………………………………………………………………………………………. 24
2.4.1.3 Phytovolatiliation ……………………………………………………………………………………………. 25
2.4.1.4 Rhizoremediation ……………………………………………………………………………………………. 25
2.4.2 Environmental considerations in phytoremediation ……………………………………………… 26
2.4.3 Key performance index in phytoremediation ………………………………………………………. 29
2.5 Comparison of Phytoremediation to Alternative Remediation Strategies ……………………….. 29
2.6 Plant Selection in Phytoremediation …………………………………………………………………………. 30
2.7 PHC Contamination in Developing Countries………………………………………………………………. 32
CHAPTER 3 ………………………………………………………………………………………………………………………….. 34
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3.0 MATERIALS AND METHODS ………………………………………………………………………………………… 34
3.1 Hydrocarbon Contaminant and Soil Samples………………………………………………………………. 34
3.2 Experimental Procedure ………………………………………………………………………………………….. 34
3.3 Baseline Parameters ……………………………………………………………………………………………….. 35
3.4 PHC Phytoremediation Index …………………………………………………………………………………… 35
3.5 Laboratory Analysis ………………………………………………………………………………………………… 35
3.5.1 TPH analysis of soil by infra-red method……………………………………………………………… 35
3.5.2 Determination of pH ………………………………………………………………………………………… 36
3.5.3 Moisture content analysis…………………………………………………………………………………. 36
3.5.4 Determination of total nitrogen by Kjeldahl method …………………………………………….. 37
3.5.5 Determination of available phosphorus ……………………………………………………………… 37
3.6 Statistical Analysis ………………………………………………………………………………………………….. 38
CHAPTER 4 ………………………………………………………………………………………………………………………….. 39
4.0 RESULTS AND DISCUSSIONS ………………………………………………………………………………………… 39
4.1 Baseline Data of Contaminated Soil ……………………………………………………………………………… 39
4.2 Remediation of PHC soil samples …………………………………………………………………………………. 39
4.3 Predicting TPH Reduction in Soil Samples ……………………………………………………………………… 42
4.4 Absorption of PHC by Kenaf (Hibiscus cannabinus L.) Plant ……………………………………………… 44
CHAPTER FIVE ……………………………………………………………………………………………………………………… 46
5.0 CONCLUSION AND RECOMMENDATION………………………………………………………………………… 46
5.1 Conclusion ………………………………………………………………………………………………………………… 46
5.2 Recommendation ………………………………………………………………………………………………………. 46
REFERENCES ………………………………………………………………………………………………………………………… 48
APPENDICES ………………………………………………………………………………………………………………………… 59
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CHAPTER ONE
1.0 INTRODUCTION
Soil is a fundamental and irreplaceable natural resource which provides a variety of ecosystem
services and is the essential link between the components air, bedrock, water and biota that
make up our environment. Contaminated land is defined as sites having levels of contaminants
present in the soil that pose a significant possibility of harm to the ecosystem (DEFRA, 2009).
There are a significant number of petroleum hydrocarbon impacted sites across the world
resulting from a wide range of past industrial, military, and petroleum production, and
distribution practices (Total Petroleum Hydrocarbon Criteria Working Group Series, 1998). The
chemical composition of petroleum products is complex and varied and changes over time and
distance when released to the environment (Bellmann & Otto, 2003). Oil pollution in soils can
cause interference with the ecosystem and in most cases causes the non-productive use of
land. The European Commission (2002; 2006a; 2006b) has identified soil contamination as one
of eight major threats to European soils. Contaminants can enter the soil from points (local) and
diffuse sources (DEFRA, 2009). It is not easy to estimate the costs of the soil contamination in
terms of rehabilitating and restoring due to the lack of sufficient quantitative and qualitative
data, but studies have pointed out that soil contamination results in great costs to society
(European Commission, 2006c).
Global industrialization over the past centuries has resulted in widespread contamination of the
environment with organic and inorganic wastes. Contaminated land has generally resulted from
industrial activities connected with the production, use, and disposal of substances potentially
hazardous to the environment. The problem is worldwide, and the estimated number of
contaminated sites is significant and increasing (Mougin, 2002; Kaimi et al., 2006). Soil
contaminants include heavy metals, mineral pollutants, monocyclic aromatic hydrocarbons,
phenolic compounds, polycyclic aromatic hydrocarbons (PAHs), chlorinated hydrocarbons,
pesticides and other pollutants such as mineral oils and gasoline (Beyer 1990). Accurate detail
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regarding the extent of hydrocarbon contamination in the terrestrial environment has been
difficult to quantify because of the unintentional nature of the contamination (largely through
accidental spillage or distribution line vandals).
In more recent years, as recognition grew of the damage around the world from decades of an
industrial economy and extensive use of chemicals, so did interest in finding technologies that
could address the residual contamination (McCutcheon & Schnoor, 2003). Many methods can
be used for the remediation of oil pollution. Methods of oil pollution remediation in the
environment can be done in three ways i.e. physical, chemical and biological (Okoh & Trejo-
Hernandez, 2010). Soil microbes as well as plants and biota are effective indicators to reflect
the levels of soil contamination. They are capable of degrading or retaining more than 99% of
all the types of soil pollutants (EA, 2006) and preventing them from entering the wider
environment. However, when the amount of contaminants exceeds the buffering capacity of a
soil, it leads to a long-term negative impact on soil quality and biodiversity, and also damages to
its functions as a producer of fiber, fuel and food. Once the contaminants enter the food chain,
they can become a threat to human health.
There have been increasing international efforts to remediate contaminated sites using “green”
technologies, either as a response to the risk of adverse health or environmental effects or to
enable site redevelopment (Vidali, 2001). Phytoremediation is a broad term that has been in
use since 1991 to describe the use of plants to reduce the volume, mobility, or toxicity of
contaminants in soil, groundwater, or other contaminated media (McCutcheon & Schnoor,
2003). Phytoremediation is an emerging technology that uses various plants to degrade,
extract, contain, or immobilize contaminants from soil and water. This technology has been
receiving attention lately as an innovative, cost-effective and widely accepted alternative to the
more established treatment methods used at hazardous waste sites (U.S. EPA, 2000). It is
suitable for low to moderate soil contamination over large areas, and to sites with large
volumes of groundwater with low levels of contamination. It takes advantage of a plant’s
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natural ability to absorb, accumulate, or metabolize contaminants from the soil or other media
in which it grows.
1.1 Problem Statement
Contamination of existing and potential agricultural lands is a major problem associated with
the processing and distribution of crude and refined petroleum products in many oil producing
countries like Nigeria (Ayotamuno et al., 2006). Since the exploration of crude oil in Nigeria,
with the influx of many oil firms, there has been high tendency of and spillage of oil onto the
ground and also into water bodies. The country has over the years experienced environmental
pollution of different forms especially in the Niger-Delta region of the country, which has
resulted in the formation of many militant groups fighting for compensation and better
management of their polluted lands and water bodies. Efforts are being made by both
governmental and non-governmental organizations in the drive towards finding a lasting
solution to this oil pollution menace in the south-south region of the country as evidenced by
programs initiated by the Niger Delta Development Commission.
Hydrocarbon contaminants in soil are potentially phytotoxic to plants and can interfere with
plant establishment and growth (Adam and Duncan, 1999). The problems of pollution have led to
the exploration of many remedial approaches to effect the clean-up of the polluted soils.
Pollution control strategies involving physico-chemical methods have often aggravated the
problem rather than eliminate it. Numerous sites are contaminated worldwide with crude or
refined oil in different countries. Hence, there is a vast need of various plants especially native
ones for the phytoremediation of petroleum-polluted soils.
1.2 Objectives of the Study
The general objective of this study is to assess the potential of the use of a Nigerian native plant
(Kenaf (Hibiscus cannabinus L.)) in the phytoremediation of a simulated petroleum hydrocarbon
(PHC) contaminated soil.
The specific objectives of the study are:
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i. To plant Kenaf (Hibiscus cannabinus L.) in a three media of simulated diesel polluted
soil samples – soil treated with fertilizer (urea and sulphate of ammonia), treated
with compost and untreated.
ii. To monitor the rate of reduction of TPH in the soil samples with time;
iii. To determine pollutant concentration in the plants parts and to identify parts where
the pollutant is stored;
iv. To identify which media combinations is most suitable for the effective breakdown
of diesel in the contaminated soil samples.
1.3 Project Justification
Phytoremediation technologies are in the early stages of development, with laboratory
research and limited field trials being conducted to determine processes and refine methods.
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 (Ralinda & Miller, 1996). Although phytoremediation
may not be the perfect remedial solution that some envisioned when its use at hazardous
waste sites was first pioneered, its implementation continues to be appropriate or even
preferable at a variety of sites. As the technology matures and its use expands beyond research
laboratories and government-funded remediation, site owners and consultants will want
comparative data on phytoremediation to determine its appropriateness for a particular site
(Amanda, 2006).
Growing awareness of the harm that pollutants do to the soil as well as to the whole ecological
chain has led to more research into how to clean up contaminated sites. Due to the great
diversity of pollutants, however, there is no common solution to solve all types of soil
contamination. Therefore studies related to petroleum hydrocarbon contamination of soil and
its biological cleanup is of great importance. The provision of a viable phytoremediation
technology would offer an economically feasible and environmentally sustainable option for
the remediation of hydrocarbon contaminated sites in Nigeria especially in the south–south
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region of the country. This research work, therefore, seeks to assess the efficiency of
phytoremediation technology of the hydrocarbon contaminated soil as an effective method of
remediating oil polluted soil. The findings will be useful in the remediation of oil contaminated
soils in Niger-Delta region of the country and any other oil polluted part of the country.
Biodegradation is recently being favoured as a good option for the remediation of polluted sites
mainly because it uses inexpensive equipment, environmentally friendly and simple.
Phytoremediation is one of the forms of biodegradation which involves the in situ use of plants
and associated microbes for the remediation of polluted sites. It has been evaluated by several
research studies to remediate petroleum polluted soils (Merkl et al., 2005; Issoufi et al., 2006;
Diab, 2008).
1.4 Scope of the Study
The study was limited to the study of the phytoremediation potential of Kenaf (Hibiscus
cannabinus L.) using a simulated environment comprising of soil samples contaminated with
diesel fuel only and amended with fertilizer and compost.
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