The aim of the study is to use Senna alata L. to remediate soil polluted by spent engine oil (SEO). One hundred and twenty polythene bags filled with 20 kg of soil were separated into two groups A (60) and B (60). Group A contained S. alata seedlings while group B had no plant. They were set up in completely randomized design. Both parts were polluted with different concentrations (0.15% v/w, 0.75% v/w and 3.75% v/w) of SEO 57 days after planting (DAP). One hundred and six days after pollution, the hydrocarbon and heavy metal contents of the vegetated and unvegetated soil, the unused SEO, leaves, stems and roots of S. alata were analyzed. Also, vegetative and reproductive parameters of S. alata were recorded and analyzed. Results showed that percentage of total hydrocarbons degraded/removed from 0.15% v/w, 0.75% v/w and 3.75% v/w vegetated soils were 99.95%, 99.68% and 99.28%, respectively. S. alata alone removed 0.06%, 0.18% and 8.05% hydrocarbons for the same pollution concentrations, respectively. Polycyclic aromatic hydrocarbons accumulated in the leaves, stems and roots of S. alata. Percentage of total hydrocarbons accumulated in the leaves, stems and roots of S. alata in 3.75% v/w polluted vegetated soils were 112.47%, 1.49% and 1.35%, respectively. Heavy metals such as Copper (Cu), Lead (Pb), Zinc (Zn), Iron (Fe) and Aluminium (Al) were detected in the unused spent engine oil. There were higher concentrations of each of the heavy metals in the polluted unvegetated soils than the vegetated soils. Heavy metals accumulated in various vegetative parts of S. alata. Copper was found more in the stems than in the leaves and roots while Fe and Pb were found more in the leaves than in the stems and roots. Zinc and Al were found more in the roots than in the leaves and stems. Moreover, heavy metal concentrations (ppm) were more in the vegetative parts of S. alata than in the polluted soil. Also, plant height, number of leaves, number of pinnules per leaf, leaf area, stem circumference and number of roots increased significantly (P ≤ 0.05) after pollution. Root circumference decreased significantly (P ≤ 0.05), with increase in the concentrations of SEO applied but root length did not vary among the treatments and control. Number of inflorescences and dry weight of seeds decreased significantly (P ≤ 0.05) but number of flowers, pods and seeds did not vary among the treatments and control. Hence, S. alata is an ideal plant for the removal (phytoremediation) of hydrocarbons and heavy metals in SEO contaminated soil. The plant can be regarded as a hyper accumulator for some polycyclic aromatic hydrocarbons and heavy metals.

Title page


Certification page ii

Dedication iii

Acknowledgement iv

Abbreviations v

List of tables vi

List of plates vii

List of figures viii

Abstract ix

Table of content x


Background information1

Spent engine oil2


Objectives of the study3


Engine oil4

Engine oil additives4

Properties of engine oil6

Regeneration of used engine oil7

Effects of spent engine oil on the ecosystem8

Nutrient requirements of Senna plant8

Medicinal uses of Senna9


Phytoremediation of hydrocarbons10

Phytoremediation of heavy metals13

Phytoremediability of Senna14


Planting and pollution of Senna plant15

Total hydrocarbon analysis17

Heavy metals analysis                                                                                                                       18

3.3 Determination of vegetative parameters of Senna alata 18

Determination of reproductive parameters of Senna alata19

Data analysis19


Result of the total hydrocarbon analysis20

Percentage compositions of total hydrocarbons in the samples24

Result of the heavy metal analysis                                                                                                     29

4.3 Result of the vegetative parameters of Senna alata 34

4.4 Result of the reproductive parameters of Senna alata 49







SEO - Spent engine oil

% - Percentage Wt Weight Etc Etcetera

TBN - Total base number

˚C - Degree Celsius W Weight

NPK - Nitrogen, Phosphorous, Potassium

g Gram l Liter

PCs Phytochelatins

GSH - Glutathione

ml - Milliliter

V/W - Volume per weight

GLC/MS - Gas Liquid Chromatography/Mass Spectroscopy

FAAS  - Flame Atomic Absorption Spectroscopy

mm - Millimeter m Meter

μm - Micrometer

cm/min - Centimeter per minute

μl Micro liter

AAS - Atomic Absorption Spectrophotometer

Cm3 - Centimeter cube

C14-C22 - Fourteen carbon atoms to twenty-two carbon atoms

Mg/ml - Milligram per milliliter

THC - Total hydrocarbons Ppm Part per million Cm2 Centimeter square

< Less than


Table 1 - Studies on phytoremediation of PAH contaminants in soil 12

Table 2 - Composition and quantities of hydrocarbons in the unused spent engine oil, unvegetated and vegetated soil samples of Senna alata polluted with spent engine oil 21

Table 3 - Composition and quantities of hydrocarbons in the unused spent engine oil and vegetative plant parts of Senna alata polluted with spent engine oil 23

Table 4 - Percentage composition of total degraded hydrocarbons in the analyzed soil samples of Senna alata polluted with spent engine oil 25

Table 5 - Percentage accumulation of hydrocarbons in Senna alata polluted with spent engine oil 27

Table 6 - Composition, quantity (ppm) and percentage of heavy metals in the vegetated and unvegetated soils of Senna alata polluted with spent engine oil 30

Table 7 - Composition, quantity (ppm) and percentage of heavy metals accumulated in the root, stem and leaf samples of Senna alata polluted with spent engine oil 32

Table 8 - Vegetative parameters of Senna alata before and after pollution (57 and 163 days after planting, respectively) 35

Table 9 - Root parameters of Senna alata 163 days after planting 40

Table 10 - Reproductive parameters of Senna alata 294 days after planting 50


Plate 1 - Senna alata seedlings, 57 days after planting (DAP) 16

Plate 2 - Senna alata plants 163 days after planting (106 days after pollution) 38

Plate 3 - Control Senna alata showing no aerial roots produced (56 days after pollution) 41

Plate 4 - Control Senna alata produced adventitious roots that entered the soil instead of aerial roots (106 days after pollution) 42

Plate 5 - 0.15% v/w (30 ml) treatment showing aerial roots produced by Senna alata (56 days after pollution) 43

Plate 6 - 0.15% v/w (30 ml) treatment showing aerial roots produced by Senna alata (106 days after pollution) 44

Plate 7 - 0.75% v/w (150 ml) treatment showing aerial roots produced by Senna alata (56 days after pollution) 45

Plate 8 - 0.75% v/w (150 ml) treatment showing aerial roots produced by Senna alata (106 days after pollution) 46

Plate 9 - 3.75% v/w (750 ml) treatment showing numerous aerial roots produced by Senna alata (56 days after pollution) 47

Plate 10 - 3.75% v/w (750 ml) showing numerous aerial roots produced by Senna alata (106 days after pollution) 48

Plate 11 - Senna alata polluted with spent engine oil at flowering stage 51

Plate 12 - Pods of Senna alata polluted with spent engine oil 52

Plate 13 - Seeds of Senna alata polluted with spent engine oil 53


Figure 1: Percentage degraded hydrocarbons by Senna alata polluted with spent engine oil 26

Figure 2: Percentage accumulation of hydrocarbons in the root, stem and leaf samples of Senna alata

polluted with spent engine oil 28

Figure 3: Percentage quantities of heavy metals in the unvegetated soil and soil vegetated with Senna alata 31

Figure 4: Percentage quantities of accumulated heavy metals in the root, stem and leaf samples of

Senna alata polluted with different concentrations of spent engine oil 33

Figure 5: Vegetative parameters of Senna alata before pollution (57 DAP) 36

Figure 6: Vegetative parameters of Senna alata after pollution (163 DAP) 37



Background information

The disposal of spent engine oil (SEO) into gutters, water drains, open plots and farms is a common practice in Nigeria especially by motor mechanics. These oils, also called spent lubricating or waste engine oil, is usually obtained after servicing and subsequently drained from automobile and generator engines (Anoliefo and Vwioko, 2001) and much of this oil is poured into the soil. This indiscriminate disposal of spent engine oil adversely affect plants, microbes and aquatic lives (Nwoko et al., 2007; Adenipekun et al., 2008) because of the large amount of hydrocarbons and highly toxic polycyclic aromatic hydrocarbons contained in the oil (Wang et al., 2000; Vwioko and Fashemi, 2005). Heavy metals such as vanadium, lead, aluminium, nickel and iron which are found in large quantities in used engine oil may be retained in soil, in form of oxides, hydroxides, carbonates, exchangeable cation and/or bound to organic matters in the soil (Ying et al., 2007). These heavy metals may lead to build up of essential organic (carbon, phosphorous, calcium, magnesium) and non-essential (magnesium, lead, zinc, iron, cobalt, copper) elements in soil which are eventually translocated into plant tissues (Vwioko et al., 2006). Although heavy metals in low concentration are essential micronutrients for plants, but at high concentrations, they may cause metabolic disorder and growth inhibition for most of the plant species (Yadav, 2010). According to Nwadinigwe and Onwumere (2003), contamination of soil arising from oil spills affect the growth of plants and causes great negative impacts on food productivity (Onwurah et al., 2007). Therefore, these indiscriminate disposals of spent engine oil on the environment and the adverse effects on living organisms were the main reason for this research and so, there is a dire need to adopt a control measure that employs environmentally friendly methods. One of these methods is the use of plants to extract or degrade the pollutants into harmless chemicals. The use of plants to reclaim a damaged environment is called phytoremediation. In this work, attempt was made to use Senna alata L. to phytoremediate hydrocarbons and heavy metals present in SEO-polluted soil.

Spent engine oil

Spent engine oil contains complex mixtures of paraffinic, naphthalenic and aromatic petroleum hydrocarbons and various contaminants that may contain one or more of the following: carbon deposits, sludge, wear metals and metallic salt, aromatic and non aromatic solvents, water (as water- in-oil emulsion), glycols, silicon based antifoaming compounds, fuel, polycyclic aromatic hydrocarbons [PAHs] and miscellaneous lubricating oil additive materials (Ayoola and Akaeze, 2012). Engine oil becomes contaminated as a result of physical and chemical reactions. Metals from engine from time to time erode into the engine oil forming impurities. Oxidation of hydrocarbon chains bond together to form sludge due to high temperature. Incombustible gasoline up to about 5% wt often leak from fuel injector line, contaminating the oil (Fedak, 2001). Some additives such as multiple sulfur-based detergents which keep materials from depositing on the engine piston often begin to break down as sludge and accumulate in motor oil (Fedak, 2001). Used motor oils are also characterized by high concentrations of PAHs. Dominguez-Rosado and Pichtel (2003) found that the PAHs content of used motor oil was often between 34 and 90 times higher than new oil. PAHs belong to a group of over 100 hazardous substances of organic pollutants consisting of two or more fused-benzene aromatic rings (Obini et al., 2013). In nature, PAHs may be formed by high temperature pyrolysis of organic materials or low to moderate temperature diagenesis of sedimentary organic materials to form fossil fuel or direct biosynthesis by microbes and plants (GFEA, 2012 and USGS, 2014). Sources of PAHs can be both natural and anthropogenic. Natural sources include forest and grass fire, oil seeps, volcanoes, chlorophyllous plants, fungi and bacteria. Anthropogenic sources include petroleum, power generation, refuse incineration, home heating, internal combustion engine etc. (GFEA, 2012 and USGS, 2014). PAHs have low solubility in water and are highly lipophilic. In water or when adsorbed on particulate matter, PAHs can undergo photodecomposition in the presence of ultraviolet light from solar radiation (Obini et al., 2013). Heavy PAHs (C16-C50) are more stable and toxic than the light PAHs (C6-C16) (ATSDR, 1995). According to Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) list of hazardous substances, PAHs ranked 7th in 2005 in the biennial ranking of chemicals deemed to pose the greatest possible risk to human health (Christopher, 2008). Some PAHs have been demonstrated to be mutagenic and carcinogenic in humans and those that have not been found to be carcinogenic may, however, synergistically increase the carcinogenicity of other PAHs (Obini et al., 2013).


Senna alata (L.) Roxb. (syn. Cassia alata L.) (Aigbokhan, 2014) commonly known as candle stick senna, wild senna, ringworm cassia and king of the forest, is a medium-sized flowering shrub belonging to the Family Fabaceae (Mansuang et al., 2010). It is widespread in warm areas of the world. Senna is native to Amazon rain forest but spread widely in the tropical and subtropical regions. It starts its life mainly through seeds, though an in vitro propagation which induces maximum number of shoots and beneficial shoot length by nodal and hypocotyl explants was proposed by Thirupathi and Jaganmohan (2014). The leaves which often fold at night are large, bilaterally symmetrical and even-pinnate. Leaflets are 4-26 (two to thirteen pairs) with lanceolate shape and smooth margin. It reaches a height of about 2.5 meters and produces yellow flowers in the leaf axils. The inflorescence is an erect waxy yellow spike that resembles fat candle before the individual blossom opens. The flower is covered with orange bracts which fall off when the flower opens. The flower buds are rounded with five overlapping sepals and five free but less equal petals narrowed at the base. The flower is bisexual and zygomorphic. The ovary is superior with marginal placentation. The fruit is a winged black pod and seeds are small, square and rattle in the pod when dry. The pericarp is dry when mature and dehisces along the suture. Due to the beauty of the plant, it has been cultivated around the world as an ornamental plant. The leaves of Senna plant are often attacked by foliage eating caterpillars while the seeds are attacked by weevil in storage. No disease is of major concern, though some species are attacked by virus (Wikipedia, 2015).

Objectives of the study

The objectives of this work are:

1. To determine the quantity of hydrocarbons degraded by Senna alata.

2. To ascertain the changes in hydrocarbon contents of soil unvegetated and vegetated with S. alata and polluted with spent engine oil.

3. To ascertain the type and quantity of heavy metals that can be removed or accumulated by S. alata in soil contaminated with spent engine oil.

4. To determine the vegetative and reproductive parameters of S. alata growing on different concentrations of spent engine oil.




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