The dynamics of Vetiver (Vetiveria zizanioides) and Guinea grass (Panicum maximum) Amended with Organic Manures in Remediation of Crude Oil Contaminated Soil in Port Harcourt

Greener Journal of Agricultural Sciences

Vol. 10(2), pp. 86-94, 2020

ISSN: 2276-7770

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The dynamics of Vetiver (Vetiveria zizanioides) and Guinea grass (Panicum maximum) Amended with Organic Manures in Remediation of Crude Oil Contaminated Soil in Port Harcourt

^1*Chukwumati, JA; ¹Omovbude, S

¹Department of Crop and Soil Science, Faculty of Agriculture, University of Port Harcourt, P. M. B. 5323, Choba, Port Harcourt, Rivers State, Nigeria.

ARTICLE INFO

ABSTRACT

Article No.: 031120049

Type: Research

In a field study, conducted at the Teaching and Research farm of Rivers State University, soil polluted with Bonny Light crude oil at 0% and 2% v/w was subjected to remediation processes using vetiver (Vetiveria zizanioides) and guinea grasses (Panicum maximum) amended with organic manures for a period of twelve months. Two weeks after pollution, poultry and Rabbit manures were applied at 0, 10, 20 and 30 tons/ha respectively. Vetiver and Guinea grasses were planted two weeks later. It was fitted in factorial split plot. Results showed 80% of vetiver survived in contaminated unamended plots against 85% in control, percentage survival in guinea grass was 60% in contaminated unamended against 85% in control. There was initial delay in germination on contaminated plots for the two grasses. Amendment of the soil with organic manure improves the growth and performance of the grasses. Vetiver height was significantly (p<0.05) different from guinea grass in contaminated unamended plots implying that vetiver has better adaptation to pollution than guinea grass. Remediation of soil with vetiver and guinea grasses degraded the THC in the soil to 23 and 21% respectively; amendment of soil with different levels of organic manure increased the level of degradation to 70.6 and 67.9% for vetiver and guinea grasses respectively. Vetiver uptake of THC in plant tissues was significantly (p<0.05) different from that of guinea grass. Amendment of the soil with organic manure reduced the uptake. Generally, both grasses were tolerant to THC with vetiver being more tolerant with higher survival rate. Poultry manure as amendment material planted with vetiver grass was more effective than rabbit manure in remediation of crude oil contaminated soil.

Accepted: 17/03/2020

Published: 25/04/2020

*Corresponding Author

Chukwumati, JA

E-mail: johnprint2005@ yahoo.com

Phone: 08063573269

Keywords: Vetiver grass; Guinea grass; Crude Oil; Contamination; R emediation; Poultry; Rabbit; Manure

INTRODUCTION

Soil is one of the valuable resources for the production of food and fibre. The wealth of any nation and indeed Nigeria depends on how well it is managed and maintained.

The wealth of Nigeria in the nineteen sixties (1960’s) and early seventies (1970’s) depend mostly on revenue generated from agriculture. As a result of rapid increase in the exploration and exploitation of crude oil, there was sharp decline in the output of agricultural production due to negative impact of crude oil contamination on the environment.

Presently, about 90% of Nigeria’s economy depends largely on revenue generated from crude oil, most of this oil comes from numerous small producing oil fields located in both on, and offshore zones of Niger Delta (Zakka, 2013). The exploration and exploitation of this oil have brought about hardship and negative effects due to oil pollution which has adversely affected the soil, plants, micro-organisms and human beings dwelling within the ecosystems (Emola et al.,1992).

The Niger Delta of Nigeria has one of the world wetlands covering over 20,000km² in the South Eastern Nigeria (World Bank, 1995). Of the resources available, oil and gas are presently the most valuable in the national economy (Horsfall and Spiff, 2001). Despite these numerous natural resources, the region is threatened by diverse environmental problems of which oil pollution is most paramount.

Oil spillage is one of the major causes of crude oil pollution of soil and water. There is no oil exploration operation that is 100% efficient, equipment failure may lead to spillage Anyaegbu, 1987), when oil spillage occurs, the environment is adversely affected, the ecosystem is damaged, the food chain disrupted and it brings about emotional, socio-economic, stress and youth restiveness to the inhabitants of the environment.

It is important to note that oil contamination on soil is not itself toxic to plants rather has an indirect effect as it creates a condition that makes essential nutrients for plant growth unavailable and at the same time makes some nutrients that are toxic to plants available (Isirimah et al., 2006).

A number of biological, physical and physicochemical remediation techniques have been used to decontaminate soils and water. These techniques range from setting ablaze (fire) to the crude oil polluted site, excavation of contaminated area, use of bioremediation (micro-organism), organic manures, inorganic fertilizer and plants. The aim of all these practices is to ensure protection of human health and the environment.

Phytoremediation is an alternative method of remediation that utilizes plants to decontaminate soil, water and air environment (Prasad, 2003).

It is relatively environmentally friendly, because it uses naturally occurring organisms and presents the environment in a more natural state as opposed to mechanical clean up. It is simple, cost effective , non environmentally disruptive and its by-products can find a range of other use (Truong, 2000).

Weeds are generally referred as plants growing in place where they are not wanted. Several plant species which are regarded as weeds are useful for other purposes such as phytoremediation. An ideal plant species for phytoremediation should have one of the following characteristics: high biomass with enhanced metal uptake potential, low biomass with very high metal accumulation capacity.

Phytoremediation of soil with the use of vetiver and guinea grasses amended with organic manures in Niger Delta is very limited as revealed in literature..

The use of these remediation materials will restore the physico-chemical and biological condition of the soil and at the same time reduce the effect of heavy metal contamination of the soil and plants. The objective of this study is to remediate soil polluted with crude oil with vetiver and guinea grasses amended with organic manures.

MATERIALS AND METHODS

Study Site

The study was conducted at the teaching and research farm of Rivers State University, Nkpolu, Port Harcourt. The study site is located by latitude 4^o 5¹N and longitude 7^o 0¹E with an elevation of 18m above sea level (FAO, 1984).

The mean annual rainfall ranges from 3000 to 4000mm (FAO, 1984) and is bimodal in nature with peaks in June and September with a period of low precipitation in August. Annual temperature varies between 22 to 31^oC, (FDRD,1981), the relative humidity (RH) varies between 35 to 90% depending on the particular period of the year.

Soil of the study site

Soil of the study site was from coastal plain sands geomorphic region. It is typically sandy loam (typic paleudult) formed over sedimentary rocks. It belongs to the ultisol order of the United State Soil Taxonomy (Soil Survey Staff, 1975).

SOURCES OF CRUDE OIL

Nigerian Bonny light crude oil (fresh) obtained from shell Petroleum Company Nigerian Limited, Bayelsa State flow station was used and a concentration of 0 and 2% was used in the studied area.

Each of the experimental plots (3 x 4m) with the exception of the control plot was treated with crude oil from a watering can; evenly sprayed and worked into the soil with garden fork.

Amendment Materials

Poultry and rabbit manures were used as amendment materials. These organic manures were applied onto the soils with the exception of control plots two weeks after contaminating the soil with crude oil. The organic manures were broadcast and worked into the soil with garden fork

Poultry and rabbit manures were incorporated into the experimental plots at the rate of 0, 10, 20 and 30 tons per hectare, respectively.

Preparation and Planting of Plant Materials

The study area had been under continuous cultivation with different crops, the last being cassava and maize. The site was ploughed, and harrowed with tractor, marked and pegged. Vetiver grass (Vetiveria zizanioides) and guinea grass (Panicum maximum) collected from National Root Research Institute, Umudike, Abia State and Rivers State University Teaching and Research Farm, respectively were planted two weeks after amendment materials were added at a spacing of 20 by 30 cm and 30 by 30 cm for vetiver and guinea grasses respectively.

Experimental Design

A total of 32 treatment combinations (Table 1) were laid out in a factorial fitted into a split plot randomized complete block design with contaminated and uncontaminated as the main plots. Other factors served as sub plots. All the treatments were replicated three times making a total of 96 plots.

Table 1: Treatment combinations

Treatment code	Key
COP0	Control, no crude oil no poultry manure (0 t/ha) plus vetiver grass
COP1	No crude oil, poultry manure at 10 t/ha plus vetiver grass
COP2	No crude oil, poultry manure at 20t/ha plus vetiver grass
COP3	No crude oil, poultry manure at 30t/ha plus vetiver grass
COR0	No crude oil, no rabbit manure (0 t/ha) plus Vetiver grass
COR1	No crude oil, rabbit manure at 10 t/ha plus vetiver grass
COR2	No crude oil, rabbit manure at 20 t/ha plus vetiver grass
COR3	No crude oil, rabbit manure at 30 t/ha plus Vetiver grass
C1P0	Contaminated with crude oil, no poultry manure (0 t/ha) plus vetiver grass
C1P1	Contaminated with crude oil, poultry manure at 10 t/ha plus vetiver grass
C1P2	Contaminated with crude oil, poultry manure at 20 t/ha plus vetiver grass
C1P3	Contaminated with crude oil, poultry manure at 30t/ha plus vetiver grass
C1R0	Contaminated with crude oil, no rabbit manure (0 t/ha) plus vetiver grass
C1R1	Contaminated with crude oil, rabbit manure at 10t/ha plus vetiver
C1R2	Contaminated with crude oil, rabbit manure at 20 t/ha plus veitver grass
C1R3	Contaminated with crude oil, rabbit manure 30 t/ha plus vetiver grass
COP0	Control, no crude oil, no poultry manure (0t/ha) plus guinea grass
COP1	No crude oil, poultry manure at 10 t/ha plus guinea grass
COP2	No crude oil, poultry manure at 20 t/ha plus guinea grass
COP3	No crude oil, poultry manure at 30 t/ha plus guinea grass
COR0	No crude oil, no rabbit manure 0t/ha)plus guinea grass
COR1	No crude oil, rabbit manure at 10t/ha plus guinea grass
COR2	No crude oil, rabbit manure at 20t/ha plus guinea grass
COR3	No crude oil, rabbit manure at 30t/ha plus guinea grass
C1P0	Contaminated with crude oil, no poultry manure (0 t/ha) plus guinea grass
CIP1	Contaminated with crude oil, poultry manure at 10 t/ha plus guinea grass
CIP2	Contaminated with crude oil, poultry manure at 20t/ha plus guinea grass
CIP3	Contaminated with crude oil, poultry manure at 30t/ha plus guinea grass
CIR0	Contaminated with crude oil, no rabbit manure (0 t/ha) plus guinea grass
CIR1	Contaminated with crude oil, rabbit manure at 10 t/ha plus guinea grass
CIR2	Contaminated with crude oil, rabbit manure at 20t/ha plus guinea grass
CIR3	Contaminated with crude oil, rabbit manure at 30t/ha plus guinea grass

Collection and Preparation of Soil Sample for Laboratory Analysis

Randomly, soil samples were collected from a depth 0-20cm from each of the plots with a bucket auger. The samples were crushed with hands, spread on a flat surface, composited and left to air-dry at room temperature in the laboratory. The samples were later pulverized with mortar and pistle, sieved in a 2mm mesh screen and stored in a polythene bag for analysis.

Laboratory Analytical Procedures

Total hydrocarbon content was estimated using the method of Odu et al., (1985). 10g portion of the soil sample was shaken with 10ml of carbon–tetrachloride. The hydrocarbon was extracted and determined by the absorbance of the extract at 420nm spectrophotometer. Standard curve of the absorbance of different known concentrations of equal amount of crude oil in the extractant was first drawn after taking reading from the spectrometer.

Plant Sampling and Data Collection

The following data were collected from the weed species (vetiver and guinea grass).

Plant Survivability

Two weeks after planting of vetiver and guinea grasses, the percent survivability count was taken in all the plots.

Plant Height

Five plants from each net plots at the middle were randomly selected, tagged and were used for data collection. The average of the five plants was taken as value per plant for each treatment plot.

Plant height for both vetiver and guinea grasses within the experimental periods was measured with a 30 meter measuring tape from the base of the plant to the tip of the leaves; the results were recorded in centimeters (cm) thirty days after planting. Subsequent measurements were done at thirty days interval for a period of three hundred and sixty days.

Preparation of Plant Samples for Chemical Analysis

The plant tissue (root and shoot) parts were washed using tap water to remove dust, mucor and soil particles and dried at 80⁰C, in muffle furnance for 12 hours, and thereafter ground for analysis. The samples were digested with concentrated nitric acid (HNO₃₎ and hyperchloric acid (HCLO₄,).

Statistical Analysis

Statistical analysis used for the study is Analysis of variance (ANOVA). Duncan-test was used to test the data

RESULTS AND DISCUSSION

Effect of Treatments on Plant Survivability

Effect of the treatments on the mean percentage survivability of the plants is presented in Table 2. The percentage plant survivability count for vetiver grass (Vetiveria zizanioides) was 90% as mean. Average of 80% survived in contaminated unamended plot as against 85% that survived in control plot. This is in complete contrast to that of guinea grass (Panicum maximum) where the mean percentage survivability recorded was 41% indicating poor adaptability to oil pollution. There was a delay in growth of most of the guinea grass plant. The overall percentage that survived was poor 41% for guinea grass unlike vetiver grass that recorded very high survival rate 90%. Generally, there was initial delay in growth especially on the contaminated plots for all the plants. This agrees with Asuquo et al., (2005) that even small amount of contamination of soil with crude oil can delay plant germination while large amount can cause reduction of growth.

From the statistical analysis, it was found that the growth of plant (vetiver grass) in terms of percentage survivability and growth rate was not significantly different between the contaminated unamended plots and the control plot implying that the crude oil contamination did not affect the survival and growth rate of vetiver grass. This finding confirmed the report of Truong, (2000) that vetiver grass is highly tolerant and could grow in crude oil contaminated soil. This is in contrast to guinea grass plots where a significant difference was observed between the contaminated unamended and control plots.

Vetiver grass performed better in terms of survival rate in crude oil contaminated soil over that of guinea grass. The ability of these grasses to survive and grow well in harsh soil condition could be attributed to their ability to establish a symbiotic association with soil microbes; this is in line with the finding of Siripin (2000) who observed from his study that Vetiver establishes a strong symbiotic association with a wide range of soil microbes in the rhizosphere that provide nutrients(Nitrogen fixing bacteria, phosphate solubilizing bacteria and fungi) and phytohormones (plant growth regulator bacteria) for plant development. Amendment of the soil with organic manures only gave slight improvement on vetiver over guinea grass. In guinea grass, there was no germination on plots C1R2 and C1R3 (Contaminated with crude oil and amended with rabbit manure at 20t/ha and 30t/ha respectively.

Effect of Treatments on Plant Height

Table 3 shows the mean plant height of vetiver grass and guinea grass. The result of the plant height of vetiver and guinea grasses ranged from 30.3 to 158.3cm and 6.2 to 301.6cm, respectively for the 12 months under investigation. The results revealed that plant height decreased from 42.2 in control plots to 30.3cm in contaminated unamended plots and 10.2cm in control to 6.2cm in contaminated unamended plots for vetiver and guinea grass respectively within the first 30 days of measurement.

This trend continued up to the 120^th day for vetiver, thereafter, the plant height increased to 150.2cm on contaminated unamended plots as against 124.0cm recorded in control plots for vetiver grass. This is in contrast to guinea grass where the decrease continued throughout the 12^th months under investigation as the plant height rose to 298.0cm in control plots against 118.7cm recorded in contaminated unamended plots.

Result of the study revealed a significant reduction in plant height from control plot to contaminated unamended plot within the first 120^th day for vetiver grass, thereafter the plant height significantly increased, implying that contamination of the soil with crude oil initially reduced the height of vetiver plant but with time the height was vetiver grass was significantly higher in contaminated unamended plots than control plots. The trend in vetiver was in contrast to that of guinea grass where there was a significant reduction in plant height in contaminated unamended plots over that of control throughout the period of the experiment. The reason for the reduction in plant height could be attributed to anaerobic conditions prevalent in crude oil contaminated soil, insufficient aeration, increase in oxygen demand caused by oil decomposing micro-organisms and interference with uptake of soil water by the root system Rowell, (1977); Gudin and Syrat, (1975) as quoted by De-Jong, (1980). Amendment of the soil with organic manures significantly increased the plant height in both vetiver and guinea grasses remediated plots.

The improvement noticed on plant height in contaminated unamended plots as against the control plots could probably be as a result of increase in organic matter, addition of nutrients from microorganisms killed by crude oil contamination and possibly Nitrogen fixation in the soil as reported by Odu, (1981) in Isirimah, (1989).

Addition of organic manures increased the height of the plants. The result showed that guinea grass plant has the highest height of 301.6 cm as against vetiver grass height of 158.3cm.This finding confirmed the report of Truong, (2000) that vetiver grass is highly tolerant and could grow in crude oil contaminated soil. This is in contrast to guinea grass plots where a significant difference was observed between the contaminated unamended and control plots.

The ability of these grasses to survive and grow well in harsh soil condition could be attributed to their ability to establish a symbiotic association with soil microbes; this is in line with the finding of Siripin, (2000) who observed from his study that Vetiver establishes a strong symbiotic association with a wide range of soil microbes in the rhizosphere that provide nutrients (Nitrogen fixing bacteria, phosphate solubilizing bacteria and fungi) and phytohormones (plant growth regulator bacteria) for plant development. Amendment of the soil with organic manures improves the growth of the grasses (vetiver and guinea).

Table 3: Effect of treatments on plant height (cm) of vetivar grass and guinea grass

Treatment Number of Days

120

150

180

210

240

270

300

330

360

Guineagrass

COPO

10.2h

38.6f

83.6b

118.3b

168.3b

234.0a

265.1b

283.2b

289.1b

293.5b

298.0b

290.2b

COP2

15.8f

45.1d

87.2a

125.0a

171.8a

241.1b

272.1a

289.0a

300.1a

301.0a

301.6a

294.4a

CIPO

6.2j

22.6i

35.1n

65.7h

78.4j

88.8k

100.0d

114.4k

116.0k

118.2n

118.7l

114.2n

CIP1

8.0i

19.5j

38.6l

51.8d

67.1d

95.0 i

109.1j

116.3j

126.2j

123.0l

128.9i

126.0l

CIP2

14.1g

30.3g

40.8m

56.2i

78.1j

88.3 k

95.2e

103.6e

117.8m

125.0k

126.1j

130.1k

CIP3

13.4g

28.6h

48.6l

65.4h

83.6 i

96.5h

118.4g

141.3e

152.6d

152.8d

153.0e

145.3h

COR3

12.5g

41.3e

80.5c

119b

148.0c

196.3c

220.1c

235.6c

240.6c

240.8c

242.0c

234.8c

CIR1

7.2i

20.6k

30.8o

47.3j

66.8k

71.2m

85.4l

92.4f

105.1n

105.8o

106.1m

109.3o

Vetivar grass

COPO

42.2b

55.4b

74.0d

82.5e

86.0h

88.6l

105.4k

115.1k

118.2m

120.5m

122.4k

124.0m

COP1

40.1c

56.2b

68.5g

85.0d

88.4g

90.0k

101.4l

114.8k

120.0l

123.5l

126.1j

126.5f

COP2

44.0a

60.1a

70.4f

81.2f

88.0g

94.0i

105.0k

116.0j

123.1k

130.2j

135.0h

140.1j

COP3

41.8b

56.0b

74.8d

88.0c

92.5e

98.6g

110.3j

122.7i

127.0j

136.3i

141.1g

143.0i

CIPO

30.3e

42.0e

58.2k

81.5f

87.0g

92.5j

115.1h

126.0h

130.1i

139.2h

145.0d

150.2g

CIP1

32.8e

40.8e

60.4j

83.2e

88.7g

94.0i

113.2i

128.1g

132.4h

140.1h

148.2f

155.1e

CIP2

31.2e

42.8e

63.1i

86.1d

89.8f

97.3h

118.0g

130.1f

132.0h

145.1f

142.8g

151.2f

CIP3

34.5d

41.3e

65.0h

84.3e

90.7f

99.0g

120.2f

131.2f

135.6g

143.7g

146.0d

154.0e

COR1

42.0b

54.2b

70.0f

86.0d

91.8e

114.1f

122.4e

130.3f

135.1g

144.0f

147.2f

152.1f

COR2

40.8c

48.5c

72.1e

88.9c

90.1f

116.2e

125.4d

132.0f

137.1f

147.1e

150.2f

150.8g

COR3

44.8a

45.0d

65.7h

83.4e

94.1e

118.5d

112.0e

143.0d

140.3e

149.1e

152.1e

156.1d

CIR1

31.7e

40.8e

65.7h

68.4g

96.0d

118.0d

120.0c

143.0d

140.0e

148.5e

148.9f

151.0g

CIR2

33.8d

42.0e

60.7e

68.8e

91.2b

120.2a

125.0b

145.1b

143.1b

150.1b

158.0a

156.0b

CIR3

33.6d

44.7d

62.3d

70.5d

88.5c

119.6a

127.2a

148.1a

149.8a

152.0a

153.1b

158.3a

Means in column followed by the same letter are not significantly different at 5% level of probability by Duncan Multiple Range Test

CONCLUSION

Based on the result of this work, phytoremediation through the use of vetiver and guinea grasses amended with organic manures is effective in the remediation of crude oil polluted soils. The study showed that vetiver grass amended with poultry manure was more effective than guinea grass.

Both grasses were tolerant to total Hydrocarbon content (THC), however, vetiver grass was found to be more tolerant than guinea grass. The study also revealed that vetiver grass has high survival rate of 90% compared with 41% of guinea grass.

Application of organic manures (poultry and rabbit) increased the ability of the grasses to n degrade THC, in the soil and reduce the intake ability of these grasses to absorb THC in their tissues. Therefore, application of amendment materials improved the capability of these grasses to remediate crude oil polluted soil.

REFERENCES

Anyaegbu, BA.(1987). Medical aspects of the impact of environmental pollution. Proceedings on the Petroleum Industry and Nigerian Environment. 352-357.

Asuquo, FE, Ibang, IJ and Idungafa, N. (2005). Effects of quo Iboe Crude Oil contamination on Germination and growth of Okra and fluted pumpkin www.ecoservepublishers.org/list.htm#5:

Banks, MK., Lee, E and Schwab, AP. (1999). Evaluation of dissipation mechanisms for Benzol [a] pyrene in the Rhizosphere of Tall Fescue. Jour. Env. Qual. 28: 294-298.

Biondini M, Klein DA and Redente E (1988). Carbon and Nitrogen Losses through roots exudation by Agropyron Cristatum, a Smithii, and Bouteloua Gracilis. Soil Biol. Biochem 20: 477 – 482.

Cook FD, West and Lake DWS (1976). Biodegradability of Northern crude Oils. ALUR 75-81 Indian and Northern Affairs Publication. O, 8116-000 EE-AL University of Alberta, Edmonton, Canada.

De-Jong E (1980). The Effect of Crude Oil Spill on Cercals. Department of Soil Science University of Sask Canada S7N Owo. Env. Poll. Sr. 22 (A): 187-196.

Emola, B.,Nnadi, G., Ede, E and N naji, E. (1992). August 24. Angry oil States on the war path. African concord. 7(14), 8-24.

FAO (Food and Agricultural Organization) (1984): Food and Agricultural Organization year book, FAO Rome Italy 4: 122-127.

Federal Department of Rural Development Area Programme. (1981). Federal Department of Rural Development Area Programme Preparatory Report. November, 1981.

Gudin, C and Syratt, W. J. (1975). Biological aspects of land rehabilitation. Following hydrocarbon contamination. Environmental Pollution. 8, 107-112.

Horsfall, M and Spiff, A (2001). Principle of Environmental Pollution (With Physical, Chemical and Biological Emphasis): 1^st Edition Published and Printed by metro Prints Ltd. Port Harcourt Nigeria.

Hutchinson, SL, Banks, MK and Schwab AP (2001). Phytoremediation of aged petroleum sludge: effect inorganic Fertilizer, J. Envron. Qual. (30): 95

Isirimah, NO (2002).Understanding the nature and properties of waste for quality environment. Tom and Harry Publications, Port Harcourt.

Isirimah N, Chinda A and Braide S (2006). Environmental Protection; Problems, progress, practice principles and prospects: Case for Niger Delta. Paper presented, Nigerian environmental society of Nigeria at RSUST, Port Harcourt .

Isirimah N, Zuofa K and Loganathan P (1989). Effects of crude oil on maize performance and soil chemical properties in the humid forest zone of Nigeria. Discovery and innovation:1 (3):95-98.

Lee, E and Banks MK. (1993). Bioremediation of Petroleum contaminated soil using Vegetation: microbial study. J. Env. Sci. Health 28(A): 2187-2198.

Odu, CTI. (1981). Degradation and weathering of crude oil under tropical condition. Proceedings of Seminar of Petroleum Industry and the Nigeria Environment.

Odu CTI, Nwobishi LC, Esuruoso OF and Ogunwale JA (1985). Environmental Study of the Nigerian Agip Oil company Operational Areas. In The Petroleum Industry and the Nigerian Environment. Proceedings FMW and H and NNPC conference, 274-283.

Prasad, NMR (2003). Phytoremediation of metal polluted ecosystem. Hope for commercialization. RUSS. Jour. Plant physiol. (50): 764-780.

Rowell, MJ. (1977). Oil Contaminated soils and some aspects of reclamation in soil Science Conservation Remediation research, Alberta Soils Workshop, reddeer Alberta (Proceedings in Press).

Siripin, S (2000). Microbiology associated with the vetiver plant. Proc. Second Int: Vetiver conf. (ICV-2) (January 18-22), Thailand.

Soil Survey Staff (1975). Soil taxonomy. A basic system of soil classification for making and interpreting soil survey USDA Agricultural handbook 436 Washington D.C. PP 754.

Truong, P (2000). Vetiver grass for mine site rehabilitation and reclamation. Extended Abstract. Proc. Remade lands International conf, Fremantle, Australia.

World Bank. (1995). Defining an Environmental Department Strategy for the Niger Delta. West Central Africa, Department world Bank, Washington D. C. p. 150.

Weed species	Treatment	THC (ug/g)
Vetiver grass	CIPO	1252.0 ^c
	CIPI	2879.2 ^b
	CIP2	3348.2 ^a
	CIP3	3882.3^a
	CIR1	2721.0^b
	CIR2	2978.13 ^b
	CIR3	3533.7 ^a
Guinea grass	CIPO	1157.6 ^c
	CIP1	2755.4 ^b
	CIP2	2717.25 ^b
	CIP3	3173.1^d
	CIR1	2620.9 ^b
	CIR2	0.0^d
	CIR3	0.0^d

Weed species	Treatment	THC(μg/g)
Vertivar Grass	COP0	0.04^k
	CIP0	878.3^a
	CIP1	832.6^c
	CIP2	668.4^g
	CIP3	578^j
	CIR1	812^d
	CIR2	698.4^f
	CIR3	575.9^j
Guinea Grass	COP0	0.04^k
	CIP0	846.1^b
	CIP1	760.2^e
	CIP2	644.0^g
	CIP3	525.8^j
	CIR1	605.4^h

Weed species
Treatment	Vetiver	Guinea Grass
COP0	85	80
COP1	85	0
COP2	95	85
COP3	100	10
CIP0	80	60
CIP1	85	45
CIP2	90	80
CIP3	94	80
COR1	95	0
COR2	90	0
COR3	96	78
CIR1	82	50
CIR2	90	0
CIR3	93	5