Attenuation of Petroleum Hydrocarbons at Idu-Ekpeye Oil Spillage Site in Niger-Delta, Nigeria

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Attenuation of Petroleum Hydrocarbons at Idu-Ekpeye Oil Spillage Site in Niger-
Delta, Nigeria
Inimfon A. Udoetok
†
, Leo C. Osuji
‡
†
Akwa Ibom State University of Technology, Mkpat Enin, Akwa Ibom State;
‡
Department of Industrial and Pure Chemistry,
University of Port Harcourt, P.M.B. 5323, Choba, Port Harcourt, Nigeria
Copyright 2009, Cells & Environmental Systems Inc.
This paper was prepared and selected for presentation at the 2009
International Conference, Workshop and Exhibition on Biotechno-
logies for Improved Production of Oil and Gas in the Gulf of Guinea
held in Abuja, Nigeria, 1 April – 3 April 2009.
Abstract
Soil samples from Idu-Ekpeye oil spillage site in
Niger
-Delta, Nigeria were analyzed within two
seasonal variations. The results revealed alterations
in the distribution and composition of total
petroleum hydrocarbon (TPH), polycyclic aromatic
hydrocarbons (PAH’s), and benzene, toluene,
ethylbenzene and xylene (BTEX) in the spilled oil.
The significant concentration of hydrocarbons was
within the kerosene range (n-C
10
- n-C
14
), especially
the n-C
12
and n-C
13
fractions, two months after the
oil spillage. The complete disappearance of the n-C
8
to n-C
23
hydrocarbons, including the acyclic
isoprenoids (pristane and phytane), and the reduced
amount of PAH and BTEX fractions six months
after the oil spillage indicated that the spilled oil was
only partially degraded two months after the
recorded incidence of the spillage and extensively
depleted six months after. This provided substantial
evidence of attenuation at the oil spillage site.
Introduction
Petroleum refers to the three major forms of
hydrocarbons, namely crude oil, natural gas and
condensate. Crude oil, the liquid form of petroleum,
is a complex mixture that contains thousands of
different compounds with those of three minor
elements, nitrogen, sulfur and oxygen (NSO), as
well as trace metals like nickel and vanadium
(Connan et al.,1980). Crude oil spills release
hydrocarbons into the environment. One of the
problems usually encountered with profiling spilled
hydrocarbons at the sites is attenuation via
“weathering” (Osuji et al., 2006). Weathering is the
change in composition of hydrocarbons with time,
through the action of volatilization,
leaching,
evaporation, chemical reaction and biotransforma-
tion (Langsley
et al.
, 2003). Thus substantial
evidence of hydrocarbon attenuation can be obtained
by direct monitoring of the disappearance of
hydrocarbon fractions from an affected area. The
present study therefore takes a look at the
attenuation of hydrocarbons at the study site within
two time periods (two months and six months) of the
recorded incidence of the spillage.
Experimental Methods
Site Description and Sample Collection
The study site is located in Idu-Ekpeye, Ahoda West
Local Government Area of Rivers State, Nigeria.
Sampling was carried out within intervals of two
months and six months after the spill. The first
sampling exercise was on April 04, 2004. Sampling
area and technique were adopted after approach of
Osuji and Adesiyan, 2005.
Oil Extraction and Chromatographic Analysis
Homogenized samples (5g) were accurately weighed
into clean, dry breakers. The weighed samples were
extracted with 10ml of hexane, resp., and passed
through a filter paper. The extract (the
hydrocarbon/hexane mix), now ready for GC, was
injected into a Varian model 3400 gas
chromatograph with the following operation
conditions: flow rate (H
2,
30ml/min; air, 300ml/min
and N
2,
30ml/min); injection temperature, 50
0
C;
detector temperature, 320
0
C; recorder voltage, 1mV
and chart speed, 1cm/min. For interpretation of
results, the GC recorder was interfaced to a Hewlett
Packard (hp) computer (6207AA Software, Kayak
XA PIT/350 W/48
megabytes CD-ROM). The
chromatograms were quantified with respect to int-
ernal standards.
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Results and Discussion
Results of the total petroleum hydrocarbon (TPH)
content of the oil impacted soils (Tables 1 and 2)
revealed a substantial concentration of the n-C
8
– n-
C
23
hydrocarbon fraction and polycyclic aromatic
hydrocarbons (PAH’s) two months after the spillage.
The benzene, toluene, ethylbenzene and xylene
(BTEX) content (Table 3) in the soils after two
months of the spill was also substantial although
they are volatile and are easily degraded under
aerobic conditions. This implies that two months
after the spillage, the spilled oil was still fresh at
site, with only minor degradation of petroleum
hydrocarbons.
Six months after the spillage, the results obtained
show complete disappearance of the n-C
8
- n-C
23
hydrocarbon fractions including the isoprenoids
(pristane and phytane), leaving only the n-C
13
, n-C
14
,
n-C
19
and n-C
30
hydrocarbons (Table 1). The results
obtained for the PAH’s, (Table 2) show that
naphthalene, acenaphthalene, benzo(a)anthracene,
benzo(k)fluoranthrene and indeno[1,2,3–cd]pyrene
were likely most prone to biodegradation and other
forms of attenuation as observed in the marked
reduction of the fractions below detectable limit (<
1x10
-6
mg/kg).
Similarly, a mass reduction of the BTEX fractions
(Table 3) was observed in each of the samples
analyzed which corroborates the significant
alteration adduced from the other parameters.
Prince et al. (1990) reported that pristane and
phytane which were originally thought to be
resistant to biodegradation can only be used to
monitor the earliest stages of a biodegradation
treatment program as they are known to be
biodegradable under natural conditions. Jobson et al.
(1972) also reported the degradation of pristine and
phytane during twenty-one day of incubation of
worth coastal (Saskatechewan) oil.
Additionally, the decreasing amount of the
petroleum fractions (Tables 1-3) provides more
proof of hydrocarbon attenuation and rehabilitation
of the affected site. The reduction in their
concentration confirms extensive consumption of
these hydrocarbons and subsequent reduction of
these containments at the study site.
Furthermore, the observed depletion of petroleum
hydrocarbon fractions may have been enhanced by
the weathering activities within the period of samp-
sampling. Peters and Moldowan, (1993); Hunt
(1996) and Zhu et al
. (2001) reported that intense
water washing and weathering activities cause
preferential loss of saturated hydrocarbons.
Thus the hydrocarbon distribution at the study site
two months and six months after the oil spillage
provided evidence of attenuation.
Conclusions
Attenuation of petroleum hydrocarbons at Idu-
Ekpeye oil spillage site was evaluated using
chromatographic analysis of soil samples. The
results obtained show that two months after the oil
spillage, the aliphatic, PAH and BTEX components
of the oil had not undergone significant alteration.
Six months later, the results revealed that there was
severe attenuation at the site as depicted by the
disa
ppearance of the acyclic isoprenoids. Following
a ranking profile of 1 to 10 (minor to extreme) as
created by the work of Nicodem et al. (1997), the
level of hydrocarbon attenuation at the study site can
be rated as “extensive” based on the change in the
m
olecular composition and distributions of the
hydrocarbons.
Acknowledgements
The authors would like to acknowledge the support
and assistance provided by the Shell Petroleum
Development Company (SPDC) Nigeria which made
it possible to conduct this research.
References
Connan, J. Reslte, A. and Albrecht, P.,
Biodegradation of crude oil in Aquitane basin. In
Advances in Organic Geochemistry
, (Douglas, A.
and Maxwell, J. R., eds.), Oxford Pergamon Press
(1980).
Hunt, J. M., Petroleum Geochemistry and Geology,
2nd edition, W. H. Freeman and Company, New
York (1996).
Jobson, A., Cook, F. D. and Westlake, D. W. S.,
1972. Microbial utilization of crude oil. Applied
Microbiol 23:1082–1089.
Langsley, A. Gilgely, M., and Kennedy, B.,
Assessment of Site Contamination. In the
Proceedings of the 5th National Workshop on
Assessment of Inter Contamination, NEPC Service
Corp, 2003.
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Table 1. Seasonal variation of total petroleum hydrocarbons (TPH) content of soils two two months and
six months after oil spill.
TOTAL PETROLEUM HYDROCARBON (TPH [mg/kg]
±
±±
±
S.E
Hydrocarbon
Fraction
1st Sampling (two months) Amount
[mg/kg] x 10
3
2nd Sampling (six months) Amount
[mg/kg] x 10
3
C
8
C
9
C
10
C
11
C
12
C
13
C
14
C
15
C
16
C
17
Pristane
C
18
Phytane
C
19
C
20
C
21
C
22
C
23
1.10
±
0.07
0.43 ± 0.02
0.22 ± 0.02
0.04 ± 0.00
1.07 ± 0.04
5.34 ± 0.01
0.48 ± 0.00
0.84 ± 0.01
0.14 ± 0.00
1.65 ± 0.00
0.48 ± 0.05
0.27 ± 0.00
0.02 ± 0.01
0.02 ± 0.01
0.07 ± 0.01
0.03 ± 0.01
0.09 ± 0.01
0.03 ± 0.00
-
-
-
-
-
0.13 ± 0.01
0.03 ± 0.01
-
-
-
-
-
-
0.27 ± 0.00
-
-
-
-
S.E. is standard error at 95% confidence limit.
Osuji, L. C., Udoetok, I. A. and Ogali, R. E.,
2006.
Attenuation of petroleum hydrocarbons by
weathering. A case study. Chem. Biodiv. 3:422–
433.
Osuji, L. C. and Adesiyan, S. O., 2002.
The
Isiokpo oil-
pipeline leakage: total organic
carbon/organic matter contents of affected soil.
Chem. Biodiv. 2:1-7.
Peters, J. and Moldowan, J. M.
The
Biomarker Guide; Interpreting Molecular
Fossils in Petroleum and Ancient Sediments.
Prentice Hall, Englewood Cliffs, N. J. (1993).
Prince, R. C., Emendory, D. L., Lute, J. R.,
Hsu, C. S., Haith, C. E., Senius, J. D.,
Dechert, G. J., Douglas, G. S. and Butler,
E. L., 1994. 17 and (H, 21 & (H) – Hopane as
a conserved internal marker for estimating the
biodegradation of crude oil. Environ. Sci.
Tech. 28:142–145.
Zhu, X., Venosa, A. D., Guidan, M. T. and
Lee, K, Guidelines for the Bioremediation of
Marine Shorelines and Fresh Water Wetlands.
U. S. Environmental Protection Agency,
Cincinnati, OH (2001).
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Table 2. Seasonal variation in polycyclic aromatic hydrocarbons (PAH) content of soil samples
two months and six months after oil spill.
Hydrocarbon Fraction 1st Sampling (two months
after) Amount [mg/kg] 2nd Sampling (six months after)
Amount [mg/kg]
Naphthalene 7.7
±
1.2 BDL
Acenaphthylene 70.9
±
5.7 BDL
Acenaphthene 98.3
±
10.0 0.3
±
0.1
Flourene 135
±
16.8 2.9
±
1.4
Phenanthrene 137
±
8.0 BDL
Anthracene 134
±
24.5 39.1
±
0.5
Fluoranthene 97
±
7.8 18.6
±
6.2
Pyrene 135
±
8.0 21.8
±
12.4
Benzo [a] anthracene 221
±
26.4 BDL
Chrysene 138
±
2.4 27.4
±
8.0
Benzo [b] fluoranthene 231
±
10.2 22.4
±
2.1
Benzo [k] fluoranthene 79.6
±
9.6 BDL
Benzo [a] pyrene 318
±
13 80.8
±
0.8
Indeno [1,2,3-cd] pyrene 246
±
48 BDL
Dibenzo [a,b] anthracene 131
±
12 16.1
±
4.4
Benzo [ghi] perylene 103
±
6.4 69.1
±
7.0
BDL = Below Detectable Limit (where detectable limit is 1x10
-
6
mg/kg).
Table 3. Seasonal variation of benzene, toluene, ethylbenzene, and xylene (BTEX) contents of
soils two months and six months after oil spill.
Hydrocarbon Fraction 1st Sampling (two months)
Amount [mg/kg] 2nd Sampling (six months)
Amount [mg/kg]
Benzene 48.2
±
12.5 BDL
Chlorobenzene 32.3
±
4.6 BDL
1,2-Dichlorobenzene 20.6
±
4.8 BDL
1,3-Dichlorobenzene 412.8
±
66.5 BDL
1,4-Dichlorobenzene 4.5
±
2.1 BDL
Ethylbenzene 11.7
±
1.9 BDL
Toluene 18.1
±
6.6 BDL
m,p-Xylene 22.1
±
12.2 BDL
0 –Xylene 3.8
±
1.6 BDL
BDL = Below Detectable Limit (where detectable unit is 1x10
-
6
mg/kg).
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