Journal of Environmental Protection, 2011, 2, 848-854
doi:10.4236/jep.2011.26096 Published Online August 2011 (
Copyright © 2011 SciRes. JEP
Proximal Input of Polynuclear Aromatic
Hydrocarbons (PAHs) in Groundwater Sources of
Okrika Mainland, Nigeria
C. G. Okoli, D. H. Ogbuagu*, C. L. Gilbert, S. Madu, R. F. Njoku-Tony
Department of Environmental Technology, Federal University of Technology, Owerri, Nigeria.
Received April 14th, 2011; revised May 26th, 2011; accepted July 9th, 2011.
The Port Harcourt Refinery Company situated at Okrika Mainland discharges its effluent into the Creeks surrounding
this coastal land. The current study examined the presence of polynuclear aromatic hydrocarbons in groundwater
sources of the coasta l settlement. Ten replicate samples were collected from 10 boreholes in the settlemen t using steril-
ized amber glass bo ttles and fixed with co ncentrated H2SO4. They were later analyzed using Ga s chroma tography (GC).
The Pearson product moment correlation coefficient (r) was used to determine the interactions of the PAHs detected
while the One-way ANOVA was used to determine spatial variance equality in means of the PAHs components at P <
0.05. Further structure detection was made with means plots, utilizing pH as a predictor variab le. High concentration s
of PAHs which exceeded the WHO maximum permissible limit for the PAHs in drinking water (0.002 mg/L) were re-
corded from the b orehole samples. Acenaphthene had the highest concentration of 0.88317 (0.202494 ± 0.0652) mg /L,
while acenaphthylene had the least maximum concentration of 0.18837 (0.04978 ± 0.0123). However, naphthalene r e-
corded concentrations of between 0.00058 and 0.52510 (0.0874576 ± 0.03 472) mg/L, fluorene 0.00018 and 0.20438
(0.0527435 ± 0.01564) mg/L, phenanthrene 0.00041 and 0.26732 (0.0603780 ± 0.018634) mg/L, and anthracene be-
tween 0.00029 and 0.25084 (0.0692785 ± 0.0176569) mg/L. There was significant variance inequality in means of the
PAHs measured across the sampling locations at P < 0.05 [F(971.1318) > Fcrit(3.85563)]. A further structure detection re-
vealed that the inequalities were con tributed by all the PAH co mponents, especially between BH 3 and BH 1, BH 4 and
BH 2 and 5, as well as between BH 6 and BH 10. Very strong associations were observed between the PAH components
at P < 0.01. BH 8 recorded the highest contamination level of the various PAHs due basically to its proximity to the
refinerys effluent discharge point (Ekerekana Creek) and channel. Hence the source of these pollutants could best be
fingerprinted to the nearby Port Harcourt Refinery Companys effluent discharges. These PAHs are not only ingested
by drinking contaminated waters, but are further consumed when this water is used to prepare foods. This creates a
great cause for public health concerns especially as several PAHs are known carcinogens. It is therefore, recommended
that technologically advanced techniques of water treatment be developed in order to take care of the presence of PAHs
in drinking water sources of the coastal dwellers.
Keywords: Carcinogenic, Polynuclear Aromatic Hydrocarbons, Groundwater, Gas Chromatography, Okrikamainland
1. Introduction
Crude oil refining processes generates a lot of solid, li-
quid, and gaseous wastes into the environment. The li-
quid wastes, collectively called effluents are usually dis-
charged into nearby water bodies by operators. One of
the toxic components of crude oil are the polynuclear
aromatic hydrocarbons (PAHs). According to ATSDR
[1], PAHs are generally formed during the incomplete
combustion of coal, oil, gas, wood, or other organic sub-
stance such as tobacco and charbroiled meat, and have
been reported to be the most abundant of the main hy-
drocarbons found in crude oil mixture [2,3]. They have
also been identified in soils at uncontrolled disposal sites,
including wood preservation, oil wastes, and coal gasifi-
cation sites [4]. Marten and Frankenberger, Jr., [5] esti-
mated that the half-life of PAHs can range from as short
as 2 days (for naphthalene) to almost 400 days (for fluo-
ranthene) in soils. Anthropogenic sources such as indus-
trial production, transportation and waste incineration
Proximal Input of Polynuclear Aromatic Hydrocarbons (PAHs) in Groundwater Sources of Okrika Mainland, Nigeria849
also generate significant amounts of PAHs [6].
They resist degradation and are able to be retained in
sediments and could also accumulate in fatty tissues and
thus pass up the food chain, eventually to man [7,8].
Groundwater pollution from PAHs is possible and the
use of this water for domestic purpose represents a risk to
human health and safety [9]. It is a worldwide problem
that often emanates due to the seepage of contaminants
from waste disposal sites, oil spills, surface and under-
ground storage tank leakages, agricultural activities, ef-
fluent discharges, etc. [10] Such contamination of ground-
water resources potentially poses a substantial risk to
local resources users and to the natural environment [11].
The main source of drinking water in Okrika Mainland,
a coastal settlement, is groundwater, which is pumped
from wells drilled into aquifers; some of which are shal-
low hand-dug wells while others are deep wells. In recent
times, there have been public complaints of drinking
odorous and crude oil-tainted waters, as well as observa-
tions of the formation of oil films on waters surfaces
sourced from the community boreholes by inhabitants of
the mainland. The porous soil and high water table in the
settlement, together with the environmentally unfriendly
method of discharge of oily effluents by the nearby re-
finery could thus provide a fingerprint to the contribution
of the suspected contaminants to groundwater source.
This contamination, unknown to the consumers may con-
tain some concentrations of PAHs, some of which have
been classified by the WHO and ATSDR as carcinogenic
[1,12]. Consumption of these waters could therefore pose
a health risk to members of the community.
Unfortunately, no research work has been carried out
on the assessment of polynuclear aromatic hydrocarbons
in ground water sources of this mainland, even as in-
habitants continue to use them. It is therefore necessary
to carry out an assessment of the presence of these toxic
pollutants in groundwater sources of this area of the Ni-
ger Delta of Nigeria.
2. Materials and Methods
2.1. Study Area
Okrika, Rivers State falls within the Niger Delta area of
Nigeria and is spatially located between latitude 04˚ and
50'N, and longitude 07˚ and 10'E (Figures 1 and 2).
About 95% of the total area is wetland; characterized by
a network of meandering water channels, comprising
mainly of creeks and small rivers which drain into short
swift coastal rivers. The geology of Okrika is of the ear-
lier deposits of the marine sediments of the Lower and
Upper Cretaceous age, and it constitutes the economi-
cally important structure where petroleum was formed
and preserved. The soil prevalent in the area could be
classified as coarse, loamy, highly weathered, and mod-
erately acidic with low soluble salt content. The pristine
vegetation is characterized by thick mangrove forest of
Figure 1. Map of Rivers State showing Okrika Local Government Area.
Copyright © 2011 SciRes. JEP
Proximal Input of Polynuclear Aromatic Hydrocarbons (PAHs) in Groundwater Sources of Okrika Mainland, Nigeria
Figure 2. Map of Okrika LGA showing the study area.
the red variety type which attains heights up to 50 m and
girth up to 27 m, though urban and industrial develop-
ments have reduced them to secondary growth, and
caused a drastic reduction in height and girth. The cli-
mate is tropical and characterized by frequent precipita-
tion which reaches 300 - 450 cm annually; with a long
wet season (March-September). Mean monthly tempera-
ture range between 24˚C and 27˚C and humidity is about
80% [13]. The major economic activity of the people is
2.2. Field Sample Collection
Two replicate water samples were collected from each of
10 boreholes, using 1liter amber glass bottles fitted with
a screw cap and lined with foil and labeled BH1, BH2,
BH3, BH4, BH5, BH6, BH7, BH8, BH9, and BH10.
Samples were transported to the laboratory as soon as
possible in ice-packed cooler to maintain their integrity.
2.3. Apparatus
A gas chromatograph coupled with flame ionization de-
tector (GC-FID model HP 5890); utilizing the column
chromatograph for cleaning of sample extracts was util-
ized in the analysis of samples. Glasswares were all
washed with detergents and hot water and subsequently
rinsed with distilled water.
2.4. Reagents
All chemicals used are of analytical grade and of highest
purity. Reagents used include N-hexane (solvent), silica
gel (GC grade) as desiccant, conc. H2SO4 (for preserva-
tion of samples), and reagent water (prepared by passing
tap water through a carbon filter bed containing about
0.5 kg activated carbon, using a water purification sys-
tem). A PAH standard mixture containing 1000 ppm
each of naphthalene, acenaphthylene, acenaphthene, fluo-
rene, phenanthrene and anthracene was used.
2.5. GC Parameters
The GC parameters used include helium (carrier gas), air
and hydrogen(fuel gases), nitrogen (back up gas), detec-
tor temperature of 35˚C, in-let temperature of 25˚C, ini-
tial and final temperatures for oven of 5˚C and 300˚C,
respectively, hydrogen, air, nitrogen, and helium flow
rates of 30, 300, 30, and 30 ml/minute, respectively.
2.6. Sample Extraction
About 50 ml of borehole water was measured into 1 liter
separating funnel.1 drop of concentrated H2SO4 was
added to the sample in the separating funnel to release
the hydrocarbon components. 5 ml of the solvent (N-
hexane) was added to the sample and samples vigorously
Copyright © 2011 SciRes. JEP
Proximal Input of Polynuclear Aromatic Hydrocarbons (PAHs) in Groundwater Sources of Okrika Mainland, Nigeria851
shaken for 5 minutes and allowed to stand for another 20
minutes. Layers were formed that separated the extract
(the top layer) from the lower layer (which was discarded)
and the extract collected for GC analysis in a glass vial.
2.7. Cleaning of Extract
A column chromatography was set up using silica gel
and a glass wool and extracts passed through the column
to clean and remove biogenics.
2.8. GC Analysis
Cleaned extract was loaded using micro-GC syringe and
the GC prompted to run for about 41 minutes. At the end,
results containing the chromatograms were integrated
and printed.
3. Statistical Analysis
The Pearson product moment correlation coefficient (r)
was used to determine the interactions of the PAH com-
ponents detected. Furthermore, the one-way ANOVA
was used to determine spatial variance equality in means
of PAH variables at P < 0.05, and subsequently structure
detection made with means plots.
4. Results
4.1. Variations in PAH Concentrations in
Groundwater Sources
Wide variations were observed in the concentrations of
the component PAHs detected in the groundwater sam-
ples (Table 1). Naphthalene concentration ranged be-
tween 0.00058 and 0.52510 (0.087458 ± 0.0347) mg/L,
acenaphthylene ranged between 0.00041 and 0.18837
(0.04978 ± 0.0123) mg/L, acenaphthene between 0.00053
and 0.88317 (0.202494 ± 0.0652) mg/L, and fluorene
between 0.00018 and 0.20438 (0.052744 ± 0.0156) mg/L.
However, phenanthrene and anthracene concentrations
ranged from 0.00041 - 0.26732 (0.060378 ± 0.0186) and
0.00029 - 0.25084 (0.069279 ± 0.0177) mg/L, respec-
Table 1. Variations in PAHs concentration (mg/L) of ground-
water samples in Okrika Mainland.
PAH Minimum Maximum Mean SE
Naphthalene 0.00058 0.52510 0.0874576 0.03471941
Acenaphthylene 0.00041 0.18837 0.0497795 0.01230182
Acenaphthene 0.00053 0.88317 0.2024935 0.06519860
Fluorene 0.00018 0.20438 0.0527435 0.01564219
Phenanthrene 0.00041 0.26732 0.0603780 0.01863347
Anthracene 0.00029 0.25084 0.0692785 0.01765686
SE = standard error.
4.2. Spatial Variations in PAHs
All the PAH components (except anthracene) recorded
highest concentrations in BH8. While acenaphthylene,
acenaphthene, and anthracene recorded least concentra-
tions of 0.00043, 0.00056, and 0.00029 mg/L, respec-
tively in BH7, fluorene and phenanthrene recorded least
values of 0.00019 and 0.00041 mg/L, respectively in BH
10 (Figures 3-5).
A test of variance equality using the analysis of vari-
ance (ANOVA) revealed high significant spatial inequal-
ity in means of the PAH concentrations across the bore-
hole samples [F(971.1318) > Fcrit(3.85563)] at P < 0.05. A fur-
ther structure detection utilizing pH as predictor in
means plots revealed that the inequalities were contrib-
uted by all the PAH components measured. The highest
inequalities were observed between BH3 and BH1, BH4
Figure 3. Spatial variation in naphthalene and acenaphthy-
lene concentrations of groundwate rs of Okrika Mainland.
Figure 4. Spatial variation in acenaphthene and fluorene
concentrations of groundwate rs of Okr i ka Mainland.
Figure 5. Spatial variation in phe nanthrene and anthrac ene
concentrations in groundwaters of Okrika Mainland.
Copyright © 2011 SciRes. JEP
Proximal Input of Polynuclear Aromatic Hydrocarbons (PAHs) in Groundwater Sources of Okrika Mainland, Nigeria
and BH2 & 5 and between BH6 and BH10 (Figures
6-11), while the least inequality was observed between
BH 5 and BH 6. However, no inequality was observed
between BH1 and BH4.
Figure 6. Structure detec tion in naphthalene concentrations
using means plot.
Figure 7. Structure detection in acenaphthylene concentra-
tions using means plot.
Figure 8. Structure detection in acenaphthene concentra-
tions using means plot.
Figure 9. Structure detection in fluorene concentrations
using means plot.
Figure 10. Structure detection in phenanthrene concentra-
tions using means plot.
Figure 11. Structure detection in anthracene concentrations
using means plot.
4.3. Relationship between Polynuclear Aromatic
Though pH had no significant influence on them, the
Copyright © 2011 SciRes. JEP
Proximal Input of Polynuclear Aromatic Hydrocarbons (PAHs) in Groundwater Sources of Okrika Mainland, Nigeria
Copyright © 2011 SciRes. JEP
PAHs showed very strong significant influences on one
another. At P < 0.01, all the PAHs showed significant
interactions with one another, except between naphtha-
lene and anthracene (Table 2).
5. Discussion
The high concentrations of PAHs detected in the ground-
water samples could readily be fingerprinted to petro-
leum contamination of the groundwater aquifers from the
poorly treated refinery effluents in the neighbourhood.
The refinery operators have continuously discharged oil-
contaminated wastewaters into the surrounding Creeks
bordering the small coastal settlement for some fourty
five years now. The possibility of seepage and subse-
quent contamination of the groundwater aquifers by sur-
face pollutants have been severally identified by other
authors, [14,15]. [16] had also identified components of
the PAHs in ground waters of some Niger Delta region
of Nigeria; whereby he detected high concentrations of
benzo(a)pyrene, especially in those sources from oil pro-
ducing communities. The World Health Organization [17]
has 0.002 mg/L as the maximum permissible limit for
these PAHs in drinking water, besides that of benzo(a)
pyrene (0.0001 mg/L), which corresponds to an excess
life time cancer risk of 105. Values from this study far
exceed this standard for PAHs. Undoubtedly, these re-
sults create a great cause for public health concerns, es-
pecially as PAHs have been confirmed to be carcino-
genic [1], and are not only ingested by drinking con-
taminated waters alone, but also when the water is used
to prepare foods, thereby increasing the risk of elevated
concentrations in tissues of man and animals. Inevitably
man suffers the greatest risk of bioaccumulation due to
his position in the trophic chain; being a tertiary con-
sumer in addition to his predisposition to other route of
entry into his body. Worse still, carcinogenicity is trans-
genic, as oncogenes (cancer prone genes) could be inher-
ited by filial generations [18,19].
The significantly uncorrelated relationship between
pH and PAH components imply that hydrogen ion con-
centration does not play any role in the biogeochemical
availability of PAHs, rather their concentrations are an-
thropogenic in nature [1]. Moreover no research has
shown any correlation between pH and PAHs. However
the very strong significant associations observed between
most of the polynuclear aromatic hydrocarbons agrees
with the work of El-Deeb and Emara [20]. The source of
PAHs in this study is therefore generally believed to be
of petrogenic origin and components are closely related
due to their molecular weights [21].
The observed spatial variations in PAH concentrations
indicates differential levels as well as proximal inputs of
contaminations in the boreholes. BH8, which had the
highest concentrations of almost all the PAHs measured
is located very close to the refinery’s effluent discharge
point (Ekerekana Creek). Similarly, BH 4, which is situ-
ated few meters from the Ogan waterside; a highly con-
taminated slow flowing Creek, also had very high con-
centrations of anthracene. In contrast, BH10 and BH7
which had the lowest level of contamination from most
of the PAHs measured are located relatively far from the
effluent discharge point and route. The source of their
contamination could be relatively prolonged seepages
from the surrounding Creeks.
6. Summary, Conclusions and
Data obtained from this work revealed that the activities
of a refinery can cause a serious contamination of
groundwater supply of its host community, resulting in
potential, chronic detrimental health effects. The ob-
served spatial variation in concentrations indicates pro-
ximal inputs, even as the PAH components exhibited
very high relatedness. The presence of these polynuclear
aromatic hydrocarbons in alarming concentrations, higher
than the stipulated maximum contamination level (MCL)
of regulatory agency [17] calls for intervention to save
the ignorant coastal dwellers from impending debilitating
health problems.
The refinery’s effluents should be properly treated and
disposed of using environmentally friendly practices that
are in line with regulatory standards and guidelines. Fur-
Table 2. Correlation matrix of the PAH components.
pH Naphthalene Acenaphthylene Acenaphthene Fluorene Phenanthrene
Naphthalene –0.368
Acenaphthylene –0.310 0.932**
Acenaphthene –0.296 0.888** 0.975**
Fluorene –0.365 0.884** 0.873** 0.896**
Phenanthrene –0.150 0.909** 0.955** 0.955** 0.847**
Anthracene –0.222 0.399 0.637** 0.751** 0.674** 0.625**
** = significant at P < 0.01.
Proximal Input of Polynuclear Aromatic Hydrocarbons (PAHs) in Groundwater Sources of Okrika Mainland, Nigeria
thermore, strategies should be put in place by the com-
pany to contain the expanding groundwater plume. There
is however the need for further research into the presence
of PAHs in soils impacted by oil activities, the lives of
aquatic organisms, macrobenthal organisms, plankton
assemblages, microbial communities, and air in the in-
dustrial mainland.
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