Proximal Input of Polynuclear Aromatic Hydrocarbons (PAHs) in Groundwater Sources of Okrika Mainland, Nigeria

doi:10.4236/jep.2011.26096

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Journal of Environmental Protection, 2011, 2, 848-854

doi:10.4236/jep.2011.26096 Published Online August 2011 (http://www.SciRP.org/journal/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.

Email: [email protected]

Received April 14th, 2011; revised May 26th, 2011; accepted July 9th, 2011.

ABSTRACT

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

refinery’s effluent discharge point (Ekerekana Creek) and channel. Hence the source of these pollutants could best be

fingerprinted to the nearby Port Harcourt Refinery Company’s 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.

Proximal Input of Polynuclear Aromatic Hydrocarbons (PAHs) in Groundwater Sources of Okrika Mainland, Nigeria

850

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

fishing.

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

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-

tively.

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.

Proximal Input of Polynuclear Aromatic Hydrocarbons (PAHs) in Groundwater Sources of Okrika Mainland, Nigeria

852

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

Hydrocarbons

Though pH had no significant influence on them, the

Proximal Input of Polynuclear Aromatic Hydrocarbons (PAHs) in Groundwater Sources of Okrika Mainland, Nigeria

853

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 10−5. 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

Recommendation

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

854

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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