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Levels of polycyclic aromatic hydrocarbons (PAHs) in the Densu River Basin of Ghana

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  • CSIR-WATER RESEARCH

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The concentrations of 16 polycyclic aromatic hydrocarbons (PAHs) in Densu River Basin in Ghana were measured using gas chromatograph. Surface water samples were collected from nine stations, namely, Potroase, Koforidua Intake, Suhyien, Mangoase, Asuboi, Nsawam Bridge, Afuaman, Ashalaga, and Weija Intake in the Densu Basin. Total PAH concentrations varied from 13.0 to 80.0 μg/mL in the Densu River, with a mean value of 37.1 μg/mL. The two- to three-ring PAHs (low-molecular-weight PAHs) were found to be dominant in the Densu River Basin. Total PAH concentrations showed the following pattern: Koforidua Intake (80.0 μg/mL) > Asuboi (50.8 μg/mL) > Afuaman (47.9 μg/mL) > Weija Intake (45.0 μg/mL) > Suhyien (27.6 μg/mL) > Nsawam (23.5 μg/mL) > Ashalaja (22.9 μg/mL) > Potroase (23.3 μg/mL) > Mangoase (13.0 μg/mL). According to the Agency for Toxic Substances and Disease Registry (ATSDR), background levels of PAHs in drinking water supplies in the USA range from 0.004 to 0.024 μg/mL. PAH levels from all sites exceeded the range set by ATSDR. B[a]P contributed the highest carcinogenic exposure equivalent (0.3 μg/mL), followed by B[a]A (0.132 μg/mL) and B[b]F (0.08 μg/mL), contributing 52.6%, 23.2%, and 4.6%, respectively, of the total carcinogenicity of surface water PAH in the Densu River Basin. The carcinogenic potency was estimated to be 0.57 μg/mL. The presence of PAHs was an indication of the water sources being contaminated, with potential health implications.
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Environmental Monitoring
and Assessment
An International Journal
Devoted to Progress in the Use
of Monitoring Data in Assessing
Environmental Risks to Man
and the Environment
ISSN 0167-6369
Volume 174
Combined 1-4
Environ Monit Assess (2010)
174:471-480
DOI 10.1007/s10661-010-1471-
y
Levels of polycyclic aromatic
hydrocarbons (PAHs) in the Densu River
Basin of Ghana
1 23
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Environ Monit Assess (2011) 174:471–480
DOI 10.1007/s10661-010-1471-y
Levels of polycyclic aromatic hydrocarbons (PAHs)
in the Densu River Basin of Ghana
Joyce Amoako ·Osmund D. Ansa-Asare ·
Anthony Y. Karikari ·G. Dartey
Received: 17 July 2009 / Accepted: 7 April 2010 / Published online: 12 May 2010
© Springer Science+Business Media B.V. 2010
Abstract The concentrations of 16 polycyclic aro-
matic hydrocarbons (PAHs) in Densu River Basin
in Ghana were measured using gas chromato-
graph. Surface water samples were collected from
nine stations, namely, Potroase, Koforidua Intake,
Suhyien, Mangoase, Asuboi, Nsawam Bridge,
Afuaman, Ashalaga, and Weija Intake in the
Densu Basin. Total PAH concentrations varied
from 13.0 to 80.0 μg/mL in the Densu River, with
a mean value of 37.1 μg/mL. The two- to three-
ring PAHs (low-molecular-weight PAHs) were
found to be dominant in the Densu River Basin.
Total PAH concentrations showed the following
pattern: Koforidua Intake (80.0 μg/mL) >Asuboi
(50.8 μg/mL) >Afuaman (47.9 μg/mL) >Weija
Intake (45.0 μg/mL) >Suhyien (27.6 μg/mL) >
Nsawam (23.5 μg/mL) >Ashalaja (22.9 μg/mL) >
Potroase (23.3 μg/mL) >Mangoase (13.0 μg/mL).
According to the Agency for Toxic Substances
and Disease Registry (ATSDR), background lev-
els of PAHs in drinking water supplies in the USA
range from 0.004 to 0.024 μg/mL. PAH levels
J. Amoako (B)·O. D. Ansa-Asare ·
A. Y. Karikari ·G. Dartey
Environmental Chemistry Division,
CSIR Water Research Institute,
P. O. Box AH 38, Achimota, Ghana
e-mail: jeamoako@yahoo.co.uk
from all sites exceeded the range set by ATSDR.
B[a]P contributed the highest carcinogenic expo-
sure equivalent (0.3 μg/mL), followed by B[a]A
(0.132 μg/mL) and B[b]F (0.08 μg/mL), contribut-
ing 52.6%, 23.2%, and 4.6%, respectively, of the
total carcinogenicity of surface water PAH in
the Densu River Basin. The carcinogenic potency
was estimated to be 0.57 μg/mL. The presence of
PAHs was an indication of the water sources being
contaminated, with potential health implications.
Keywords PAHs ·Gas chromatograph ·
Contamination ·Densu River Basin ·
Surface water
Introduction
Water pollution by organic compounds, mostly
known to be toxic or carcinogenic, is of con-
siderable concern worldwide. Polycyclic aromatic
hydrocarbons (PAHs) are a group of ubiquitous
organic pollutants containing two or more fused
benzene rings, of great environmental concern be-
cause of the documented carcinogenicity in exper-
imental animals and the widespread occurrence of
several of its members (Manoli et al. 2000).
Due to their ubiquitous occurrence, recal-
citrance, and suspected carcinogenicity and
mutagenicity, PAHs are included in the US
Environmental Protection Agency (EPA) and in
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472 Environ Monit Assess (2011) 174:471–480
the European Union priority lists of pollutants.
The US EPA fixed 16 parent PAHs as priority
pollutants, the latest being effective from 1997
(Baumard et al. 1997; Mastral and Callén 2000;
Magi et al. 2002; Szolar et al. 2002; Schubert et al.
2003), some of which are considered to be possible
or probable human carcinogens. Endocrine-
disrupting activities of PAHs have also been
recently reported (Clemons et al. 1998; Brun et al.
2004).
PAHs have been detected in the atmosphere,
water, soil, sediments, and food (Ferreira 2001).
PAHs are introduced into the environment
through natural and anthropogenic combustion
processes. Anthropogenic sources include auto-
mobile exhaust and tire degradation, industrial
emissions from catalytic cracking, air blowing of
asphalt, coking coal, domestic heating emissions
from coal, oil, gas, and wood, refuse incineration,
and biomass burning. The major mobile anthro-
pogenic sources are vehicles and tobacco smok-
ing (Shui-Jen et al. 2003). Volcanic eruptions and
forest and prairie fires are among the major nat-
ural sources of PAHs in the atmosphere (Baek
et al. 1991; Manoli et al. 2000). In general, more
PAHs form when materials burn at low temper-
atures, such as in wood fires or cigarettes. High-
temperature furnaces produce fewer PAHs. Fires
can form fine PAH particles. They bind to ash
particles and can move long distances through the
air. Atmospheric deposition has been regarded as
a main pathway for the loading of PAHs to many
water bodies (Golomb et al. 1997).
As streams and rivers, lakes, and ponds are
frequently used for potable water supply and the
reuse of water is common, contamination of water
sources is particularly undesirable (Manoli and
Samara 1999). Therefore, PAH distributions in
the environment and potential human health risks
have become the focus of much attention.
The Densu River, for its size, is one of the
most exploited rivers in Ghana (WRC 2003). It
traverses several towns (Koforidua, Nsawam, Ak-
wadum, etc.) and serves as the main source of
water supply for a number of communities. The
river is confronted by three main agents of degra-
dation: bad farming practices, deforestation, and
pollution (domestic and industrial wastewater).
The activities of farmers (high use of fertilizer
and other chemicals), especially large-scale com-
mercial farming enterprises in the catchment of
the river, are causing a lot of havoc both to the
water quality and quantity. The Densu River is
presently one of the most polluted rivers in the
country due to the impact of growing population
densities, industrialization, and intensification of
agricultural activities (WRC 2003). The Densu
River enters the Weija reservoir which is one of
the two main sources of water supply systems for
thecityofAccra.
In Ghana, very limited studies on the moni-
toring of PAHs in surface waters are available.
Available water quality data (physicochemical) on
the Densu Basin include those of Amuzu (1975),
Kpekata and Biney (1979), Biney (1987), Ansa-
Asare (1992,1996), and Karikari and Ansa-Asare
(2006). All these studies concentrated on other
forms of pollution and degradation, but not on
PAHs. The current study focuses on identifying
and characterizing PAHs in light of their toxic
and carcinogenic effects on human health and
aquatic environment using quantitative gas chro-
matograph with micro-electron capture detector
(GC-μECD) method.
Materials and methods
Chemicals
Standard PAHs (16 components) from the
National Institute of Standard Technology
(NIST) of concentration 60 μg/ml, deuterated
PAHs internal standards (IS) in cyclohexane
3,6,-dimethylphenanthrene (3,6-DMP) and β,β-
Ginaphthyl (β,β-BN) and dichloromethane
were obtained from Sigma, BDH, and Supelco.
Working standards of these micro-pollutants
(PAHs) were prepared by combining the standard
mixture with the corresponding IS stock solution,
respectively. These solutions were further diluted
with hexane to prepare calibration solutions in the
range 1–15 μg/ml. All solvents (dichloromethane,
cyclohexane, hexane, and methanol) used for
sample preparation were of high-performance
liquid chromatography (HPLC) grade. Organic-
free distilled water was used.
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Environ Monit Assess (2011) 174:471–480 473
Study area
The Densu Basin located between latitude
530Nto6
20N and longitude 010Wto
035W (Fig. 1) has an estimated drainage
area of 2,564 km2(WRC 2003). It takes its
source from the Atewa-Atwiredu mountain
range near Kibi in the Eastern Region of Ghana
and flows southwards for 116 km entering the
Weija Lake at Ashalaja. It discharges into the
Sakumo II Lagoon, 4 km south of the Weija Dam,
before subsequently emptying into the Atlantic
River
0 5 10 15 K m.
0 5 10 Miles
STUDY AREA
G H A N A
I N S E T
Asuboi Mangoase
Ashalaja
Sampling Station
Catchment Boundary
Road
L E G E N D
D E N S U B A S I N
Koforidua
Suhyien
Afuaman
Weija Intake
Nsawam Bridge
Potroase
Intake
Fig. 1 Map of Densu Basin (Ghana) indicating sampling sites
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474 Environ Monit Assess (2011) 174:471–480
Ocean at Bortianor situated southwest of Accra
(Amuzu 1975). The Densu River catchment
area encompasses the following rivers which are
tributaries: Adaiso, Suhyien, Doboro, Nsaki, and
Kuia (Fig. 1), all of which flow through densely
populated areas, forests, and areas of intense
farming activities where fertilizers and pesticides
are heavily used (Ayibotele and Tuffuor-Darko
1979). Mainly crystalline rocks, comprising five
formations, namely, Birimian, Granites, Togo
series, Dahomayean, and Accraian, underlie the
basin. With the exception of Accraian, the rest are
Precambrian. The dominant soils are ochrosols,
with patches of gleisols and lithosols.
The inhabitants are mainly peasant farmers
who grow foodstuffs, vegetables, fruits, and cash
crops (e.g., cocoa). In addition, many large-scale
commercial farmers grow crops for the export
market. Timber and lumber are extracted from
the forest in the basin. The river waters are ex-
tensively used for drinking and other domestic
purposes.
Sampling and sample treatment
Nine sampling stations were selected based on
accessibility and closeness to major population
centers where human activities can indirectly be
assessed. The nine sampling stations have been
arranged from upstream near the headwaters
to downstream. Sampling followed this order:
Potroase—S1, Koforidua Intake—S2, Suhyien—
S3, Mangoase—S4, Asuboi—S5, Nsawam
Bridge—S6, Afuaman—S7, Ashalaga—S8, and
Weija Intake—S9. The sampling stations included
two intake points (headworks) of the Ghana
Water Company Limited, namely, Koforidua and
Weija.
The study was conducted between March and
December 2004, covering dry and rainy seasons.
Each station was sampled three times. The surface
water samples were collected at a depth of 20–
30 cm (to ensure proper mixing) into pre-cleaned
1-L glass containers. The water samples were pre-
served at pH <2 with the addition of 5 mL conc.
HCl. All the samples were tightly sealed and kept
in an ice chest stored at 4C and transported to
the Council for Scientific and Industrial Research-
Water Research Institute laboratory and kept in a
refrigerator (at 4C) for a maximum of 1 week and
analyzed using Agilent 6890 gas chromatograph.
Sampling was mainly confined to the midstream
of the river courses except on few occasions where
unavailability of a boat limited sampling to the
banks.
Sample extraction, analytical quality control,
and statistical analysis
Sample extraction
IS in cyclohexane were added to the water sam-
ples. The internal standards were 3,6-DMP and
β,β-BN for analysis with gas chromatograph using
flame ionization detector (GC-FID). The sam-
ples were Soxhlet-extracted with cyclohexane for
8 h. The extracts were purified by partitioning
dimethylformamide/water. The PAHs were then
eluted with cyclohexane from columns filled with
5 g of silica gel deactivated with 15% water.
The identification and quantification of PAHs was
accomplished using a gas chromatograph (GC;
Hewlett-Packard 6890 A) with split/splitless injec-
tor and FID. The column is a capillary column
HP-5MS (60 m ×0.25 mm i.d. ×0.25 μm film
thickness). Nitrogen (purity of 99.9999%) was
used as the carrier gas at a constant flow of
1.4 mL/min. A 2 μL volume was injected by
applying a hot splitless injection technique. The
temperature program of the oven was as follows:
from 60C (initial time, 3 min) to 120Cata
rate of 10C/min, 120C to 280Catarateof
5C/min, and held at 280C for 10 min. The GC
chemstation (version A.08.04) was controlled by
computer workstation. Identification of the PAH
compounds was performed by comparing GC
retention time with those of authentic stan-
dards. Quantification of individual compounds
was based on comparison of peak areas with those
of the recovery standards.
Analytical quality control
All data were subjected to strict quality control
procedures. For PAHs, deuterated internal stan-
dards 3,6-DMP and β,β-BN were to compensate
for losses during sample extraction and work-up.
Before sample analysis, relevant standards were
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Environ Monit Assess (2011) 174:471–480 475
analyzed to check column performance, peak
height, and resolution and the limits of detection.
For each set of samples to be analyzed, a solvent
blank, a standard mixture, and a procedural blank
were run in sequence to check for contamination,
peak identification, and quantification. Standard
reference material (SRM 1491) from National In-
stitute of Standards and Technology (NIST) was
used for GC calibration and relative accuracies. In
general, 16 different individual PAHs have been
quantified. A given amount of distilled water was
taken and then spiked with known amount of
Esso Marine Special Oil (certified reference ma-
terial from Norwegian Water Research Institute,
NIVA) and analyzed as normal sample. Blank
samples of distilled water were also analyzed to
ensure that there was no petroleum compounds
present, which will give too high extraction yields.
The recovery efficiencies of 16 individual PAHs
were determined by processing a solution con-
taining known PAH concentrations through the
same experimental procedure used for the sam-
ples. Total recovery efficiency of PAHs in this
study ranged from 73.9% to 110.8% and averaged
95.8%. RSD (%) of recovery efficiency was up to
17%, and the value of potential error for PAHs
analysis was estimated to be 18%. Procedural
blanks were analyzed concurrently with the sam-
ples. No detectable concentrations of PAHs were
present in any of the procedural blanks.
Statistical analysis
The Spearman’s rank correlation was used to
examine the correlation between low molecular
weight (LM-PAHs, two- to three-ringed PAHs)
and high molecular weight (HM-PAHs, five- to
six-ringed PAHs); between LM-PAHs and mid-
dle molecular weight (MM-PAHs, four-ringed
PAHs); and between MM-PAHs and HM-PAHs
in the water samples for the various stations.
A probability value of p<0.05 was considered
as statistically significant in this study (data not
shown).
PAH identification and quantification
The following PAH species were identified and
quantified in this study: two-ring, naphthalene;
three-ring, including acenaphthylene, acenaph-
thene, fluorene, phenanthrene, anthracene; four-
ring, including fluoranthene, pyrene, benzo[a]
anthracene, chrysene; five-ring, including benzo
[b]fluoranthene, benzo[ j,k]fluoranthene, benzo[a]
pyrene (B[a]P); and six-ring, including indeno[1,
2,3-cd]pyrene, dibenzo[a,h]anthracene, and benzo
[ghi]perylene. The total PAH concentration was
regarded as the sum of the concentrations of 16
PAH species for each collected sample. In or-
der to understand PAH homologue distribution
for each collected sample, the concentrations of
PAH species with LM-PAHs (containing two- to
three-ringed PAHs), MM-PAHs (containing four-
ringed PAHs), and HM-PAHs (containing five- to
six-ringed PAHs) were also determined.
Results and discussion
The mean concentration ranges of individual and
total PAHs in the Densu River Basin at the vari-
ous stations are shown in Table 1. The results are
compared to the background levels of PAHs in
drinking water from USA which range from 0.004
to 0.024 μg/mL (ATSDR 1995).
Table 1 Mean concentrations (μg/mL) of PAHs in water from Densu River
Potroase Koforidua Suhyien Mangoase Asuboi Nsawam Afuaman Ashalaja Weija Mean SD
intake intake
LM 5.73 63.33 20.4 6.15 40.86 10.52 40.10 14.75 34.10 26.22 19.62
MM 14.18 7.67 2.75 2.90 5.91 7.99 2.49 1.70 5.40 5.67 3.94
HM 3.42 9.04 4.44 3.95 3.98 4.97 5.28 6.41 5.57 5.23 1.70
Total 23.33 80.04 27.59 13.00 50.75 23.48 47.87 22.86 45.07 37.12 25.26
PAHs
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476 Environ Monit Assess (2011) 174:471–480
PAH concentrations in Densu River water
Total PAH concentrations ranged from 13.0 to
80.0 μg/mL in the Densu River, with mean value
of 37.1 μg/mL (Table 1). The highest concentra-
tion of total PAH (80.0 μg/mL) was observed at
Koforidua intake, S2 (Fig. 2). With increasingly in-
tense, agricultural activities, urban and industrial
development, and expansion work at the intake,
the amount of PAHs detected at the intake may
be related to urban runoffs and vehicular exhaust
emission. At the time of sampling, there were
vehicular trucks working during the expansion
work at the Koforidua Intake point. Similarly,
high concentration (50.7 μg/mL) was also found at
Asuboi, S5. The station is close to heavy vehicular
traffic. In addition, there were a lot of commer-
cial vegetable farms and cattle rearing upstream
of the river at Asuboi. Runoffs from farm lands
and many other non-point sources may contribute
to the high concentrations of PAHs detected at
Asuboi.
Therefore, the analytical results from this study
indicated that total PAHs in water from the sta-
tions increased in the order: Koforidua intake >
Asuboi >Afuaman >Weija intake >Suhyien >
Nsawam >Ashalaja >Potroase >Mangoase.
Levels of PAHs from all the nine sampling sites
exceeded background levels of PAHs in drink-
ing water from USA which range from 0.004 to
0.024 μg/mL.
PAHs compositional pattern
The compositional pattern of PAHs by molecular
weight along the basin (upstream to downstream)
is shown in Fig. 3. It can be observed that two-
and three-ringed PAHs (naphthalene, acenaph-
thylene, acenaphthene, fluorene, phenanthrene,
and anthracene) constituting the LM-PAHs are
the most abundant PAHs, which averaged 64% of
total PAHs (Table 2) in the Densu River Basin,
followed by four-ringed PAHs constituting the
MM-PAHs which averaged 19% of total PAHs
in the Densu River Basin. The five- to six-ringed
PAHs constituting the HM-PAHs which averaged
17% of total PAHs in the Densu River Basin
were the least present. Work done by Wei et al.
(2009) revealed higher concentrations of dissolved
PAHs (LM-PAHs) than that of particulate PAHs
at many sites of the Daliao River in China. Com-
mon sources of PAHs are vehicle exhaust, coal
tar, and municipal or industrial activities that in-
volve combustion. High-molecular-weight PAHs
enter rivers and streams through atmospheric de-
position and stormwater runoff. During their at-
mospheric residence, PAHs are redistributed in
the atmosphere between the gas and the particulate
Fig. 2 Mean
concentrations of low
molecular weight
(LM-PAHS), comprising
two to three-ringed PAHs
middle molecular weight
(MM-PAHs), comprising
four-ringed PAHs, and
high molecular weight
(HM-PAHs), comprising
five to six-ringed PAHs in
the Densu Basin
alongside total PAH
0
10
20
30
40
50
60
70
80
90
Potroase
Koforidua Intake
Suhyien
Mangoase
Asuboi
Nsawam
Afuaman
Ashalaja
Weija Intake
Sites
PAHs (µg/ml)
LM-PAHs
MM-PAHs
HM-PAHs
T.PAHs
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Environ Monit Assess (2011) 174:471–480 477
Fig. 3 Composition
pattern of total PAHs in
Densu Basin showing the
low molecular weight
(LM-PAHS), comprising
the two to three-ringed
PAHs, middle molecular
weight (MM-PAHs),
comprising four-ringed
PAHs, and high
molecular weight
(HM-PAHs), comprising
five to six-ringed PAHs of
the various sites sampled
0%
20%
40%
60%
80%
100%
Potroase Koforidua
Intake
Suhyien Mangoase Asuboi Nsawam Afuaman Ashalaja Weija
intake
Sites
PAHs
HM MM LM
phase (Bourotte et al. 2005), transported over
long distances, and enter water bodies by wet and
dry deposition and or by gas–water interchange
(Fang et al. 2004).
At Potroase, the mean LM-PAHs and HM-
PAHs were 24.6% and 14.7% of the total PAHs,
respectively, indicating moderate influence of par-
ticulates from the atmosphere. Thus, at Potroase,
MM-PAHs (60.8%) dominated the water. Ko-
foridua Intake recorded LM-PAHs of 79.1%
of the total PAHs. It recorded HM-PAHs of
11.3%. This indicated moderate influence of par-
ticulates from the atmosphere. Low levels of
MM-PAHs (9.6%) were also recorded for the
station. The sources of PAHs may be from wa-
ter running off asphalt roads and exhaust from
cars and trucks. The LM-PAHs also dominated
at Suhyien, recording 74% of the total PAHs. It
recorded HM-PAHs of 16% and MM-PAHs of
10%. Mangoase station also showed low MM-
PAHs of 22.3% and HM-PAHs of 30.4%. The
LM-PAHs for Mangoase was 47.3%, being the
dominant PAHs. The low levels of HM-PAHs
for Suhyien and Mangoase could be attributed to
moderate atmospheric deposition and stormwater
runoff. At Asuboi, the LM-PAHs recorded 80.5%
of the total PAHs, dominating over the rest of
Table 2 Percentage
compositional pattern of
PAHs within the entire
Basin
PAHs Percentage
LM 64
MM 19
HM 17
the PAH. The MM-PAHs and the HM-PAH were
11.6% and 7.8%, respectively. Similar trend of
LM-PAHs dominating the rest of the distribu-
tion pattern was observed at Nsawam, Afuaman,
Ashalaja, and Weija Intake stations. At low to
moderate temperature, as in the wood stove (Lake
et al. 1979) or as from the combustion of coal,
low-molecular-weight total PAH compounds are
abundant. At high temperature, such as vehicle
emissions, the high-molecular-weight total PAH
compounds are dominant (Laflamme and Hites
1978).
In terms of MM-PAHs and HM-PAHs, be-
tween the different sites, no significant difference
in PAH concentrations was observed. Concentra-
tions of PAH between low-molecular-weight and
high-molecular-weight PAHs at Asuboi showed
a statistically significant difference (p=0.046).
This could probably be due to increased par-
ticulate matter deposition from the atmosphere.
The difference between LM-PAHs and HM-
PAHs at Koforidua showed a trend toward a
non-significant difference (p=0.050). The cor-
responding difference between LM-PAHs and
MM-PAHs for Suhyien, Afuaman, and Ashalaja
showed a trend toward a non-statistical signifi-
cance (p=0.050).
Assessing PAH exposure profiles
Evidence that mixtures of PAHs are carcino-
genic in humans comes primarily from occupa-
tional studies of workers. Cancer associated with
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478 Environ Monit Assess (2011) 174:471–480
exposure to PAH-containing mixtures in humans
occurs predominantly in the lung and skin follow-
ing inhalation and dermal exposure, respectively
(WHO 1998). Several PAH species including
benzo[a]pyrene have been classified into proba-
ble (2A) or possible (2B) human carcinogens by
the International Agency for Research on Can-
cer (IARC 1987). Benzo[a]pyrene is a five-ring
(C20H12 ) compound which is mutagenic for hu-
man cells in culture (Osborne and Crosby 1987)
and carcinogenic in animal assays (Cerna et al.
2000). The toxic equivalent factor (TEF) for B[a]P
is 1 according to Bostrom et al. (2002), which
is highest among all the PAHs. Therefore, the
risk associated with the intake of carcinogenic
PAHs from Densu River Basin was estimated
using TEFs for individual PAHs. TEFs have been
devised as a means of comparing the carcinogenic-
ity of the individual PAHs to the carcinogenicity
of B[a]P. Till date, only a few proposals of TEFs
for PAHs are available (Masih et al. 2008). In
this work, TEFs given by Tsai and Shih (2004)
were employed. Benzo[a]pyrene equivalents for
each carcinogenic PAH were calculated by mul-
tiplying mean concentrations with corresponding
TEF values (Table 3). The above method has the
main advantage of being relatively easy to apply
in the environments affected by human sources,
Table 3 BaPeq exposure profiles in Densu River Basin
(μg/mL)
PAHs Mean TEFs BaP exposure
Naphthalene 5.06 0.001 0.00506
Acenaphthylene 13.63 0.001 0.01363
Acenaphthene 3.73 0.001 0.00373
Fluorene 1.51 0.001 0.00151
Phenanthrene 0.90 0.001 0.0009
Anthracene 1.39 0.01 0.0139
Fluoranthene 0.63 0.001 0.00063
Pyrene 1.58 0.001 0.00158
Benzo[a]anthracene 1.32 0.1 0.132
Chrysene 2.14 0.01 0.0214
Benzo[b]fluoranthene 0.80 0.1 0.08
Benzo[k]fluoranthene 2.18 –
Benzo[a]pyrene 0.30 1 0.3
Indeno[1,2,3-cd]pyrene 0.96 –
Dibenzo[a,h]anthracene 0.45 –
Benzo[ghi]perylene 0.53 0.01 0.0053
Total 37.11 1.23 0.57
however may underestimate risk due to not all
PAH but only limited compounds are considered
(WHO/IPCs 1998). The mean concentration of
total PAH of 37.1 μg/mL corresponds to a B[a]P
equivalent exposure of 0.57 μg/mL with respect
to carcinogenicity. B[a]P contributed the high-
est carcinogenic exposure equivalent (0.3 μg/mL),
followed by B[a]A (0.132 μg/mL) and B[b]F
(0.08 μg/mL), contributing 52.6%, 23.2%, and
4.6%, respectively, of the total carcinogenicity of
surface water PAH in the Densu River Basin.
Conclusions
Sixteen priority PAHs were determined in wa-
ter from nine locations from the Densu River
Basin. The levels of PAHs in the Densu River
Basin ranged from 13.0 to 80.0 μg/mL, exceed-
ing the background levels of PAHs in drink-
ing water from USA (0.004–0.024 μg/mL). The
PAH profiles of water samples revealed that the
dominant PAHs were of low molecular weight
(two- and three-ringed) as naphthalene, acenaph-
thylene, acenaphthene, fluorene, phenanthrene,
and anthracene. The concentration of PAH
for the various stations increased in the order
Koforidua Intake >Asuboi >Afuaman >Weija
Intake >Suhyien >Nsawam >Ashalaja >
Potroase >Mangoase. Asuboi showed a statis-
tically significant difference (p=0.046) between
LM-PAH and HM-PAH. Using a TEF approach,
the mean concentration of total PAH equates
to about 0.57 μg/mL of B[a]P exposure with re-
spect to carcinogenic potency. B[a]P contributed
the highest carcinogenic exposure equivalent
(0.3 μg/mL), followed by B[a]A (0.132 μg/mL)
and B[b]F (0.08 μg/mL). The findings point to the
need to establish a monitoring program for these
organic micro-pollutants since the river is a source
of drinking water supply.
Acknowledgements The authors wish to thank the gov-
ernment of Ghana for sponsoring this research, staff of the
Council for Scientific and Industrial Research-Water Re-
search Institute (CSIR-WRI), the Ghana Water Company
Limited for their assistance during sampling at their intake
points.
Author's personal copy
Environ Monit Assess (2011) 174:471–480 479
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