Star Paper 5 (1)

Nigerian Journal of Fisheries Vol. 12 (2) 2015
©Fisheries Society of Nigeria 912
HEAVY METAL ACCUMULATION IN CATFISH SPECIES (Malapterurus electricus,
Chrysichthys nigrodigitatus AND Synodontis clarias) INHABITING THE LEKKI
LAGOON, LAGOS, NIGERIA
*UKWA, U.D., EYIARO, T.O., ORJI, I.K., BAWA-ALLAH, K.A. & J.K. SALIU
Department of Zoology, Faculty of Science, University of Lagos, Nigeria
*Correspondence: ukwadavid@gmail.com, +2347085122532
ABSTRACT
The concentration of heavy metals; Lead, Nickel, Zinc and Iron in surface waters and sediment as well as in liver of
catfish species; Malapterurus (=Erpetoichthys) electricus, Chrysichthys nigrodigitatus and Synodontis clarias
collected from Lekki Lagoon were investigated. Heavy metal concentrations were determined in water, sediment,
liver of fish species using Atomic Absorption Spectrophotometer. Higher concentrations of heavy metals were
detected in sediment as compared to concentrations detected in surface water. The trend of metal concentrations in
surface water was; Zn > Ni > Fe < Pb, and sediment was; Ni > Zn > Fe > Pb. M. electricus had the highest
concentrations of hepatic lead, iron and nickel; Pb (0.98±0.79 mg kg-1
), Fe (24.54±55.07 mg kg-1
), Zn (6.83±8.20
mg kg-1
), Ni (3.42±6.26 mg kg-1
) as compared to the other species; S. clarias which had, Pb (0.02±0.04 mg kg-1
), Fe
(0.61±0.21 mg kg-1
), Zn (0.38 ± 0.20 mg kg-1
), Ni (0.04±0.01 mg kg-1
) and C. nigrodigitatus which had the Pb
(0.01±0.04 mg kg-1
), Fe (5.58±5.38 mg kg-1
), Zn (29.81±25.10 mg kg-1
), Ni (0.68±0.75). S. clarias showed the lowest
accumulation efficiency of heavy metals form surface water and sediment as compared to bio-accumulation factors
recorded for M. electricus and C. nigrodigitatus. M. electricus and S. clarias had similar trend in hepatic metal
concentrations; Fe > Zn > Ni > Pb while C. nigrodigitatus had; Zn > Fe > Ni > Pb. The difference in trend could
be attributed to bioavailability, intrinsic fish processes, and trophic structure variation. Concentrations of the heavy
metals analyzed in the edible fish species were above the safe limits recommended by FEPA and WHO (Pb, 0.01 mg
kg-1
, Ni, 0.02 mg kg-1
, Fe, 0.2 mg kg-1
, Zn, 3.0 mg kg-1
). Therefore measures should be taken to monitor the Lekki
lagoon for heavy metals pollution. Use of multiple indicator species in bio-monitoring should be encouraged and M.
electricus which has shown better bio-indicator capability according to results obtained from this study should be
considered a preferred fish model in bio-monitoring program.
Keywords: Atomic Absorption Spectrophotometer, heavy metals, bioaccumulation factor, bioindicator
INTRODUCTION
The pollution of the aquatic environment with
heavy metals has become a worldwide problem
during recent years, because they are indestructible
and most of them have toxic effect on organisms
(MacFarlane and Burchett, 2000). Heavy metal
concentrations in aquatic ecosystems are usually
monitored by measuring their concentration in water,
sediments and biota. They generally exist in low
levels in water and attain considerable concentration
in sediments and biota (Namminga and Wilhm,
1976). Heavy metals including both essential and
non-essential elements have a particular significance
in eco-toxicology, since they are highly persistent
and all have the potential to be toxic to living
organisms. These elements are toxic to living
organisms at excessive concentration, but some are
essential for normal healthy growth and reproduction
by either plant or animals at low but critical
concentrations.
The fish fauna of Lagos lagoon were classified
by Fagade and Olaniyan (1974) into three main
ecological groups namely the marine group made up
of fishes that use the lagoon as nursery ground, these
were made up of thirty-one species. The freshwater
fishes that dominate the lagoon during the low
salinity periods consisted of seventeen species and
the euryhaline group which included twenty-four
species that were found in the lagoon throughout the
year. Over the years the resources of the Lagos
lagoon have been contaminated with a high level of
industrial and domestic pollutants (Akpata and
Ekundayo, 1978; Ajao and Fagade, 1990; Akpata,
2002; Emmanuel, 2004).
Elemental toxicants could enter fish either
directly through the digestive tract due to
consumption of contaminated water and food or non-
dietary routes across permeable membranes such as
gills (Burger et al., 2002). The pollution has
invariably affected the lives of fishes inhabiting the
lagoon. The fisheries are declining in the lagoon and
adjacent creeks and many of the fish species are
greatly threatened (Emmanuel, 2004; Emmanuel and
Kusemiju, 2005). The residents depend on these
resources as a major source of livelihood (Emmanuel,
2004). Fish, as human food, is considered as a good

UKWA, U.D., EYIARO, T.O., ORJI, I.K., BAWA-ALLAH, K.A. & J.K. SALIU
source of protein, polyunsaturated fatty acids
(particularly omega-3 fatty acids), calcium, zinc (Zn),
and iron (Chan et al., 1999). In future, seafood will
be an even more important source of food protein
than they are today and the safety for human
consumption of products from aquaculture is of
public health interest (WHO, 1999). Chan et al
(1999), Gibbs and Miskiewicz, (1995) and Tariq et
al. (1993) had reported that fishes from industrial and
sewage impacted estuaries and coastal waters contain
high heavy metal concentrations. Metal
concentrations in the fish flesh are of high risk, as
reflected by the high metal concentrations recorded in
the water and sediments (Wong et al., 2001). The rate
of bioaccumulation of heavy metals in aquatic
organisms depend on feeding habit of the organism,
the ability of the organisms to digest the metals and
the concentration of such metal in the environment.
Aquatic animals such as fish bio-accumulate trace
metals in considerable amounts and stay over a long
period.
Fishes have been used as good indicators of
organic and inorganic pollutants including heavy
metals (King and Jonathan, 2003). Age of fish, lipid
content in the tissue and mode of feeding are
significant factors that affect the accumulation of
heavy metals in fishes. They are finally transferred to
other animals including humans through the food
chain. The discharge of industrial wastes containing
toxic heavy metals into water bodies may have
significant effects on fish and other aquatic
organisms, which may endanger public health
through consumption of contaminated seafood and
irrigated food crops. Hence, there is a need evaluate
bio-accumulation patterns of heavy metals in edible
fish species inhabiting polluted ecosystems such as
the Lekki lagoon. A robust data-base is a necessary
tool that would be needed in evaluating and
monitoring public health risk associated with
consumption of such edible fish species. This study
therefore aims to investigate the heavy metal bio-
accumulation pattern of cat fish species
(Malapterurus electricus, Chrysichthys
nigrodigitatus and Synodontis clarias) inhabiting the
Lekki Lagoon.
The bio-accumulation pattern of heavy metals
in fishes and the water is quite often different (Eneji,
2010). This difference in pattern was attributed to
bioavailability, intrinsic fish processes, and trophic
structure variation (Eneji, 2010). Studies have shown
high bioaccumulation factors in fishes; Lawani and
Alawode, (1987) reported fish species accumulating
lead 225 times more than that in the water at the
River Niger at Jebba, Okoye, (1991) reported a
bioaccumulation factor of 604 for manganese in T.
guineensis and 248 for lead in the Lagos lagoon.
Obodo, (2002), studied the lower reaches of River
Niger at Onitsha and reported a bioaccumulation
factor of 300 and 220 for manganese and lead
respectively in Synodontis membranaceus and 254
and 250 for manganese and lead respectively in
Tilapia zillii.
MATERIALS AND METHODS
Study Area
The Lekki Lagoon is part of an intricate
system of waterways made up of Lagoons and creeks
that are found along the coast of South Western
Nigeria from the Dahomey border to the Niger Delta
stretching over a distance of about 200km. It is fed
by the River Oni discharging to the North Eastern
parts and Rivers Osun and Saga discharging into
North Western parts of the Lagoon. Lekki Lagoon is
characterized by dry and rainy seasons typical of
tropic ecosystems. The rich fish fauna of the Lagoon
includes Heterotis niloticus, Gymnarchus niloticus,
Clarias gariepinus, Malapterurus electricus,
Synodontis clarias, Chrysichthys nigrodigitatus,
Channa, obscura, Mormyrus rume, Calamoichthys
(= Erpetoichthys) calabaricus, Tilapia zillii, Tilapia
galilaea, Hemichromis fasciatus and Sarotherodon
melanotheron (Kusemiju 1981).

A1
A2
A3
B1
B2
B3
Fig. 1: Map of Lekki lagoon showing sampling sites
Water and Sediment Collection
Surface water and sediment samples were
collected from six geo-referenced sites on the lagoon
(A1, A2, A3, B1, B2 and B3). The water and
sediment samples of each of these sites were
collected using a water sampler and an Ekman grab.
Fish Sample Collection
A total of 35 fish samples each of
Malapterurus electricus, Chrysichthys nigrodigitatus
and Synodontis clarias species were purchased at
random from the fishermen’s catch at Lekki Lagoon.
The weight and total length of each fish sample was
measured and recorded.
The condition factor also known as the
Ponderal index or the Fulton Coefficient of condition
was computed using the formula described by
Worthington and Ricardo (1936)
b = Value obtained from the growth
exponent in the length
W = Total weight of fish (g)
L = Standard length (cm)
K = Condition factor
Heavy Metal Analysis
Water and Sediment Samples
Collected Water samples were filtered and
digested using standard digestion procedure (APHA,
AWWA, WPCF 1995). Sediment samples were air-
dried, sieved through a 200 micrometer sieve to
normalize for particle size and digested using the
method provided by Agemian and Chau (1976).
Analysis of Heavy Metals in Fish
The fish samples were dissected using sterile
dissecting tools and the liver was extracted for heavy
metal analysis. The liver samples were oven dried at
105 °C for 24 hours and grounded into powder. Ten
millimeters (10 ml) of concentrated nitric acid was
then added to each sample and the mixture was
heated on a hot plate in a fume cupboard for 3 hours
until the brown fumes turned white. Samples were
allowed to cool at room temperature for five minutes.
The samples were then made up to 50ml using
distilled water. The mixture was filtered and the
residue was analyzed for heavy metals using the
atomic absorption spectrophotometer (Perkins Elmer
analyst 200).

The Bio Accumulation Factor (BAF)
The bioaccumulation factor of heavy metals
for the fish species was calculated using the formula.
Statistical Analysis
Results are presented as means ± S.D and
differences among mean values were tested using
One-Way ANOVA (SPSS, 15.0).
RESULTS
Morphometrics and condition factor of catfish
species in Lekki lagoon, Lagos, Nigeria
Total length of Malapterurus electricus,
Synodontis clarias and Chrysichthys nigrodigitatus
ranged between 120.00 – 135.00 cm, 14.00 –
24.00cm and 10.50 – 43.60 cm respectively. The
weight of the catfish species ranged between 4.00 –
146.00 g, 37.00 – 85.00 g and 21.00 – 759.00 g
respectively. M. electricus and S. clarias had
condition factors ranging from 1.05 – 2.35 and 0.20 –
4.89 respectively, while C. nigrodigitatus had 0.22 –
4.35 (Table 1).
Heavy Metal concentrations in the water,
sediment and liver of fish samples collected from
the Lekki lagoon, Lagos, Nigeria
Higher concentrations (p < 0.05) of heavy
metals were recorded in sediments as compared to
surface water samples (Sediment: Pb; 0.01 ± 0.00 mg
kg-1
, Fe; 0.09 ± 0.05 mg kg-1
, Zn; 0.80 ± 0.04 mg kg-1
and Ni; 0.95 ± 0.03 mg kg-1
. Water: Pb; 0.01 ± 0.00
mg kg-1
, Fe; 0.04 ± 0.00 mg kg-1
, Zn; 0.18 ± 0.0 mg
kg-1
and Ni; 0.15 ± 0.03 mg kg-1
). The trend in metal
concentrations in surface water was; Zn > Ni > Fe >
Pb, and sediment was; Ni > Zn > Fe > Pb (Table 2).
The concentration of Lead was significantly higher (p
< 0.05) than other heavy metals M. electricus (Pb;
0.98 ± 0.79 mg kg-1
, Fe; 24.54 ± 55.07 mg kg-1
, Zn;
6.83 ± 8.20 mg kg-1
and Ni; 3.42 ± 6.26 mg kg-1
). In
C. nigrodigitatus, Lead concentration was
significantly lower (p < 0.05) than other metals (Pb;
0.01 ± 0.04 mg kg-
1, Zn; 29.81 ± 25.10 mg kg-1
, Fe;
5.58 ± 5.38 mg kg-1
and Ni; 0.68 ± 0.75 mg kg-1
).
There were no significant differences in
concentrations of heavy metals recorded in S. clarias
(Pb; 0.02 ± 0.04 mg kg-1
, Fe; 0.61 ± 0.21 mg kg-1
, Zn;
0.38 ± 0.20 mg kg-1
and Ni; 0.04 ± 0.01 mg kg-1
). M.
electricus had the highest hepatic Lead and Iron
concentrations while S. clarias had the highest
hepatic Zinc concentration (Table 2). M. electricus
and S. clarias had similar trend in hepatic metal
concentrations; Fe > Zn > Ni > Pb while C.
nigrodigitatus had; Zn > Fe > Ni > Pb.
Concentrations of all the heavy metals analyzed were
above the safe limits recommended by FEPA and
WHO in all the fish species studied (Pb; 0.01 mg kg-
1
, Ni; 0.02 mg kg-1
, Fe; 0.2 mg kg-1
, Zn; 3.0 mg kg-1
).
Table 1: Range values in total length, weight and condition factor among the fish species in
Lekki lagoon, Lagos, Nigeria
Fish Species (n=35) Total Length (cm) Weight (g) Condition Factor
M. electricus 120.00 – 135.00 4.00 – 146.00 1.05 – 2.35
S. clarias 14.00 – 24.00 37.00 – 85.00 0.20 – 4.89
C. nigrodigitatus 10.50 – 43.60 21.00 – 759.00 0.22 – 4.35

Table 2: Heavy Metal concentrations in the water, sediment and liver of fish samples collected from the Lekki
lagoon, Lagos, Nigeria
Liver of fish /Medium Lead (mg kg-1
) Iron (mg kg-1
) Zinc (mg kg-1
) Nickel (mg kg-1
)
Water 0.01 ± 0.00* 0.04 ± 0.00* 0.18 ± 0.02** 0.15 ± 0.03**
Sediment 0.01 ± 0.00* 0.09 ± 0.05* 0.80 ± 0.04** 0.95 ± 0.03**
M. electricus 0.98 ± 0.79* 24.54 ± 55.07 6.83 ± 8.20 3.42 ± 6.26
S. clarias 0.02 ± 0.04 0.61 ± 0.21* 0.38 ± 0.20* 0.04 ± 0.01*
C. nigrodigitatus 0.01 ± 0.04 5.58 ± 5.38 29.81 ± 25.10 0.68 ± 0.75
WHO Standard, 1993. 0.01 0.20 3.00 0.02
* mean value is significant at p < 0.05 level ** mean value is significant at p < 0.01 level
Bioaccumulation factors of Fish Species collected
from the Lekki lagoon, Lagos, Nigeria
The bio-accumulation factors (BAF) in M.
electricus as compared to surrounding media (water
and sediment) were 98 for Lead in water and
sediment, 614 and 31 for Iron in water and sediment
respectively, 57 and 76 for Zinc in water and
sediment respectively and 23 and 4 for Nickel in
water and sediment respectively. S. clarias did not
accumulate nickel and showed low bioaccumulation
potential for the other metals as well (Table 3). C.
nigrodigitatus accumulated Iron 140 times and 7
times more than water and sediment respectively,
Zinc 248 times and 331 times more than water and
sediment respectively but showed low
bioaccumulation potential for the other metals.
Table 3: Bioaccumulation factors of Fish Species collected from the Lekki lagoon, Lagos, Nigeria
Heavy
Metals
Malapterurus electricus Synodontis clarias Chrysichthys nigrodigitatus
BAF (water) BAF (sediment) BAF (water) BAF (sediment) BAF (water) BAF (sediment)
Lead 98 98 2 2 1 1
Iron 614 31 15 1 140 7
Zinc 57 76 3 4 248 331
Nickel 23 4 0 0 5 1
DISCUSSION
Sediments are considered an important
indicator for environmental pollution; they act as
permanent or temporary sink for pollutants including
heavy metals in aquatic ecosystems. Sediments have
frequently been analyzed to identify sources of trace
metal in the aquatic environment because of the high
accumulation rates exhibited (Forstner and
Wittmann, 1981). Sediment analysis allows
contaminants that are absorbed by particulate matter,
which escape detection by water analysis, to be
identified. The non residual fraction of the sediment
is considered to be mobile and therefore, is likely to
become available to aquatic organisms (Waldichuk,
1985). Concentrations of heavy metals in sediment
usually exceed the levels of the overlying water by 3
to 5 orders of magnitude Oguzie (2003). Results from
this study showed higher concentration of all metals
(Fe, Ni, Zn and Pb) in sediment as compared to
surface water.
The concentration of heavy metals in fish is
related to several factors such as the food habits and
foraging behaviors of the organism (Obasohan and
Oronsaye, 2004); tropic status, source of a particular
metal, distance of the organism from the
contamination source and presence of other ions in
the milieu (Giesy and Wiener, 1977). Bio-
magnification and/or bio-diminishing of a particular
metal (Barlas, 1999); food availability,
metallothioneins and other metal detoxifying proteins
in the body of the animal (Deb and Fukushima,
1999); temperature, transport of metal across the
membrane and the metabolic rate of the animal
(Oronsaye, 1989) are also factors that can affect
accumulation of heavy metals in aquatic organisms.
Results from this study have shown that essential

heavy metals (Zinc and Iron) were accumulated in
higher concentrations by the catfish species as
compared to non-essential heavy metals (Lead). The
essential element such as zinc is regulated to
maintain certain homeostatic status in fish (Chen and
Chen, 1999). On the contrary, the non-essential
element such as lead, have no biological function or
requirement and their concentrations in fish tissues
examined were generally low. The low concentration
of non-essential heavy metals could be attributed to
the metabolic regulatory functions of the fish species
as excretion of metals can occur through the gills,
bile (via faeces), and kidney and skin. Also, different
degrees of the metals accumulated in various tissues
depend on the biochemical characteristics of the
metal (Farkas et. al., 2000). Jobling (1995) attributed
the high accumulation of heavy metals in liver to the
metallothionein proteins which are synthesized in
liver tissues when fishes are exposed to heavy metals
and detoxify them. These proteins are thought to play
an important role in protecting them from damage by
heavy metal toxicants. Moreover, Saleh (1982)
reported that the amount of pollutants in the fish liver
is directly proportional to the degree of pollution in
the aquatic environment by heavy metals. Fish are
known to accumulate nickel in different tissues when
exposed to elevated levels in their environment
(Nussey et al, 2000; Obasohan and Oronsaye, 2004).
Nickel is also extensively bio-accumulated from
intake of contaminated food (Singh and Ferns, 1978).
In this study, nickel accumulation level was higher
than the recommended levels of WHO (0.02mg/kg)
in food, indicating that the fish might be a source of
nickel contamination to final consumers including
humans. Lead is known to accumulate in fish tissues
(bone, gills, liver, kidneys, scales), while gaseous
exchange across the gills to the blood stream is
reported to be the major uptake mechanism (Oguzie,
2003). Lead toxicity is dependent on life stage of
fish, pH, water hardness and presence of other
organic materials (Merkini and Pozzi, 1977). In man,
Lead toxicity is known to cause musculo-skeletal,
renal, ocular, neurological immunological,
reproductive and developmental effects (ATSAR,
1999). Pb levels recorded in this study were high
when compared to the 0.13mg/kg reported for H.
fasciatus from Warri River by Ezemonye, (1992).
Oguzie (2003) also reported lower levels (0.007-
0.022mg/kg) for fishes of Ikpoba River in the same
locality. All the heavy metals in the studied fish
species were above the safe limits recommended by
FEPA and WHO (Pb, 0.01mg/kg, Ni, 0.02mg/kg, Fe,
0.2mg/kg, Zn, 3.0mg/kg). Hence, there may be public
health risks associated with consumption of the
species and the need to monitor the Lekki lagoon for
heavy metal pollution and associated ecological and
public health risks cannot be over emphasized.
CONCLUSION
In conclusion, M. electricus had the highest
bio-concentration factors for all heavy metals tested
from water and sediment respectively as shown by
results from this study. This indicates that the species
can be a good bio-indicator of heavy metal pollution
in aquatic ecosystems where they thrive as compared
to the other species examined in this study. Bio-
indicator organisms are essential tools for bio-
monitoring in environmental pollution studies.
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