Research Journal
 
of 
Chemical 
Sciences 
___
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______
____
___
 
ISSN 22
31
-
606X
 
 
Vol. 
3
(
3
), 
70
-
75
, 
March
 
(201
3
)
 
Res.
 
J.
 
Chem. 
Sci.
 
 
 
 
International Science Congress Association
 
 
 
 
    
70
 
Assessment of Some Trace Metals Content of 
Oreochromis niloticus 
Obtained
 
from River Okpokwu, Apa Benue State, 
Nigeria
 
 
Abah J.
*
, Ubwa S.T., Onyejefu D.I. and Nomor S.A.
 
Department of Chemistry, Benue State University, P.M.B. 102119, Makurdi NIGERIA
 
 
Avail
able online at: 
www.isca.in
 
Received 
5
th
 
February
 
201
3
, revised
 
13
th
 
February 
201
3
, accepted
 
28
th
 
February 
201
3
 
 
 
 
Abstract 
 
This study was conducted with the aim of determining the concentrations of As, Mn, Cu, Pb, Cd and
 
Fe in whole 
Oreochromis niloticus (tilapia) and its fresh water habitat using recommended analytical procedures and compare the 
results with WHO‟s permissible limits. Samples of fresh water and the fish were collected weekly at the peak of rainy and dry
 
s
easons in the study area (October, 2010 and February, 2011) respectively at three locations; Auke, Odejo and Ochalanya 
along the river. Across the sampling points, the results obtained using Unicam Solar (32) Atomic Absorption 
Spectrophotometer showed that
 
the trace metal contents of Oreochromis niloticus varied between 0.05�0.01�g/g As to 
0.38�0.04�g/g Fe in October, 2010 and 0.09�0.03�g/g As to 0.28�0.02�g/g Fe in February, 2011. The water levels of the 
trace metals ranged from 0.06�0.02�g/L As to 1.24�0.
05�g/L Fe in October, 2010 and 0.04�0.01�g/L As to 0.59�0.10�g/L 
Fe in February, 2011. There were positive correlations between the concentrations of the trace elements in the whole fish 
and river water. T
-
test analyses of the levels of the trace metals be
tween the sampling periods were statistically significant (P 
< 0.05). The levels of the trace metals recorded in this study were below WHO‟s permissible limits. Therefore, the water and 
Oreochromis niloticus obtained from the study area have not become con
taminated by the trace metals studied. However, 
periodic review should be sustained to monitor possible accumulations of the heavy metals in future due to the proliferation 
of anthropogenic activities around river Okpokwu.
 
 
Key
w
ords: 
Agrochemicals, 
o
reochr
omis niloticus
, 
t
race 
m
etals, 
r
iver 
o
kpokwu
.
 
 
Introduction
 
Trace metals are natural components of the environment but 
they have become a matter of great concern because of the 
continuous increase in concentration of these metals in our 
environment. The p
ollution of water bodies in the urban, 
industrial and agricultural areas has resulted to increased 
concentration of heavy metals and minerals in the internal body 
of fish
1
. This situation was further aggravated by the rapid 
growth of population, increased 
urbanization and expansion of 
industrial activities, exploration and exploitation of natural 
resources as well as the modern agricultural practices and lack 
of environmental regulations
2
-
4
. As heavy metals cannot be 
degraded, they are deposited, assimilate
d or incorporated in 
water, sediment and aquatic animals
5
 
and present great dangers 
to organisms in the food chain. Research works have shown that 
heavy metals can be bio
-
accumulated and biomagnified via the 
food chain and finally assimilated by human cons
umers with the 
attendant adverse health effects
6
. As a consequence, fish are 
often used as indicators of heavy metals contamination in the 
aquatic ecosystem because they occupy high trophic levels and 
are important food source
6,7
. Unacceptable levels of le
ad and 
mercury were reported in the study on tissues of African catfish, 
Clarias
 
gariepinus
 
from River Niger
8
. Similarly, the levels of 
lead, copper and zinc reported in the study on Nile tilapia, 
Oreochromis
 
niloticus
 
caught from River Delimi, Jos were to
o 
high for frequent human consumption
9
.
 
It has been observed that the functioning of the natural 
ecosystems is increasingly being affected by human activities. 
Research work has shown that it is difficult to find a river or 
other water bodies whose natural
 
regime has not been modified 
by man‟s activities
10
. The unsanitary habits of depositing 
industrial wastes at dumps without adequate treatment or 
directly into the aquatic environment is a common sight in many 
industrial cities in Nigeria
11
. Among the rura
l populace also, 
there has been indiscriminate usage of different agrochemicals 
in farm lands at the banks of rivers which provide sources of 
water to the host communities for domestic and agricultural 
purposes. The result is that toxic and hazardous mater
ials 
including heavy metals are transported to several water bodies 
(rivers, streams, lake, and ponds) with potential effects on 
aquatic organisms. 
 
 
Over the years there has been a remarkable degradation in the 
quality of River Okpokwu and its portability
 
due to the 
proliferation of chemical
-
based agriculture, mining and block 
industry activities in the major settlements along the rivers. 
Agricultural contamination of many resources through fallout, 
drainage and runoff erosion is highly probable in rivers 
within 
the vicinity of intensive agricultural activities. Furthermore, 
there is no clear documentation of any effect of anthropogenic 
activities around River Okpokwu. Thus, this study provides a 
baseline data of the levels of some heavy metals in 
Oreochrom
is 
niloticus
 
and water from River Okpokwu and the result formed 
Research Journal of 
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Vol. 
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-
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Res. J. Chem. Sci.
 
  
 
International Science Congress Association
 
 
71
 
basis for monitoring the pollution by the heavy metals in River 
Okpokwu.
 
 
Material and Method
s
 
The Study Area: 
River Okpokwu is one of the relief features in 
Apa LGA of Benue State, Nigeria. I
t is located on longitude 
7.80
o
E and latitude 7.58
o
N. The River is located 4km away from 
Ugbokpo, Apa Local Government Headquarters. River 
Okpokwu meets river Ochekwu at Odejo, Agatu LGA and they 
flow into River Benue at Ocholonya, also in Agatu LGA. Unlik
e 
other rivers within the locality, River Okpokwu never dries up 
completely during dry season. The volume and size of the river 
increase very rapidly during rainy season. Thus, it sustains high 
agricultural and fishing activities. Near the source of this r
iver, 
there is high gravel mining activity while along the river, there 
are high chemical
-
based farming activities and block industries. 
These activities constitute potential sources of surface and 
underground water pollution.
 
 
Samples Collections and Pres
ervation: 
A total of eighteen 
(18) samples each of 
Oreochromis niloticus 
(Tilapia) and water 
were collected from three locations; Auke, Odejo and 
Ocholonya in River Okpokwu during the months of October, 
2010 and February, 2011. These periods were chosen to
 
represent the peaks of rainy and dry seasons in the study area. 
Oreochromis niloticus
 
is a surface feeder and it feeds from its 
water habitat. The fish were collected and transported to the 
laboratory in ice boxes and rinsed with deionized water and 
froze
n at 
-
10
o
C prior to analyses
12
. The samples were preserved 
in a refrigerator at 5
o
C
1
.
 
 
Water samples were collected at each extremity and median part 
of the river by immersion of polythene bottles to approximately 
30cm below the water surface and allowed t
o overflow. All 
containers used for sampling and storage were thoroughly 
washed with solution of detergent and distilled water. They 
were then soaked in 10% “Analar” nitric acid overnight 
followed by rinsing with distilled water to remove trace 
elements co
ntamination
13
. 
 
 
Samples Preparations and Analyses
: 
Water Sample:
 
Raw 
water was subjected to wet digestion. 100ml unfiltered water 
was measured into a 250ml beaker and 20ml “Analar” nitric 
acid solution plus 10ml of 50% hydrochloric acid solution were 
adde
d. The acidified water was then evaporated to almost 
dryness on a hot plate and 5ml of 50% hydrochloric acid was 
again added and heated for 15 minutes. The beaker was 
removed and cooled to room temperature before transferring the 
content into a 100ml volum
etric flask and made up to the mark 
with distilled water
13
. The digested water was filtered and 
analyzed for the levels of As, Mn, Cu, Pb, Cd and Fe using 
Unicam Solaar (32) Atomic Absorption Spectrophotometer 
(AAS).
 
 
Oreochromis niloticus
: 
The fishes were
 
discaled and 
inviscerated and then transferred to electric oven at 40
o
C. They 
were dried in the oven at this temperature for 24hours and then 
pulverized in a clean dry porcelain mortar
12
. The pulverized fish 
samples were dried further for 1hour at reduced
 
temperature of 
20
o
C and put into clean dried bottles
14
. 3.00g of the dried fish 
samples were weighed into a silica crucible and ashed in a 
muffle furnace at a temperature of 600
o
C for 5hours
14,1
. The 
ashes were cooled to room temperature and filtered to r
emove 
particles and then transferred into a 250ml conical flask. 
Thereafter, 20ml of concentrated HNO
3
 
was added and then 
diluted to 50ml with deionised water and swirled gently. The 
volume was made up to 100ml marks in a volumetric flask with 
deionised wa
ter and analyzed for heavy metals as in the water.
 
 
Data Handling: 
The data generated were subjected to t
-
test (p 
0.05) to determine the significance of mean metal 
concentrations between the sampling periods. Correlation 
analysis was also carried out to 
assess the relationship between 
fish metals content and those of its water habitat.  
 
 
Results and Discussion
 
The results in 
t
able
-
1 presents the concentrations (�g/g) of the 
trace metals in 
Oreochromis niloticus
 
(tilapia) obtained from 
River Okpokwu in th
e months of October, 2010 and February, 
2011. Across the sample locations,
 
A
s and Mn concentrations in 
Oreochromis niloticus
 
ranged from 0.05�0.02 to 
0.11�0.03(�g/g) and 0.08�0.04 to 0.17�0.02(�g/g) in October, 
2010 and  while the concentrations in Februar
y, 2011 revealed 
0.09�0.03 to 0.16�0.04(�g/g) and 0.19�0.02 to 0.22�0.03(�g/g) 
respectively. Copper (Cu) concentrations varied between 
0.10�0.03 to 0.15�0.02(�g/g) and 0.14�0.02 to 0.23�0.03(�g/g) 
during the same period respectively. Cadmium (Cd) was not 
d
etected in the fish but Pb concentrations ranged from 
0.03�0.01 to 0.05�0.02(�g/g) and 0.05�0.02 to 
0.08�0.01(�g/g), Fe concentrations varied between 0.31�0.05 to 
0.38�0.03(�g/g) and 0.21�0.08 to 0.28�0.02(�g/g) in the 
months of  October, 2010 and February
, 2011 respectively. T
-
test analyses of the variations of paired mean (October, 2010 
and February, 2011) are statistically significant (P 0.05). The 
overall mean concentrations of the trace metals recorded in the 
fish in this study (
f
igure
-
1) showed very
 
high level of iron in 
October. Generally, the results of the mean concentrations of the 
trace metals were higher in February than October. This may be 
due to the effect of bioaccumulation over the periods that the 
fish lived and fed in its water habitat. 
Studies have shown that 
direct absorption and bioaccumulation of toxic heavy metals are 
common in aquatic environment where organisms are exposed 
to the same concentrations of the substances present in the water 
environment
15
.
 
 
The concentrations (�g/l) of
 
the trace metals in the river water 
(Table
-
2) showed that arsenic (As) varied between 0.06�0.02 to 
0.09�0.04(�g/l) in October, 2010 and 0.02�0.01 to 
0.05�0.01(�g/l) in February, 2011. The other results showed 
that Mn ranged from 0.26�0.05 to 0.34�0.08(�g/
l), Cu varied 
between 0.54�0.05 to 0.74�0.02(�g/l), Pb varied between 
0.06�0.01 to 0.31�0.02(�g/l) and Fe ranged from 1.03�0.02 to 
Research Journal of 
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606X
 
Vol. 
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), 
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-
75
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March
 
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International Science Congress Association
 
 
72
 
1.24�0.05(�g/l) in October, 2010. Similar results in February, 
2011 revealed 0.20�0.03 to 0.41�0.04(�g/l) Mn, 0.25�0.06 to 
0.
37�0.08(�g/l) Cu, 0.12�0.03 to 0.16�0.04(�g/l) Pb and 
0.40�0.03 to 0.59�0.10(�g/l) Fe. Cadmium (Cd) was also not 
detected in the water. 
 
 
The overall mean concentrations of the trace metals in the river 
water (
f
igure
-
2) revealed significantly (p 0.05) hi
gher levels 
of iron and copper in October, 2010. This may be attributed to 
the input by surface run
-
off through quarry sites, agricultural 
fields and domestic wastes located along the river. Furthermore, 
the high iron
 
and copper levels of the river may als
o depend on 
hydrological situation. In a study on the distribution pattern of 
trace metal pollutants in the sediments of an urban wetland in 
Southwest coast of India it was observed that trace metals are 
among the most common environmental pollutants and t
heir 
occurrence in waters indicate the presence of natural or 
anthropogenic sources
16
. It has also been reported that heavy 
metals or their compounds may be discharged from industries, 
farmlands, municipal urban water runoffs, and agricultural 
activities i
nto surface water and can cause pollution
17
. Most of 
the iron in river is particle
-
bound which suggests why the total 
iron content of the river water is influenced by the amount of 
suspended solids in the water and by the concentration of iron 
on these par
ticles. Copper is an essential trace element used in 
pesticides formulations. The agricultural fields along the river 
received different types of pesticides during pests control of the 
cropping season. Thus, during the peak of raining season where 
the rive
r water was very high and received maximum effluents 
from drainages through farms and quarry industries; the flood 
events mobilised varying degree of contaminants into the river 
so that concentration peaks may occur. Heavy metals are highly 
persistent and 
can easily enter a food chain and accumulate until 
they reach toxic levels. In February however, the rain fall has 
stopped and the volumes of effluents discharge into the river via 
surface run off have reduced. Consequently, substantial amount 
of the chemi
cal residues initially washed into the river during 
rainfall settled at the bottom sediment of the river and less 
contents are possible in the river water. This may be responsible 
for the general lower levels of most of the trace metals recorded 
in the riv
er water in February.
 
 
The concentrations of the trace metals in 
Oreochromis niloticus
  
are positively correlated with the heavy metals in water (
t
able
-
3). This suggests that the water metals content have significant 
effect on the availability of the trace
 
metals to the fish and 
hence, the bioaccumulation into the tissues. 
 
 
The results of the bio
-
accumulation factors of the trace metals 
(
f
igure
-
3) revealed very high absorption of arsenic in both 
October, 2010 and February, 2011. This may present serious 
he
alth challenge to the consumers of 
Oreochromis niloticus
 
in 
the study area. Fish, shellfish, meat, poultry, dairy products and 
cereals have been reported as the main sources of dietary intake 
of arsenic. However, the arsenic content of fish and shellfish 
u
sually involves organic compounds (e.g. arsenobetaine) that 
are of low toxicity
18
. A report of the World Health Organisation 
indicated that the International Agency for Research on Cancer 
(IARC) classified arsenic and arsenic compounds as 
carcinogenic to h
umans (
g
roup 1), which means that there is 
sufficient evidence for their carcinogenicity in humans
19
. 
Generally, the levels of the trace metals recorded in this study 
were below the WHO‟s Permissible Limits of 0.05mg/L As, 
1.0mg/L Cu, 0.01mg/L Pb, 0.30mg/L
 
Fe and 0.10mg/L Mn for 
water and 0.03mg/g Cu , 0.10mg/g Fe, 0.02mg/g Pb and 
0.01mg/g Mn for fish respectively
20
.
 
 
 
Table
-
1
 
Concentrations (�g/g) of the trace metals in 
Oreochromis niloticus
 
obtained from river Okpokwu in October, 2010 and 
February, 2011
 
Heavy Metals
 
Auke
 
Odejo
 
Ocholonya
 
Oct. 2010
 
Feb. 2011
 
Oct. 2010
 
Feb. 2011
 
Oct. 2010
 
Feb. 2011
 
As
 
0.11
a
�0.03
 
0.16
b
�0.04
 
0.05
a
 
�0.02
 
0.09
a
 
�0.03
 
0.07
a
�0.03
 
0.11
b
�0.02
 
Mn
 
0.17
 
a
 
�0.02
 
0.21
b
�0.06
 
0.13
a
�0.01
 
0.22
b
�0.03
 
0.08
a
�0.04
 
0.19
b
�0.02
 
Cu
 
0.13
a
 
�0.05
 
0.17
b
�0.04
 
0.10
a
�0.03
 
0.14
b
�0.02
 
0.15
a
�0.02
 
0.23
b
�0.03
 
Cd
 
-
 
-
 
-
 
-
 
-
 
-
 
Pb
 
0.05
 
a
�0.02
 
0.07
b
�0.03
 
0.04
a
�0.02
 
0.08
b
�0.01
 
0.03
a
�0.01
 
0.05
b
�0.02
 
Fe
 
0.31
 
a
�0.05
 
0.21
b
�0.08
 
0.38
a
�0.03
 
0.28
b
�0.02
 
0.37
a
�0.06
 
0.27
b
�0.04
 
„„
-
‟‟ = Not detected. T
-
test of paired mea
n (October, 2010 and February, 2011) with different alphabets are statistically significant (P  0.05). Data 
presented are mean � SD of replicate analyses (n=4). SD = standard deviation
 
 
Research Journal of 
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606X
 
Vol. 
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-
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Res. J. Chem. Sci.
 
  
 
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73
 
Table
-
2
 
Concentrations (�g/L) of the trace metals in water obtained f
rom river Okpokwu in October, 2010 and February, 2011
 
 
Auke
 
Odejo
 
Ocholonya
 
Heavy Metals
 
Oct. 2010
 
Feb. 2011
 
Oct. 2010
 
Feb. 2011
 
Oct. 2010
 
Feb. 2011
 
As
 
0.06
a
�0.02
 
0.02
b
�0.01
 
0.07
a
 
�0.03
 
0.05
a
 
�0.01
 
0.09
a
�0.04
 
0.04
b
�0.01
 
Mn
 
0.34
a
 
�0.08
 
0.20
b
�0.03
 
0.31
a
�0
.02
 
0.41
b
�0.04
 
0.26
a
�0.05
 
0.36
b
�0.03
 
Cu
 
0.54
a
 
�0.05
 
0.35
b
�0.02
 
0.59
a
�0.04
 
0.37
b
�0.08
 
0.74
a
�0.02
 
0.25
b
�0.06
 
Cd
 
-
 
-
 
-
 
-
 
-
 
-
 
Pb
 
0.31
a
�0.02
 
0.16
b
�0.04
 
0.08
a
�0.01
 
0.13
b
�0.02
 
0.06
a
�0.01
 
0.12
b
�0.03
 
Fe
 
1.06
a
�0.05
 
0.40
b
�0.03
 
1.03
a
�0.02
 
0.58
b
�0.03
 
1.24
a
�0.05
 
0.5
9
b
�0.10
 
„„
-
‟‟ = Not detected. T
-
test of paired mean (October, 2010 and February, 2011) with different alphabets are statistically significant 
(P 0.05). Data presented are mean � SD of replicate analyses (n=4). SD = standard deviation
 
 
Table
-
3
 
Correlatio
n Coefficient of the Concentrations of the Trace Metals in the River Water and 
Oreochromis niloticus
 
 
As
 
Mn
 
Cu
 
Pb
 
Fe
 
As
 
1.0000
 
 
 
 
 
Mn
 
0.7327
 
1.0000
 
 
 
 
Cu
 
0.4989
 
0.9554
 
1.0000
 
 
 
Pb
 
0.8788
 
0.9687
 
0.8520
 
1.0000
 
 
Fe
 
0.3931
 
0.9138
 
0.9930
 
0.7843
 
1.0000
 
 
 
 
Figure
-
1
 
Overall mean concentrations (ppm) of the trace matals in 
Oreochromis niloticus
 
 
 
 
Figure
-
2
 
Overall mean concentrations (ppm) of the trace matals in the river water
 
Research Journal of 
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606X
 
Vol. 
3
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), 
70
-
75
, 
March
 
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)
 
 
 
 
 
 
 
 
          
 
          
Res. J. Chem. Sci.
 
  
 
International Science Congress Association
 
 
74
 
 
 
Figure
-
3
 
Bio
-
accumulation factors of the trace metals in 
Oreochromis niloticus
,
 
Bio
-
accumulation factor =  Metal concentration in 
fish
/
Metal concentration in river water
 
 
Conclusion
 
The results of this study revealed variable concentrations of As, 
Mn, Pb, Cu and Fe in 
Oreochromis niloticus
 
(Tilapia) and water 
obtained from river Ok
pokwu in October, 2010 and February, 
2011. The water recorded elevated levels of the trace metals in 
October which may due to the high surface runoff of effluents 
from agricultural lands, quarry industries and domestic waste 
into the river. The fish conten
ts of the trace metals were higher 
in February, probably due to the effect of bioaccumulation over 
the periods of its habitation and feeding in the water 
environment. However, the levels of the trace metals recorded 
in this study were below the WHO‟s Permi
ssible Limits. 
Accordingly, the water and 
Oreochromis niloticus
 
from the 
study area have not become contaminated by the trace metals 
studied. Therefore, periodic review should be sustained to 
monitor possible accumulations of the trace metals in future due
 
to the proliferation of anthropogenic activities around river 
Okpokwu.
 
 
Acknowledgement
 
The authors are thankful to the management of Sheda Science 
and Technology Complex (SHESTCO), Abuja for providing the 
required laboratory facilities and skills for the
 
analyses.
 
 
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es 
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