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International Journal of Aquaculture, 2014, Vol.4, No.06
http://ija.sophiapublisher.com
40
Table 2 Concentration heavy metals (p.p.m.) in water from four sampling stations along the sewage-treatment canal.
Heavy metals
Sampling points
Zn
Cu
Ni
Cd
Cr
Pb
Sr
Fe
Station 1
0.001
0.001
0.003
0.032
0.033
0.154
7.86
11.54
Station 2
0.001
0.001
0.015
0.033
0.032
0.106
6.32
10.6
Station 3
0.001
0.001
0.01
0.033
0.037
0.198
7.36
11.41
Station 4
0.001
0.001
0.034
0.027
0.03
0.183
6.96
11.58
(0.02 to 0.04 mg/kg) of lead in muscle tissues of some
species of freshwater fish from Cross River in Nigeria
and Oladimeji and Offen (1989) noticed in
O. niloticus
,
that the gills consistently accumulated higher amount
of lead as lead nitrate. Lead is highly toxic to aquatic
organisms, especially fish (Rompala et al., 1984). The
biological effects of sublethal concentrations of lead
include delayed embryonic development, suppressed
reproduction, and inhibition of growth, increased
mucous formation, neurological problems, enzyme
inhalation and kidney dysfunction (Leland and
Kuwabara, 1985). The level of lead in muscle and
gills of
O. niloticus
was below the (0.5μg/g) limits.
The accumulation of both cadmium and chromium
was higher in muscles compared to fish gills. Dural et
al. (2007) reported highest levels of cadmium, lead,
copper, zinc and iron in the liver and gills of fish
species viz.
Sparus aurata
,
Dicentrachus labrax
,
Mugil cephalus
and
Scomberomorus cavalla
. Yilmaz
et al. (2007) reported maximum accumulations of
cadmium, cobalt and copper in the liver and gills of
Leuciscus cephalus
and
Lepornis gibbosus
, while
these accumulations were least in the fish muscle.
However, as could be deduced from the present study,
the muscles accumulate more of these metals. Both Cd
and Cr are toxic elements which have no known
biological function and show their carcinogenic effect
on aquatic biota and humans. Cadmium is widely
distributed at low levels in the environment and is not
an essential element for humans, animals and plants.
The European and National Drinking Water Quality
Standards maximum residue limit (MRL) permitted in
fish is 0.3 µg/g for Pb and 0.1 µg/g for Cd (WHO,
1996).
High level of Cu was also detected in both muscle and
fish gills. For the gills samples, it may be due to the
fact that freshwater fish’s gills might be expected to be
the primary route for the uptake of water borne
pollutants. WHO (1989) reported that copper toxicity
in fish is taken up directly from the water via gills and
stored in the liver, the present study showed
accumulation of copper in the gills and muscles.
However, toxic heavy metals are available to aquatic
environment from various sources of industrial
effluents. Fish may uptake heavy metals from water,
food or sediment and therefore can easily enter or
transported to the food chains (Kalfakakon and
Akrida-Demertzi, 2000). The efficiency of metal
uptake from contaminated water may differ in relation
to ecological needs, metabolisms, and the
contamination gradient of water, food and sediment as
well as other environmental factors such as salinity,
temperature and interacting agent (Al-Weher, 2008;
Rauf et al., 2009). When fish are exposed to elevated
metal levels in an aquatic environment, they can
absorb the available metals directly from the
environment via the gills and skin or through the
ingestion of contaminated water and food, thus
accumulates them in their tissues and enter the food
chains and extent to many other problems to humans
(Ahmad and Othman, 2010).
Although, the concentrations of heavy metals Zn, Cu,
Pb, Ni, Cr and Cd determined were very low and
below the detection limit, the continuous discharge
from the sewage treatment plant into the White Nile
might be the contributor of heavy metal accumulation
and other possible pollutants in the fish samples. The
high load of heavy metals is due to the presence of
major sources of metal pollution, intensive human
activity and discharge of municipal waste and
industrial effluents. In conclusion, the levels of Fe, Sr,
Zn, Cu, Pb, Cr and Cd observed would have harmful
effect on the health of the community in the study area.
Heavy meals are one of the more serious pollutants in
our natural environment due to their toxicity,
persistence and bioaccumulation problems, thus fish
species will not be safe for human consumption.