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International Journal of Aquaculture, 2014, Vol.4, No.06
http://ija.sophiapublisher.com
37
pollution and risk potential of human consumption
(Authman, 2008; Ekeanyanwu et al., 2011).
Several studies have indicated enhanced levels of both
non-essential and essential heavy metal load in muscle
and liver tissues of fishes (Ogbeibu and Ezeunara,
2002; Ekpo et al., 2008) The concentration of heavy
metal were found to be higher in the liver, kidneys and
gills than in the gonad and muscle tissues some fish
species (Mohamed, 2005; Sabo et al., 2008) and the
concentrations in the tissue of freshwater fish vary
considerably among different studies.
With the increased urbanization and industrialization
in Khartoum, there has been a rapid increase in the
municipal waste water (sewage water and industrial
effluents), which in turn has intensified the
environmental pollution. Huge amount of heavy
metals is released in the Nile waters from the sewage
treatment plant and industrial wastewater, where there
may have been metal deposits. Effluents discharged
into Nile may affect aquatic organism and fish, either
directly or indirectly.
Tilapia nilotica (O. niloticus)
is
one of the aquatic organisms affected by heavy metals,
so in many cases was used as metal biological marker
in toxicological studies (Mohamed et al., 1990; Prusty,
1994; Rashed, 2001b). This fish is exposed to
continuous wastewater and industrial effluents
discharged into the White Nile. Therefore, the present
work aimed to detect the pollutants levels of the heavy
metals: Cadmium (Cd), Chromium (Cr), Nickel (Ni),
Lead (Pb), Copper (Cu), Zinc (Zn), Iron (Fe) and
Strontium (Sr) and their accumulation in the muscle
tissues and gills of the commercially important Nile
fish (
Oreochromis niloticus
) as well as in sewage-
treated water from where fish was collected for the
study.
2 Materials and Methods
2.1 Study area
The sewage rehabilitation project consists of three
major ponds, located south of Khartoum state between
lat. 15°35′ long., 32°33′ alt. (Figure 1). The
dimensions of the primary pond were 100×170×3m;
the secondary pond 239.1×785×1.2m and the tertiary
pond 239.1×220×1.2m. The waste water from the
tertiary pond is released in one common canal of 3m
width. On its way this canal received the waste water
from the military factories and flow straight to release
its contents in the White Nile at Al-Ozozab city in
Khartoum west.
2.2 Fish and water samples collection
Fish samples of the Nile Tilapia (
Oreochromis
niloticus
, Linnaeus, 1758; Trewavas, 1983) of about
the same size (length ±5”) were collected at two
points (Figure 1): from the effluent discharge canals of
the sewage treatment plant (St 1) and from the effluent
discharge point of the sewage-treated water into the
White Nile (St 5). Fish specimens were immediately
preserved on ice prior to heavy metal analysis.
Water samples were collected from a depth 15 cm
from four stations (Figure 1) in the sewage treatment
canals (one sample from each) using automated water
sampler (21 cc capacity) and stored in amber-coloured
polyethylene bottles (1 L) pre-washed with 1 (N)
HNO
3
and deionised water. To prevent further
oxidation or any fungal growth 5mL concentrated
HNO
3
was added to the sampled water.
2.3 Samples treatment and analysis
Fish muscle tissues and gills were taken from each
specimen after removing the scales and skin, and each
was cut into small pieces, ground well thoroughly to
achieve homogeneity and used to prepare the ash
solution for ICP-OES analysis. About 4g of the each
sample were kept in muffle furnace on a hot plate at
550
℃
for 3 hours to obtain the ash. Ash was
dissolved in 10 ml of 20% HCl then filtered in a
100ml volumetric flask and the volume was
completed with distilled water to 50ml. Each ash
solution was analyzed for heavy metals: Cadmium
(Cd), Chromium (Cr), Nickel (Ni), Lead (Pb), Copper
(Cu), Zinc (Zn), Iron (Fe) and strontium (Sr) using
ICP-OES. Water samples were not subjected to any
further treatment and were also analyzed for the same
heavy metals using ICP-OES. The concentration of
each metal was detected in a triplicate ash samples of
fish muscles and gills as well as water samples, and
recorded in ppm (μg/g, μg/L) according to APHA
(1998).