International Journal of Marine Science 2015, Vol.5, No.58: 1-6
2
complex compound contamination (Chaerun et al.,
2004).
Hence, the present study evaluates the trace metal
concentrations of Qua Iboe estuary and to assess its
suitability for fish production and as well as its safety
as source of drinking water.
2 Materials and Methods
2.1 Study Area
Qua Iboe estuary, situated close to the Exxon-Mobil
oil effluent treatment and discharge plant, receives
water from Qua Iboe River (confluence of rivers from
different sources) flowing into the Gulf of Guinea
(Atlantic Ocean). The substratum consists mainly of
fine sand and mud, with decaying macrophytes and
debris. The estuary receives municipal wastes, urban
runoff, industrial discharges as well as other solid
wastes (garbage, metal scraps, etc.).The structure and
hydrology of the estuary is described by Uwah et al.
(2013) and Oze et al.
(2006).
Three sampling stations were established through
Global Positioning System (GPS) (Figure 1). Station 1
situated on longitude 7°58.555ʹ in the East, and
latitude 4°34.085ʹ in the North, has a water depth of
0.43-0.68m and sediment type of fine sand mixed with
mud. It is located within Ukpenekang an area
considered to be heavily perturbed by human activity.
Station 2 (7
0
59.1874 ʹ E; 4
0
33.7639 ʹ N) is located at
the mouth of Stubbs Creek about 1,300 km from
station 1. The water depth ranged from 0.28-0.41 m
and the sediment is characterized mainly of mud.
The area is minimally impaired by human activity.
Station 3 (7
0
59.0832 ʹ E; 4
0
033.7639 ʹ N) is located
at Qua Iboe jetty about 1,100 km from station 2 where
human activity is also minimal but the station is
closest to Exxon-Mobile crude oil effluent processing
and treatment facility. The water depth ranged from
0.35-0.59 m and the river bed is covered with mud
and occasionally with silt.
2.2 Sample collection
Sample collections were carried out between January
and June 2013 from three stations (Figure 1) during
the dry (January-March) and wet (April-June) seasons.
One hundred and eight (108) surface water and
sediment samples were obtained separately in
triplicates from each location for six months.
Surface water samples for trace metal analysis were
collected at a depth of 15cm in opposite direction to
the flow of the river with well labeled plastic bottles.
All samples were acidified with 4 mL concentrated
HNO
3
in order to stabilize the metal ions and prevent
precipitation. Sediment samples were obtained with
the aid of an improvise bottom grab device. The
content of the grab were emptied into well-labeled
black polyethene and sealed. The samples were
immediately transported to the laboratory in an ice
box and stored at 4°C in the refrigerator prior to
chemical analysis. The chemical analysis was
analyzed at the Akwa Ibom State Water Corporation
Central Laboratory, Uyo using standard methods
(AWWA, 1980).
2.3 Determination of Trace Metal
Nitric-perchloric acid digestion was performed,
following the method recommended by AOAC (1990).
Ten milliliter
of concentrated HNO
3
and 5mL of
concentrated HClO
4
were added to One gram of dried
ground sediment samples in 100mL beaker. The mixture
was placed on a hot plate in a fume cupboard and
heated to near dryness. Heated mixture was allowed to
cool before leaching the residue with 5mL of 20%
HNO
3
.The mixture was filtered using Whatman 42
filter paper and the volume of the filtrate made up to
50 mL with distilled water and analyzed for metals
using Atomic Absorption Spectrophotometer (HACH
DR/2010 model).
Hundred milliliter of the water sample was placed in
125ml conical flask and digested with concentrated
HNO
3
until a clear solution was obtained. The
solution was then filtered using a 0.45µm membrane
filter. The filtrate was made up to a 50 mL with
distilled water in volumetric flask and analyzed for
metals using Atomic Absorption Spectrophotometer
(HACH DR/2010 model).
The instrument was calibrated according to manufacturer
specifications and the corresponding wavelength for
each metal was selected. The instrument was
standardized using a standard blank cuvette, making it
ready for measurement. The standard cuvette was
removed and another cuvette filled with 25ml of the
filtrate was inserted into the instrument. It was then
delayed for about 30 seconds before pressing ‘read
direct’ and results were obtained on the display screen
(AWWA, 1980). The methods were confirmed using
