Biological Evidence 2018, Vol.8, No.3, 21-31
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zinc etc are essential because they are required by living organisms at certain concentration. While several others
including cadmium, lead, arsenic and mercury is highly toxic even at low concentration (Izah et al., 2016; Izah
and Angaye, 2016a).
In the Niger Delta region of Nigeria several inland water systems are available (Ogamba et al., 2017a). Several
anthropogenic activities such as transportation, dredging, recreation (swimming), washing, fishing etc are often
carried out in the water ways (Ogamba et al., 2017a). The effect of these activities could reflect in the sediment of
the water as well. Typically, sediment quality has a relationship with water quality (Seiyaboh et al., 2016a;
Kigigha et al., 2018). Since surface water is a habitat to several aquatic organisms, an alteration in water and
sediment quality could influence the fish composition, distribution, abundance etc in such water system (Ogamba
et al., 2017a).
Environmental risk assessment posed by heavy metals is used to show the extent of pollution due an activity (Izah
et al., 2017b). Several indices are available for assessing the level of heavy metal contaminant in an environment
(viz: soil, sediment and water). Some of these indices include index of geo-accumulation (Muller, 1969; Ghaleno
et al., 2015; Bhutiani et al., 2017; Izah et al., 2017c), contamination factor, degree of contamination (Hakanson,
1980; Singovszka et al., 2014; Bhutiani et al., 2017; Izah et al., 2017b), pollution load index (Tomlison et al.,
1980; Bhutiani et al., 2017; Izah et al., 2017d), quantification of contamination (Bhutiani et al., 2017), ecological
risk index (Hakanson, 1980; Bhutiani et al., 2017; Izah et al., 2018).
In Bayelsa state, several studies have been carried with regard to surface water quality (Agedah et al., 2015;
Ogamba et al., 2015a-c; Seiyaboh et al., 2017a,b; Aghoghovwia et al., 2018) and sediments (Inengite et al., 2010;
Seiyaboh et al., 2016a; b; 2017c; Ogamba et al., 2017b; Kigigha et al., 2018). But information of the potential
ecological risk of heavy metals in sediment of lower Nun River is scanty in literature. Hence, this study aimed at
assessing the environmental risk assessment of heavy metals in sediment of Nun River at Tombia and Gbarantoru
in Yenagoa local government Area of Bayelsa state, Nigeria.
1 Materials and Methods
1.1 Study area
The study area (Tombia town and Gbarantoru) is in Yenagoa local Government area of Bayelsa state. The area is
within the sedimentary basin (Kigigha et al., 2018; Aghoghovwia et al., 2018). Oil and gas facilities, dredging
(using motorized and artisan methods), fishing, swimming, boating are some of the common activities being
carried out along the lower Nun River in Bayelsa state (Aghoghovwia et al., 2018). The Nun River is also a major
recipient of wastes streams resulting from human activities especially at household level (Aghoghovwia et al.,
2018). Probably due to the topography of the area, Nun River receives runoff resulting from rainfall. Fish farming
is a major occupation of indigenous people of the area. The climatic condition of the area is similar to other
regions of Bayelsa state that have been previously reported by authors (Agedah et al., 2015; Izah et al., 2015;
Ogamba et al., 2015a; b; c; Seiyaboh et al., 2016a; b; Seiyaboh and Izah, 2017a).
1.2 Sampling techniques
Triplicate samples of the sediment were collected from three different locations (A-around oil and gas installations,
B-Gbarantoru and C-Tombia town for three consecutive months i.e.
December 2017 to February 2018
). The
sediment samples were obtained from respective sampling sites with the aid of Eckman grab and packaged with
aluminum foil plates. The samples were properly labeled, and transported to the laboratory in an ice pack less than
an hour after sample collection where they were processed and analyzed.
1.3 Sample preparations
Acid digestion was employed for the preparation of the sediment samples. The sediment samples were air dried
for 24 hours and then transferred into an oven set at 70ºC for 6 hours. Then 5.0 g of the sediment samples was
weighed into a 100 ml beaker, and 10 ml of concentrated nitric acid was added to the samples. The mixture was
heat continuously with stirring until a clear solution formed. The mixture was then discontinued and allowed to
