Speciation of Some Heavy Metals in Sediments of the Pennington River, Bayelsa State, Nigeria

Speciation helps in the identifications and quantification of the defined geochemical fractions, forms or
phases in which an element exists in the environment. Speciation in sediment compartment is a
significant step to understand the potential environmental risk, distribution, mobility and bioavailability
of pollutants. The total heavy metal concentrations of some environmentally toxic metals in sediments
of the Pennington River System, Bayelsa state, Nigeria was examined. The concentrations of heavy
metals in each fraction were determined using a ANALYST 400 Perkin-Elmer AAS. The mean
concentrations (mg/kg) for the six metals in dry season sediment samples were: 0.14±0.17(As),
0.39±0.55(Co), 2.43±5.06(Cu), 26.82±22.19(Fe), 0.69±1.10(Pb), and 1.22±1.19(Zn), while the mean
metal concentrations (mg/kg) in wet season samples were:0.11±0.18(As),0.37±0.6(Co),
2.07±4.35(Cu), 26.65±24.79(Fe), 0.61±1.08(Pb), and 1.11±1.00(Zn) respectively. Speciation study
applying the five-stage sequential extraction scheme revealed that As, Co, and Pb in sediment
prevails mostly in exchangeable fraction. Cu and Zn were more prevalent in residual fraction, while Fe
was found more in residual and Fe/Mn-Oxide fractions. In an attempt to infer anthropogenic input from
natural input, comparison with sediment quality guideline (SQGs) and ecotoxicological sense of heavy
metal contamination was employed. The concentration of the studied heavy metals in Pennington
River System does not pose a threat to the sediment dwelling fauna and anyone who consumes
aquatic animals, particularly fish, from the Pennington River. According to SQGs, the studied heavy
metals of the Pennington River sediments were under the category of non-polluted. Speciation is a
powerful and versatile technique for predicting the degree of contamination risk of a river system. In
this present study, all heavy metals investigated are relatively stable under normal conditions of
Pennington River system. This means that there is a low source of pollution arriving to the Pennington
River system. Iron was found to be the highest occurring heavy metal and arsenic was the least
occurring heavy metal in this study. Furthermore, there is no heavy metal pollution threat pose to
sediments dwelling fauna and anyone who consume aquatic animals, particularly fish from the
Pennington River system. To preserve the unpolluted state of the Pennington River system it remains
important that allochthonous inputs are devoid of heavy metals.