DISTRIBUTION AND PARTITIONING OF TRACE METALS IN
SEDIMENTS OF THE LOWER REACHES OF THE NEW CALABAR
RIVER, PORT HARCOURT, NIGERIA
M. HORSFALL JR. and A. I. SPIFF
Department of Pure and Industrial Chemistry, University of Port Harcourt, Uniport, P.O. Box 402,
Choba, Port Harcourt, Nigeria
(Received 12 March 2001; accepted 5 October 2001)
Abstract. The distribution of trace metals in sediments of the lower reaches of the New Calabar
River, Nigeria was evaluated together with the partitioning of their chemical species between five
geochemical phases. Samplings were made in five zones at the lower reaches of the New Calaber
River. All the trace metals were determined by AAS after selective chemical extractions and con-
centrations given in µggm
−1
(dry weight basis). The average total concentrations found for trace
metals in the sediment were (mean ± rsd.) Pb: 41.6 ± 0.29, Zn: 31.60 ± 0.42, Cd: 12.80 ± 0.92, Co:
92 ± 0.25, Cu: 25.5 ± 0.65 and Ni: 3.2 ± 0.25. Maxima and minima concentrations are inconsistent
with previous studies in other rivers of this region. Spatial distribution revealed that the sources of
trace metals into the river appeared to be of non-point. Five contamination indices were applied
in studying the partitioning of the trace metals in the sediment. These indices provided bases for
ascertaining the potential environmental risk of trace metals in the river system. The results denote
high partition levels in the more mobile and more dangerous phases.
Keywords: New Calabar River, partition, pollution, sediment, trace metals
1. Introduction
Due to their particle reactivity trace metals tend to accumulate in sediment (Forst-
ner and Wittman, 1981) and as a result may persist in the environment long after
their primary sources has been removed. The sediments existing at the bottom
of the water column play a major role in the pollution scheme of a river system
by heavy metals (Forstner, 1985). They reflect the current quality of the water
system and can be used in detecting the presence of contaminants that do not
remain soluble after discharge into surface water. The analyses of trace metals in
sediment permit pollutant detection that could escape water analysis and provides
information about the critical sites of the system under consideration. The major
mechanism for accumulation of trace metals in sediments as summarized by Gibs
(1973), leads to the existence of five geochemical phases. These are (1) bound to
adsorptive and exchangeable phases (2) bound to carbonate phases (3) bound to
oxides, (4) bound to organic matter and sulphides, and (5) bound to detrital or
lattice metals. These phases have different behaviours with respect to remobiliza-
tion under changing environmental conditions (Pardo et al., 1990). Because of the
Environmental Monitoring and Assessment 78: 309–326, 2002.
© 2002 Kluwer Academic Publishers. Printed in the Netherlands.