ASSESSMENTS OF HEAVY METALS IN SEDIMENT FROM RIVER TRANSECTS IN THE WOURI ESTUARY

Sediment and water pollution in coastal regions is of growing global concern. Given that about 40% of the world population live within 100 km of coasts, natural contamination and pollution from anthropogenic sources can add significant stress on coastal waters, soil, and marine life. The Wouri estuary hosts a thriving urban center, seaport and industrial community in the Atlantic Coast of West Africa. It is surrounded by mangrove forests and drains three main rivers over different geologic terrains – igneous, sedimentary, and metamorphic. The rivers converge in the estuary, and flow through the Gulf of Guinea into the Atlantic Ocean. River-bed sediments and estuarine water samples were collected from locations along transects on the three estuarine rivers. Samples were measured for major ions and elemental concentrations of metals. Sediment samples were analyzed using X-ray fluorescence and water samples were analyzed by ion chromatography.

Elemental concentrations of metals from sediments were divided by background values of the Upper-Continental Crust, based on previous studies to determine their enrichment factor (EF). The calculated EF were used to assess the relative enrichment levels of the metals. Mean EFs of Mn, Ni, Pb, Hg, Zn, Cu, Ni, Co, Mn, Cr, Cd, Pd and Nb ranged from 0 to 1.70. The values suggest these metal contents vary from deficient to minor enrichments in the sediments. The EFs of Fe and Mo ranged from 0.52 to 5.20, with a mean of 2.70, and 1.50 to 13.62 with a mean of 4.70, respectively, indicating moderate enrichment. Relative enrichment in the amounts of both Fe and Mo suggest possible contributions from anthropogenic sources. The EFs of As ranged from 2.32 to 9.33 with a mean of 6.65 suggesting significant enrichment above background levels. The significant enrichment in As amounts is likely due to both anthropogenic pollution and contamination from weathering.