• Trace Element Distribution and Enrichment in the Stream Sediments of the Lake Togo Watersheds (South of Togo)

    A. Avumadi1, 2, K. Gnandi2, J.L. Probst1

    1. Laboratoire d’Ecologie Fonctionnelle et Environnement (EcoLab); Université de Toulouse; CNRS; UPS; INPT; Avenue de l’Agrobiopole, 31326 Castanet-Tolosan cedex, France.
    2. Laboratoire des Sciences de la Terre, Faculté des sciences, Université de Lomé, B.P 1515, Lomé, Togo.

    Abstract: To evaluate the level of sediment contamination in watershed of lake Togo (south of Togo), the concentrations of twelve trace elements, TE (As, Sn, Cr, Co, Ni, Cu, Zn, Zr, Cd, Pb, Th, U) are analyzed using inductively coupled plasma-mass spectrometry (ICP-MS) in eighteen stream sediment samples from Zio and Haho rivers draining into the lake Togo and from lake Togo itself. The results obtained allow to characterize each sediment sample by its TE geochemical distribution pattern.  Average TE concentration in the finest fractions (< 63 µm) is ranked from the hightest to the lowest content: Cr>Ni>Zn>Cu>Co>Pb> Th> Sn>U>As>Cd. The degree of contamination of these stream sediments is evaluated by calculating sediment quality parameters such as enrichment factors (EF), anthropogenic and naturel contribution. Globally, 70% of TE have an EF lower than 1.5, particularly for As, Sn, Co, Cu, Zn, Pb, Th and U. However, 30% of the samples are more contaminated (1.5<EF<6), particularly for Ni, Cr, Cd from one sampling point to another. Nevertheless, the anthropogenic contribution could represent only 18% of the total content, 82% originating from natural rock weathering processes. A single chemical extraction by EDTA allows to assess the non-residual (labile) fractions for Zio and Haho river sediments. For Co, Cu, Cd and Pb, the EDTA extracted fractions represent respectively 38%, 32%, 25% and 24% of the total concentration. The EF values are subjected to multivariate statistical analysis in order to evaluate the origins of TE in the study area. Most of TE are controlled by clay, oxi-hydroxide minerals and organic matter.

    Keywords: Trace metals, stream sediments, enrichment factor, labile fraction, natural and anthropogenic contributions.

    Pages: 87 – 114 | Full PDF Paper