theFig. 2. Concentrations of the following important metal wastes Al (light grey column), Cd (black grey), Hg (white), Ni (medium grey), and Pb (black) found at the samplingsites presented in Fig. 1. Succession of the sampling sites from left to right represents increasing distance from the source of pollution. Al concentrations are expressed inpercentages of elements that occur in clay sediment with high percentage indicating higher property of the sediment to adsorb contaminants. Metal concentrations in mgper 1 kg of sediment (dry weight). Data have been log-transformed to even out the weight of very high versus low values and allow all values to fit in a single graph (datacompiled from Sauzade et al., 2007).