Transport of heavy metal pollution from the Wadi El Bey basin toward the Tunisian Gulf

Wadi El Bey, which drains 60% of the pollutant load of several urban centres in the northeast of Tunisia, provides a good example of the transfer of heavy metals that result from industrial and urban activity, and can be used to show how these metals are transported and discharged into the Gulf of Tunis. In the dissolved fraction, Cd, Pb, Co and Hg were not detected, while the Zn content varied between 0.0129 and 0.0658 mu g/L. The heavy metal (Mn, Zn, As, Ni, Pb, Cu and Cd) concentrations were higher in suspended particulate matter compared to the dissolved fraction, with a partition coefficient Kd of about 106. The highest metal pollution of Wadi El Bey was found for Zn, Pb and Cu: the concentrations varied between 1698.9 and 14575, 0 and 2153.7, and 0 and 3431.8 mu g/g, respectively. The variation in the spatial distribution of heavy metal concentrations confirms the wastewater (domestic and industrial) impact on the water quality of Wadi El Bey. By comparing the heavy metal concentrations in the three phases-dissolved solids, suspended matter and sediments-we concluded that the metal pollution was transported via the Soliman salt flat to the Gulf of Tunis principally by the particulate fraction. Comparison of the concentration of various elements (Pb, Cu and Cd) in the sediments of the river with that of Zn shows an increase at the confluence of the Oued el Bey and its tributary the Oued El Meleh, which suggests that this tributary sediment supply controls the chemical signature of sediments in the Wadi El Bey.