Vecteur de la pollution metallique du bassin versant de l’Oued El Bey vers le Golfe de Tunis (Tunisie)

Abstract

Résumé L'Oued El Bey, qui draine 60% de la charge polluante hydrique de plusieurs agglomérations urbaines du Nord-Est de la Tunisie, est un exemple représentatif du transfert des métaux lourds résultant de l'activité industrielle et urbaine. Il fournit une indication sur le devenir et la répartition des métaux lourds dans le Golfe de Tunis. Dans la fraction dissoute, Cd, Pb, Co et Hg ne sont pas détectés mais Zn varie entre 0,01 et 0,07 µg/L. Les concentrations du Mn, Zn, As, Ni, Pb, Cu et du Cd sont très élevées dans la fraction particulaire par rapport à la fraction dissoute, avec un coefficient de partage Kd de l'ordre de 10 6 , ainsi que dans les sédiments du lit de l'oued pour Pb et Zn. La pollution par les métaux la plus élevé de l'Oued El Bey a été trouvée pour Zn, Pb et Cu: les concentrations variaient respectivement entre 1698,9 et 14575, de 0 à 2153,7 et de 0 à 3431,8 µg/g. La variation spatiale des teneurs en métaux lourds confirme l'effet des eaux usées rejetées dans l'Oued El Bey. Les teneurs de ces métaux lourds dans les trois phases dissoute, particulaire (MES) et sédiments confirment que la MES constitue le vecteur de transport principal via la Sebkha Soliman vers le golfe. L'examen des rapports des différents éléments (Pb, Cu et Cd) par rapport au Zn dans les sédiments de l'oued montre une augmentation au niveau de la confluence de l'Oued El Bey et de son affluent l'Oued El Meleh, ce qui signifie que les apports sédimentaires de cet affluent contrôlent la signatutue chimique des sédiments de l'Oued El Bey.Mots clefs Oued El Bey; métaux lourds; fraction dissoute; matière en suspension; sédiment; rejets des eaux usées Transport of heavy metal pollution from the Wadi El Bey basin toward the Tunisian GulfAbstract 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 µg/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 10 6 . 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 µg/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 riv...

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