Distribution and chemical fractionation of some heavy metals in bottom sediments of Lake Nasser

Distribution and phase association of Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn and organic matter in Nile sediments taken from Lake Nasser (Aswan, Egypt) were investigated. The sediment samples were subjected to selective chemical extraction procedures designed to fractionate the particulate heavy metals into six fractions: (A) ammonium acetate-extractable metals; (B) sodium acetate-extractable metals; (C) acid oxalate-extractable metals; (D) hydroxylamine HCl-extractable metals; (E) aqua regia-extractable metals and (F) total metals (HF/HCl/HNO3 destruction). Exchangeable metals which can be extracted by ammonium acetate solution are generally considered readily bioavailable as they are weakly bound and may equilibrate easily with the aqueous phases. In the present study very small concentrations of all heavy metals considered were found in this phase. Between this phase and the metal phases which are not bioavailable (those exist in highly resistant phases) there exist several geochemical phases (fractions B, C & D) that may potentially release their associated metals under changing environmental conditions, such as pH and redox potential in the water-sediment interface. © 1998 Kluwer Academic Publishers.