Metal Speciation (Cd, Cu, Pb and Zn) in Sediments from Al Shabab Lagoon, Jeddah, Saudi Arabia

four-step sequential extraction technique was used to determine the chemical association of heavy metals (Cd, Cu, Pb, Zn) with major sedimentary phases (exchangeable and carbonates, manganese and iron oxides, sulphides and organic matter and residual minerals) in samples from Al Shabab Lagoon, Jeddah, S.A. The total metal content was also determined. The results of the present study indicate that the bottom sediments of the lagoon contain high concentrations of heavy metals such as Cd, Cu, Pb and Zn. The partitioning characteristics of the lagoon sediments also show that the percentages of metals associated with the non-residual fractions are notably greater than the residual fraction, for all studied metals, indicating the polluted nature of the sediments. The Risk Assessment Code reveals that about 30-45% of Cd at most of the sites exist in exchangeable and carbonate bound fraction and therefore comes under the high risk category and can easily enter the food chain. A sizable portion of Pb and Zn (4.6-15.4 and 2.5-14.5% of Pb and Zn, respectively) is found in exchangeable and carbonate bound fraction thus posing low to medium risk for the aquatic environment. Fractionation pattern of Cu shows no to low risk to aquatic environment.