Speciation and Mobility of Some Heavy Metals in the Coastal Sediments of Jeddah, Eastern Red Sea PDF

Keywords

Sediments, Heavy metals, Spectation Mobility, Red Sea, Jeddah

Abstract

Total and potentially mobile fractions of Fe, Mn, Cu, Zn and Pb were analyzed in 28 sediment samples collected from the coastal area of Jeddah. Sampling sites were selected to represent heavily sewage polluted areas and areas far from the effect of direct sewage dumping. Total concentrations reflected the degree of contamination and were particularly high in the confined environments. Concentrations in the mud fraction (<63 nano m) were 3 to 6 times higher than that in the sand fraction. The repartition of the elements between the exchangeable, reducible, oxidizable and residual fractions depends on the element nature and prevailing environmental conditions. Iron was mainly found in the residual fraction either as constituent of the detrital material and/or trapped in the form of insoluble sulphides. Dominance of the exchangeable fraction characterized the speciation of Mn. Mobilization of Mn under reducing conditions and its reabsorption on the particle surface is a probable explanation. Cu and Zn appear to have comparable distribution between the different fractions, however, Cu seems preferentially associated with the oxidizable fractions while reducible Zn was slightly more important than the other forms. Pb was particularly distributed between the oxidizable and the exchangeable fraction. Residual Pb participation was very low and sometimes totally absent. The interest behind the use of speciation schemes is that it permits the distinction between the fraction of the element that could be released into the water when the physico-chemical conditions are modified and the part that is permanently or quasi permanently fixed in the sediments. Most of the Fe was found held in the residual unavailable form while most of Mn, Cu, Zn and Pb were distributed between the environmentally unstable exchangeable, oxidizable and reducible fractions. Therefore, these elements are supposed to have greater mobility and may, under particular conditions, greatly influence the environmental characteristics