International Journal of Oceans and Oceanography ISSN 0973-2667 Volume 1, Number 2 (2006), pp. 303-317 © Research India Publications http://www.ripublication.com Chemical fractionation of Mn, Zn, Cu and Pb in the Sediments of Gulf of Aden, Yemen Samir M. Nasr¹, Mohamed A. Okbah*², Shaif M. Kasem³ ¹Department of Environmental Studies, Institute of Graduate Studies and Research, University of Alexandria, Alexandria, Egypt *2 Corresponding author: National Institute of Oceanography and Fisheries, Kayet Bay, Alexandria, Egypt ³University of Aden, Faculty of Education, Chemistry Department, PO Box 6014, Khormaksar, Aden, Yemen Abstract Sequential extraction technique was applied to estimate the chemical association of Mn, Zn, Cu and Pb in five chemical phases (exchangeable, carbonate, Fe-Mn oxides, organic matter and residual) in the sediments of Gulf of Aden, Yemen. The results indicated that high level of Mn was associated with the residual fraction (natural sources) than in the non-residual fraction (anthropogenic sources). Zn fractionations revealed that it was associated with Fe-Mn oxides and organic fractions than exchangeable and carbonate fractions. Most of the Cu was present in the residual form (60–72%) except the main port area (zone III) where it was associated with organic phase (77% of the total Cu content). Similarly most of Pb was bound in the residual fraction (56-71%) except the main port area where about 62% of the total Pb was bound in non-residual fractions. It was also found that Pb concentration in the exchangeable fraction was very high comparing with other metals. The risk assessment code of the metals showed low risk for Zn and Cu, while it was low to medium risk for Mn. The fractionation of Pb showed medium risk at most of the regions except at the eastern area which revealed high risk for aquatic environment. Keywords: Sequential extraction; Heavy metals, Risk assessment, Gulf of Aden.