Trace metal speciation in marine sediments from Sulaibikhat Bay, Kuwait

Abstract

The chemical speciation of trace metals (Cd, Co, Cr, Cu, Ni, Pb and Zn) in marine sediments from Sulaibikhat Bay, Kuwait was determined using a three-step sequential extraction procedure. To obtain a mass balance, a fourth step, i.e. digestion and analysis of the residue was undertaken using a microwave-assisted acid digestion procedure. The sum of the 4 steps (acid-soluble + reducible + oxidizable + residual) was in good agreement with the total content (71–116%), suggesting that the microwave extraction procedure is efficient. The results showed that all metals except for Pb and Zn were present at higher percentages in the residual fraction. The reducible fraction was the next followed by the oxidizable fraction. The exchangeable fraction was least important as a host for most metals. The mobility order of exchangeable fraction of the elements in surface sediments decreased in the order Cd > Zn > Cu > Co > Pb > Ni > Cr; the reducible fraction in the order Pb > Zn > Cu > Cd > Co > Ni > Cr; the oxidizable fraction in the order Pb > Cu > Cd > Ni > Co > Zn > Cr, and the residual fraction in the order Cr > Ni > Co > Cu > Cd > Zn > Pb. The data showed that the speciation of trace elements in sediments close to a sewage outfall was different from that of sediment from other parts of Sulaibikhat Bay. This suggests that the contribution of the sewage outfall to metal pollution in adjacent marine area is positive and is associated with fine-grained sediments with high level of organic content, which are major controlling factors for the distribution of trace metals in this part of the Bay.

Keywords:

• European Community Bureau of Reference sequential extraction
• sewage waste discharge
• organic content
• bioavailability
• marine pollution

Acknowledgements

H. Alshemmari would like to thank Dr. A. N. Al-Ghadban (Manager of Environmental Science Department at Kuwait Institute for Scientific Research [KISR]) for his encouragement and KISR for financial support. Thanks are due to Dr. Bryn Jones from the School of Civil Engineering and Geosciences, the University of Newcastle upon Tyne, UK, for his guidance during this study.

Notes

^†deceased