Spatial trends in the chemical composition of sediments on the continentalshelf and slope off the Mediterranean coast of Israel

In order to determine whether observed trends in total trace metal content were natural or due to anthropogenic inputs, major and trace elements were measured on three size fractions (fine sand (250-63 mum), silt and clay (< 63 mum) and clay (<2 mum)) of sediment collected off the Mediterranean coas t of Israel. Partitioning of trace metals into carbonate/exchangeable, iron oxide and residual phases for each grain size was also determined. The dominant source of particles was Nile derived material. There was a dec rease in Fe/Al, Ti/Al and non-carbonate Mg/Al in the fine sand fraction, in terpreted as a decrease in heavy minerals towards the north and an increase in K/Al due to increased feldspars and micas. There was a simultaneous inc rease in CaCO3 both towards the north and onshore in all grain size fractio ns due to a northward increase in local biogenic fragments and river detrit us. This is consistent with circulation and sediment transport models for t he southeast Levantine basin. The background trend in trace metals corresponds to changes in mineralogy. While the fine sand fraction appeared free of contamination. in the finer f ractions there is a significant enrichment of Zn, and Cd towards the north, which is not accounted for by changes in mineralogy. The sediments were al so enriched in Cu. Zn and Cd near Tel Aviv and Hadera. The peaks near Tel A viv may correspond to waste discharged through the Yarqon and an old sewage pipe., whilst near Hadera, the Alexander and Hadera Rivers and the termina l for a coal-fired power station may be the source of contamination. There was also clear evidence for contamination by Pb in the finest sediments. Ho wever, there was no enrichment in Pb around the point sources of the other trace metals, therefore it was concluded that the majority of Pb contaminat ion was from the atmosphere. All trace metal contamination may be subject t o 'smearing' by sediment transport, particularly in the clay Fraction. (C) 2001 Elsevier Science Ltd. All rights reserved.