Spatial trends in the chemical composition of sediments on the continental shelf 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 μm), silt and clay (<63tμm) and clay (<2μm)) of sediment collected off the Mediterranean coast 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 decrease in Fe/Al, Ti/Al and non-carbonate Mg/Al in the fine sand fraction, interpreted 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 increase in CaCO₃ both towards the north and onshore in all grain size fractions due to a northward increase in local biogenic fragments and river detritus. This is consistent with circulation and sediment transport models for the 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 fractions there is a significant enrichment of Zn, and Cd towards the north, which is not accounted for by changes in mineralogy. The sediments were also enriched in Cu, Zn and Cd near Tel Aviv and Hadera. The peaks near Tel Aviv may correspond to waste discharged through the Yarqon and an old sewage pipe, whilst near Hadera, the Alexander and Hadera Rivers and the terminal 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. However, there was no enrichment in Pb around the point sources of the other trace metals, therefore it was concluded that the majority of Pb contamination was from the atmosphere. All trace metal contamination may be subject to 'smearing' by sediment transport, particularly in the clay fraction.