Tracing natural and anthropogenic Pb in sediments along the mediterranean coast of Israel using Pb isotopes

The natural and anthropogenic sources of Pb in surface sediments offshore the Israeli Mediterranean coast were studied using the isotopic composition of Pb in diluted acid sediment extracts. Surface sediments were collected at the lower reaches of coastal streams, along a south-north offshore transect and at selected monitoring stations of the Dan Region Wastewater Plant (DRWP) outfall pipe. The background values of the Pb isotopic composition were determined from the deepest part of two representative cores collected offshore and were found to have a narrow range dominated mainly by clays derived from both inland soils and the Nilotic cell and to a lesser extent from the Saharan dust. The impact of the DRWP activated sludge can be traced to a distance of ca. 2 km from the outfall pipe. Enrichment factors of Zn, Cu, and Pb were up to 25 and are strongly correlated with each other and with the Pb isotopic composition, thus demonstrating the sludge to be their common source. The isotopic compositions of Pb in stream sediments have the widest range of values and indicate a strong anthropogenic contribution, probably from both post-1992 aerosols and point sources. However the impact of stream sediments on marine sediments could not be clearly detected.