Source Apportionment of Pb Pollution in the Coastal Waters of Elefsis Bay, Greece

Abstract

206Pb/207Pb isotope ratios were measured by ICP−MS in both seawater and sediments sampled in the severely polluted Elefsis Bay off Athens, Greece. The Pb isotope ratios found were significantly lower than those of local background or industrial sources and are influenced by the isotopic composition of gasoline lead (206Pb/207Pb = 1.06). Pb pollution of the sediments is dominated by industrial activities (70−80%) leading to enrichment factors of up to 18. However, up to 70% of dissolved Pb in Elefsis Bay is derived from gasoline lead. 206Pb/207Pb ratios in seawater were used to trace the direction of surface flow of the contaminant plume, which was from southeast to northwest during the December 1989 cruise, but with winds blown opposite to the normal trend. The lateral Pb isotope pattern points toward the Athens sewage outfall at Keratsini Channel with surface runoff from the greater Athens area as the primary source rather than direct atmospheric impact. The isotope pattern in sequential extractions of sediments suggest that the gasoline-derived Pb fraction accumulates by precipitation with sulfide phases at rates of 2 ± 0.5 mg m2 yr-1 during summer anoxia. Vertical Pb isotope profiles in seawater measured at all seasons indicate that this fraction is probably not remobilized upon breakdown of the pycnocline in winter and reoxidation of the sediment−water interface.