Source Apportionment of Pb Pollution in the Coastal Waters of Elefsis Bay, Greece MICHAEL KERSTEN* Baltic Sea Research Institute, Marine Geology Section, D-18119 Rostock, Germ any CARL-DIETER GARBE-SCHO ¨ NBERG University of Kiel, Institute of Geology, D-24118 Kiel, Germany SUSANNE THOMSEN University of Technology, Environm ental Engineering Section, D-21071 Ham burg, Germ any CHRISTOS ANAGNOSTOU AND ANDREAS SIOULAS National Centre of Marine Research, Biogeochem ical Laboratory, GR-16672 Athens-Vari, Greece 206 Pb/ 207 Pb isotope ratios were measured by ICP-M S 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 ( 206 Pb/ 207 Pb ) 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. 206 Pb/ 207 Pb 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 m 2 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. Introduction The Bay of Elefsis is a small and shallow (ca. 68 km 2 with a mean and maximum depth of 20 m and 33 m, respectively, Figure 1) semi-enclosed embayment in the northern part of the Saronicos Gulf. It is connected to the rest ofthe Saronicos Gulf by narrow and shallow channels on both the eastern and western side. In the eastern reach of Elefsis Bay lies the metropolitan basin of Greater Athens (450 km 2 ) with a population ofca.3.1million (census1991),50%ofallvehicles registered in Greece (over 1 million passenger cars), and 40% of the Greek heavy industry. The eastern Keratsini Channel is encircled by the industrial and shipyard area of Piraeus Harbor. Naturalfreshwater inputs are limited,but it receives considerable amounts of effluent from numerous anthro- pogenic sources. Four major point sources of trace metal discharge have been identified, which are (i) an iron and steelworks dischargingparticulate waste into a settlinglagoon at the northeastern part of the Bay (1); (ii) a sewage outfall discharging untreated domestic and industrial urban waste- water for most of the Greater Athens metropolitan area into the KeratsiniChannel(2);(iii)a large fertilizer factorysituated just outside the entrance to the Piraeus Harbor (3); and (iv) the Piraeus Harbor itself(4). Sedimentanalysesrevealed that the hot spot areas are relatively restricted to a few kilometers around these point sources,where trace metalconcentrations 10-200 times greater than those for backgound values were found (1-4). Spatial pollutant distribution surveys for zinc (5) and lead (6) indicate, however, that the centralpart ofthe Bay also has elevated trace metal concentrations. The increase in nutrient and pollutant load, however, has led to a doubling in the organic carbon content in the mainly fine- grained sediments within the last 20 yr (7). Massive benthic macrofauna mortalityduringsummeranoxia indicate severe ecological effects of this nutrient pollution (8-11). The multiplicity of the potential anthropogenic metal inputs to the bay precluded an unqualified identification of one principalsource usingonlytotalconcentration analyses. Therefore, complementary information on Pb isotopic com- position analyses were required. Aliterature review suggests that the relative abundances of the four stable isotopes of lead ( 204 Pb, 206 Pb, 207 Pb, and 208 Pb) may be used to trace the sources of pollutants to coastal marine waters (12). Stable Pb isotope ratios depend on the age and history of the geological system from which the lead derives, because two of these isotopes are produced by radioactive decay of uranium parent nuclides with different decay rates ( 238 U f 206 Pb, 235 U f 207 Pb). In Europe, lead from paleozoic ore deposits has been used for gasoline plumbingfor a longtime, and thislead hasa significantlydifferent isotopic composition than modern lead (12). While the ICP-MS technique has successfully been applied for lead isotope measurements in solid environmental matrices (13), the overall low concentra- tions have hampered the accurate determination of Pb isotopic composition in seawater until recently (14). The introduction ofa submersible pump sampler that is capable of preconcentrating trace metals by ion exchange columns at depths has significantly improved the ability to collect contamination-free samples (15). This system enabled us to distinguish and follow contaminant Pb plumes back to their respective sources in the Elefsis Bay, in spite ofa lack ofclean laboratory facilities on-board ship as well as at the local research institute. Experimental Section Site Description. The water circulation pattern in Elefsis Bay is mainly restricted by the shallow sills of both channels (16). The water in the bay is well mixed during winter as a result of wind mixing and the absence of a thermocline. Between early spring and July, the gradual development of a thermocline leads to a rapid reduction in vertical mixing. By May, the water becomes stratified. The upper layer (<15 m) becomes supersaturated with oxygen due to photosyn- thetic activity and export of reduced carbon. Oxygen concentration decreases with depth, and anoxic conditions with abundant free H 2Sdevelop in the deeper basins (>20 m at stations Jand K,Figure 1; 10). Thisstratification continues until October or November when a breakdown of the thermocline results in verticalremixing ofthe water column. *Corresponding author e-mail: michael.kersten@io-warnemuende. de. Environ. Sci. Technol. 1997, 31, 1295-1301 S0013-936X(96)00473-7 CCC: $14.00  1997 American Chemical Society VOL. 31, NO. 5, 1997 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 1295