TOTAL AND EXTRACTABLE TRACE ELEMENTS IN LEBANESE RIVER SEDIMENTS: DRY SEASON DATA SAMIRA IBRAHIM KORFALI 1 and BRIAN E. DAVIES 2 1 Natural Science Division, Lebanese American University, Beirut, Lebanon; 2 Department of Geological Sciences, Clemson University, Clemson, SC, USA (e-mail: skorfali@lau.edu.lb; bdavies@clemson.edu) Abstract. Years of political instability have left Lebanon with significant gaps in environmental knowledge. This paper reports new results for trace metals in bed sediments of the river Nahr- lbrahim. The drainage basin of the river Nahr-lbrahim is largely floored by karstified limestone. Metal pollution is operative within the catchment. The objectives of this study were first to identify possible sources of metals (geological and/or anthropogenic) and then to characterise the chemical partitioning of the metals in the sediments. Bed load sediments were sampled at five locations along a 13 km stretch from the river mouth, during the dry season. Samples were collected on two dates, dried and then sieved into three mechanical fractions. We report total Fe, Cu, Pb and Zn contents of the <75 μm sediment fraction for the dry season and interpret the results in terms of geology and point and non-point discharges to the river. Total metal contents were derived from summing the concentrations of metals in the chemical fractions of the sediments. A sequential chemical extraction procedure was applied to the <75 μm fraction and the data showed that, except for Fe, the carbonate fraction had the largest role in metal sediment deposition. Key words: bed load sediments, carbonate sediment fraction, Lebanon, sequential extraction, total and extractable metals 1. Introduction In the Middle East, Lebanon has, potentially, abundant water. However, Lebanese water resources are not exploited properly, and the relatively high population dens- ity (>300 persons km -2 ) makes Lebanon a water deficient country. For its domestic supply Lebanon depends mainly on ground water that is deteriorating rapidly due to salinisation by seawater intrusions and contamination by wastewater (Khair et al., 1992, 1994). Surface water is under-exploited and hydrological baseline data, in- cluding water quality, for Lebanese rivers are relatively non-existent (Sene et al., 1999). The American University of Beirut is monitoring most Lebanese rivers to determine the feasibility of using them as sources for drinking water. That study involves measurement of colour, turbidity, conductance, macro and micro chemical constituents and microbes. There is no published research on trace elements in Lebanese water or fluvial sediments, nor has the chemical fractionation of metals within sediment fractions ever been researched. This paper is the first study of trace metals (total and extractable) in bed load sediments in a Lebanese river of the 1996 dry season. The results reported here complement the broader all-Lebanon project. Data are reported for the river Nahr-lbrahim, located about 20 km north of Beirut. Environmental Geochemistry and Health 22: 265–273, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands.