"Speciation" of three Trace Elements Mercury, Lead, Cadmium in Sediments of the Lebanese Coastal Zones
"speciation" des trois elements trace mercure, plomb et cadmium dans les sediments marins des zones cotieres libanaises.
Résumé
The vertical profiles of the concentrations of Pb, Cd and Hg, the sources and the mobility of these trace metals were studied in sediment cores collected at three sites typical of the Lebanese coast (Akkar, Dora and Selaata). Akkar is located away from any direct source of contamination, Dora is under the influence of several anthropogenic activities and an enormous solid waste discharge, while Selaata is nearby a phosphate fertilizer industry. Measurements of 210Pb and 137Cs showed that the studied deposits are largely from detrital origin. Mineralogical analysis coupled to major elements (Ca, Si, Fe, Mn, Al) and trace elements (Hg, Pb, Cd, Ag, Cr, Cu, Ni, V and Zn) total quantification clearly revealed the distribution of the studied sites into three distinct types (1) carbonate sediments safe from any massive trace element contamination at Akkar, (2) mixture of silicate and carbonate sediments at Dora where high trace element contents, typical of contaminated medium, were detected, (3) silicate deposits rich in fluorite (originating from the discharges of the chemical factory), V, Ni and Cd at Selaata. Pb, Cd and Hg vertical profiles at Akkar, Dora and Selaata were normalized using Al as a tracer element which enabled us to overcome fluctuations related to the clay fraction of the sediment. The sources of Pb present in the studied deposits were also determined by measuring stable lead isotopic ratios 206Pb/204Pb, 206Pb/207Pb and 206Pb/208Pb. Thus we showed that despite low Pb and Hg concentrations detected in Akkar sediments, superficial enrichments occur and indicate the impact of diffuse anthropogenic contamination on these coastal sediments. Furthermore, high Hg, Pb and Cd concentrations coupled to low Pb isotopic signatures obtained at Dora sediments, indicate a very strong anthropisation at these deposits. Very high Cd concentrations as well as the highly radiogenic Pb isotopic signatures detected in Selaata sediments, testify of the impact of the wastes released by Selaata
Les profils verticaux des concentrations, les sources et la mobilité de Pb, Cd et Hg ont été étudiés dans des carottes sédimentaires prélevées en trois sites typiques de la côte libanaise (Akkar, Dora et Selaata). Akkar est un site éloigné de toute influence directe de contamination chimique, Dora est soumis à l