Pb isotopes in mussels as tracers of metal sources and water movements in a lagoon (Thau Basin, S. France)

Abstract

Metal concentrations (Cu, Zn, Cd, Pb) and lead isotopic compositions have been determined in mussel's fleshes from the Thau lagoon (S. France). Mussel spat from sea was introduced at different locations in the lagoon in June 1995, and subsequently sampled in October 1995, and January, May, and July 1996. Each location was chosen for its particular environment: (1) an industrial harbour at sea, (2) water treatment plant effluents, (3) nearby city with no seawater entries, and (4) the middle of the lagoon. A reference point was also kept at sea. Variations in heavy metal concentrations generally correlate with weight of the animals, but some could be linked to particular local and temporal events such as outflows or tourist activity. The Pb isotopic compositions of the soft parts allow: (1) to identify the predominant sources of Pb and their seasonal variations; (2) to estimate their respective impact; and (3) to present a dynamic vision of the water movements in the lagoon comparing with climatic observations (wind), and their mixing with seawater entries. The possible use of isotopic tools in understanding the capture and the storage of metal in different organs in the mussels is also discussed.