A 70 year Record of Contamination from Industrial Activity Along the Garonne River and its Tributaries (SW France)

Abstract

In this work, we document the historical record (≈70yr) of contamination from industrial activity along the Garonne River and its tributaries (SW France), through the geochemical study of a sediment core recovered from the inner section of a flood-tidal dock, located in the city of Bordeaux, along the Garonne River. The chronology of the core was estimated by extrapolation from and interpolation between a few geochemical datums provided by a high resolution137Cs record, the atmospheric initiation of radioactive fallout (∼1952); the maximum of atmospheric radioactive fallout (∼1963) and the Chernobyl accident (1986). Concentrations of Sc, V, Cr, Co, Ni, Cu, Zn, Cd, Sn, U, Pb and the Pb isotope composition were analyzed by ICP-MS, in the ‘exchangeable’ fraction.The pollution impact of a few heavy metals (mostly Pb, Cd, Zn, Sn) was particularly enhanced from 1950 to about 1980, due to the activity of a mining and foundry company located on the Lot, a tributary of the Garonne River. A five-step historical evolution of the foundry's activity is faithfully recorded in the sedimentary record. Despite the fact that the mining activity stopped 20 years ago, and that the contamination seems to be very limited at present, enrichments are still observed in the estuary waters and sediments. These may be due to the release of both particulate and dissolved metals from previously released tailings in the dowstream from the Decazeville mining/foundry site. Over the last 20 years, another kind of pollution by Cr and V is identified, and is related to a different industrial origin, tanneries and electrolysis factories, located along other tributaries of the Garonne River (Dordogne and Tarn). Contamination from local sources (Bordeaux) is negligible compared to the dominant influence of the remote pollution sources.