Historical levels of heavy metals and artificial radionuclides reconstructed from overbank sediment records in lower Rhone River (South-East France)

Trace metals (Cu, Cd, Cr, Ni, Pb, Zn, Hg) and artificial radionuclides (Cs-137, Am-241, Pu-238, and Pu239 + 240) were investigated in overbank sediments located in inter embankment areas of the lower Rhone River. Enrichment factors (EF) and anthropogenic factors (AF) were calculated to estimate the level of contamination in these sediment storages. The results show that in the studied sites Co, Ni and Sc display low EF values and are mainly from lithogenic origin. For the other studied trace metals a great variability of sedimentary record is observed. Significant anthropogenic enrichment was highlighted at a particular site that undergoes fluvial inputs occurring in the last 50 years. Lead is the element with the highest EF values (EF = 13), followed by Cd (EF = 11), Cu (EF = 5), Hg (EF = 7), and Zn (EF = 2). Temporal variations of Pb, Cd and Hg show a maximum in the 1960's and a decreasing trend afterward. Maximum enrichment of artificial radionuclides were observed in sediment deposit during the period 1960-1990 when maximum liquid releases from nuclear activities occurred. These results indicate that despite the high-energy conditions and the generally sandy nature of the riverbank sediments, significant anthropogenic enrichments were observed in some areas of sediment accumulation in the lower Rhone River. These enrichments are however relatively low compared to some other rivers in France and Europe due to the important suspended sediment discharge in this River, in particular during strong floods, which dilutes the anthropogenic inputs of contaminant. (C) 2011 Elsevier Ltd. All rights reserved.