A 10,000-year record of trace metal and metalloid (Cu, Hg, Sb, Pb) deposition in a western Alpine lake (Lake Robert, France): Deciphering local and regional mining contamination

Abstract

Concentrations of trace metals and metalloids (Cu, Hg, Sb, Pb), major elements, stable Pb and C isotope ratios, total organic carbon (TOC), C/N atomic ratios, were analyzed in two sediment cores encompassing 10,000 years of sedimentation sampled in Lake Robert (French Alps). The results showed that the establishment of a soil cover and vegetation during the Holocene climatic optimum increased Cu and Hg deposition in sediments. Results also enabled reconstruction of the history and local vs regional origins of pollution. During the Bronze Age (1800–1000 BC), Cu mining activities increased Hg and Sb accumulation rates (AR) by a factor of 7 (Hg) and 9 (Sb) compared to pre-Bronze Age values. The rise in Hg AR was equivalent to that of the industrial era highlighting a major local Hg point source not recorded in regional archives. During the Iron Age, Pb pollution was attributed to Sicilian ores whereas during the Roman Empire Pb pollution had the isotopic signature of Spanish Pb ores. During the Medieval period (ca. AD 1200), Pb and Hg pollution was due to the exploitation of the local Ag–Pb mines. Finally, during the industrial era, metal accumulations rates were 90 (Pb), 5 (Hg) and 20 (Sb) times higher than those in the pre-Bronze Age. The isotopic composition of Pb reflected mixed sources including industrial Pb and gasoline Pb. Synchronously, the increase in Sb and Hg pollution is attributed to global and regional atmospheric pollution.