Isotopic evolution of atmospheric Pb from metallurgical processing in Flin Flon, Manitoba: Retrospective analysis using peat cores from bogs

Atmospheric Pb deposition was reconstructed using peat cores from bogs in the vicinity of Flin Flon, Manitoba, Canada, home to a zinc refinery and copper smelter. The Sask Lake (SL4-1) core was collected 85 km NW of Flin Flon and Kotyk Lake (KOL) 30 km NE. The distribution of Sr and U show that both profiles are predominantly minerotrophic (ie groundwater-fed), but the Pb concentration profile shows that Pb was received exclusively from the atmosphere. Graphs of 208Pb/206Pb against 206Pb/207Pb document atmospheric Pb contamination dating from the early to mid-1800’s, well before the start of metallurgical processing (in 1930) and attributable to long-range atmospheric transport from other regions of North America. Industrial activities at Flin Flon clearly affected the concentrations, enrichment factor (calculated using Sc), and accumulation rates of Pb, but it is the similarity in isotopic composition, and contrast with crustal values (206Pb/207Pb ca. 1.20 to 1.22) which makes the connection to the Flin Flon ores. The KOL samples dating from 1925–1976 CE have a 206Pb/207Pb of 1.032 ± 0.002 (n = 11) which approach the values for the Flin Flon ores (206Pb/207Pb = 1.008). But even at SL4-1, the peat samples dating from 1925–1976 CE have a 206Pb/207Pb of 1.061 ± 0.022 (n = 18) which is well below the corresponding ratio of Canadian leaded gasoline (206Pb/207Pb = ca. 1.15). The SL4-1 site too, therefore, was clearly impacted by Pb from mining and metallurgy, despite the distance (88 km) from Flin Flon and being predominantly upwind. These two bogs not only provide the chronology of atmospheric Pb deposition for the past decades, but suggest that the extent of contamination may have been underestimated by previous studies. [Display omitted] •Atmospheric Pb deposition was studied using peat cores from bogs.•Pb contamination began well before metallurgical processing in 1930.•Pb isotopes trace contamination to the Zn refinery and Cu smelter.•Impacts of the smelter are clearly seen in the bog 88 km NW (upwind).•The areal extent of contamination was underestimated by earlier studies. The isotopic composition of Pb in peat bogs shows that the extent of atmospheric contamination from metallurgical processing in Flon Flon has been underestimated.