Isotopic Record of Lead Contamination in Alluvial Soils and Tree Rings on Recent Floodplains (Southern Québec, Canada)

Abstract

Current and past industrial pollution leaves many traces in the environment, in particular along rivers in industrial and urban areas. The isotopic analysis of the lead found in soils and tree rings offers a kind of environmental archive for presenting a portrait of the pollutant distribution in the environment in both spatial and temporal terms. This study is an attempt to identify and compare the source of contamination found in soils and tree rings located along two rivers affected by pollution over several years. Specifically, the focus is on the pattern of lead concentrations and lead isotopic signatures (206Pb/ 207Pb, 208Pb/206Pb, and 206Pb/204Pb) detected in soils and tree rings located on polluted floodplains. The concentration of Pb in overbank sediments does not rise with the increasing distance downstream from the point source (mining area), suggesting that significant fluvial transport of the pollutant particles over 80 km is involved. For the soil profiles, Pb concentration levels range between 12.32 and 149.13 mg/kg, with the highest concentrations found at the base of the profiles (>1 m). For the lead isotope ratios in the soil profiles, the values obtained range from 0.851 to 0.872 (206Pb/207Pb), 2.081 to 2.111 (208Pb/206Pb), and 0.547 to 0.562 (206Pb/204Pb). The tree ring analysis of red ash (Fraxinus pennsylvanica Marsh.) shows average lead concentrations of 0.63 μg/g, and the lead values of all the tree specimens range between 0.03 and 11.38 μg/g. Pb concentrations varied greatly between the specimens in selected sites and lead isotope ratios in the tree rings showed a strong variability in the time series, particularly from 1945 to 1970. The greater number of variations in the lead concentration rates and isotopic ratios suggest that many more events associated with pollution and contamination have in fact occurred in this area. The study demonstrates the utility of combining stable isotope analyses (soils and tree rings) to examine the source and dispersion of contaminant Pb in fluvial systems by providing reliable and robust indicators for the detection of environmental changes on a local and regional scale.

Hydrocarbons, Pb-Concentrations, and Pb-Isotope Ratios in Contaminated Alluvial Soils (Southern Québec, Canada)

“…Also, the Pb isotope composition obtained using on the geochemical analyses of the Pb detected in the rings of tree specimens (Red ash /Fraxinus pennsylvanica) in the same study areas leads us to believe that there were two or three discharges of oil into the river (St-Laurent et al, 2009). These spills appear to have likely occurred between 1948 and 1968 according to our dendrogeochemical analyses performed on specimens of trees found along the riverbanks (Saint-Laurent et al, 2010b). Note that Pb was still being added to gasoline during this time, and it was only later (i.e., in 1990) that the Government of Canada prohibited its use (CEPA, 1990;Health Canada, 2009).…”

“…Our previous work conducted on hydrocarbon-contamined layers found in alluvial soils (Saint-Laurent et al, 2008;2010a;2010b) showed marked differences in the Pb isotope values (e.g., 206 Pb/ 207 Pb, 208 Pb/ 206 Pb), suggesting separate spills of petroleum products in the rivers. For instance, the values obtained for Pb isotope ratios 206 Pb/ 207 Pb ranged from 0.124 to 0.175 ± 0.01 SD (Saint-Laurent et al, 2010b;2010c).…”

“…For instance, the values obtained for Pb isotope ratios 206 Pb/ 207 Pb ranged from 0.124 to 0.175 ± 0.01 SD (Saint-Laurent et al, 2010b;2010c). Also, the Pb isotope composition obtained using on the geochemical analyses of the Pb detected in the rings of tree specimens (Red ash /Fraxinus pennsylvanica) in the same study areas leads us to believe that there were two or three discharges of oil into the river (St-Laurent et al, 2009).…”

High-Precision Elevation Model to Evaluate the Spatial Distribution of Soil Organic Carbon in Active Floodplains

“…In short, overly frequent flooding can disrupt pedogenetic processes and hinder biogeochemical cycles and the development of riparian stands (Franklin et al 2009;Hamdan et al 2010). Also, flood frequency leads to fine sediments being continuously deposited on floodplains, and some of these sediments may contain contaminants such as heavy metals and pollutants (Macklin et al 2006;Saint-Laurent et al 2009;Bird et al 2010;Saint-Laurent et al 2010a).…”

Some considerations in the reconstruction of lead levels using laser ablation: lessons from the design stage of dendrochemistry study, St.John's, Canada

“…Aznar et al, 2008;Kirchner et al, 2008;Lageard et al, 2008;Saint-Laurent et al, 2010;Wu et al, 2010;Mihaljevič et al, 2011 andZuna et al, 2011). These methods offer multi-element and isotope analysis with low detection limits, but relatively large amounts of wood sample are needed.…”