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Fig. 4.10 a - b Variations in Pb concentration and 206 Pb/ 207 Pb ratios as a function of sediment
age (depth) within alluvial sediment cores extracted from selected locations along the Seine River;
c Bivariate plot showing the changes in Pb mixing through time; d Map showing the location of the
coring/sampling sites (adapted from Ayrault et al. 2012 )
the “historical” Parisian lead (Ayrault et al. 2012 ). From approximately 1968-1989,
206 Pb/ 207 Pb ratios decreased along a trend described by mixing line 1 (Fig. 4.10 c).
This decrease was attributed to an increase in the use of leaded gasoline (character-
ized by a lower isotopic ratio) and the implementation of environmental regulations
that reduced other forms of Pb input to the river. As the use of leaded gasoline
was phased out after 1986, Ayrault et al. ( 2012 ) argued that the Pb isotopic ratio
reflected a mixture of Pb from leaded gasoline and the historical Parisian lead, which
they referred to as urban lead. After about 1989, Pb concentrations decreased and
206 Pb/ 207 Pb signature progressively evolved (along mixing line 2) such that the Pb
was composed of urban Pb and Pb from natural background sources associated with
local soils (Fig. 4.10 c). The fact that mixing lines could be defined allowed them to
estimate the contributions of Pb from the two primary sources that were present for
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