4 Isotope Geochemistry in the Environment
53
In this way, aerosols from Canada and the USA could be differentiated giving
z~176
ratios of 1.151 + 0.010 and 1.221 + 0.009, respectively. Such fine
differences were not discernable at the time of Ault et al. in 1970. This study
provided the impetus for further Pb isotope studies, concentrating on the
identification of industrial lead in soils and lakes, which are derived directly from
the atmosphere.
Ftegal et al. (1989) investigated the Pb isotopic compositions of surface water
from the great lakes (Lake Ontario, Lake Erie; Fig. 4.5). The lead concentrations
of dissolved lead in surface waters are highly variable and enriched in Pb close to
industrial centres. The 2~176
ratios are equally variable and reflect the
various source regions which come into play. Most of the z~
Pb ratios of the
central and western basins of Lake Ontario lie between 1.15 and 1.16 and are
therefore consistent with ratios for the industrial centre of Toronto (1.15+/-0.01).
At two localities at the eastern end of Lake Ontario and in the port of Hamilton,
anomalously high 2~176
ratios were measured of >1.18. These values lie
between values for Canadian and American aerosols and point to a mixing of the
two. Lake Erie allows us to recognize a trend in isotopic compositions from West
to East. The highest ratios (I.19) are found in the West and the lowest (1.16) in
the East. This means that the amount of industrial American lead decreases from
West to East. Regression calculations indicate that the lead in these waters comes
from two sources only. A natural geogenic source of lead cannot be identified.
Virtually all the lead that is dissolved in the surface waters of Lake Erie and
Ontario is therefore of industrial origin and originates from both Canada and the
USA.
Various studies have shown that the residence time of lead dissolved in the
surface waters of a lake is only on the order of 4 to 7 days (Sigg, 1985). The
dissolved lead is quickly adsorbed onto particles or is complexed with organic
molecules. This complexation and adsorption strongly control the budget of lead
in surface waters. The short residence time of lead has the consequence that Pb
isotopic composition at any one time may give an idea of lake circulation and
climatic conditions (wind direction in particular).
The transport of industrial lead by river systems is discussed in detail by ElbazPoulichet et al. (1984, 1986). The difference between petrol lead and natural lead
is quite straight forward in France as 99% of lead used is imported, mostly from
Canadian and Australian Precambrian ore bodies (Fig. 4.3). In some parts of
France. lead from other sources is used, mainly for the manufacture and treatment
of iron, steel and copper. This lead can be recognized by its relatively high
2~176
ratios. The natural lead of France comes from 300 million year old
Hercynian granite plutons, which have 2~176
ratios of between 1.18 and 1.20
(Fig. 4.3). More recent sediments originate, to a high degree, from these parent
rocks and possess therefore a similar Pb isotopic composition. In this study, the
authors attempted to define the various points of origin for the lead which can be
found dissolved or in suspension in the most important French river systems
53
In this way, aerosols from Canada and the USA could be differentiated giving
z~176
ratios of 1.151 + 0.010 and 1.221 + 0.009, respectively. Such fine
differences were not discernable at the time of Ault et al. in 1970. This study
provided the impetus for further Pb isotope studies, concentrating on the
identification of industrial lead in soils and lakes, which are derived directly from
the atmosphere.
Ftegal et al. (1989) investigated the Pb isotopic compositions of surface water
from the great lakes (Lake Ontario, Lake Erie; Fig. 4.5). The lead concentrations
of dissolved lead in surface waters are highly variable and enriched in Pb close to
industrial centres. The 2~176
ratios are equally variable and reflect the
various source regions which come into play. Most of the z~
Pb ratios of the
central and western basins of Lake Ontario lie between 1.15 and 1.16 and are
therefore consistent with ratios for the industrial centre of Toronto (1.15+/-0.01).
At two localities at the eastern end of Lake Ontario and in the port of Hamilton,
anomalously high 2~176
ratios were measured of >1.18. These values lie
between values for Canadian and American aerosols and point to a mixing of the
two. Lake Erie allows us to recognize a trend in isotopic compositions from West
to East. The highest ratios (I.19) are found in the West and the lowest (1.16) in
the East. This means that the amount of industrial American lead decreases from
West to East. Regression calculations indicate that the lead in these waters comes
from two sources only. A natural geogenic source of lead cannot be identified.
Virtually all the lead that is dissolved in the surface waters of Lake Erie and
Ontario is therefore of industrial origin and originates from both Canada and the
USA.
Various studies have shown that the residence time of lead dissolved in the
surface waters of a lake is only on the order of 4 to 7 days (Sigg, 1985). The
dissolved lead is quickly adsorbed onto particles or is complexed with organic
molecules. This complexation and adsorption strongly control the budget of lead
in surface waters. The short residence time of lead has the consequence that Pb
isotopic composition at any one time may give an idea of lake circulation and
climatic conditions (wind direction in particular).
The transport of industrial lead by river systems is discussed in detail by ElbazPoulichet et al. (1984, 1986). The difference between petrol lead and natural lead
is quite straight forward in France as 99% of lead used is imported, mostly from
Canadian and Australian Precambrian ore bodies (Fig. 4.3). In some parts of
France. lead from other sources is used, mainly for the manufacture and treatment
of iron, steel and copper. This lead can be recognized by its relatively high
2~176
ratios. The natural lead of France comes from 300 million year old
Hercynian granite plutons, which have 2~176
ratios of between 1.18 and 1.20
(Fig. 4.3). More recent sediments originate, to a high degree, from these parent
rocks and possess therefore a similar Pb isotopic composition. In this study, the
authors attempted to define the various points of origin for the lead which can be
found dissolved or in suspension in the most important French river systems