Volumes 518–519, 15 June 2015, Pages 86–96
Highlights
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- Urban speleothems from underground aqueduct in Paris, France were studied.
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- Speleothems are used to reconstruct the history of sub-surface water pollution.
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- Two distinct periods of heavy metal pollution occurred during the last 300 years.
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- Lead isotope ratio is used to constrain lead contamination sources.
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- 18th century metal contamination originates from the use of urban wastes as fertilizer.
Abstract
The
first record of urban speleothems used to reconstruct the history of
heavy metal pollution of shallow groundwaters is presented. Two
speleothems grew during the last 300 years in an underground aqueduct in
the north-eastern part of Paris. They display high Pb, Mn V, Cu, Cd and
Al concentrations since 1900 due to the urbanization of the site which
triggered anthropogenic contamination of the water feeding the
speleothems. Surprisingly, these heavy metal concentrations are also
high in the oldest part. This early pollution could come from the use of
Parisian waste as fertilizers in the orchards and vineyards cultivated
above the aqueduct before urbanization. Lead isotopes were measured in
these carbonates as well as in lead artifacts from the 17th–18th
centuries (206Pb/207Pb = 1.180 +/− 0.003). The mean 206Pb/207Pb
ratio, for one of the speleothems is 1.181 +/− 0.003 unvarying with
time. These lead signatures are close to those of coal and old lead from
northern European mines, lower than the natural background signature.
It confirms that the high metal concentrations found come from
anthropogenic pollution. Conversely, the lead isotopic composition of
the second speleothem presents two temporal trends: for the oldest
levels, the mean value (1.183 +/− 0.003) is similar to the first
speleothem. For the youngest part, a lower value (1.172 +/− 0.005) is
recorded, evidencing the contribution of a new lead source at the
beginning of the industrial revolution. Pb isotopes were also measured
in recent samples from a nearby superficial site. The first sample is a
recent (AD 1975 +/− 15 years) deposit (206Pb/207Pb = 1.148 +/− 0.003), and the second, a thin subactual layer (206Pb/207Pb = 1.181 +/− 0.002).
These data are compatible with the adding of anthropogenic sources
(leaded gasoline and industrial lead from Rio Tinto ore).
Keywords
- Urban groundwater;
- Lead stable isotopes;
- Speleothems;
- Aqueduct;
- Heavy metal pollution
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