Environmental Engineering Reference
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quantify, because all the various inputs are inte-
grated in the soil over time, and urban soils are
periodically disturbed by landscaping, construction,
irrigation, and partial or total replacement, to name
a few. Nevertheless, certain general conclusions can
be drawn. Firstly, the infl uence of atmospheric depo-
sition is fairly uniform across the city and gives rise
to “urban background” levels of trace elements,
which are higher than those in natural soils. De
Miguel et al. (1998) cite enrichment factors of 2.3,
2.6, and 4.0 for Zn, Cu, and Pb, respectively, in the
urban soil of Madrid relative to natural background
levels. If the atmospheric aerosol has received contri-
butions from industrial sources, the increase in trace
element soil concentrations relative to natural levels
is much more pronounced. Ordóñez et al . (2003)
found concentrations of Zn and Cd as high as
2000
g g −1 , respectively, downwind
from a Zn smelter. Moreover, the infl uence of atmos-
pheric deposition is not restricted to soils within the
city limits. The effect of the atmospheric fallout from
the city of Madrid can be signifi cantly noticed in soils
up to a distance of 15 km from the city centre for Pb,
Cu, and Zn (Fig. 4.1), decreasing abruptly or disap-
μ
g g −1 and 8
μ
Madrid
S. Fernando
Arganda
Fig. 4.1 Infl uence of the city on soil
lead concentrations in and around
Madrid.
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