Geoscience Reference
In-Depth Information
Case study 6.1 Road-deposited sediment, Manchester, UK
Road-deposited sediments (RDS) are a major component of the urban sediment cascade
(see section 6.2.2) and are sourced from a wide range of material. An extensive data set on the
physical, chemical and mineralogical composition of RDS exists for the city of Manchester,
north-west England (see Robertson et al. 2003). The sediments contain high metal concentra-
tions, in most cases significantly above average crustal abundances. Lead ranges from 120 to
645
gg
−1
. Temporal analysis has
shown that Pb levels have decreased since the 1990s in response to the reduction in use of
μ
gg
−1
, Cu from 39 to 283
μ
gg
−1
and Zn from 172 to 2183
μ
(a)
(b)
700
600
500
400
300
200
100
0
Inner city
Outer city
Location
(c)
Pb
Cu
100%
100%
80%
Case Fig. 6.1
(a) Box plot showing
Pb levels in road-deposited sediment
(RDS) in inner city and outer city
Manchester. Note the higher levels
of Pb in the city centre related to higher
vehicular activity. (Derived from data
published in Robertson et al. 2003.)
(b) Scanning electron microscopy
images of iron rich glasses, probably
produced via hydrocarbon combustion.
Note that these glass grains are spherical
and are approximately 50
μ
m in size.
(Images courtesy of Davina Robertson).
(c) Sequential extraction analysis of
metals in RDS in Manchester. Zinc
shows a significant component in the
exchangeable fraction, suggesting
increased mobility. (From Robertson
et al. 2003.)
80%
60%
60%
40%
40%
20%
20%
0%
0%
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12345678
Sample
Sample
Zn
100%
Oxidizable
Reducible
Exchangeable
80%
60%
40%
20%
0%
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Sample
