Geoscience Reference
In-Depth Information
Table 6.2
Typical metal contents (
μ
gg
−
1
) in road-deposited sediments in selected cities. (Data from Charlesworth et al. (2003a) and,
for Manchester 2002, Robertson et al. (2003).)
City
Population
Cd
Cu
Ni
Pb
Zn
New York
16,972,000
8
355
-
2583
1811
Seoul
10,627,000
3
101
-
245
296
London
9,227,687
2.7-6250
61-512
32-74
413-3030
988-3358
Hong Kong
5,448,000
-
92-392
-
208-755
574-2397
Madrid
2,909,792
-
188
44
193
476
Manchester (1975)
2,578,900
-
-
-
970
-
Manchester (2002)
2,578,900
-
32-283
-
25-645
172-2183
Birmingham (1976)
2,329,600
-
-
-
950-1300
-
Birmingham (1987)
2,329,600
-
-
-
527-791
-
Taejon, Korea
2,000,000
-
47-57
-
52-60
172-214
Amman
1,272,000
2.5-3.4
69-117
27-33
219-373
-
Cincinnati
1,539,000
-
253-1219
-
650-662
-
Oslo
758,949
1.4
123
41
180
412
Bahrain
549,000
72
-
126
697
152
Hamilton
322,352
4.1
129
-
214
645
Christchurch
308,200
1
137
0
1091
548
Lancaster
136,700
3.7
75
-
1090
260
recent drops in sediment-Pb levels illustrate the
transitory, short-term nature of these sediments
within urban systems. Indeed, Allott et al. (1990),
using radiocaesium from the dated Chernobyl
fallout event, documented the residence time
of sediment on street surfaces to be short, in
the order of 150 to 250 days. Recently, with the
introduction of catalytic converters, attention
has been directed towards the levels of platinum
(and associated elements) within urban street
sediments (e.g. Wei & Morrsion 1994a). It has
been documented that Pt levels are increasing
in urban sediments, although health impacts of
these increasing levels remain largely undeter-
mined (Farago et al. 1998).
Data on the chemical speciation of contamin-
ants within RDS have provided information on
the mineralogical affinity and potential reactiv-
ity of contaminants (Fergusson & Kim 1991;
Stone & Marsalek 1996; Charlesworth & Lees
1999; Robertson et al. 2003). Charlesworth &
Lees (1999) found a low concentration of heavy
metals associated with the exchangeable phase,
results that have been reproduced by other
studies. Hamilton et al. (1984), however, found
Cd to be associated with the exchangeable phase,
and Robertson et al. (2003) found Zn also to
display a significant affinity to the exchangeable
fraction. Therefore, RDS may be a significant
source of Cd and Zn to urban runoff. Platinum
in urban sediments has been shown to be in a
form that may be soluble (Farago et al. 1998)
and street sediments in gully pots have also been
shown to be actively mobilizing Pt to the aquatic
phase (Wei & Morrison 1994a). The majority of
studies have found most metals to be associated
primarily with the reducible (Fe and Mn oxide)
fraction. Although this suggests that on street
surfaces contaminant mobility is generally low,
changes in pH and redox as a result of deposition
in aquatic sediments or sediment water transport
would possibly release metals back into aquatic
environments. Copper has been shown to display
a higher affinity to organic matter (Hamilton
et al. 1984; Robertson et al. 2003). Charlesworth
& Lees (1999) ascribed the preference of metals
for the organic matter fraction in Coventry to
high levels of organic matter in the sediments.
Much less direct information exists on the role
of individual minerals on contaminant behavi-
our in urban sediments. McAlister et al. (2000)
documented the stabilization of weddellite (cal-
cium oxalate dihydrate), derived from sewage,
by interactions with metals in street sediments
of Brazil. In this case, therefore, RDS acted as a
sink for oxalate, exposure to which has significant
