Geoscience Reference
In-Depth Information
Table 6.1
Contaminant sources to road-deposited sediment.
Contaminant
Source
Pb
Petrol combustion, paint, smelters, coal combustion
Zn, Cd
Tyre wear, galvanized roofs, abrasion of vehicles, lubricating oils, alloys
Cu
Brake linings, alloys, metal industry
Fe
Car exhaust particulates, corrosion of vehicle body work, background geology
Mn
Tyre wear, brake linings, background geology
Cr
Engine wear, vehicle plating and alloys, road surface wear
Ni
Engine wear, metal industry, background geology
Asbestos
Break clutch linings
Cl, Na
Road salt
PGEs (Pt, Pd, Os)
Catalytic convertors
Pesticides/herbicides
Garden application
PAHs
Biomas burning, petroleum combustion
PCBs
Petroleum combustion, industry
Bacteria
Sewage treatment works, animal faeces
Pharmaceutical compounds
Sewage treatment works
linings. Multi-element analysis of RDS, coupled
with principal component analysis, has been
used in some studies to aid in elemental source
apportionment. De Miguel et al. (1997), in a
study of Madrid, recognized distinct groups of
elements. Those derived from vehicles and con-
struction sources were Br, Cd, Co, Cu, Mg, Pb,
Sb, Ti and Zn, whereas those deriving from
natural soil material were Al, Ga, La, Mn, Na,
Sr, Tl and Y.
The platinum group elements (PGEs) Pt, Pd and
Rh are a relatively recent contribution to RDS,
having been emitted into urban environments
since the early 1990s. The PGEs act as catalysts
in catalytic converters and, with the phasing-out
of leaded fuel, are currently the metals of most
concern emitted from vehicle exhausts. There is
evidence from many studies for the widespread
dispersion and accumulation of PGEs in RDS,
as well as urban soils and airborne particulates.
Concentrations of PGEs significantly above those
of average upper crust values have been reported
for RDS for cities in Europe and Australia (Wei
& Morrison 1994a; Motelica-Heino et al. 2001;
Whitely & Murray 2003). Although PGEs in
metallic form are generally considered to be bio-
logically inert, soluble PGE salts are indicated to
be much more bioreactive (Farago et al. 1998)
and so the presence of PGE in RDS is potentially
of significant concern.
There is a whole suite of organic contaminants
(so-called persistent organic pollutants) sourced
to RDS. These include PAHs (polyaromatic
hydrocarbons), PCBs (polychlorinated biphenols),
hydrocarbons, dioxins, pesticides and herbicides.
The sources of these are various and include
both atmospheric and land-based sources. For
example, PAHs were observed to be sourced
from biomass burning and vehicular emissions
in Vancouver, Canada (Yunker et al. 2002). Prob-
ably the largest source of organic pollutants
are those derived from vehicular activity. Many
of these are found in petrol or diesel (includ-
ing benzene, toluene, naphthalene, PAHs), or
associated with automobiles (including ethylene
glycol, hydraulic fluids, styrene, oil lubricants).
Pesticides and herbicides are applied directly to
pavements or to urban soils in residential areas
and gardens, where they can be removed from
runoff or erosion and deposited in RDS.
6.2.1.2 River, canal, dock and lake sediments
The range of sediment sources for rivers and
canals is greater than that for RDS, in that as
well as the input of RDS into river sediments,
upstream and downstream input of channel-
associated material is a major contributor to
these urban aquatic sediments. Although the
origins of sediment in river basins have been
