Environmental Engineering Reference
In-Depth Information
4.2.4 Indoor dust
gardens), undeveloped land, building lots, etc.
Whereas the characterization of street dust offers an
instantaneous “snapshot” of an urban environment's
condition, urban soil rather acts as a pollutant sink
and, if undisturbed, preserves the cumulative history
of trace elements inputs into it (although not in the
orderly, sequential fashion of an urban lake
sediment).
However, soil particles do not necessarily remain
in place, but can become part of street dust or even
of the urban aerosol. Particles smaller than 100
The main sources of indoor house dust include soil
and street dust particles; these are carried indoors
adhered to clothes and shoes, swept indoors by wind
drafts, or even brought inside on the fur of domestic
animals (Tong 1998). The relative contribution of
the urban aerosol and of indoor sources of trace ele-
ments (cooking and other combustion processes,
rubber, wall paint, fabrics, pigments) has not been
conclusively evaluated (Fergusson & Kim 1991;
Adgate
et al
. 1998; Edwards
et al
. 1998). As in the
case of street dust, concern over inhalation, inges-
tion, and dermal exposure to house dust has fuelled
research on this material. House dust has been cited
as one of the major sources of exposure to pesticides
and metals, particularly lead, in children (Edwards
et al.
1998 and references therein). Turner &
Simmonds (2006) reported that, in common with
many other studies worldwide, enrichment of Cd,
Cu, Pb, Sn, and Zn in dusts from four regions across
the UK were of concern. However, Tong & Lam
(2000) found that activities such as fl oor sweeping
and dusting reduced the levels of metals in houses
in Hong Kong, although the type of paint used to
decorate the house and its age were of signifi cance
when determining indoor metal levels. Chattopadhyay
et al
. (2003) found that, whereas atmospheric con-
centrations of Pb have reduced since the introduction
of unleaded petrol (section 4.2), that of household
dusts in Sydney, Australia, have remained essentially
unchanged. This, they assert, is due not only to the
accumulation of Pb inside the house from the use of
old leaded paints, but also the historical accumula-
tion of more than 80 years of leaded petrol deposi-
tion in the urban area. As was mentioned above, one
of the vectors for the transport of contaminants
indoors is soil. It has been found that soil can act as
a repository for historical contamination not only
caused by traffi c, but also industry (see, for example,
Charlesworth
et al.
2003). The next section consid-
ers levels and sources of soil contamination in urban
areas.
m
move in “suspension” and the fi nest among them
may remain airborne for prolonged periods of time.
The process of suspension is all the more intense if
the small particles are accompanied by particles
moving by “saltation”, which upon landing back on
the surface will help to lift the fi nest material (Sehmel
1980; Nicholson 1988). Consequently, exposure to
trace elements in urban soil does not occur solely by
ingestion or dermal contact but also through inhala-
tion of resuspended soil particles. However, the most
immediate route of exposure for children, the most
sensitive segment of the population, is hand-to-
mouth activity during games and the habit of “pica”,
i.e. mouthing of non-food objects. As has been out-
lined in section 4.2.3, several investigations have sug-
gested that urban soil and dirt represent a signifi cant
intake of trace elements for children living in urban
areas (see Biggins & Harrison 1980 and references
therein; Rundle
et al.
1985; Watt
et al
. 1993;
Abrahams 2002).
Although generally lower than those found in
street dust, urban soil can contain enriched levels of
trace elements relative to natural background levels
(see, for example, Charlesworth
et al
. 2003;
Charlesworth & Foster 2005; Biasioli
et al.
2007).
The main sources of these trace elements include the
atmospheric deposition of particles generated by
automotive traffi c, heating systems, and resuspended
street dust, the uncontrolled disposal of urban and
commercial wastes, and the addition of fertilizers
and composted sewage sludge to the soil (Carey
et al
. 1980; Haines 1984; Warren & Birch 1987;
Fergusson 1990; Kabata-Pendias & Pendias 1992;
Tiller 1992; Strnad
et al
. 1993; Sánchez-Camazano
et al.
1994; De Miguel
et al
. 1998; Imperato
et al
.
2003; Shi
et al
. 2008; Yesilonis
et al
. 2008).
The exact contribution of each single source to the
load of trace elements in urban soils is diffi cult to
μ
4.2.5 Urban soil
The term “urban soil” can be understood to encom-
pass all types of non-paved land within the city
limits: public and private green areas (parks and
