Environmental Engineering Reference
In-Depth Information
roads have been found to be up to 5 times higher than in soils located some distance
from roads. In the case of PAHs, these were found to be up to 100 times higher than in
soils distant from the roads. The source for these contaminants can be traced to vehicu-
lar exhausts (Münch, 1993). Cuny et al. (2001) reports that elimination of lead in gasoline
has substantially reduced lead levels in parking and rest areas near the motorways in
France.
Acid rain is a direct result of precipitation through sulfur and nitrogen oxides emit-
ted from fossil fuel combustion in coal thermal power plants. Sulfuric and nitric acids
are deposited on (a) the soil surface and into the underlying soil and perhaps into the
groundwater, (b) surface water courses, and (c) other surfaces. Northeastern United
States and eastern Canada have experienced rain with pH values ranging from 4 to 5.
Deforestation by acid rain has been signiicant in the nineteenth and early twentieth
centuries in North America and Europe. Forests affected by acid rain, in particular, have
less ability to retain water and protect against wind erosion. Heavy metals in contami-
nated soils may also be released by the acid rain. Fish and other aquatic organisms are
susceptible to many metabolic disorders when the pH of lakes and other water bodies
drops to 5 and below. Although not directly a geoenvironmental land problem, it is
pertinent to note that respiratory problems in smog events are signiicant human health
problems.
7.3.3 Implications on Health
The pathways of exposure of urban soils include inhalation and ingestion of soil, and
dusts through respiration, and consumption of home-grown foods and contact with the
soil. Urban gardening is widely practiced. Thorton and Jones (1984) have reported on vari-
ous tests conducted in the United Kingdom regarding radish and lettuces grown in typi-
cal urban gardens with soils containing different concentrations of zinc, copper, and lead.
Measurable values of lead in the radish and lettuce were obtained, and it was concluded
that both soil splash and foliar uptake contributed to the measured lead levels.
7.3.4 Impact of Land Use
Urban land can become degraded chemically and physically. As noted previously, con-
taminants degrade soil quality through release into the soil via spills, runoff, and other
additives. Roads, sidewalk, parking lots, and other structures seal the land and reduce
water iniltration into the groundwater. The installation of cables, sewers, foundation, and
other underground structures disrupts the physical structure of the soil. Introduction of
softer soils or wastes into the natural soil changes its characteristics.
Greenields are lands that have not been disturbed. They have the capacity to main-
tain their biodiversity, ecological functions, soil quality, and can renew their groundwater
resources. Brownields, meanwhile, have been degraded by contamination from various
sources—primarily industrial and manufacturing facilities such as reineries, rail yards,
gas stations, warehouses, dry cleaners, and other commercial enterprises using or stor-
ing hazardous chemicals. Table 7.2 provides a list of the various industries, activities, and
contaminants that lead to land contamination, mainly in urban areas. Abandoned urban
lands (brownields) are clear indications of failure in complying with the principles of
sustainable development as envisaged in the Brundtland Report (World Commission on
Environment and Development, 1987) as well as that of the Club of Rome.
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