Stressors and Soil Contamination - Sustainable Practices in Geoenvironmental Engineering - page 52

containing organic compounds such as 1,1,1-trichloroethane, creosote, carbon tetrachlo-
ride, pentachlorophenols, dichlorobenzenes, and tetrachloroethylene.
2.4.2.1 Persistent Organic Chemical Pollutants
Not all the organic chemicals found in the geoenvironment will be biologically and chemi-
cally degraded. The characteristic term used to describe organic chemicals that persist in
their original form or in altered forms that pose threats to human health is persistence . The
acronym used to describe persistent organic chemical contaminants is POPs (persistent
organic pollutants). These are generally deined as organic contaminants that are toxic, per-
sistent, and bioaccumulative. Included in the POPs are dioxins, furans, the pesticides and
insecticides (aldrin, chlordane, DDT, etc.), and a whole host of industrial chemicals grouped
as polycyclic aromatic hydrocarbons (PAHs), and halogenated hydrocarbons (including
the chlorinated organics). The top 12 POPs that have been identiied by the United Nations
Environmental Program as POPs for reduction and elimination are dioxins, furans, PCBs,
hexachlorobenzene, aldrin, dieldrin, endrin, chlordane, DDT, heptachlor, mirex, toxaphene.
The majority of the top twelve POPs are pesticides. Because of their heavy use in agriculture,
golf courses, and even at the household level for control of insects and other pests, it is not
dificult to see how these ind their way into the geoenvironment.
2.5 Surface and Subsurface Soils
Surface and subsurface soils constitute the uppermost portion of the mantle of the land
environment, i.e., the unconsolidated material in the upper layer of the lithosphere. This
upper layer is an integral part of the terrestrial ecosystem (Figure 2.8). When combined
with the lora and fauna, this upper mantle constitutes the habitat for terrestrial living
organisms. Soil, as a material, can be considered as a natural capital of the geoenviron-
ment. There are many functions served by surface and subsurface soils. They provide the
physical, chemical, and biological habitat for animals and soil microorganisms. In addi-
tion, they support growth of plants and trees, and are the vital medium for agricultural
production—the virtual host for food production. Soil materials in the subsurface are very
useful in the mitigation of hydraulic and chemical impacts of liquid wastes discharged
on (and in) the land surface—because of their inherent chemical and physical buffering
capabilities. Soil is a renewable resource that is in danger of becoming a nonrenewable
renewable resource (see Chapter 10).
2.5.1 Soil as a Resource Material
Soils are considered as essential resource material. Food production, forestry, and extrac-
tion of minerals are some of the life-support activities that depend on soil. Surface and
subsurface soils constitute the primary host or recipient of contaminants and contami-
nants. From the schematic shown in Figure 2.8, it is evident that the transport and fate
of contaminants that ind their way into this land compartment of the geoenvironment
will be a function of (a) the properties of the soil, (b) the properties of the contaminants
themselves, (c) the geological and hydrogeological settings, and (d) the microenvironment
(regional controls). It is not the intent of this section or this topic to deal in detail with the