Environmental Engineering Reference
In-Depth Information
your own ecological footprint by visiting the web-
site www.redefiningprogress.org/ . Also see the Guest
Essay by Michael Cain on the website for this chapter.
According to the developers of the ecological foot-
print concept, William Rees and Mathis Wackernagel,
it would take the land area of about four more planet
earths for the rest of the world to reach U.S. levels of
consumption with existing technology. See the Guest
Essay on the website for this chapter by Norman Myers
about the growing ecological footprint of China.
1-4
POLLUTION
Science: Sources and Harmful Effects
of Pollutants
Pollutants are chemicals found at high enough levels
in the environment to cause harm to people or other
organisms.
Pollution is any addition to air, water, soil, or food that
threatens the health, survival, or activities of humans
or other living organisms. Pollutants can enter the en-
vironment naturally (for example, from volcanic erup-
tions) or through human activities (for example, from
burning coal). Most pollution from human activities
occurs in or near urban and industrial areas, where
pollution sources such as cars and factories are con-
centrated. Industrialized agriculture also is a major
source of pollution. Some pollutants contaminate the
areas where they are produced; others are carried by
wind or flowing water to other areas.
The pollutants we produce come from two types
of sources. Point sources of pollutants are single, iden-
tifiable sources. Examples are the smokestack of a coal-
burning power or industrial plant (Figure 1-8), the
drainpipe of a factory, or the exhaust pipe of an auto-
mobile. Nonpoint sources of pollutants are dispersed
and often difficult to identify. Examples are pesticides
sprayed into the air or blown by the wind into the at-
mosphere, and runoff of fertilizers and pesticides from
farmlands and suburban lawns and gardens into
streams and lakes. It is much easier and cheaper to
identify and control pollution from point sources than
from widely dispersed nonpoint sources.
Pollutants can have three types of unwanted ef-
fects. First, they can disrupt or degrade life-support
systems for humans and other species. Second, they can
damage wildlife, human health, and property. Third,
they can create nuisances such as noise and unpleasant
smells, tastes, and sights.
Science: Nonrenewable Resources
Nonrenewable resources can be economically
depleted to the point where it costs too much to
obtain what is left.
Nonrenewable resources exist in a fixed quantity or
stock in the earth's crust. On a time scale of millions
to billions of years, geological processes can renew
such resources. But on the much shorter human time
scale of hundreds to thousands of years, these re-
sources can be depleted much faster than they are
formed.
These exhaustible resources include energy re-
sources (such as coal, oil, and natural gas that cannot be
recycled), metallic mineral resources (such as iron, cop-
per, and aluminum that can be recycled), and non-
metallic mineral resources (such as salt, clay, sand, and
phosphates, which usually are difficult or too costly to
recycle).
Although we never completely exhaust a nonre-
newable mineral resource, it becomes economically de-
pleted when the costs of extracting and using what is
left exceed its economic value. At that point, we have
several choices: try to find more, recycle or reuse exist-
ing supplies (except for nonrenewable energy re-
sources, which cannot be recycled or reused), waste
less, use less, try to develop a substitute, or wait mil-
lions of years for more to be produced.
Some nonrenewable metallic mineral resources,
such as copper and aluminum, can be recycled or re-
used to extend supplies. Recycling involves collecting
waste materials, processing them into new materials,
and selling these new products. For example, dis-
carded aluminum cans can be crushed and melted
to make new aluminum cans or other aluminum items
that consumers can buy. Reuse means using a resource
over and over in the same form. For example, glass
bottles can be collected, washed, and refilled many
times.
Recycling nonrenewable metallic resources takes
much less energy, water, and other resources and pro-
duces much less pollution and environmental degra-
dation than exploiting virgin metallic resources.
Reusing such resources takes even less energy and
other resources and produces less pollution and envi-
ronmental degradation than recycling.
Science: Solutions to Pollution
We can try to prevent production of pollutants
or clean them up after they have been produced.
We use two basic approaches to deal with pollution.
One is pollution prevention, or input pollution con-
trol, which reduces or eliminates the production of
pollutants. The other is pollution cleanup, or output
pollution control, which involves cleaning up or dilut-
ing pollutants after they have been produced.
Environmental scientists have identified three
problems with relying primarily on pollution clean-
up. First, it is only a temporary bandage as long as
population and consumption levels grow without
corresponding improvements in pollution control
technology. For example, adding catalytic converters
to car exhaust systems has reduced some forms of air
pollution. At the same time, increases in the number of
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