Environmental Engineering Reference
In-Depth Information
Science: Pesticides
We use chemicals to repel or kill pest organisms
as plants have done for millions of years to
defend themselves against hungry herbivores.
To help control pest organisms, we have developed a
variety of
pesticides
—chemicals to kill or control popu-
lations of organisms we consider undesirable. Com-
mon types of pesticides include
insecticides
(insect kill-
ers),
herbicides
(weed killers),
fungicides
(fungus killers),
and
rodenticides
(rat and mouse killers).
Biocide
is a more
accurate name for such a chemical because most pesti-
cides kill other organisms as well as their pest targets.
We did not invent the use of chemicals to repel or
kill other species. Indeed, plants have been producing
chemicals to ward off, deceive, or poison herbivores
that feed on them for nearly 225 million years. This
battle produces a never-ending, ever-changing coevo-
lutionary process: Herbivores overcome various plant
defenses through natural selection; then new plant de-
fenses are favored by natural selection in this ongoing
cycle of evolutionary punch and counterpunch.
Since 1950, pesticide use has increased more than
50-fold, and most of today's pesticides are more than
ten times as toxic as those used in the 1950s. Three-
fourths of these chemicals are used in developed coun-
tries, but their use in developing countries is soaring.
One-fourth of pesticide use in the United States is
devoted to ridding houses, gardens, lawns, parks,
playing fields, swimming pools, and golf courses of
pests. According to the U.S. Environmental Protection
Agency (EPA), the average lawn in the United States is
doused with ten times more synthetic pesticides per
hectare than U.S. cropland. Each year, more than
250,000 people in the United States become ill because
of household pesticide use, and such pesticides are a
major source of accidental poisonings and deaths for
young children.
Broad-spectrum agents
are toxic to many species.
Se-
lective,
or
narrow-spectrum, agents
are effective against a
narrowly defined group of organisms. Pesticides vary
in their
persistence,
the length of time they remain
deadly in the environment. In 1962, biologist Rachel
Carson warned against relying on synthetic organic
chemicals to kill insects and other species we deem
pests (see Individuals Matter, right).
Proponents of conventional chemical pesticides con-
tend that their benefits outweigh their harmful effects.
Conventional pesticides have a number of important
benefits.
They save human lives.
Since 1945, DDT and other
chlorinated hydrocarbon and organophosphate insec-
ticides probably have prevented the premature deaths
of at least 7 million people (some say as many as 500
million) from insect-transmitted diseases such as
malaria (carried by the
Anopheles
mosquito), bubonic
plague (carried by rat fleas), and typhus (carried by
body lice and fleas).
They increase food supplies.
According to the FAO,
55% of the world's potential human food supply is lost
to pests—about two-thirds of that before harvest and
the rest after (Figure 10-27). Without pesticides, these
losses would be worse, and food prices would rise.
They increase profits for farmers.
Pesticide compa-
nies estimate that every $1 spent on pesticides leads to
an increase in U.S. crop yields worth approximately
$4. (Studies have shown this benefit drops to about $2
if the harmful effects of pesticides are included.)
They work faster and better than alternatives.
Pesti-
cides control most pests quickly and at a reasonable
cost, have a long shelf life, are easily shipped and ap-
plied, and are safe when handled correctly by farm
workers. When genetic resistance occurs, farmers can
use stronger doses or switch to other pesticides.
When used properly, their health risks are very low
compared with their benefits.
According to Elizabeth
Whelan, director of the American Council on Science
and Health (ACSH), which presents the position of the
pesticide industry, “The reality is that pesticides, when
used in the approved regulatory manner, pose no risk
to either farm workers or consumers.”
Study descriptions of three major pesticides along with their
chemical formulas at Environmental ScienceNow.
Science and Economics: Advantages
of Modern Synthetic Pesticides
Modern pesticides save lives, increase food supplies,
increase profits for farmers, work fast, and are safe if
used properly.
Figure 10-27
Global outlook:
rats, such as these caught by a farmer
in India, destroy much of the world's wheat and rice before and after
harvest.
