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Transcript
Grade 9 Science
PESTS AND PESTICIDES
BIOACCUMULATION
PESTS AND PESTICIDES

Pests are organisms that compete with or damage
crop species. Examples include weeds,
caterpillars, and mice.

To maximize the growth of a crop, farmers try to
eliminate pests.

In nature, there are no such things as pests. All
organisms are producers or consumers within food
webs.

By controlling pests, farmers grow crops in
an environment with hardly any consumers
or competitors.

When farmers plant monocultures, they
create ideal environments for pests. If not
controlled, pest populations could increase
enough to devastate the entire crop.
Pesticides
are poisons that
kill pests.
Types of pesticide include
herbicides, insecticides, and
rodenticides.
CHARACTERISTICS OF PESTICIDES

Long-lived pesticides persist in the environment for
many years.

Short-lived pesticides degrade in a matter of days.

Broad-spectrum pesticides are toxic to a wide range
of pest species.

Narrow-spectrum pesticides are toxic to a limited
number of species.

Pesticides work by causing biological or physical harm
to organisms.
ISSUES WITH PESTICIDES

Pesticide use has many benefits, but also has
significant environmental costs.

Sprayed pesticides that land on soil or are carried
away by the air may become sources of pollution.

Pesticides often kill species they were not intended
to kill. For example, a broad-spectrum pesticide
might kill the predatory insects that feed on pests.

Improper use of pesticides, such as spraying
at the wrong time of year, can also kill nontarget species.

The consequences of non-target killing can
be surprising and serious, such as the chain
of events that took place on Borneo after
spraying DDT to kill mosquitoes.
WHAT IS DDT?

colorless contact insecticide, toxic to humans
and animals when swallowed or absorbed
through the skin
WHERE IS BORNEO?
Borneo is the third biggest island in the world
 It comprises three countries – Malaysia as well
as Brunei on the north side and Indonesia on
the south
 The Dayak tribe are the indigenous people that
live there

http://www.youtube.com/watch?v=dYXCjENbqSs
BORNEO AND DDT
In the early 1950s, there was an outbreak of a serious disease
called malaria amongst the Dayak people in Borneo. The World
Health Organization tried to solve the problem. They sprayed
large amounts of a chemical called DDT to kill the mosquitoes
that carried the malaria. The mosquitoes died and there was
less malaria. That was good. However, there were side effects.
One of the first effects was that the roofs of people's houses
began to fall down on their heads. It turned out that the DDT
was also killing a parasitic wasp that ate thatch-eating
caterpillars. Without the wasps to eat them, there were more
and more thatch-eating caterpillars. Worse than that, the
insects that died from being poisoned by DDT were eaten by
gecko lizards, which were then eaten by cats. The cats started
to die, the rats flourished, and the people were threatened by
outbreaks of two new serious diseases carried by the rats, the
plague and typhus. To cope with these problems which it had
itself created, the World Health Organization had to parachute
live cats into Borneo.
DDT AND RACHEL CARSON
http://www.youtube.com/watch?v=uARFfWFcV5A
&feature=related
ISSUES WITH PESTICIDES - BIOACCUMULATION

Some pesticides do not break down in the body. If
an individual eats food contaminated with the
pesticide, it accumulates in the body.

The pesticide may continue to accumulate
as the organism eats more contaminated
food. This process is called
bioaccumulation.
DDT BIOACCUMULATES UP THE FOOD CHAIN
BIOAMPLIFICATION

Pesticides that bioaccumulate are soluble in fats and oils,
not water.

Pesticides stored in the fat of organisms at one trophic level
are passed on to consumers at the next trophic level.

The higher up the food chain, the more concentrated the
pesticides become. This process is called
bioamplification.

Arctic ecosystems are particularly vulnerable to
bioamplification. Many long-lived top consumers live in the
Arctic, such as whales, polar bears, and walrus. Inuit living
in these environments rely on these species for food.
BIOAMPLIFICATION OF MERCURY
PESTICIDE RESISTANCE

Pest species may become resistant to a pesticide
if it is used for a long time.

When a pest species develops resistance, farmers
need to apply a greater concentration of pesticide,
or switch to a different pesticide.

Pesticide resistance is a serious concern
worldwide.