4-The effect of excessive use and long - Fellows-Science

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14 Δεκ 2012 (πριν από 4 χρόνια και 8 μήνες)

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P
ART

4
-
L
ESSON

1

The effect of excessive use and long
-
term
consequences of using some pesticides

I
NTRODUCTION


The use of pesticides can have both positive and
negative effects. It can eliminate pests which
would otherwise destroy crops however it can
initiate problems.

I
NTRODUCTION


A pesticide is a chemical specifically designed to
kill insects, weeds and diseases. Their use at
time is essential to protect crops. Today as we
learn more and more about ecosystems and the
environment we are becoming more concerned
about the harms that they can cause.

I
NTRODUCTION


Farmers are being encouraged today to use
alternates to pesticides which may eventually
eliminate the use of chemicals all together.

A
LTERNATIVES

TO

PESTICIDES


There are several options to eliminate the use of
pesticides. The first and most obvious is to
choose plants appropriate for growth in the area.
Native plants are often the best choice.








Because most of our staple food crops are not
native, growing native crops is not ideal.


A
LTERNATIVES

TO

PESTICIDES



Rotating crops is
another solution. This
can disrupt a ‘pests’
life cycle or create an
environment not
suitable for it’s
survival. This would
eliminate the
possibility of a pest to
infest an area.

A
LTERNATIVES

TO

PESTICIDES


Physical barriers can also be an effective way to
fight pests. For example:


Using nets to enclose crops protects them from
insects and birds.


Wide metal strips can stop slugs


Tape around the base of trees


Traps


A
LTERNATIVES

TO

PESTICIDES


Biological controls are another successful option.
Introducing a predator species into the area can
ensure pest populations are controlled.








This option often has controversy attached to it.
Can you think of a reason for this?

A
LTERNATES

TO

PESTICIDES


Genetic engineering is another controversial
method to eliminate pesticides. This procedure
genetically alters crops to become more resistant
to pests.







For example introducing genes from one crop to
another to enable the new plant to produce toxic
proteins which pests cannot tolerate.

A
LTERNATIVES

TO

PESTICIDES



Why would genetic manipulation be
controversial?






Many methods of biological control are currently
being used but along with pesticides. This is
called integrated pest management. This allows
farmers to reduce the amount of chemicals being
used and how often it’s used.

A
LTERNATIVES

TO

PESTICIDES


Plant derived pesticides are also being used.
These can be just as potent and synthetic
pesticides but break down more easily and
rapidly without building up in the environment.

A
CTIVITY


Complete Activity 3.6 pg 122
-
123 HSC Spotlight
Text together.

H
OMEWORK


Read pages 127
-
128 HSC Spotlight Text

Update electronic vocabulary

Complete DOT Point 4.3
-
4.4

P
ART

4
-
L
ESSON

2

The effect of excessive use and long
-
term
consequences of using some pesticides


T
HE

LEGACY


Pesticides have had a positive impact on farming.
For example:


Increased yields


Enabled growth on unsuitable land


Extended growing seasons







However we need to consider the negative
impacts too.

T
HE

L
EGACY


Pesticides are
chemicals designed for
killing weeds, insects
and diseases. Most of
which are applied by
spraying. How do you
think this affects the
other organisms of the
area?

T
HE

L
EGACY


Overspray and run
-
off can transport pesticides to
other environments and even make their way
into our water system. The pesticide is then said
to be brought into contact with ‘non
-
target
organisms’.

T
HE

L
EGACY


This can have negative effects and may cause
problems worse than the initial pest problem.
For example non
-
target organisms can be killed
by the misuse of pesticides.

T
HE

L
EGACY


Pesticides that are
absorbed into
environments can also
endanger non
-
target
organisms. A famous
example of this is
DDT.
(dichlorodiphenyltrich
loroethane)

T
HE

L
EGACY


DDT was a great
pesticide because it
did not break down
easily and killed pests
for a long time. It was
widely used during
WWII to control
mosquito populations.

T
HE

L
EGACY


DDT did reduce mosquito populations which led
to good things such as reduce the spreading of
malaria, however bad things were also
happening.


T
HE

L
EGACY


DDT killed other
insects. Some of these
insects were eaten by
lizards which in turn
were eaten by cats.
The DDT absorbed in
the insects and lizards
was strong enough to
kill the cats.

T
HE

LEGACY


Soon rat populations began to explode because
the cat population decreased. This is one
example of a negative effect of pesticides and
there are many more including insects evolving
to become resistant to the chemical.

T
HE

L
EGACY


Even worse problems were notices in the 1960’s.
DDT was linked to Bioaccumulation and
Biomagnification. Bioaccumulation is the
increase in concentration of a pollutant from the
environment into the first organism in a food
chain.


DDT was being detected in plants which meant it
was accumulating in their tissues. These plants were
then being eaten by other organisms which would
also accumulate DDT in their systems but at higher
concentrations because of repeat feeding.


T
HE

L
EGACY


DDT was being passed
through food chains at
higher and higher
concentrations! This
affects the non
-
target
species in the area
which eat the target
species or any other
organism living within
the sprayed area.

T
HE

L
EGACY


In order to accumulate, a pesticide must be long
lasting in the environment. DDT has a half life
of 15 years. This means that if 100 kilograms of
DDT was sprayed onto an area, 15 years later 50
kilograms would still be around.

T
HE

L
EGACY


DDT is also fat soluble. This means once in an
organisms system it is not easily excreted.
Bioaccumulation can produce concentrations is
organisms which make them toxic to their
predators.

T
HE

L
EGACY


Further study of
animals have shown
that DDT and other
pesticides can cause
cancers, mutations,
birth defects and
other life threatening
defects. Today new
pesticides undergo
more rigorous testing.

T
HE

L
EGACY


Pesticide use is becoming less popular and the
adoption of integrated pest control by many
farmers is welcome and encouraged.



R
EVIEW
:




Discuss Activity 3.9 pg 131



Science Skills pg 132

H
OMEWORK

Read pages 129
-
131 Spotlight Text

Update electronic vocabulary

Complete ‘To Think About’ page 133

Complete DOT Point 4.1
-
4.2 pages 66
-
67