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Topic 2 – A Growing Concern

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					Topic 2 – A Growing
      Concern
    Grade 9 Science
               Pesticides
• Chemicals used to control “pests”
(1) Herbicides – control unwanted plants.
(2) Insecticides – control unwanted insects.
(3) Fungicides – control unwanted fungus
    pests.
                       DDT
•   Also used to prevent pest damage to crops.
•   10 yrs. After its first use, problems appeared.
•   Birds, fish, and frogs found dead.
•   Fat in their bodies had high levels of DDT.
•   DDT remained in soil and water for years.
•   DDT found in bodies of animals around the
    world, in places where DDT had not been used.
    Also showed up in human tissue.
                  DDT
• Populations of
  hawks, eagles, and
  osprey were hit
  hard. DDT caused
  their eggs to be
  very thin and to
  break easily.
             Biological
   Magnification/Biomagnification
• process whereby chemicals accumulate in
  the tissues of organisms along the food
  chain.
        DDT – Good or Bad?
Pro’s                    Con’s
Reduce mosquitoes –       Kills animals
reduction in the
incidence of malaria.
Saves lives.
Of 2000 chemical          Biomagnification
studied as substitutes to
DDT, none has been
found as effective or as
safe.

				
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posted:7/16/2013
language:English
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