Topic 2 – A Growing
Grade 9 Science
• Chemicals used to control “pests”
(1) Herbicides – control unwanted plants.
(2) Insecticides – control unwanted insects.
(3) Fungicides – control unwanted fungus
• 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.
• Populations of
hawks, eagles, and
osprey were hit
hard. DDT caused
their eggs to be
very thin and to
• process whereby chemicals accumulate in
the tissues of organisms along the food
DDT – Good or Bad?
Reduce mosquitoes – Kills animals
reduction in the
incidence of malaria.
Of 2000 chemical Biomagnification
studied as substitutes to
DDT, none has been
found as effective or as