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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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