Today. Pesticides. Benefits of DDT. Glory years of DDT. DDT (p,p - dichloro-diphenyltrichloroethane) Success of DDT in controlling malaria

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1 Today Pesticides 1. The Science of DDT 2. Alternative Pesticides Coming Up: Monday: Carbaryl Seminar Tuesday: Flow Wednesday: No Class (finals) Thursday: Exam 3! 10:30-12:30 12:30 How do Pesticides present an environment al problem? DDT (p,p - dichloro-diphenyltrichloroethane) First synthesized in 1874 by Zeidler, insecticide properties discovered only in 1938 by Müller and colleagues Benefits of DDT Highly specific neurotoxicity for insects and extremely low toxicity to humans and mammals Cheap synthesis (therefore available for use in developing countries) Highly persistent: continues to kill insects for months after application Used to virtually eliminate malaria and other mosquito-borne diseases Estimated to have saved about 50 million human lives and to have prevented more than a 1,000 million human illnesses Success of DDT in controlling malaria Country Year Cases India Taiwan Venezuela Italy ,000, ,962 1,000, ,171, , Glory years of DDT used to control disease-carrying insects and agricultural pests 1948 Müller received Nobel Prize in Medicine for discovery of insecticide properties of DDT Discovery of other chlorinated insecticides Chlordane, mirex, dieldrine, lindane, methoxychlor, etc. Massive insect-controlling projects Gypsy moth (MA, ), fire ants Increased DDT production ,000,000 pounds ,000,000 pounds ,000,000 pounds 1

2 Published in 1962 Silent Spring Written by Rachel Carson, a respected marine biologist An expose of the damage to the environment from indiscriminate use of chlorinated pesticides Silent Spring Over increasingly large areas of the United States spring now comes unheralded by the return of birds, and the early mornings are strangely silent where once they were filled with the beauty of bird song Rachael Carson (1962) Silent Spring Ecological effects of DDT Decline in populations of raptors associated with egg thinning in turn associated with DDT and DDE accumulation Average shell weight in peregrine falcon Pre-DDT ( ) 1946) g Post-DDT ( ) 3.1 g Decrease in hatching success due to eggshell breakage (only thinning of 10% or more has reproductive consequences) Other chlorinated hydrocarbons (dieldrin, PCBs) may have contributed to the observed effects Experimental support for causality between DDT exposure and shell thinning Ratcliffe (1970) close correlation between eggshell thickness and residue levels of DDT in 14 species of birds including raptors and fish-eating birds Hickey and Anderson (1967) correlation between eggshell thickness and residue levels l of DDT in Larus argentatus Johnston et al. (1996) 15% decrease in eggshell thickness in peregrine falcon breeding in Canadian Arctic due to DDT exposure Lundholm (1997) - laboratory exposure to DDT and DDE resulted in 19-26% decrease in eggshell thickness in ducks Different species have different sensitivity to DDT Highly sensitive (30% or more thinning) peregrine falcon, brown pelican, some ducks, gulls Intermediately sensitive (5-15% thinning) Japanese quail, American kestrel Insensitive species (no thinning) domestic fowl, Bengalese finch 2

3 Biotransformation of DDT Aerobic dehydrochloration Anaerobic reductive dechloration Do these products look water soluble or fat soluble? Why is this important to know? Problems of DDT Persistency in organisms and the environment (biological half-life 8 years) Considerable environmental transport Lipid solubility Chemical resistance to biotransformation into water soluble compounds, which may be excreted Bioaccumulation and Biomagnification! Biomagnification of DDT and its derivatives Some Biology: What has to happen for a muscle to contract? How are we going to get the message across this gap?!? Some Biology: What has to happen for a muscle to contract? The binding of acetylcholine, the messenger, triggers the opening of sodium channels. The flow of sodium across the membrane triggers muscle contraction. You Try! With your group, diagram how the junction between a nerve cell and a muscle cell works. Use your diagram to answer the following questions: 1. What would happen if the sodium channels got stuck in their open position? 2. What would happen if the acetylcholine just stayed in the space between the nerve and the muscle cell forever?? 3

4 See the Effects! Tanny s Story Other Problems With Pesticides So why use DDT?!? Other Ecological Effects of DDT Use? Some More Biology: What is Malaria?? Milestones towards the DDT ban (1972) Scientific Advisory Committee convened by the President Madison Conference (1965) Environmental Defense Fund (1967) Creation of EPA (1969) EPA bans DDT (1972) 4

5 Impact of Silent Spring Call for a new attitude toward nature and recognition of the possibly destructive effects of humanity s action on the environment and associated responsibility Birth of the environmental movement in the USA DDT: the end of story? The return of the sting Pre- and post-ddt ban distribution of malaria in South America The use of DDT in the 1940s and 1950s almost eliminated the mosquitoes that carry the parasite that causes malaria. Post-DDT ban: Malaria rates in Africa are now higher than they are ever known to have been, except for Swaziland where DDT use was never stopped Africa Pre- and post-ddt ban distribution of Aedes aegypti Pre- and post-ddt ban distribution of hemorrhagic fever 5

6 You Decide: Take-home messages Congratulations! Your group has been selected to participate in a prestigious scientific advisory committee. You get to vote on renewing the global ban on DDT. Each person gets on vote. What will your team decide?? Future for DDT? WWF and Greenpeace have suspended their arguments against the use of DDT in malarial areas, provided application is limited to indoor spraying, particularly on to wall surfaces, to protect people, minimizing environmental effects Examples of other Pesticides organophosphates carbamates a botanical pesticide rotenone molting accelerators--diacylhydrazines Green Chemistry Activity 6