Biochemistry Of Pesticides Essay

Submitted By HeyThere-Delilah
Words: 1602
Pages: 7

Biochemistry of Pesticides

Agricultural Pests ­ any organism that causes economic damage or disease to crops or livestock. Pesticides ­ chemicals that block a vital metabolic process in the organism to which they are toxic. Synthetic organic compounds ­ chemical basis for hundreds of products such as synthetic fibers, plastics, solvents, and pesticides.

I. Insecticides First Generation Pesticides: A. Botanicals ­ plants have evolved natural organic compounds to discourage herbivory Characteristics: non­persistent in environment, low toxicity to mammals, narrow spectrum Examples:
papain ­ found in pineapple and papaya, contains cyanogenic glycosides 2) nicotine ­ found in tobacco leaves, interacts with acetylcholine receptor 3) pyrethrum ­ found in chrysanthemums, attacks nervous system of insects 4)
Cyanogenic glycosides ­ found in passion vine which is the host plant for Heliconius butterflies. As glycosides, these compounds are non­toxic and contained in an intracellular compartment. A specific glycosidase enzyme resides in a separate compartment. When an herbivore munches on green tissues of a passion vine, the enzyme is brought into contact with the glycoside and cyanide is released. Passion vine produce stipules that look like fake Heliconius butterfly eggs. Since Heliconius caterpillars are sometimes cannibalistic, female butterflies reject plants that appear to be occupied by someone else's eggs. Fake Heliconius eggs on passion vine leaves

B. Inorganic Compounds of arsenic, lead, mercury
Toxic to mammals ­ use has resulted in human poisoning and fatalities
Accumulate in soil
Persistent in the environment
Farmers abandoned this approach in 1947 when DDT came on the market

Second Generation Pesticides (synthetic organic compounds):
A. Chlorinated Hydrocarbons ­ introduced as pesticides during the 1950s
● non­biodegradable, persistent
● high solubility in fats, low solubility in water
● high toxicity to insects, low toxicity to humans
● bioaccumulate
● biomagnify
● broad spectrum, goes after any insect good or bad
● many are known to be or suspected to be carcinogenic
● become widely distributed geographically
● half life is > 30 yrs bioaccumulation
: the accumulation of a substance such as a pesticide (DDT) in an organism or part of an organism biomagnification : a process in which chemical substances (DDT) become more concentrated at each high trophic level, 10 million time increase Most well known organochlorine insecticide is DDT ­ dichloro diphenyl trichloro ethane. Background:
● effectively killed mosquitoes that carried malaria and yellow fever, fleas that carried the plague, and body lice that carried typhus during WWII
● used to wipe out malaria in the U.S.
● banned in U.S. in 1972 by EPA
● still widely used in developing countries for malaria control
● DDT (propeller insecticidal), DDE (planar non­insecticidal), and DDD (propeller insecticidal) are probable human carcinogens (EPA)
● insects develop resistance over time
● stopped used DDT because it stopped working

Mechanism by which DDT kills insects:
Holds channel open, lets Na drain out, continuous transmission of nerve impulses, results in paralysis or convulsion Mechanism by which DDT decimated bird populations:
DDE is product of DDT, DDE interferes with distribution of calcium in bird eggs DDT and other chlorinated hydrocarbon pesticides are listed on the “Dirty Dozen” of
Persistent Organic Pollutants 2004 Stockholm Convention on Persistent Organic Pollutants ­ a global treaty that aims to protect human health and the environment from the effects of persistent organic pollutants
. Outlaws nine of the dirty dozen chemicals, limits the use of DDT to malaria control, and curtails inadvertent production of dioxins and furans.