ENSC 201 Lecture Notes - Lecture 13: Allethrins, Tetramethrin, Permethrin

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ENSC 201 Week 7 Lecture 1
Lecture 13: Pesticides
Modern Pesticides – non Persistent
If pesticide must be non-persistent, may need to be more toxic
oOrganophosphates are older but good example
Specificity Problem for Organophosphate Pesticides
Mode of action is neurotoxicity through inhibition of acetylcholinesterase
oNerves that fire release acetylcholine, then Ache enzyme removes
acetylcholine
oWithout enzyme, nerve synapse can’t reset, get paralysis
Problem – this enzyme is also in many non-target organisms, including
humans
Better Approaches to Pesticides
Modern approach: if non persistent, must have high acute toxicity
oTo avoid hazard, toxicity must be more selective, learn from nature?
oInsecticides – pyrethrins
Isolated from chrysanthemum – some plants have evolved over many years
to have natural defense against insects
oPyrethins – low toxicity to humans
oCan be used indoor (domestic), short term outdoors
Not stable enough for agriculture use
oCommercial synthetic variations on natural structure are more stable
Still not persistent
o‘raid’ uses allethrin, permethrin and other pyrethrins
omoderate toxicity to insects requires extended exposure – needs
regular application or improved technology (can include wax to coat
pests and stabilize while delivering over longer time)
Organic Contaminants – Pesticides
marketing of ‘raid’
okills most bugs
omore stable synthetic variations on pyrethins (allethrin, tetramethrin)
onaturally extracted pyrethrins used instead of more stable synthetics
herbicides
ohistorically in wider use than insecticides, less toxic to humans
take advantage of different plant physiology
atrazine and triazines
ointerfere with photosynthesis, many good properties
used to control weeks among less sensitive crop plants (corn)
do not bioaccumulate (are moderately less water soluble)
low human/environmental toxicity
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