Pesticides Flashcards
What is a synthetic chemical?
A substance not occuring in nature, mostly organic compounds using petroleum or natural gas for a carbon source.
What is the common mechanism of pesticides?
Blocking of a metabolic process.
What are categories of pesticide?
Insecticide, herbicide, fungicide, rodenticide etc…
What has pesticide use facilitated?
Scaled production of food, less labour-intensive, small amounts of land…
What are examples of how extensively they are used?
Half pesticides in North America used for agriculture, 85% worldwide.
Where are these majorly applied in US?
Insecticides for cotton, herbicides for corn and soya.
What are examples of policies controlling them?
As half food eaten in US contains measurable quantities, many have been banned
How have pesticides been used outside of agriculture?
Prevent disease incidence: malaria, yellow fever, bubonic plague, west nile virus…
How extensive is insect damage to crops?
About 1/3 of total crop yield destroyed by pests or weeds in growth.
What compound was common in pesticides of the 50s/60s?
Organochlorides, organic compounds containing chlorides.
What are the properties of organochlorides?
Stability against decomposition, low water solubility, high solubility in hydrocarbon like environments, like fatty material, and high toxicity to insects.
How were they regulated politically?
The UNEP “dirty dozen”, being ‘Persistent Organic Pollutants’, banned and being phase-out through international agreements.
What are example of some still in use?
Dichlorobenzene’s 1,4 isomer as an insecticide.
Why are organisms susceptible to OC contamination?
It’s small solubility and ‘preference’ for absorption in organic matter.
How can the extent of this be exemplified?
Consuming one fish from an organochloride contaminated lake can provide more organochlorides than if you were to drink the entire lake.
What was the life cycle of DDT?
Used as an insecticide in WW2, ‘saving many lives’, however with devastating ecological effects (consider systems thinking)
What is its structure?
An ethane of 1 carbon and 3 Cl (replacing the H), with the other carbon containing two benzene rings
Why does it harm animals?
Metabolism by eliminating HCL, creating DDE (a metabolite), interfering with calcium-distributing enzyme, birds producing eggs (CaCO3), with too thin shells to withstand weight of parents.
What made it so persistent?
Low vapor pressure thus low evaporation rates, low reactivity to light, chemicals, and microorganisms, and low solubility in water (highly soluble in animal fats)
What is an example illustrating impacts of political regulation of DDT?
In lake trout from Lake Michigan, levelled to non-zero amounts in three decades.
How did DDT pollution demasculate alligators and african clawed frogs?
Its endocrine-disrupting properties.
What is the endocrine system?
This is a network of glands and organs producing and secreting hormones.
How does it act as an endocrine disruptor?
Mimic and interfere with action of hormones in the endocrine systems, like androgens (testosterone).