Chapter 12: Pesticides Flashcards
What is pesticides?
Any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating any pest.
Why are we using pesticides with greater efficacy?
So we can use less of the active ingredient
What are the major routes of exposure for humans?
Ingestion, inhalation, dermal
The ancient Sumerians used what to control fungi?
elemental sulfur
Rotenone from various legume families was used to kill what? what is the mechanism of action?
fish
interferes with oxidative phosphorylation
Pyrethrins from Chrysanthemum flowers was used to kill what? what is the mechanism of action?
used to kill mosquitos and ticks
blocks sodium ion channels
DDT belongs to what class of insecticides?
organochlorine
What is the mode of action for DDT and pyrethroids?
- action potential is produced by pumping Na+ ions to the inside, K+ ions outside
- when the neutron fires, sodium channels let the Na+ ions in to create a ‘wave’ of depolarization that flows down the neuron
- The sodium channels quickly close to allow the neuron to go back to its resting state.
- DDT binds to the sodium channels and keeps them open
This basically causes repetitive ‘firing’ of the neuron
The repetitive firing of neurons leads to what?
spastic paralysis
What is the LD50 of DDT?
LD50=220mg kg-1 in rats
What is acute exposure to DDT not a concern?
the LD50 is relatively low compared to other pesticides to the acute exposure does not pose a big risk to humans
Why is chronic exposure to DDT a bigger concern than acute?
Because of it’s persistence and ability to biomagnify, chronic exposures are a bigger concern.
Why is DDT thought to be an endocrine disruptor? What is the IC50 of DDE and DDT? What is the classification of DDT?
It can alter hormone signalling. The DDT metabolite, DDE inhibits androgen signalling. DDT also activates estrogen receptors. DDT and its breakdown may contribute to breast cancers.
classified as a probably carcinogen.
DDE-IC50=5 DDT-IC50=5
What is meant by IC50? and what does a lower vs a higher value mean?
IC50 values = concentrations at which a molecule can bind to a receptor as an agonist or antagonist (lower values = stronger binding)
Type I and II Pyrethrins are made from what (natural)?
Type I and II Pyrethrins are made from the plant Chrysanthemum cinerariaefolium.
Why do natural pyrethrins low persistence in the environment? why do synthetic pyrethrins have a higher persistence in the environment?
they are very liable, and low persistence due to cleavage of the ester bond.
synthetic xenobiotics have a higher half life in the environment bc things in nature that would typically break the ester bond of a natural pyrethrins have not evolved to break the ester bond of synthetic pyrethrin
What makes pyrethrins different from other insecticides?
unlike many other insecticides, sodium channels with more affinity compared to animal sodium channels (i.e., more selective).
How do OPs (organophosphates) lead to neurotoxicity?
they are acetylcholinesterase inhibitors
Describe the regular and inhibited function of AChE
Normally, the acetyl group from acetylcholine is transferred onto a serine of the AChE enzyme. This acetyl group is rapidly hydrolyzed and the enzyme can now do another reaction.
OPs transfer their phosphoryl group onto the same serine, but this configuration is stable. it can take hours to days for water to hydrolyze it. This effectively sops AChE activity. If it hangs around long enough, one of the phosphoryl groups can be removed. this configuration cannot be hydrolyzed and the serine enzyme is permanently dead
What happens if there is no AChE activity?
too much acetylcholine in the synaptic cleft, which causes continuous nerve signal transmission
What is the LD50 of malathion in rats?
1g kg-1
Why do we use malathion despite the toxicity?
Because mammals have an enzyme (carboxyl esterase) that rapidly breaks down malathion. insects do not.
How was sarin used?
sarin has been used in chemical warfare
What is glyphosate? What does it inhibit?
Glyphosate is a general herbicide (therefore not specific) and it inhibits the EPSP synthase, an enzyme in the pathway that makes the aromatic amino acids.
What is Paraquat? how does it work? what is the danger of working with paraquat?
General non-selective herbicide for broad leaf and grass weeds.
‘steals’ electrons from photosynthetic transport chain and NADPH to make reactive oxygen species. Danger is that it can steal electrons from anywhere even though the specification is the photosynthetic chain. so it can steal electrons from our mitochondria and will eventually make its way to the lungs and kidneys cause ROS.
Parkinson’s disease results from what?
Dopamine generating cells
