Chapter 12: Pesticides

Question 1

What is pesticides?

Answer 1

Any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating any pest.

Question 2

Why are we using pesticides with greater efficacy?

Answer 2

So we can use less of the active ingredient

Question 3

What are the major routes of exposure for humans?

Answer 3

Ingestion, inhalation, dermal

Question 4

The ancient Sumerians used what to control fungi?

Answer 4

elemental sulfur

Question 5

Rotenone from various legume families was used to kill what? what is the mechanism of action?

Answer 5

fish
interferes with oxidative phosphorylation

Question 6

Pyrethrins from Chrysanthemum flowers was used to kill what? what is the mechanism of action?

Answer 6

used to kill mosquitos and ticks
blocks sodium ion channels

Question 7

DDT belongs to what class of insecticides?

Answer 7

organochlorine

Question 8

What is the mode of action for DDT and pyrethroids?

Answer 8

1. action potential is produced by pumping Na+ ions to the inside, K+ ions outside
2. when the neutron fires, sodium channels let the Na+ ions in to create a ‘wave’ of depolarization that flows down the neuron
3. The sodium channels quickly close to allow the neuron to go back to its resting state.
4. DDT binds to the sodium channels and keeps them open

This basically causes repetitive ‘firing’ of the neuron

Question 9

The repetitive firing of neurons leads to what?

Answer 9

spastic paralysis

Question 10

What is the LD50 of DDT?

Answer 10

LD50=220mg kg-1 in rats

Question 11

What is acute exposure to DDT not a concern?

Answer 11

the LD50 is relatively low compared to other pesticides to the acute exposure does not pose a big risk to humans

Question 12

Why is chronic exposure to DDT a bigger concern than acute?

Answer 12

Because of it’s persistence and ability to biomagnify, chronic exposures are a bigger concern.

Question 13

Why is DDT thought to be an endocrine disruptor? What is the IC50 of DDE and DDT? What is the classification of DDT?

Answer 13

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

Question 14

What is meant by IC50? and what does a lower vs a higher value mean?

Answer 14

IC50 values = concentrations at which a molecule can bind to a receptor as an agonist or antagonist (lower values = stronger binding)

Question 15

Type I and II Pyrethrins are made from what (natural)?

Answer 15

Type I and II Pyrethrins are made from the plant Chrysanthemum cinerariaefolium.

Question 16

Why do natural pyrethrins low persistence in the environment? why do synthetic pyrethrins have a higher persistence in the environment?

Answer 16

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

Question 17

What makes pyrethrins different from other insecticides?

Answer 17

unlike many other insecticides, sodium channels with more affinity compared to animal sodium channels (i.e., more selective).

Question 18

How do OPs (organophosphates) lead to neurotoxicity?

Answer 18

they are acetylcholinesterase inhibitors

Question 19

Describe the regular and inhibited function of AChE

Answer 19

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

Question 20

What happens if there is no AChE activity?

Answer 20

too much acetylcholine in the synaptic cleft, which causes continuous nerve signal transmission

Question 21

What is the LD50 of malathion in rats?

Answer 21

1g kg-1

Question 22

Why do we use malathion despite the toxicity?

Answer 22

Because mammals have an enzyme (carboxyl esterase) that rapidly breaks down malathion. insects do not.

Question 23

How was sarin used?

Answer 23

sarin has been used in chemical warfare

Question 24

What is glyphosate? What does it inhibit?

Answer 24

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.

Question 25

What is Paraquat? how does it work? what is the danger of working with paraquat?

Answer 25

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.

Question 26

Parkinson’s disease results from what?

Answer 26

Dopamine generating cells