Lecture 11: Insecticides Flashcards by Zoe Phillips

a _______ is any substance or mixture of substances intended for preventing,
destroying, repelling, or mitigating any pest

pesticide

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T/F: global pesticide use is
generally increasing

true

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although globally increasing, where has pesticide use leveled off?

NA and Europe
using more targeted methods so not as widespread

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Greater than 300 thousand
people die each year from
_____ pesticide poisoning

acute

exposures can be accidental, intentional, occupational

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what are the major routes of human pesticide exposure?

ingestion, inhalation, dermal

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_____ pesticide exposure can come from pesticide residue in food or pesticides in
drinking water

Chronic

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what are two examples of ancient pesticide use? we’ve applied them to crops for a long time!

2500 BCE Sumerians used sulfur compounds as
insecticides
- Ancient Egyptians used herbs and metals (e.g., Hg, As)

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from 1500s to 1900s, what were the main pesticides used?

metal salts
arsenic salts were used in NA until 50s

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from 1900s to today, what are some of the main pesticides used?

Rotenone from various members of the Legume family.
- Used to effectively kill fish.
- Interferes with oxidative phosphorylation.

Pyrethrins from Chrysanthemum flowers.
- Used to kill mosquitos and ticks.
- Interferes with sodium channels.

Predominantly use xenobiotics over the past few decades.
- some remain problematic as legacy pollutants.

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Insecticides are the most acutely ____ of the
widely used pesticides

toxic

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Most insecticides used today have
_____ effects

neurotoxic

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most ________ are not very selective (i.e., do not
preferentially affect target insects more than
non-target organisms including humans or
other vertebrates)

insecticides

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DDT belongs to a class of insecticides called ______ insecticides

organochlorine

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when was DDT banned in the US? in canada?

1972
registered use in 1985

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when was DDT banned worldwide? from which convention?

2001 in Stockholm convention (one of the dirty dozen)

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T/F: DDT may still be used in countries with severe issues with malaria

true

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DDT stands for…

Dichlorodiphenyltrichloroethane

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_______: Synthesized by Authman Zeidler in
1874
- Insecticidal properties noted by Paul
Hermann Müller in 1939
- This discovery was important because
we could try to eradicate the Anopheles
mosquitoes - vectors for malaria
- Muller received the Nobel prize in
Medicine for this

DDT

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what is the mode of action of DDT and pyrethrins/pyrethroids

bind to sodium channels and keeps them open, causes repetitive firing of neuron (neurotoxin!)

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_____ toxicity
- The repetitive firing of neurons leads to a ‘spastic
paralysis’, which kills insects.

DDT

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T/F: DDT is not super acutely toxic compared to other insecticides, but
still considered as ‘moderately toxic’

true

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why are chronic DDT exposures so worrisome?

its so persistent and able to biomagnify, what makes it dangerous!

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T/F: Classified as a ‘possible’ human carcinogen… rats fed a
lot of DDT developed liver tumors

true

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T/F: DDT may be an endocrine disruptor as it can alter hormone
signaling

true

why is DDT a possible endocrine disruptor?

The DDT metabolite DDE interferes with androgen signaling (IC50 = 5) - an antagonist DDT also activates estrogen receptors (IC50 = 5) - an agonist DDT and its breakdown products (DDE) may contribute to breast cancers because of effects of endocrine disruption. Classified as a probable carcinogen.

what is one secretion from humans that we can measure chronic DDT exposure?

breast milk, values can give us an idea of last time DDT was used in their environment (low values means exposure was more recent)

DDT is also detectable in Inuit populations… why is this so worrisome?

far from where DDT was ever used

where is the superfund site (needs to be cleaned up its that bad) for DDT in the US? why did the EPA declare it a superfund site?

LA Montrose Chemical Corp. of California was the largest producer of DDT in the USA. Contracted the California Salvage company to barge acid waste that contained DDT residue offshore to dump (peaked in 1950s). Discovered recently that the DDT waste may have been just poured into the ocean. around or over 56000 barrels of waste!!!

what can we measure in oceans to track DDT levels?

sediment cores! help us figure out when/how much was dumped

T/F: OCP have been found in shark livers, from agricultural practices (less industrial)

true All have similar diets, therefore higher OCPs in hammerhead and sharpnose shark due to their migration to other polluted regions

Type I and II ______ are made from the plant Chrysanthemum cinerariaefolium

Pyrethrins

what is the mode of action of pyrethrins?

same as DDT, keep NA channels open

_____: Low persistence in the environment due to cleavage of the ester bond – relatively fast breakdown

pyrethrins

what are the synthetic versions of pyrethrins?

pyrethroids, which have longer half lives

_____ now account for 15 to 20% of all insecticides used

synthetic pyrethroids

are the LD50 values of pyrethroids high or low

relatively high! so low toxicity

T/F: Unlike many other insecticides, pyrethrins/pyrethroids bind insect sodium channels with more affinity compared to vertebrate sodium channels (i.e., more selective).

true

T/F: Pyrethroids are used in the airline industry to prevent the spread of potential insect pests (pre- flight is permethrin, during flight is D-phenothrin)

true!!! they used to use DDT

what kind of mutation would mosquitos that can survive airports/flights have?

mutations related to resistance to pyrethroid pesticides (i.e. mutations in sodium channels), not effectively killed by pre-flight sprays

Upwards of 50% of all insecticides used today are_______

organophosphates

OPs lead to neurotoxicity because they are ________ inhibitors

acetylcholinesterase If the acetylcholine isn’t removed, the receptor will keep being activated, sending the signal in the next cell

______: were developed in 1930s high acute toxicity (4x more toxic than DDT)

OPS transfer a phosphoryl group onto AChE, which is what removes acetylcholine from synaptic cleft they stop AChE activity by doing this, what is the final result of this process?

enzyme cannot regenerate quickly and needs to be replaced

malathion is a _____

why do we spray malathion in winnipeg? (have switched to deltamethrin)

we have a carboxylexterase enzyme (mammals) that can breakdown malathion so even if we get exposed, we can break it down (and its just as good of an AChE as other OPs!)

T/F: OPs, and malathion in particular, are not carcinogenic. In vitro studies show that they may be endocrine disrupting, but not clear evidence of this in humans

true

T/F: Some OPs are more highly acutely toxic to humans than others. Some of these have been developed specifically to kill people

true

______ has been used in chemical warfare, its an OP

sarin

_____ gas is 100x more deadly than sarin, it killed Kim Jong Un's brother in 2017

VX gas its resistant to hydrolysis, which is what makes it so much more toxic

why didn't Kim Jong Nam's antidote work, when two women combined harmful substances to make VX

it was in pill form, so it couldn't absorb fast enough to be effective (dermal absorption is faster than GI)

______ – Nerve agent developed in Russia in the 1970s and 80s. 5-8x more toxic than VX.

Novichok

afoxolaner is a ____

isoxaline

_______ used to kill ticks on your dog. Dog ingests the chews once a month so the chemical circulates in the blood.

Afoxolaner

how does afoxolaner work?

When the tick obtains a blood meal, the chemical binds to GABA receptors and impairs the nervous system – leads to paralysis. Dogs have GABA receptors too, but there is some specificity. Relative dose is important!!

TreeAzin used to treat ash trees for emerald ash borer (EAB) in Winnipeg, what does the TreeAzin solution contain?

azadirachtin – a plant derived compound from the neem seed

how does azadirachtin work?

acts as an anti-feedant (affects chemoreceptors and digestion) and can even lead to behavioural avoidance in EAB toxic to aquatic animals, but can be injected right into the tree (systemic treatment)

what can azadirachtin be toxic to? why is the treatment performed after blooming season?

toxic to bees

what are insecticide effects on non-target organisms?

Reduced growth and reproduction Decrease in animal behaviours related to fitness (e.g. locomotor activity, feeding rate, attack rate) Disruption in physiological biomarker response (e.g. enzymatic activities, metabolic reaction, photosynthesis)