Lecture 11: Insecticides Flashcards
a _______ is any substance or mixture of substances intended for preventing,
destroying, repelling, or mitigating any pest
pesticide
T/F: global pesticide use is
generally increasing
true
although globally increasing, where has pesticide use leveled off?
NA and Europe
using more targeted methods so not as widespread
Greater than 300 thousand
people die each year from
_____ pesticide poisoning
acute
exposures can be accidental, intentional, occupational
what are the major routes of human pesticide exposure?
ingestion, inhalation, dermal
_____ pesticide exposure can come from pesticide residue in food or pesticides in
drinking water
Chronic
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)
from 1500s to 1900s, what were the main pesticides used?
metal salts
arsenic salts were used in NA until 50s
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.
Insecticides are the most acutely ____ of the
widely used pesticides
toxic
Most insecticides used today have
_____ effects
neurotoxic
most ________ are not very selective (i.e., do not
preferentially affect target insects more than
non-target organisms including humans or
other vertebrates)
insecticides
DDT belongs to a class of insecticides called ______ insecticides
organochlorine
when was DDT banned in the US? in canada?
1972
registered use in 1985
when was DDT banned worldwide? from which convention?
2001 in Stockholm convention (one of the dirty dozen)
T/F: DDT may still be used in countries with severe issues with malaria
true
DDT stands for…
Dichlorodiphenyltrichloroethane
_______: 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
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!)
_____ toxicity
- The repetitive firing of neurons leads to a ‘spastic
paralysis’, which kills insects.
DDT
T/F: DDT is not super acutely toxic compared to other insecticides, but
still considered as ‘moderately toxic’
true
why are chronic DDT exposures so worrisome?
its so persistent and able to biomagnify, what makes it dangerous!
T/F: Classified as a ‘possible’ human carcinogen… rats fed a
lot of DDT developed liver tumors
true
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)
OP
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 _____
OP
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)
