9 pesticides

Question 1

what is the definition of a pesticide?

Answer 1

any physical, chemical or biological agent (i.e. not just chemicals) that will kill an undesirable plant or animal pest
-goal is to selectively kill pest with little or no toxicity to non-target species
-problem is highly conserved nature of many biological processes (e.g. nerve transmission, energy production)(have specific targets)

Question 2

pesticides are mainly:

Answer 2

-insecticides, herbicides and fungicides
-but also include: molluscicides, rodenticides

Question 3

what is the history of pesticides?

Answer 3

Question 4

what is the graph of the agricultural consumption of pesticides worldwide?

Answer 4

reason: population growth
-lose 200 billion dollars of crops to pests each year

Question 5

how much has pesticide used increased in each continent?

Answer 5

Question 6

what is the graphs on the pesticide usage and contamination in the canadian prairies?

Answer 6

WPOI=wetland pesticide occurrence index

Question 7

what was discovered about global human exposure?

Answer 7

Question 8

what are the pathways of pesticide contamination?

Answer 8

Question 9

how is the background pesticide exposure widespread?

Answer 9

-in humans: detectable metabolites in 92% of childrens, 82% of adults’ urine samples
-in food: detectable residues of at least one pesticide on 72% fruits/vegetables
-in homes: 3 to 9 pesticide residues in typical home
-in air: indoor air levels 10-100x> outdoor air
-in water: >90% stream samples, 50% of wells

Question 10

what are the physio-chemical properties of pesticides?

Answer 10

-solubility, persistence, volatility, etc
-toxicity, acute/chronic, dose-response

Question 11

what is the risk assessment of pesticides?

Answer 11

-pesticide use a deliberate poisoning of the environment
-if we understand their properties, fate and transport, and toxicity, then we can make estimates of risks
-label requirements, limits on use, bans
-pesticide development is very expensive

Question 12

what are the major types of insecticides?

Answer 12

Question 13

what are the four classes of organochlorine insecticides?

Answer 13

-DDT and its derivatives
-hexachlorocyclohexane
-cyclodienes
-polychloroterpenes

Question 14

what is the chemistry and kinetics of organochlorine insecticides?

Answer 14

-synthetic compounds
-some amount of Cl substitution for H on a hydrocarbon backbone (e.g. DDT, lindane)
-also includes compounds that have oxygen incorporated in their structure (e.g. methoxychlor)
-highly lipophilic (rapidly absorbed and enters CNS)
-resistant to biological/chemical breakdown, persistent
-most have high biomagnification potential

Question 15

what are some comparisons of organochlorines?

Answer 15

Question 16

what is the chemistry and kinetics of pyrethroid insecticides?

Answer 16

-synthetic analogs of naturally produced pyrethrins (chrysanthemum spp.)
-low water solubility
-natural products, and undergo rapid biodegradation and metabolism (not very presistent)
-low mammalian toxicity, but toxic to fish and invertebrates at low doses
-mechanism of toxicity similar to the organochlorines
-some require ‘synergists’

Question 17

what are pyrethroid synergists?

Answer 17

piperonyl butoxide and sesamex
-non-toxic themselves (potentiators)
-not effective with all insecticides

mechanism
-inhibitors of detoxifying enzymes (CYP)
-CYPs rapidly breakdown pyrethrum and some pyrethroids in absence of a synergist

Question 18

what are the generations of pyrethroid insecticides?

Answer 18

pyrethrum (i.e. Pyrethrin 1)
-4 different plant compounds
-unstable in sunlight, requires synergist

1st and 2nd generation pyrethroids (i.e. allethrin)
-improved stability, greater efficacy
-still requires synergist
-household uses

3rd and 4th generation pyrethroids (i.e. permethrin)
-photostable, no synergist required (incorporation of halogens into structure)
-agricultural uses

Question 19

which pesticides affect which channels?

Answer 19

Question 20

what are the chronic effects of organochlorine insecticides?

Answer 20

DDE causes endocrine disruption
-disrupt reproductive functions in many species including humans
-binds to and activates estrogen receptor causing feminization
-interferes with calcium metabolism during egg production in birds causing eggshell thinning, and causes embryonic mortality

some OC compounds and their metabolites are teratogenic, and/or carcinogenic

Question 21

what does the graph of eggshell thickness tell us?

Answer 21

time when pesticides like DDT started being use

Question 22

what continent has continued the use of organochlorines?

Answer 22

Question 23

what were the results of the contamination of food in african countries?

Answer 23

> 30% of food samples exceeded MRLs
-MRL=highest amount of pesticide residue that’s allowed to remain in food

Question 24

what are the structures of common organophosphates?

Answer 24

some have halogens

Question 25

what are the structures of common carbamates?

Answer 25

usually dont have halogens

Question 26

what is the chemistry and kinetics of organophosphorus (OPs) and carbamate pesticides?

Answer 26

-OPs are derivatives or orthophosphoric acid -moderately water-soluble (little or no halogenation of OPs used as insecticides) -carbamates are synthetic derivatives of carbamic acid -typically more polar and water-soluble than OPs -both compounds rapidly degrade in the environment, not very persistent

Question 27

what is the comparisons of toxicities between OCs, OPs and carbamates?

Answer 27

Question 28

what is the graph of synaptic transmission?

Answer 28

NT=acetylcholine which binds to nicotinic receptor

Question 29

what is the graph of the mode of action of OPs/Cbs?

Answer 29

acetylcholinesterase inhibitors -gets metabolized by CYP, which can create oxon metabolites which are toxic and also attack acetylcholinesterase -channel stays open, will keep firing: increase intracellular Ca or Na, and in mitochondria which releases cytochrome C which triggers apoptosis -cell will also undergo major oxidative stress -net effect: unregulated nerve twitches in body

Question 30

what is the chemical graph of the inactivation of acetylcholinesterase?

Answer 30

many binding sites on AChE

Question 31

what are the toxicological effects of OPs?

Answer 31

acute toxicity -#1 group responsible for acute insecticide toxicities in humans in canada (responsible for 90%) -target PNS, CNS and muscle chronic toxicity -lethargy, amnesia, depression and neurological disorders such as dementia, autism, hyperactivity disorder, and parkinson's disease

Question 32

do OPs only effect those that are exposed?

Answer 32

looked at pee for OP metabolites -even low level exposure can cause offspring problems

Question 33

what is carbofuran (case study)?

Answer 33

-the granular formulation was used extensively (and legally) in the US corn belt from 1978 to 1985 -estimated to kill 17 to 19 million birds per year on the corn belt during that period -a single grain was found lethal to a wide variety of bird species (birds mistook the information for grit or feed) -review of use led first to restrictions on use and then a complete ban (including canada and EU)

Question 34

what are the three most commonly used neonics?

Answer 34

chemically modeled like nicotine -low Kow so not lipophilic, which means high solubility -tend to bind to organic carbon in water with low affinity

Question 35

what are new generation pesticides?

Answer 35

neonicotinoids -nACh receptor agonist (bind to nicotinic receptor) -launched in 1990s, now the most widely used pesticide in the prairies -stable in soil and water (half-life 1-2 years) -supposedly less toxic to mammals than in insects -recent research shows accumulation on toxicity to non-target species (e.g. honey bees, birds)

Question 36

what is the effect of neonics?

Answer 36

net effect: same as OPs, makes receptor remain open

Question 37

what are the effects of neonics on birds?

Answer 37

-loss

Question 38

what are some country-specific effects of neonics on honey bees and wild bees?

Answer 38

more accumulation=less number of queens and less reproductive cells in their body

Question 39

what is the graph of the number of colonies effects versus total?

Answer 39

Question 40

what did ontario do?

Answer 40

Question 41

what is the current regulation of neonicotinoid usage?

Answer 41

-in 2018, EU banned 2 neonics (imidacloprid, clothianidin and thiamethoxam) -these were to be phased out by health canada's pest management regulatory agency (PMRA) -in 2018, PMRA recommended that these 3 neonics should be phased out over 3-5 yeats -however, in 2021, health canada changed its decisions, and deemed these neonics to be "largely acceptable with some mitigation"