9 pesticides Flashcards
what is the definition of a pesticide?
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)
pesticides are mainly:
-insecticides, herbicides and fungicides
-but also include: molluscicides, rodenticides
what is the history of pesticides?
what is the graph of the agricultural consumption of pesticides worldwide?
reason: population growth
-lose 200 billion dollars of crops to pests each year
how much has pesticide used increased in each continent?
what is the graphs on the pesticide usage and contamination in the canadian prairies?
WPOI=wetland pesticide occurrence index
what was discovered about global human exposure?
what are the pathways of pesticide contamination?
how is the background pesticide exposure widespread?
-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
what are the physio-chemical properties of pesticides?
-solubility, persistence, volatility, etc
-toxicity, acute/chronic, dose-response
what is the risk assessment of pesticides?
-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
what are the major types of insecticides?
what are the four classes of organochlorine insecticides?
-DDT and its derivatives
-hexachlorocyclohexane
-cyclodienes
-polychloroterpenes
what is the chemistry and kinetics of organochlorine insecticides?
-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
what are some comparisons of organochlorines?
what is the chemistry and kinetics of pyrethroid insecticides?
-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’
what are pyrethroid synergists?
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
what are the generations of pyrethroid insecticides?
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
which pesticides affect which channels?
what are the chronic effects of organochlorine insecticides?
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
what does the graph of eggshell thickness tell us?
time when pesticides like DDT started being use
what continent has continued the use of organochlorines?
what were the results of the contamination of food in african countries?
> 30% of food samples exceeded MRLs
-MRL=highest amount of pesticide residue that’s allowed to remain in food
what are the structures of common organophosphates?
some have halogens
what are the structures of common carbamates?
usually dont have halogens
what is the chemistry and kinetics of organophosphorus (OPs) and carbamate pesticides?
-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
what is the comparisons of toxicities between OCs, OPs and carbamates?
what is the graph of synaptic transmission?
NT=acetylcholine which binds to nicotinic receptor
what is the graph of the mode of action of OPs/Cbs?
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
what is the chemical graph of the inactivation of acetylcholinesterase?
many binding sites on AChE
what are the toxicological effects of OPs?
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
do OPs only effect those that are exposed?
looked at pee for OP metabolites
-even low level exposure can cause offspring problems
what is carbofuran (case study)?
-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)
what are the three most commonly used neonics?
chemically modeled like nicotine
-low Kow so not lipophilic, which means high solubility
-tend to bind to organic carbon in water with low affinity
what are new generation pesticides?
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)
what is the effect of neonics?
net effect: same as OPs, makes receptor remain open
what are the effects of neonics on birds?
-loss
what are some country-specific effects of neonics on honey bees and wild bees?
more accumulation=less number of queens and less reproductive cells in their body
what is the graph of the number of colonies effects versus total?
what did ontario do?
what is the current regulation of neonicotinoid usage?
-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”
