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Pesticides Flashcards

1
Q

What is a synthetic chemical?

A

A substance not occuring in nature, mostly organic compounds using petroleum or natural gas for a carbon source.

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2
Q

What is the common mechanism of pesticides?

A

Blocking of a metabolic process.

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3
Q

What are categories of pesticide?

A

Insecticide, herbicide, fungicide, rodenticide etc…

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4
Q

What has pesticide use facilitated?

A

Scaled production of food, less labour-intensive, small amounts of land…

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5
Q

What are examples of how extensively they are used?

A

Half pesticides in North America used for agriculture, 85% worldwide.

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6
Q

Where are these majorly applied in US?

A

Insecticides for cotton, herbicides for corn and soya.

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7
Q

What are examples of policies controlling them?

A

As half food eaten in US contains measurable quantities, many have been banned

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8
Q

How have pesticides been used outside of agriculture?

A

Prevent disease incidence: malaria, yellow fever, bubonic plague, west nile virus…

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9
Q

How extensive is insect damage to crops?

A

About 1/3 of total crop yield destroyed by pests or weeds in growth.

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10
Q

What compound was common in pesticides of the 50s/60s?

A

Organochlorides, organic compounds containing chlorides.

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11
Q

What are the properties of organochlorides?

A

Stability against decomposition, low water solubility, high solubility in hydrocarbon like environments, like fatty material, and high toxicity to insects.

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12
Q

How were they regulated politically?

A

The UNEP “dirty dozen”, being ‘Persistent Organic Pollutants’, banned and being phase-out through international agreements.

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13
Q

What are example of some still in use?

A

Dichlorobenzene’s 1,4 isomer as an insecticide.

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14
Q

Why are organisms susceptible to OC contamination?

A

It’s small solubility and ‘preference’ for absorption in organic matter.

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15
Q

How can the extent of this be exemplified?

A

Consuming one fish from an organochloride contaminated lake can provide more organochlorides than if you were to drink the entire lake.

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16
Q

What was the life cycle of DDT?

A

Used as an insecticide in WW2, ‘saving many lives’, however with devastating ecological effects (consider systems thinking)

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17
Q

What is its structure?

A

An ethane of 1 carbon and 3 Cl (replacing the H), with the other carbon containing two benzene rings

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18
Q

Why does it harm animals?

A

Metabolism by eliminating HCL, creating DDE (a metabolite), interfering with calcium-distributing enzyme, birds producing eggs (CaCO3), with too thin shells to withstand weight of parents.

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19
Q

What made it so persistent?

A

Low vapor pressure thus low evaporation rates, low reactivity to light, chemicals, and microorganisms, and low solubility in water (highly soluble in animal fats)

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20
Q

What is an example illustrating impacts of political regulation of DDT?

A

In lake trout from Lake Michigan, levelled to non-zero amounts in three decades.

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21
Q

How did DDT pollution demasculate alligators and african clawed frogs?

A

Its endocrine-disrupting properties.

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22
Q

What is the endocrine system?

A

This is a network of glands and organs producing and secreting hormones.

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23
Q

How does it act as an endocrine disruptor?

A

Mimic and interfere with action of hormones in the endocrine systems, like androgens (testosterone).

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24
Q

How do they become feminized?

A

Florida Lake Apopka heavily contaminated with DDT, alligators developing smaller penis size, reduced testosterone levels, and impaired reproduction, as DDT acts as estrogenic compounds.

25
Q

How did African Clawed Frogs exhibit intersex characteristics?

A

Male frogs exhibiting male and female reproductive organs, resulting from disrupted sexual differentiation due to endocrine disruption.

26
Q

What are other examples of ecological devestation due to pollutants?

A

Polychlorinated Biphenyls and Beluga Whales in St. Lawrence Estuary in Canada. Merecury and Avian reproduction. Lead and Waterfowl Mortality.

27
Q

How did PCB’s impact beluga whales?

A

PCB contamination disrupts the endocrine system, interfering with hormone function.

28
Q

What is the chemical basis of how organochlorides accumulate in organisms?

A

Solubility in hydrocarbon-likem edia, thus diffusing from water in the gills into fish flesh.

29
Q

What is the bioconcentration factor?

A

Equilibrium ratio of concentration of a chemical in fish relative to concentration in surrounding water.

30
Q

How is this determined?

A

Experimental equilibriation tests between two-phase systems of 1-octanol (alcohol surrogating fatty acids) and water

31
Q

How does bioaccumulation impact flesh DDT levels?

A

Increases linearly with increasing trophic level, thus accumulating in birds consuming fish.

32
Q

How can this principle be exemplified?

A

Measurements of DDT in Long Island Sound is 0.000003 ppm, but 0.04ppm in plankton, 0.5ppm in minnow fat, 2ppm in needlefish, and 25ppm in osprey and cormorants.

33
Q

Why are DDT analogs effective in replicating its impacts? -

A

It’s more related to its shape rather than to its chemical interactions.

34
Q

How is its shape important?

A

It wedges within nerve channels leading out from nerve cell, which normally transmits impulses via Na ions, the DDT holding open the channel, meaning continuous series of Na nerve impulses, causing convulsions and death.

35
Q

What are the ways in which chemicals breakdown in the environment?

A

Chemical hydrolysis, photodegradation, microbial degradation, volatization, absorption and sequestration.

36
Q

What is the structure of organophosphates?

A

Derivatives of phosphoric acid, with a pentavalent P atom.

37
Q

What bondings occur to this central P?

A

O/S double bond to P, or two methoxy or two ethoxy groups bound to P, or an R groups singly bound.

38
Q

How are organophosphates toxic?

A

They inhibit nervous system function, specifically the acetylcholine neurotransmitter.

39
Q

How do they impact acetylcholine?

A

ATC requires destruction following signal transduction, OP inhibiting enzyme facilitating this

40
Q

How do OP differ from OC?

A

Whilst less persistent, they are more toxic to humans and mammals.

41
Q

Why is it dangerous despite low persistence?

A

Its extensive use in homes, commerical buildings, lawns, and agriculture.

42
Q

How are they degraded in the environment?

A

Hydrolysis, a H2O splitting P-S/P-O bonds by addition of H to S/O and OH to the P

43
Q

What is the most important modern inseciticde?

A

Malathion

44
Q

What is the most important modern inseciticde?

A

O exposure, conversion to malaoxon, doubly bonded S replaced by O, more toxic.

45
Q

Why is this less harmful to mammals?

A

Enzyme rapidly converting it to harmless forms faster than they convert P=S to P=O, instead harming insects.

46
Q

Where has it been mis-used?

A

malaria eradication in Pakistan in 1976, resulting in thousands of sicknesses and 5 spray worker deaths.

47
Q

What are examples of its usage?

A

Control of medittareana fruit fly in California and Chile.

48
Q

What is a similar class of insecticides?

A

Carbamates, containing carbon instead of phosphorous, attacking ATC-destroying enzymes.

49
Q

What are examples of plant-produced insecticides used as green chemicals? -

A

Nicotine, rotenone, and pheromones, and most importantly the pyrethrins, coming from a species of chrysanthemum.

50
Q

How are these used domestically?

A

Synthetically due to its degradation in sunlight, called pyrethroids

51
Q

What are pyrethroids combined with?

A

Mixture with piperonyl butoxide, which inhibits enzymes within insects that detoxify pyrethrins.

52
Q

How can inseciticdes be applied most environmentally friendly?

A

Isolating a function that is unique to a particular organism and inhibiting that.

53
Q

What is an example?

A

1998 development of Confirm, Mach 2, and Intrepid, to control caterpillars.

54
Q

How does this impact caterpillars?

A

Through shedding of cuticle through molting of 20-hydroxyecdysone, which increases during molting, which the caterpillar ceases to feed upon production, resuming when it ends, where the insecticides mimic these compounds.

55
Q

What are examples of organochlorine insecticides and their impacts?

A

DDT (Dichhlorodiphenyltrichloroethane), Aldrin and Dieldrin, Lindane, and Chlordane.

56
Q

What are symptoms of acetylcholine esterase inhibitor?

A

A class of chemicals blocking acetylcholinesterase activity, which breaks down acetylcholine neurotransmitters, terminating its action on postsynaptic receptors.

57
Q

Why is AC breakdown important?

A

Else accumulates in synaptic cleft, resulting in overstimulation of cholingergic receptors.

58
Q

How does poisoning occur?

A

With high levels, Ach levels increase, overstimulating, leading to muscle weakness, excessive salivation, and respiratory diseases.

59
Q
A

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