1. Pesticides Insecticides: organochlorines organophosphates carbamates
Herbicides:
triazines
chloroacetamides
phosphonates
phenoxy
Fungicides

2. Pesticides ~109 kg used in North America annually (all uses)
~108 kg used in California for agriculture
The EPA stopped tracking pesticide use in 2001
50% used for agriculture (North America)
85% used for agriculture worldwide
insecticide – cotton
herbicide – corn and soybeans

3. Pesticides
From: NIH

4. Pesticides
Concerns:
exposure of the public to pesticides through food (chronic).
50% of the food eaten in the US has measurable levels of at least 1 pesticide.
exposure of farm workers to pesticides (acute).
exposure through home use of pesticides.
Some toxicologists believe ‘normal’ exposure to pesticides is not harmful.

5. Pesticides
History
1000 years ago – Greeks burned sulfur to create sulfur dioxide gas to control insects – used up until the 1800s and sulfur dust is used today as a fungicide.
Romans used arsenic to control insects – used through WWII.
Many inorganic compounds (NaF, B(OH)3) have been used throughout history.
Natural oils from petroleum, fish, and whales, have also been used.
Usually the doses needed were enough to be very toxic to humans.
Organic compounds were synthesized for pesticide use beginning with WWII.

6. Pesticides Organochlorines
stable – do not require frequent application
highly toxic to insects, low toxicity to humans
persistent in the environment
bioaccumulate – to toxic levels for animals high on the food chain
para-dichlorodiphenyltrichloroethane
DDT
hexachlorobenzene
HCB
agricultural fungicide
banned in the US, however it is a byproduct of other processes.
very persistent in the environment
dichlorodiphenyldichloroethane
DDE

7. Pesticides Organochlorines major replacement for DDT
highly toxic to fish – lakes cannot be restocked for years
relatively volatile – transported through air
currently banned in US – but sparsely used in other countries
LD50 = 50mg/kg
toxaphene
flame retardant and insecticide
still used in China and Australia against giant termites
currently banned in US
LD50 = 235mg/kg
mirex
similar structure and effectiveness as DDT and DDE
less persistent due to the reactive methoxy groups
metabolization by organisms rather than bioaccumulation
currently used in the US to control flies and mosquitoes
LD50 = 5000mg/kg
methoxychlor

8. Pesticides Organochlorines endosulfan
From: USGS
Use is permitted since it is not as persistent as other organochlorines (sulfur/oxygen bond). However its degradation product is somewhat persistent.
Close to being banned in the US.
Highly toxic and endosulfan sulfate (degradation product) is also highly toxic.
LD50 is mg/kg in rats.
Is blamed for the decline of several fish and amphibian species in areas of high use.

9. Pesticides Organophosphates derivatives of phosphoric acid
decompose within days to weeks after application
break down to phosphoric acid, alcohols, and thiols
metabolized quickly by animals – no bioaccumulation
tend to be more acutely toxic than organochlorines
distributed widely both for agriculture and domestic uses
Three types: A: B: C:
tend to be the most volatile
break down the fastest
more stable than type A
break down into type A
some insects absorb type B and C better than type A
generally, but not always less toxic than type A

10. Pesticides Organophosphates type A highly toxic – LD50 = 25mg/kg
used in fly strips and flea collars due to its volatility
dichlorvos
type B
extremely toxic – LD50 = 3mg/kg
non-specific – can easily kill birds and fish and bees
may be responsible for more human deaths than any other pesticide
still used in developing countries
parathion
type C
slightly toxic – LD50 = 985mg/kg
widely used agriculturally and domestically
used to spray communities to reduce mosquitoes and other pests
malathion

11. Pesticides Carbamates derivatives of carbamic acid
dermal toxicity tends to be lower than for organophosphates
break down within weeks
decompose to CO2, alcohols, and amines
highly toxic towards honeybees
carbamic acid
carbamate

12. Pesticides Carbamates extremely toxic – LD50 = 8mg/kg
one crystal, mistaken for a seed by a bird, will kill the bird
absorbed through plant roots and distributed to green vegetation
effectively banned in the US this year
carbofuran
somewhat toxic – LD50 = 307mg/kg
widely used in lawn and gardens
extremely toxic toward honeybees
somewhat soluble and tends to contaminate water supplies
production in India caused Union Carbide disaster in Bhopal
carbaryl
extremely toxic – LD50 = 1mg/kg
may only be handled by professional applicators
banned for domestic use
aldicarb

13. Pesticides Organophosphates and Carbamates as Neurotoxins
Both interfere with cholinesterase activity.
Cholinesterase is an enzyme that breaks down acetylcholine.
Acetylcholine is an important neurotransmitter.
High levels of acetylcholine cause convulsions, irregular heartbeat, and death.
Most poisoning occurs through acute exposure of people applying the insecticides.
A particular problem in developing nations where safety regulations and bans on particularly toxic chemicals are not in place.
Insecticides are also commonly used for committing suicide.
10,000 – 40,000 die annually, and millions suffer illness from insecticide exposure. (30 die in the US and 20,000 require medical care.)

14. Pesticides Triazines general formula of a herbicide triazine
substitute a Cl, and 2 amines at the carbons
represents 40% of all weed killer applied in the US
used mostly on corn, since corn is resistant
works by blocking the transformation of CO2 to sugars by photosynthesis
tends to accumulate in water and has been banned in some countries
LD50 = 2000mg/kg
atrazine

15. Pesticides
From: USGS

16. Pesticides Chloroacetamides derivatives of chloroacetic acid
replace the OH with a tertiary amine
usually used with atrazine in intensively planted areas
LD50 ~ 1000mg/kg
commonly found in groundwater near applied areas
alachlor

17. Pesticides Phosphonates commonly known as Roundup
extensively used commercially and domestically
inhibits the synthesis of essential amino acids
LD50 = 5000mg/kg
some crops have been genetically engineered to resist glyphosate
absorbs to soil better than other herbicides (doesn’t end up in the water as much)
glyphosate

18. Pesticides Phenoxy most widely used herbicide in the world
kills broadleaf weeds, but not grass
LD50 =640mg/kg
component of Agent Orange
2,4 D
good for clearing brush – used on roadsides
LD50 =500mg/kg
component of Agent Orange
manufacturing process usually introduces unacceptable amounts of the dioxin TCDD
banned in the US
2,4,5-T

19. Pesticides Natural pesticides found in chrysanthemum flowers
unstable in sunlight
stable derivatives are usually used (pyrethroids)
common in household insecticides
extremely toxic to aquatic life
LD50 = ~1000mg/kg
pyrethrin
derived from roots of tropical plants
extremely toxic to fish
LD50 = ~400mg/kg
rotenone

20. Pesticides Integrated Pest Management
The use of pesticides has decreased in many developed countries over the past decades due to:
chemical control – the use of both synthetic and natural chemical pesticides.
biological control – reducing pest populations by introducing predators, parasites, or pathogens.
cultural control – using farming practices that minimize pests.
host-plant resistance – using plants that are resistant to pest attack, including genetically engineered plants.
physical control – using non-chemical methods to reduce pests
regulatory control – preventing the invasion of an area by new pests.