Download Origins of the Elements

Pesticides
Insecticides:
• organochlorines
• organophosphates
• carbamates
Herbicides:
• triazines
• chloroacetamides
• phosphonates
• phenoxy
Fungicides
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
Pesticides
From: NIH
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.
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.
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
dichlorodiphenyldichloroethane
DDE
hexachlorobenzene
HCB
•agricultural fungicide
•banned in the US, however it is a
byproduct of other processes.
•very persistent in the environment
Pesticides
Organochlorines
toxaphene
•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
•flame retardant and insecticide
•still used in China and Australia against giant termites
•currently banned in US
•LD50 = 235mg/kg
mirex
methoxychlor
•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
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 80-160 mg/kg in rats.
•Is blamed for the decline of several fish and amphibian species in areas of high use.
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:
•tend to be the most volatile
•break down the fastest
B:
C:
•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
Pesticides
Organophosphates
dichlorvos
•type A
•highly toxic – LD50 = 25mg/kg
•used in fly strips and flea collars due to its
volatility
•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
malathion
•type C
•slightly toxic – LD50 = 985mg/kg
•widely used agriculturally and domestically
•used to spray communities to reduce mosquitoes and
other pests
Pesticides
Carbamates
•derivatives of carbamic acid
carbamic acid
carbamate
•dermal toxicity tends to be lower than for organophosphates
•break down within weeks
•decompose to CO2, alcohols, and amines
•highly toxic towards honeybees
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
aldicarb
•extremely toxic – LD50 = 1mg/kg
•may only be handled by professional applicators
•banned for domestic use
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.)
Pesticides
Triazines
•general formula of a herbicide triazine
•substitute a Cl, and 2 amines at the carbons
atrazine
•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
Pesticides
From: USGS
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
Pesticides
Phosphonates
glyphosate
•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)
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
2,4,5-T
•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
Pesticides
Natural pesticides
pyrethrin
•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
•derived from roots of tropical plants
•extremely toxic to fish
•LD50 = ~400mg/kg
rotenone
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.