PesticidesInsecticides:• 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 – cottonherbicide – corn and soybeans

Pesticides

From: NIH

PesticidesConcerns:

•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.

PesticidesHistory1000 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.

PesticidesOrganochlorines•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

dichlorodiphenyldichloroethaneDDE

para-dichlorodiphenyltrichloroethaneDDT

hexachlorobenzeneHCB

•agricultural fungicide•banned in the US, however it is a

byproduct of other processes.•very persistent in the environment

PesticidesOrganochlorines

toxaphene

mirex

methoxychlor

•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

•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

PesticidesOrganochlorines

•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.

endosulfan

From: USGS

PesticidesOrganophosphates•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 usesThree 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

PesticidesOrganophosphates

•type A•highly toxic – LD50 = 25mg/kg•used in fly strips and flea collars due to its volatilitydichlorvos

•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

•dermal toxicity tends to be lower than for organophosphates•break down within weeks

•decompose to CO2, alcohols, and amines•highly toxic towards honeybees

carbamic acidcarbamate

PesticidesCarbamates

carbofuran

•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

carbaryl

•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

aldicarb

•extremely toxic – LD50 = 1mg/kg•may only be handled by professional applicators•banned for domestic use

PesticidesOrganophosphates 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

alachlor

•usually used with atrazine in intensively planted areas •LD50 ~ 1000mg/kg•commonly found in groundwater near applied areas

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

2,4 D

2,4,5-T

•most widely used herbicide in the world•kills broadleaf weeds, but not grass•LD50 =640mg/kg•component of Agent Orange

•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

rotenone

•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

PesticidesIntegrated 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.