9 history of pesticides Flashcards
what is a pesticide?
kills pests
-herbicides: plants
-insecticides: insects
-piscicides: fish
-fungicide: fungi
-vermicide: worms
-acaracide: mites and ticks
what can a pesticide be?
-natural: plant extracts
-pests of the pests
-natural or GMO pathogens
-chemicals
how long have pesticides been used for?
used for millennia
what was the first known pesticide?
-elemental sulfur dusting used in ancient Sumer about 4,500 years ago in Mesopotamia
-the Rig Veda (indian sacred text), which is about 4,000 years old, mentions the use of poisonous plants for pest control
what was the medieval pest control?
-by the 15th century, toxic chemicals such as arsenic, mercury, and lead were being applied to crops to kill pests. In the 17th century, nicotine sulfate was extracted from tobacco leaves for use as an insecticide
-up until the 19th century toxic metals, were the main ingredients in pesticides
-the 19th century saw the introduction of two more natural pesticides, pyrethrum, which is derived from chrysanthemums and rotenone, which is derived from the roots of tropical vegetables
what was arsenic in paint and insecticides?
-by the dawn of the 20th century, Scheele’s green had completely fallen out of use as a pigment but was still in use as an insecticide into the 1930s
-Wilhelm Sattler and Friedrich Russ in germany for the wilhelm dye and white lead company produced paris green while attempting to produce a more stable pigment than scheeles green
what is bordeaux mix?
a fungicide
-mixture of copper sulphate and lime
-initially used to discourage locals from picking grapes near roads
-later observed by botany professor Pierre-Marie-Alexis Millardet to be effective at reducing powdery mildew (fungus)
-still used today
-can be used for some “organic’ produce
-over use can lead to pollution of soil and aquatic environment
what are herbicides?
-control problem plants (weeds)
-but not killing the crop we are producing
-many function by mimicking plant hormones
what are the two major divisions of plants?
-monocots= grasses and cereal crops (wheat, corn etc.)
-dicots= everything else
-the two divisions have different biochemistries and so can be differentially targeted by herbicide chemicals
what are some modern herbicides?
chemical herbicides became common in the 1960s, let by triazine and other nitrogen-based compounds
-we were starting to see the development of designer chemicals where structures could be modified to enhance properties
-also significant were phenoxycarboxylic acids such as 2,4-dichlorophenoxyacetic acid (2,4-D)
-eventually glyphosate based products would also become significant
what are two of the oldest ‘modern’ herbicides used as defoliants?
2.4-D and 2,4,5-T
how are 2,4-D and 2,4,5-T absorbed?
absorbed by broad-leafed plants, killing them by causing excessive hormonal growth
-were designed to selectively kill weeds and unwanted plants in croplands
when were 2,4-D and 2,4,5-T introduced?
-first introduced in the beginning of World War II
-widespread use in agriculture following the end of the war
-when 2,4-D was commercially released in 1946, it triggered a worldwide revolution in agricultural output and became the first successful selective herbicide
what does 2,4-D allow?
allows greatly enhanced weed control in wheat, maize, rice and similar cereal grass crops, because it kills dicots (broadleaf plants) but not more monocots (grasses)
-low cost of 2,4-D has led to continued use today
-remains one the the rmost commonly used herbicides in the world
what is agent orange?
-a herbicide and defoliant chemical, one of the ‘tactical use; rainbow herbicides
-widely known for its use by the US millitary as part of its, operation ranch hand, during the vietnam war from 1961 to 1971
-a mixture of equal parts of two herbicides (2.4.5-T and 2,4-D)
-in addition to the herbicides traces of dioxin (mainly TCDD, the most toxic dioxin) were present in the mixture (dioxin was a chemical contaminant, not a herbicide)
-dioxin has been linked to potential health problems for many exposed individuals
what was operation ranch hand?
-many planes spreading agent orange
-not actually orange
is atrazine popular?
-in 2014, it was the second-most widely used herbicide in the US after glyphosate
-US 2014: 76 millions pounds (34 thousand metric tons)
-as of 2001, was the most commonly detected pesticide in drinking water in the US
-44 studies suggest it is an endocrine disruptor, an agent that can alter the natural hormonal system
what is round-up?
-glyphosate
-broad-spectrum systemic herbicide and desiccant
-it is an organophosphorus compound
-monsanto marketed in 1974 as roundup
-kills wide variety of plants: grasses, broadleaf, woody plants
-one of the most widely used herbicides globally
-in 2007, was most used in US 180-185 million pounds
-“roundup ready” crops are genetically modified to be resistance to glyphosate
what are modern insecticides?
-until the 1950s, arsenic-based insecticides were dominant
-paul herrman muller discovered DDT as a very effective insecticide
-thereafter, a range of organochlorines (OCs) (chemicals with chlorine in their structures) such as DDT were dominant
-others include: heptachlor, endrin, dieldrin, hexachlorobenzene
-they were replaced in the US by organophosphates and carbamates during the 1970s
-eventually, other compounds became dominant
what are some other persistent organochlorines?
-seeking to avoid resistance
-different insect targets
-different environmental conditions
what was the development of insect resistance (biomagnification)?
-although no harmful effects from average exposures to DDT have been seen in humans, DDT and other chlorinated hydrocarbons have been shown to harm other species, such as fishes, earthworms, and robins
-the hazard of DDT to non target animals is particularly acute for those species at the top of food chains
-carnivores at the ends of long food chains (eg. ospreys, pelicans, falcons, and eagles) once suffered serious declines in fecundity and hence in population size because of this
-high levels of chlorinated hydrocarbons interfere with forming eggshells of normal thickness
organophosphate pesticides are closely related to _________
NERVE GAS AGENTS
-applicators in developing countries may no have appropriate protective equipment
-improper application practices can impact ‘civilians’ due to vapor spread and water contamination
-in many countries like canada and the US you need to be licensed to be able to purchase and apply these poisons
what are carbamates?
carbamate insecticides are also inhibitors of acetylcholinesterase, but their action is reversible
-some examples: carbaryl, aldicarb, methomyl
-rapidly detoxified and excreted so their risk to warm-blooded animals is less
-degraded rapidly in the environment so persistence is not a problem
-they are, however, a danger to many useful insects, especially honeybees
what are pyrethroids?
based on natural toxins isolated from chrysanthemum flowers
-chemical modifications to design target organisms and environmental behavior
-many different compounds: chemists went crazy
-blocks sodium channels in insects but does not bind well to human sodium channels; also poor uptake in humans
-break down fairly rapidly in the environment
-still very toxic to aquatic invertebrates and fish
what are neonicotinoids?
nicotine itself is an effective insecticide
-chemists once again modified the base chemical to tailor to target organisms and to desire environmental properties
-now some of the most extensively used insecticides
-linked to honey bee die offs
