Flashcards in Q 2 Text Deck (53)
The US Environmental Protection Agency's definition of a pesticide is as follows:
The purpose of a pesticide is usually to kill or repel some form of life.
"A pesticide is any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating any pest. Though often misunderstood to refer only to insecticides, the term pesticide also applies to herbicides, fungicides, and various other substances used to control pests."
Pesticide formulations contain both "active" and "inert" ingredients. Active ingredients are what kill the pest, and inert ingredients help the active ingredients to work more effectively
Pesticide formulations contain both "___" and "____" ingredients. _____ ingredients are what kill the pest, and _____ ingredients help the active ingredients to work more effectively
Active and Inert
The two largest classes of synthetic pesticides are ________ and ________,
insecticides, which are designed to kill insects, and herbicides, which are designed to kill plants.
3 other types of pesticides that aren't the main two.
Other classes of pesticides include fungicides (for molds and fungi), rodenticides (for mammals), and antimicrobials (for microorganisms such as bacteria and viruses). Antimicrobial pesticides are used as preservatives, sterilizers, and disinfectants in home, institutional, and commercial environments.
A common insecticide used to kill fleas on cats is imidacloprid. This insecticide is also used to control insects such as aphids, whiteflies, termites and a range of other soil insects, and some beetles. It is also very toxic to honey bees.
Imidacloprid is toxic to the nervous system, causing an overstimulation of acetylcholine and consequent paralysis and death in insects.
The total use of pesticides in the United States is about __ billion pounds a year, ___ billion pounds of which is used in agriculture.
carbofuran (n-methyl carbamate) is a broad-spectrum insecticide used on rice, alfalfa, table and wine grapes, cotton, potatoes, and soybeans. Carbofuran insecticide inhibits cholinesterase, causing an increase in the neurotransmitter acetylcholine. Elevated acetylcholine levels cause tremor, paralysis, and death in insects, and can have similar effects on wildlife, such as birds, as well as humans. Due to its toxicity to humans and mammals, the US EPA moved to ban all use of carbofuran in 2008.
____ was banned in 2008 by the US EPA due to its toxicity to humans and mammals.
One of the first pesticides was sulfur, used by the Chinese in around 1000 BC to control bacteria and mold (fungus). Sulfur is still widely used today. For example, it is used in fungicides to control diseases on both agricultural and ornamental plants, and in the wine industry, sulfur is used to control unwanted bacterial growth in empty wine barrels and is commonly added to wine to kill unwanted yeast
One of the first pesticides was _____, used by the Chinese in around 1000 BC
The Chinese also pioneered the use of arsenic-containing compounds to control insects. Arsenic has a long history of use both as an insecticide and herbicide, and also as a medicine. Arsenic trioxide was used as a weed killer (herbicide) in the late 1800s, and lead arsenate, containing both lead and arsenic, was used as an insecticide, particularly in orchards, prior to the development of synthetic pesticides following WWII
Plants have provided several other important nonsynthetic pesticides. In the late 1600s _____.
an extract from tobacco leaves, was recognized as a potent insecticide and is now in limited use as a pesticide
4 non-synthetic pesticides?
nicotine, rotenone, pyrethrums, strychnine.
Synthetic chemistry advanced rapidly in the ____s and by the early ____s, a range of new pesticides had been developed, including organochlorine insecticides like DDT.
In 1937 the first _________ compounds were synthesized by a group of German chemists.
4 most common synthetic insecticides?
The most prominent classes of insecticides are organochlorines, organophosphates, carbamates, and pyrethroids.
While organochlorines have the advantage of being cheap to manufacture and are effective against target species, they have serious unintended consequences. Organochlorines disrupt the movement of ions such as calcium, chloride, sodium, and potassium into and out of nerve cells. Depending on the specific structure of the organochlorine chemical, it may also affect the nervous system in other ways. At one time organochlorines were thought to be ideal because they are very stable, slow to degrade in the environment, dissolve in fats (and are therefore readily taken up by insects), and seemingly harmless to mammals. Unfortunately it eventually became clear that the attributes of persistence and fat solubility were actually very undesirable: the organochlorines passed up the food chain, where they bioaccumulated in the fat of large animals and humans and were passed on to nursing young.
Organophosphates and Carbamates
Organophosphates were initially developed in the 1940s as highly toxic biological warfare agents (nerve gases). Modern derivatives, including sarin, soman, and VX, were stockpiled by various countries and now present some difficult disposal problems. Researchers created many different organophosphates in their search for insecticides that would target selected species and would be less toxic to mammals. When the organophosphate parathion was first used as a replacement for DDT, it was believed to be better as it was more specific. Unfortunately there were a number of human deaths because workers failed to appreciate the fact that parathion's short term (acute) toxicity is greater than DDT's.
One of the newer classes of insecticide, synthetic pyrethroids are loosely based upon the naturally occurring pyrethrum found in chrysanthemum flowers. Synthetic pyrethroids were first developed in the 1980s, but the naturally occurring pyrethrum was first commercially used in the 1800s. Their use has increased significantly over the last 20 years. The chemical structure of pyrethroids is quite different from that of organochlorines, organophosphates, and carbamates but the primary site of action is also the nervous system. Pyrethroids affect the movement of sodium ions (Na+) into and out of nerve cells, causing the nerve cells to become hypersensitive to neurotransmitters. Structural differences between various pyrethroids can change their toxic effects on specific insects and even mammals.
Synthetic pyrethroids are more persistent in the environment than natural pyrethrum, which is unstable in light and breaks down very quickly in sunlight.
Herbicides are used to kill or damage plants and are the most rapidly growing type of pesticide. Prior to the 1930s, herbicides were nonspecific and often very toxic to humans as well as other animals. In the 1930s, researchers discovered several chemicals that selectively killed plants while developing new insecticides. These chemicals are now widely used to increase food production by killing weeds that choke out or compete with food crops.
The most well known herbicides are the chlorophenoxy compounds that include 2,4-D
The most well known herbicides are the chlorophenoxy compounds that include 2,4-D
85 and 2,4,5-T.
This herbicide mixture, sometimes called Agent Orange in the 1960s, was widely used to kill broadleaf plants in agricultural fields, along roadsides, and on rights of way for power lines. It was also extensively used as a chemical warfare agent to kill unwanted vegetation, for example in jungles. The mechanism of action of this class of chemicals is poorly understood, but the herbicides appear to interact with plant growth hormones. (See Pesticides - History for discussion of the contamination of 2,4,5-T with dioxin.)
Paraquat and diquat
Paraquat and the related chemical diquat are nonselective herbicides that are also toxic to mammals. Occupational or accidental exposure to paraquat can occur by ingestion, skin exposure, or inhalation, all of which can cause serious illness or death. While seldom used in the United States at this time, paraquat is still widely used in developing countries. At one time it was used in marijuana plant eradication programs, but it was discontinued when a number of fatalities were observed in smokers of paraquat-contaminated marijuana
Fungicides were developed to control the fungi and mold that may grow on crops, stored foods and seeds, and in our bodies. Control of plant fungus in agriculture is important not only because fungi can damage crops, but also because some fungi produce toxic chemicals (mycotoxins)
hexachlorobenzene and Mercury
In the 1940s and 50s, hexachlorobenzene, a synthetic fungicide, was widely used to protect seed grain from fungal rot. Mercurial compounds were also applied to seed grains to protect them from soil fungus. Both of these chemicals caused severe illness when people ate treated grains intended for planting as crops. These two fungicides are now rarely used and have been replaced by less-toxic ones, but careful harvest and storage procedures for seeds are necessary to prevent potential contamination of food supplies.
_______ _______ ______ reduces the need to use dangerous fungicides on growing plants.
Integrated Pest Management
One of the first anticoagulant rodenticides was warfarin
Rodenticides are a broad class of pesticides designed to kill small mammals such as rats and mice. Some rodenticides are anticoagulants and work by inhibiting bloodclotting; these are often used to control rat populations. One of the first anticoagulant rodenticides was warfarin, which is related to plant-derived coumadin (from spoiled sweet clover). Inthe 1950s rats developed resistance to warfarin, which prompted scientists to develop more potent anticoagulants, which are termed second-generation anticoagulants. Other rodenticides include fluoroacetic acid and zinc phosphide (which are both very toxic), and thiourea-based compounds.
One of the problems of rodenticides is that they may also harm wildlife that mistake pesticide-containing baits or pellets for food. Wildlife, such as wolves or birds of prey, may also be harmed by eating rodents or other animals that have been poisoned. The primary alternative to using chemical rodenticides is trapping
Molluscicides are used to control slugs and snails. Mollusks are a group of invertebrate animals that include shellfish, cephalopods (such as squid and octopus), slugs, and snails.
The most commonly used active ingredient in molluscicides is metaldehyde
The World Health Organization estimates that there are ___ million cases of pesticide poisoning each year and up to ______ thousand deaths, primarily in developing countries.