Pesticide

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The U.S Environmental Protection Agency (EPA) defines a pesticide as "any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating any pest".

A pesticide may be a chemical substance or biological agent (such as a virus or bacteria) used against pests including insects, plant pathogens, weeds, mollusks, birds, mammals, fish, nematodes (roundworms) and microbes that compete with humans for food, destroy property, spread disease or are a nuisance. Pesticides are usually, but not always, poisonous to humans.

1 Types of Pesticides
2 History
3 Regulation
4 Dangers of pesticides
5 Managing pest resistance
6 Continuing development of pesticides
7 Pesticide use maps in the US
8 See also
9 References
10 External links
- 10.1 Pesticide regulatory authorities

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Types of Pesticides

Bactericides [1] for the control of bacteria
Herbicides for the control of weeds
Fungicides for the control of fungi
Insecticides for the control of insects
Miticides for the control of mites
Nematicides for the control of worms
Rodenticides for the control of rodents
Virucides [2]

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History

Since before 500 BC, humans have used pesticides to prevent damage to their crops. The first known pesticide was sulfur. 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. The 19th century saw the introduction of two more natural pesticides, pyrethrum which is derived from crysanthemums, and rotenone which is derived from the roots of tropical legumes.

In 1939, Paul Müller discovered that DDT was a very effective insecticide. It quickly became the most widely-used pesticide in the world. However, in the 1960s, it was discovered that DDT was preventing many fish-eating birds from reproducing which was a huge threat to biodiversity. Rachel Carson wrote the best-selling book "Silent Spring". DDT is now banned in at least 86 countries, but it is still used in some developing nations to prevent malaria and other tropical diseases by killing mosquitos and other disease-carrying insects.

Pesticide use has increased 50-fold since 1950, and 2.5 million tons of industrial pesticides are now used each year. Glyphosate (the active ingredient in Roundup) is currently the world's most used herbicide.

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Regulation

In most countries, in order to sell or use a pesticide, it must be approved a government agency. For example, in the US, the the EPA does so. Complex and costly studies must be conducted to indicate whether the material is effective against the intended pest and safe to use. During the registration process, a label is created which contains directions for the proper use of the material. Based on acute toxicity, pesticides are assigned to a Toxicity Class. Pesticide misuse is illegal.

Image:Hazardous-pesticide.jpg Some pesticides are considered too hazardous for sale to the general public and are designated restricted use pesticides. Only certified applicators, who have passed an exam, may purchase or supervise the application of restricted use pesticides. Records of sales and use are required to be maintained and may be audited by government agencies charged with the enforcement of pesticide regulations.

"Read and follow label directions" is a phrase often quoted by extension agents, garden columnists and others teaching about pesticides. This is not merely good advice; it is the law, at least in the USA. Similar laws exist in limited parts of the rest of the world. The Federal Insecticide, Fungicide, and Rodenticide Act of 1972 (FIFRA) set up the current system of pesticide regulations. It was amended somewhat by the Food Quality Protection Act of 1996. Its purpose is to make pesticide manufacture, distribution and use as safe as possible. The most important points for users to understand are these: it is a violation to apply any pesticide in a manner not in accordance with the label for that pesticide, and it is a crime to do so intentionally.

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Dangers of pesticides

Pesticides can present danger to consumers, bystanders, or workers during manufacture, transport, or during and after use. There is concern that pesticides used to control pests on food crops are dangerous to the consumer. These concerns are one reason for the organic food movement. Food crops, including many fruits and vegetables such as apples, celery, cherries, grapes, nectarines, peaches, pears, peppers, potatoes, red raspberries, spinach and strawberries, may contain pesticide residues after being washed or peeled. Residues, permitted by US government safety standards, are limited to tolerance levels that are considered safe, based on average daily consumption of these foods by adults and children. Tolerance levels are derived from scientifically-based risk assessments that pesticide manufacturers are required to support by producing toxicological studies, exposure modeling and residue studies prior to a product's registration for use on a particular food crop. Other exposure routes, particularly pesticide drift, may be significant to the general public as well. Risk of exposure to pesticide applicators, or other workers in the field after pesticide application, may also be significant and is regulated as part of the pesticide registration process.

Besides human health risks, pesticides also pose dangers to the environment. Non-target organisms can be severely impacted. In some cases, where a pest insect has some controls from a beneficial predator or parasite, an insecticide application can kill both pest and beneficial populations. The beneficial almost always takes longer to recover than the pest. Applications performed to control adult mosquitoes, for example, may temporarily depress mosquito populations but result in a larger population in the long run by damaging controlling factors.

Misuse of pesticides can cause pollinator decline which is a food supply issue.

An early discovery relating to pesticide use, is that pests may eventually evolve to become resistant to chemicals. When sprayed with a pesticides, many pests will initially be very susceptible. However, not all pests are killed, and some with slight variations in their genetic make-up are resistant and therefore survive. Through natural selection, the pests may eventually become very resistant to the pesticide. Farmers may resort to increased use of pesticides, exacerbating the problem.

‘'Persistent Organic Pollutants’' (POPs) are another less-known problem the environment faces as a result of pesticides. POPs may continue to poison non-target organisms in the environment and increase risk to humans by disruption in the endocrine system, cancer, infertility and mutagenic effects, although very little is currently known about these ‘chronic effects’. A wide variety of these chemical are persistent soil contaminants, whose effects may endure for decades, and adversely affect soil conservation.

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Managing pest resistance

Pest resistance to a pesticide is commonly managed through pesticide rotation or tankmixing with other pesticides.

Rotation involves alternating among pesticide classes with different modes of action to delay the onset of or mitigate existing pest resistance. Different pesticide classes may be active on different pest sites of action. The U.S. Environmental Agency (EPA or USEPA) designates different classes of fungicides, herbicides and insecticides. Pesticide manufacturers may, on product labeling, require that no more than a specified number of consecutive applications of a pesticide class be made before alternating to a different pesticide class. This manufacturer requirement is intended to entend the useful life of a product.

Tankmixing pesticides is the combination of two or more pesticides with different modes of action. This practice may improve individual pesticide application results in addition to the benefit of delaying the onset of or mitigating existing pest resistance.

Pesticide resistance cannot blanketly be managed with mixtures. Some mixtures rather potentiates the toxicity or are synergistic. Again resistance which is genetically based may not necessarily be broken with alternating biocides over shorter generations. Sometimes revertant species can also emerge when a biocide application is alternated, whose mechanism of resistance can be much complex.

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Continuing development of pesticides

Pesticides are tools of convenience and are highly efficient for producers who are in the business of mass food production. Pesticide safety education and pesticide applicator regulation are designed to protect the public from pesticide misuse, but do not eliminate all misuse. Reducing the use of pesticides and replacing high risk pesticides is the ultimate solution to reducing risks placed on our society from pesticide use. For over 30 years, there has been a trend in the United States and in many other parts of the world to use pesticides in combination with alternative pest controls. This use of integrated pest management (IPM) is now commonplace in US agriculture. With pesticide regulations that now put a higher priority on reducing the risks of pesticides in our food supply and emphasize environmental protection, old pesticides are being phased out in favor of new reduced risk pesticides. Many of these reduced risk pesticides include biological and botanical deriviatives and alternatives. As a result, old, more hazardous, pesticides are being phased out and replaced with pest controls that reduce these health and environmental risks. Chemical engineers continually develop new pesticides to produce enhancements over previous generations of products. In addition, applicators are being encouraged to consider alternative controls and adopt methods that reduce the use of chemical pesticides. This process is on-going and will not solve all of our problems of pesticide use risks overnight.

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Pesticide use maps in the US

The US Geological Survey's National Water-Quality Assessment Program published a 1997 Pesticide Use Maps which shows estimates of pesticide type and intensity of pesticide use by business of mass food production. Pesticide safety education and pesticide applicator regulation are designed to protect the public from pesticide misuse, but do not eliminate all misuse. Reducing the use of pesticides and replacing high risk pesticides is the ultimate solution to reducing risks placed on our society from pesticide use. For over 30 years, there has been a trend in the United States and in many other parts of the world to use pesticides in combination with alternative pest controls. This use of integrated pest management (IPM) is now commonplace in US agriculture. With pesticide regulations that now put a higher priority on reducing the risks of pesticides in our food supply and emphasize environmental protection, old pesticides are being phased out in favor of new reduced risk pesticides. Many of these reduced risk pesticides include biological and botanical deriviatives and alternatives. As a result, old, more hazardous, pesticides are being phased out and replaced with pest controls that reduce these health and environmental risks. Chemical engineers continually develop new pesticides to produce enhancements over previous generations of products. In addition, applicators are being encouraged to consider alternative controls and adopt methods that reduce the use of chemical pesticides. This process is on-going and will not solve all of our problems of pesticide use risks overnight.

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