A cropduster spraying pesticide on a field

A pesticide is any substance or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.^[1] A pesticide may be a chemical substance, biological agent (such as a virus or bacterium), antimicrobial, disinfectant or device used against any pest. Pests include insects, plant pathogens, weeds, molluscs, birds, mammals, fish, nematodes (roundworms), and microbes that destroy property, spread disease or are a vector for disease or cause a nuisance. Although there are benefits to the use of pesticides, there are also drawbacks, such as potential toxicity to humans and other animals.

[edit] Definition

FAO has defined the term of pesticide as:

any substance or mixture of substances intended for preventing, destroying or controlling any pest, including vectors of human or animal disease, unwanted species of plants or animals causing harm during or otherwise interfering with the production, processing, storage, transport or marketing of food, agricultural commodities, wood and wood products or animal feedstuffs, or substances which may be administered to animals for the control of insects, arachnids or other pests in or on their bodies. The term includes substances intended for use as a plant growth regulator, defoliant, desiccant or agent for thinning fruit or preventing the premature fall of fruit, and substances applied to crops either before or after harvest to protect the commodity from deterioration during storage and transport.^[2]

[edit] History

Since before 2000 BC, humans have utilized pesticides to protect their crops. The first known pesticide was elemental sulfur dusting used in ancient Sumer about 4,500 years ago in ancient Mesopotamia. 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 chrysanthemums, and rotenone, which is derived from the roots of tropical vegetables.^[3] Until the 1950s, arsenic-based pesticides were dominant.^[4] Paul Müller discovered that DDT was a very effective insecticide. Organochlorines such as DDT were dominant, but they were replaced in the U.S. by organophosphates and carbamates by 1975. Since then, pyrethrin compounds have become the dominant insecticide.^[4] Herbicides became common in the 1960s, lead by "triazine and other nitrogen-based compounds, carboxylic acids such as 2,4-dichlorophenoxyacetic acid, and glyphosate".^[4]

In the 1940s manufacturers began to produce large amounts of synthetic pesticides and their use became widespread.^[5] Some sources consider the 1940s and 1950s to have been the start of the "pesticide era."^[6] Pesticide use has increased 50-fold since 1950 and 2.3 million tonnes (2.5 million short tons) of industrial pesticides are now used each year.^[3] Seventy-five percent of all pesticides in the world are used in developed countries, but use in developing countries is increasing.^[7] In 2001 the EPA stopped reporting pesticide use statistics; the only comprehensive study of pesticide use trends was published in 2003 by the National Science Foundation's Center for Integrated Pest Management.^[4]

In the 1960s, it was discovered that DDT was preventing many fish-eating birds from reproducing, which was a serious threat to biodiversity. Rachel Carson wrote the best-selling book Silent Spring about biological magnification. The agricultural use of DDT is now banned under the Stockholm Convention on Persistent Organic Pollutants, but it is still used in some developing nations to prevent malaria and other tropical diseases by spraying on interior walls to kill or repel mosquitoes.^[8]

[edit] Classification

Pesticides can be classified by target organism, chemical structure, and physical state.^[9] Pesticides can also be classed as inorganic, synthetic, or biologicals (biopesticides),^[9] although the distinction can sometimes blur. Biopesticides include microbial pesticides and biochemical pesticides.^[10] Plant-derived pesticides, or "botanicals", have been developing quickly. These include the pyrethroids, rotenoids, nicotinoids, and a fourth group that includes strychnine and scilliroside.^[11]:15

Many pesticides can be grouped into chemical families. Prominent insecticide families include organochlorines, organophosphates, and carbamates. Organochlorine hydrocarbons (e.g. DDT) could be separated into dichlorodiphenylethanes, cyclodiene compounds, and other related compounds. They operate by disrupting the sodium/potassium balance of the nerve fiber, forcing the nerve to transmit continuously. Their toxicities vary greatly, but they have been phased out because of their persistence and potential to bioaccumulate.^[11]:239-240 Organophosphate and carbamates largely replaced organochlorines. Both operate through inhibiting the enzyme acetylcholinesterase, allowing acetylcholine to transfer nerve impulses indefinitely and causing a variety of symptoms such as weakness or paralysis. Organophosphates are quite toxic to vertebrates, and have in some cases been replaced by less toxic carbamates.^[11]:136-137 Thiocarbamate and dithiocarbamates are subclasses of carbamates. Prominent families of herbicides include pheoxy and benzoic acid herbicides (e.g. 2,4-D), triazines (e.g. atrazine), ureas (e.g. diuron), and Chloroacetanilides (e.g. alachlor). Phenoxy compounds tend to selectively kill broadleaved weeds rather than grasses. The phenoxy and benzoic acid herbicides function similar to plant growth hormones, and grow cells without normal cell division, crushing the plants nutrient transport system.^[11]:300 Triazines interfere with photsynthesis.^[11]:335 Many commonly used pesticides are not included in these families, including glyphosate.

• Algicides or algaecides for the control of algae
• Avicides for the control of birds
• Bactericides for the control of bacteria
• Fungicides for the control of fungi and oomycetes
• Herbicides (e.g. glyphosate) for the control of weeds
• Insecticides (e.g. organochlorines, organophosphates, carbamates, and pyrethroids) for the control of insects - these can be ovicides (substances that kill eggs), larvicides (substances that kill larvae) or adulticides (substances that kill adults)
• Miticides or acaricides for the control of mites
• Molluscicides for the control of slugs and snails
• Nematicides for the control of nematodes
• Rodenticides for the control of rodents
• Virucides for the control of viruses

Pesticides can be classified based upon their biological mechanism function or application method. Most pesticides work by poisoning pests.^[12] A systemic pesticide moves inside a plant following absorption by the plant. With insecticides and most fungicides, this movement is usually upward (through the xylem) and outward. Increased efficiency may be a result. Systemic insecticides, which poison pollen and nectar in the flowers, may kill bees and other needed pollinators.

In 2009, the development of a new class of fungicides called paldoxins was announced. These work by taking advantage of natural defense chemicals released by plants called phytoalexins, which fungi then detoxify using enzymes. The paldoxins inhibit the fungi's detoxification enzymes. They are believed to be safer and greener.^[13]

[edit] Uses

Pesticides are used to control organisms considered harmful.^[14] For example, they are used to kill mosquitoes that can transmit potentially deadly diseases like west nile virus, yellow fever, and malaria. They can also kill bees, wasps or ants that can cause allergic reactions. Insecticides can protect animals from illnesses that can be caused by parasites such as fleas.^[14] Pesticides can prevent sickness in humans that could be caused by mouldy food or diseased produce. Herbicides can be used to clear roadside weeds, trees and brush. They can also kill invasive weeds that may cause environmental damage. Herbicides are commonly applied in ponds and lakes to control algae and plants such as water grasses that can interfere with activities like swimming and fishing and cause the water to look or smell unpleasant.^[15] Uncontrolled pests such as termites and mould can damage structures such as houses.^[14] Pesticides are used in grocery stores and food storage facilities to manage rodents and insects that infest food such as grain. Each use of a pesticide carries some associated risk. Proper pesticide use decreases these associated risks to a level deemed acceptable by pesticide regulatory agencies such as the United States Environmental Protection Agency (EPA) and the Pest Management Regulatory Agency (PMRA) of Canada.

Pesticides can save farmers' money by preventing crop losses to insects and other pests; in the U.S., farmers get an estimated fourfold return on money they spend on pesticides.^[16] One study found that not using pesticides reduced crop yields by about 10%.^[17] Another study,conducted in 1999, found that a ban on pesticides in the United States may result in a rise of food prices, loss of jobs, and an increase in world hunger.^[18]

DDT, sprayed on the walls of houses, is an organochloride that has been used to fight malaria since the 1950s. Recent policy statements by the World Health Organization have given stronger support to this approach.^[19] Dr. Arata Kochi, WHO's malaria chief, said, "One of the best tools we have against malaria is indoor residual house spraying. Of the dozen insecticides WHO has approved as safe for house spraying, the most effective is DDT."^[19] However, since then, an October 2007 study has linked breast cancer from exposure to DDT prior to puberty.^[20] Poisoning may also occur due to use of DDT and other chlorinated hydrocarbons by entering the human food chain when animal tissues are affected. Symptoms include nervous excitement, tremors, convulsions or death. Scientists estimate that DDT and other chemicals in the organophosphate class of pesticides have saved 7 million human lives since 1945 by preventing the transmission of diseases such as malaria, bubonic plague, sleeping sickness, and typhus.^[7] However, DDT use is not always effective, as resistance to DDT was identified in Africa as early as 1955, and by 1972 nineteen species of mosquito worldwide were resistant to DDT.^[21] A study for the World Health Organization in 2000 from Vietnam established that non-DDT malaria controls were significantly more effective than DDT use.^[22] The ecological effect of DDT on organisms is an example of bioaccumulation.

[edit] Regulation

Preparing for pesticide application.

In most countries, pesticides must be approved for sale and use by a government agency.^[23] For example, in the United States, the Environmental Protection Agency (EPA) does so. Complex and costly studies must be conducted to indicate whether the material is safe to use and effective against the intended pest. During the registration process, a label is created. The label contains directions for proper use of the material. Based on acute toxicity, pesticides are assigned to a Toxicity Class.

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.^[23] Records of sales and use are required to be maintained and may be audited by government agencies charged with the enforcement of pesticide regulations.

In Europe, recent EU legislation has been approved banning the use of highly toxic pesticides including those that are carcinogenic, mutagenic or toxic to reproduction, those that are endocrine-disrupting, and those that are persistent, bioaccumulative and toxic (PBT) or very persistent and very bioaccumulative (vPvB). Measures were approved to improve the general safety of pesticides across all EU member states.^[24]

Though pesticide regulations differ from country to country, pesticides and products on which they were used are traded across international borders. To deal with inconsistencies in regulations among countries, delegates to a conference of the United Nations Food and Agriculture Organization adopted an International Code of Conduct on the Distribution and Use of Pesticides in 1985 to create voluntary standards of pesticide regulation for different countries.^[23] The Code was updated in 1998 and 2002.^[25] The FAO claims that the code has raised awareness about pesticide hazards and decreased the number of countries without restrictions on pesticide use.^[2]

Three other efforts to improve regulation of international pesticide trade are the United Nations London Guidelines for the Exchange of Information on Chemicals in International Trade and the United Nations Codex Alimentarius Commission^{[citation needed]}. The former seeks to implement procedures for ensuring that prior informed consent exists between countries buying and selling pesticides, while the latter seeks to create uniform standards for maximum levels of pesticide residues among participating countries.^[26] Both initiatives operate on a voluntary basis.^[26]

Reading and following label directions is required by law in countries such as the United States and in limited parts of the rest of the world.

One study found pesticide self-poisoning the method of choice in one third of suicides worldwide, and recommended, among other things, more restrictions on the types of pesticides that are most harmful to humans.^[27]

[edit] Environmental effects

Pesticide use raises a number of environmental concerns. Over 98% of sprayed insecticides and 95% of herbicides reach a destination other than their target species, including non-target species, air, water and soil.^[7] Pesticide drift occurs when pesticides suspended in the air as particles are carried by wind to other areas, potentially contaminating them. Pesticides are one of the causes of water pollution, and some pesticides are persistent organic pollutants and contribute to soil contamination.

In addition, pesticide use reduces biodiversity, reduces nitrogen fixation,^[28] contributes to pollinator decline,^{[29][30][31][32]} destroys habitat (especially for birds),^[33] and threatens endangered species.^[7]
It also happens that some of the pest adapt to the pesticide and don't die. What is called pesticide resistance, to eliminate the offspring of this pest, will be needed an new pesticide or an increase the dose of pesticide. This will cause a worsening of the ambient pollution problem.

[edit] Health effects

Pesticides may cause acute and delayed health effects in those who are exposed.^[34] A 2007 systematic review found that "most studies on non-Hodgkin lymphoma and leukemia showed positive associations with pesticide exposure" and thus concluded that cosmetic use of pesticides should be decreased.^[35] Strong evidence also exists for other negative outcomes from pesticide exposure including neurological, birth defects, fetal death^[36], and neurodevelopmental disorder.^[37]

The American Medical Association recommends limiting exposure to pesticides and using safer alternatives:^[9]

Particular uncertainty exists regarding the long-term effects of low-dose pesticide exposures. Current surveillance systems are inadequate to characterize potential exposure problems related either to pesticide usage or pesticide-related illnesses'Considering these data gaps, it is prudent'to limit pesticide exposures'and to use the least toxic chemical pesticide or non-chemical alternative.

The World Health Organization and the UN Environment Programme estimate that each year, 3 million workers in agriculture in the developing world experience severe poisoning from pesticides, about 18,000 of whom die.^[7] According to one study, as many as 25 million workers in developing countries may suffer mild pesticide poisoning yearly.^[38]

[edit] Pesticide accidents

The Bhopal disaster occurred when a pesticide plant released 40 tons of methyl isocyanate (MIC) gas, a chemical intermediate in the synthesis of some carbamate pesticides. The disaster immediately killed nearly 3,000 people and ultimately caused at least 15,000 deaths.^[39]

[edit] Continuing development

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 choosing less toxic pesticides may reduce risks placed on society and the environment from pesticide use.^[15] Integrated pest management, the use of multiple approaches to control pests, is becoming widespread and has been used with success in countries such as Indonesia, China, Bangladesh, the U.S., Australia, and Mexico.^[7] IPM attempts to recognize the more widespread impacts of an action on an ecosystem, so that natural balances are not upset.^[5] New pesticides are being developed, including biological and botanical derivatives and alternatives that are thought to reduce health and environmental risks. In addition, applicators are being encouraged to consider alternative controls and adopt methods that reduce the use of chemical pesticides.

Pesticides can be created that are targeted to a specific pest's life cycle, which can be environmentally more friendly.^[40] For example, potato cyst nematodes emerge from their protective cysts in response to a chemical excreted by potatoes; they feed on the potatoes and damage the crop.^[40] A similar chemical can be applied to fields early, before the potatoes are planted, causing the nematodes to emerge early and starve in the absence of potatoes.^[40]

[edit] Alternatives

Alternatives to pesticides are available and include methods of cultivation, use of biological pest controls (such as pheromones and microbial pesticides), genetic engineering, and methods of interfering with insect breeding.^[7] Application of composted yard waste has also been used as a way of controlling pests.^[41] These methods are becoming increasingly popular and often are safer than traditional chemical pesticides. In addition, EPA is registering reduced-risk conventional pesticides in increasing numbers.

Cultivation practices include polyculture (growing multiple types of plants), crop rotation, planting crops in areas where the pests that damage them do not live, timing planting according to when pests will be least problematic, and use of trap crops that attract pests away from the real crop.^[7] In the U.S., farmers have had success controlling insects by spraying with hot water at a cost that is about the same as pesticide spraying.^[7]

Release of other organisms that fight the pest is another example of an alternative to pesticide use. These organisms can include natural predators or parasites of the pests.^[7] Biological pesticides based on entomopathogenic fungi, bacteria and viruses cause disease in the pest species can also be used.^[7]

Interfering with insects' reproduction can be accomplished by sterilizing males of the target species and releasing them, so that they mate with females but do not produce offspring.^[7] This technique was first used on the screwworm fly in 1958 and has since been used with the medfly, the tsetse fly,^[42] and the gypsy moth.^[43] However, this can be a costly, time consuming approach that only works on some types of insects.^[7]

Another alternative to pesticides is the thermal treatment of soil through steam. Soil steaming kills pest and increases soil health. citation needed.

In India, traditional pest control methods include using Panchakavya, the "mixture of five products." The method has recently experienced a resurgence in popularity due in part to use by the organic farming community.^{[citation needed]}

[edit] Effectiveness

Some evidence shows that alternatives to pesticides can be equally effective as the use of chemicals. For example, Sweden has halved its use of pesticides with hardly any reduction in crops.^[7] In Indonesia, farmers have reduced pesticide use on rice fields by 65% and experienced a 15% crop increase.^[7] A study of Maize yields in northern Florida found that the application of composted yard waste with high carbon to nitrogen ratio to agricultural fields was highly effective at reducing the population of plant-parasitic nematodes and increasing crop yield, with yield increases ranging from 10% to 212%; the observed effects were long-term, often not appearing until the third season of the study.^[41]

[edit] See also

• Index of pesticide articles

[edit] References

[edit] Further reading

Books

• Greene, Stanley A.; Pohanish, Richard P. (editors) (2005). Sittig's Handbook of Pesticides and Agricultural Chemicals. SciTech Publishing, Inc. ISBN 0-8155-1516-2. 
• Tomlin, Clive (editor) (2006). "The Pesticide Manual", 14th edition, 1350 pages. British Crop Protection Council (BCPC). ISBN 1-901396-14-2. 
• Hamilton, Denis; Crossley, Stephen (editors) (2004). Pesticide residues in food and drinking water. J. Wiley. ISBN 0-471-48991-3. 
• Hond, Frank et al. (2003). Pesticides: problems, improvements, alternatives. Blackwell Science. ISBN 0-632-05659-2. 
• Kegley, Susan E.; Wise, Laura J. (1998). Pesticides in fruits and vegetables. University Science Books. ISBN 0-935702-46-6. 
• Levine, Marvin J. (2007). Pesticides: A Toxic Time Bomb in our Midst. Praeger Publishers. ISBN 978-0-275-99127-2. 
• Ware, George W.; Whitacre, David M. (2004). Pesticide Book. Meister Publishing Co. ISBN 1-892829-11-8. 
• Watson, David H. (editor) (2004). Pesticide, veterinary and other residues in food. Woodhead Publishing. ISBN 1-85573-734-5. 

Journal articles

• Walter A. Alarcon, et al. (July 2005). "Acute Illnesses Associated With Pesticide Exposure at Schools". Journal of the American Medical Association 294 (4): 455'465. doi:10.1001/jama.294.4.455. PMID 16046652. 

News

• Janofsky, M (August 4, 2006). "E.P.A. recommends limits on thousands of uses of pesticides". New York Times. http://www.nytimes.com/2006/08/04/washington/04pest.html. Retrieved 2006-08-24. 
• Janofsky, M (2006-08-02). "Unions say E.P.A. bends to political pressure". New York Times. http://www.nytimes.com/2006/08/02/washington/02pest.html. Retrieved 2007-10-10. 
• Kaiser, J (June 2005). "Endocrine disrupters trigger fertility problems in multiple generations". Science 308 (5727): 1391'1392. doi:10.1126/science.308.5727.1391a. PMID 15933166. 
• Kaiser, J (May 2005). "House would foil human pesticide studies". Science 308 (5726): 1234. doi:10.1126/science.308.5726.1234b. PMID 15919959. 
• Webster, P (Dec 2004). "Study finds heavy contamination across vast Russian Arctic". Science 306 (5703): 1875. doi:10.1126/science.306.5703.1875a. PMID 15591171. 
• Stokstad, E (Nov 2004). "EPA criticized for study of child pesticide exposure". Science 306 (5698): 961. doi:10.1126/science.306.5698.961. PMID 15528421. 
• Helmuth, L (Nov 2000). "Pesticide causes Parkinson's in rats". Science 290 (5494): 1068. doi:10.1126/science.290.5494.1068a. PMID 11184997. 
• Adam, D (Nov 2000). "Pesticide use linked to Parkinson's disease". Nature 408 (6809): 125. doi:10.1038/35041740. PMID 11089940. 

[edit] External links

Wikimedia Commons has media related to: Pesticides

• National Pesticide Information Center (NPIC) Information about pesticide-related topics.
• Pesticide laws guidance on NetRegs.gov.uk
• Pesticide Modes of action (International Pesticide Application Research Centre)
• Beyond Pesticides, founded in 1981 as the National Coalition Against the Misuse of Pesticides - Source of information on pesticide hazards, least-toxic practices and products, and on pesticide issues. Website has Daily News Blog relating to pesticides.
• Compendium of Pesticide Common Names: Classified Lists of Pesticides Lists of pesticide names by type.
• Pesticide Action Network. PAN Pesticides Database. Compilation of multiple regulatory databases into a web-accessible form.
• Pesticide Information [1] Supplies resources and a dialogue for improved understanding of argumaets for and against pesticides.
• Pesticide pathfinder Information about pesticide use in the workplace and links to U.S regulatory information.
• USDA Pesticide Data Program, tracking residue levels in food

Pesticide regulatory authorities

• [2] College voor toelating bestrijdingsmiddelen en biociden. Regulatory authority in the Netherlands - information available in English
• UK Pesticides Safety Directorate
• European Commission pesticide information
• Lake Ontario Waterkeeper (May 21, 2008) -- Pesticide legislation suggests industry lobby is still alive and well
• United States Environmental Protection Agency Office of Pesticides Program

Human health

• NIH encyclopedia pages with emergency treatment of Insecticide exposure
• Durango Software - Provides risk assessment tools for pesticide use
• Environmental Working Group (July 14, 2005), The Pollution in Newborns.
• Hazard Communications for Agricultural Workers (October 2007)
• National Agricultural Workers Survey
• Pesticides and Health -- Greenpeace China
• David Suzuki Foundation: Protecting Your Health from Pesticides

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