A pesticide may be a chemical substance, biological agent (such as a virus or bacteria), antimicrobial, disinfectant or device 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 or are a vector for disease or are a nuisance. Many pesticides are poisonous to humans.
Types of Pesticides
- Bactericides for the control of bacteria
- Fungicides for the control of fungi and oomycetes
- Herbicides for the control of weeds
- Insecticides for the control of insects - these can be Ovicides, Larvicides or Adulticides
- Miticides 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 also be classed as synthetic pesticides or biological pesticides, although the distinction can sometimes blur.
A systemic pesticide moves inside a plant following absorption by the plant. This movement is usually upward (through the xylem) and outward. Increased efficacy may be a result. Systemic insecticides which poison pollen and nectar in the flowers may kill needed pollinators.
Since before 2500 BC, humans have used pesticides to prevent damage to their crops. The first known pesticide was elemental sulfur dusting used in Sumeria about 4,500 years ago. 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.
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 about biological magnification. 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 mosquitoes and other disease-carrying insects.
In most countries, in order to sell or use a pesticide, it must be approved by a government agency. For example, in the United States, 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 in most coun tries.
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 U.S. 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.
Effects of pesticide use
On the environment
Pesticides have been found to pollute virtually every lake, river and stream in the United States, according to the US Geological Survey. Pesticide runoff has been found to be highly lethal to amphibians, according to a recent study by the University of Pittsburgh. Pesticide impacts on aquatic systems are often studied using a hydrology transport model to study movement and fate of chemicals in rivers and streams. Pesticides are strongly implicated in pollinator decline, including through the mechanism of Colony Collapse Disorder
The use of pesticides also decreases biodiversity in the soil. Not using them results in higher soil quality with the additional effect that more life in the soil allows for higher water retention. This helps increase yields for farms in drought years where there is less rain. For example, during drought years, organic farms have been found to have yields 20-40% higher than conventional farms.
There have been many studies of farmers with the goal of determining the health effects of pesticide exposure. 
Research in Bangladesh suggests that many farmers' do not need to apply pesticide to their rice fields, but continue to do so only because the pesticide is paid for by the government.  Organophosphate pesticides have increased in use, because they are less damaging to the environment and they are less persistent than organochlorine pesticides. These are associated with acute health problems such as abdominal pain, dizziness, headaches, nausea, vomiting, as well as skin and eye problems. Additionally, many studies have indicated that pesticide exposure is associated with long-term health problems such as respiratory problems, memory disorders, dermatologic conditions, cancer, depression, neurologic deficits,  miscarriages, and birth defects.          Summaries of peer-reviewed research have examined the link between pesticide exposure and neurologic outcomes and cancer, perhaps the two most significant things resulting in organophosphate-exposed workers.  
A study published by the United States National Research Council in 1993 determined that for infants and children, the major source of exposure to pesticides is through diet. A recent study in 2006 measured the levels of organophosphorus pesticide exposure in 23 school children before and after replacing their diet with organic food (food grown without synthetic pesticides). In this study it wa s found that levels of organophosphorus pesticide exposure dropped dramatically and immediately when the children switched to an organic diet .
Pesticide residues in food
The Pesticide Data Program, a program started by the United States Department of Agriculture is the largest tester of pesticide residues on food sold in the United States. It began in 1990, and has since tested over 60 different types of food for over 400 different types of pesticides - with samples collected close to the point of consumption. Their most recent summary results are from the year 2005:
For example, on page 30 is comprehensive data on pesticides on fruits. Some example data:
| Fresh Fruit and
| Number of
| Samples with
| Percent of
| Total Residue|
They were also able to test for multiple pesticides within a single sample and found that:
- These data indicate that 29.5 percent of all samples tested contained no detectable pesticides [parent
- compound and metabolite(s) combined], 30 percent contained 1 pesticide, and slightly over 40 percent
- contained more than 1 pesticide. - page 34.
The Environmental Working Group used the results of nearly 43,000 tests for pesticides on produce collected by the USDA and the U.S. FDA between 2000 and 2004, to produce a ranking of 43 commonly eaten fruits & vegetables.
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. Many food crops, including fruits and vegetables, contain pesticide residues after being washed or peeled (see Pesticide residues in food, above). 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 obtained using scientific risk assessments that pesticide manufacturers are required to produce by conducting toxicological studies, exposure modelling and residue studies before a particular pesticide can be registered, however, the effects are tested for single pesticides, and there is no information on possible synergistic effects of exposure to multiple pesticide traces in the air, food and water .
The remaining exposure routes, in particular pesticide drift, are potentially significant to the general public . 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.
Children have been found to be especially susceptible to the harmful effects  of pesticides. A number of research studies have found higher instances of brain cancer, leukemia and birth defects in children with early exposure to pesticides, according to the Natural Resources Defense Council.
Peer-reviewed studies now suggest neurotoxic effects on developing animals from organophosphate pesticides at legally-tolerable levels, including fewer nerve cells, smaller birth weights, and lower cognitive scores. The EPA finished a 10 year review of the organophosphate pesticides following the 1996 Food Quality Protection Act, but did little to account for developmental neurotoxic effects, drawing strong criticism from within the agency and from outside researchers. 
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 organism almost always takes longer to recover than the pest. A study comparing biological pest control and use of pyrethroid insectide for diamondback moths, a major cabbage family insect pest, showed that the insecticide application created a rebounded pest population due to loss of insect predators, whereas the biocontrol did not show the same effect.  Likewise pesticides sprays in an effort to control adult mosquitoes, may temporarily depress mosquito populations, however they may result in a larger population in the long run by damaging the natural controlling factors .
Pesticides inflict extremely widespread damage to biota, and many countries have acted to discourage pesticide usage through their Biodiversity Action Plans. Misuse of pesticides can also cause pollinator decline, which can adversely affect food crops.
An early discovery relating to pesticide use, is that pests may eventually evolve to become resistant to chemicals. When sprayed with 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 one of the lesser-known environmental issues raised as result of using 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’. Many of the chemicals used in pesticides are persistent soil contaminants, whose impact may endure for decades, and adversely affect soil conservation .
A new study conducted by the Harvard School of Public Health in Boston, has discovered a 70% increase in the risk of developing Parkinson’s disease for people exposed to even low levels of pesticides.
Managing pest resistance
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 extend 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.
Continuing development of pesticides
Pesticides are often very cost-effective for farmers. 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 derivatives and alternatives. As a result, older, 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 is not an immediate solution to the risks of pesti cide use.
In 2006, the World Health Organization suggested the resumption of the limited use of DDT to fight malaria. They called for the use of DDT to coat the inside walls of houses in areas where mosquitoes are prevalent. 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."
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.
- Endangered arthropod
- List of environmental health hazards
- Pesticide misuse
- Federal Insecticide, Fungicide, and Rodenticide Act
- Integrated Pest Management
- Nonpoint source pollution
- Pesticide poisoning
- Soil contamination
- Daminozide or Alar
- Pesticide toxicity to bees
- Transgenic maize Bt corn
- Non-pesticide management
- Water pollution
- ↑ What is a Pesticide? (US EPA definitions) retrieved June 24, 2006
- ↑ Miller, G. Tyler Jr. (2002). Living in the Environment (12th Ed.). Belmont: Wadsworth/Thomson Learning.
- ↑ Miller, G. Tyler Jr. (2002). Living in the Environment (12th Ed.). Belmont: Wadsworth/Thomson Learning.
- ↑ Johnston, A. E. (1986). "Soil organic-matter, effects on soils and crops". Soil Use Management 2: 97-105.
- ↑ Lotter, D. W., Seidel, R. & Liebhardt W. (2003). "The performance of organic and conventional cropping systems in an extreme climate year". American Journal of Alternative Agriculture 18: 146-154.
- ↑ Linda A. McCauley, et.al. (2006). "Studying Health Outcomes in Farmworker Populations Exposed to Pesticides". Environmental Health Perspectives 114.
- ↑ Jaga K, Dharmani C. 2003. Sources of exposure to and public health implications of organophosphate pesticides. Pan Am J Public Health 14(3):171–185.
- ↑ Ecobichon DJ. 1996. Toxic effects of pesticides. In: Casarett and Doull's Toxicology: The Basic Science of Poisons (Kla assen CD, Doull J, eds). 5th ed. New York:MacMillan, 643–689.
- ↑ Arcury TA, Quandt SA, Mellen BG. 2003. An exploratory analysis of occupational skin disease among Latino migrant and seasonal farmworkers in North Carolina. Journal of Agricultural Safety and Health 9(3):221–32.
- ↑ O'Malley MA. 1997. Skin reactions to pesticides. Occupational Medicine 12:327–345.
- ↑ Daniels JL, Olshan AF, Savitz DA. 1997. Pesticides and childhood cancers. Environmental Health Perspectives 105: 1068–1077.
- ↑ Kamel F, et.al. (2003). "Neurobehavioral performance and work experience in Florida farmworkers". Environmental Health Perspectives 111: 1765-1772.
- ↑ Firestone JA, Smith-Weller T, Franklin G, Swanson P, Longsteth WT, Checkoway H. 2005. Pesticides and risk of Parkinson disease: a population-based case-control study. Archives of Neurology 62(1):91–95.
- ↑ Engel LS, O'Meara ES, Schwartz SM. 2000. Maternal occupation in agriculture and risk of limb defects in Washington State, 1980-1993. Scandinavian Journal of Work, Environment & Health 26(3): 193–198
- ↑ Cordes DH, Rea DF. 1988. Health hazards of farming. American Family Physician 38:233–243
- ↑ Das R, Steege A, Baron S, Beckman J, Harrison R. 2001. Pesticide-related illness among migrant farm workers in the United States. Int J Occup Environ Health 7: 303–312
- ↑ Eskenazi B, Bradman A, Castorina R. 1999. Exposures of children to organophosphate pesticides and their potential adverse health effects. Environmental Health Perspectives 107 (suppl 3):409–419
- ↑ Garcia AM. 2003. Pesticide exposure and women's health. American Journal of Industrial Medicine 44(6):584–594.
Moses M. 1989. Pesticide-related health problems and farmworkers. AAOHN 37:115–130
- ↑ Schwartz DA, Newsum LA, Heifetz RM. 1986. Parental occupational and birth outcome in an agricultural community. Scandinavian Journal of Work, Environment & Health 12:51–54
- ↑ Stallones L, Beseler C. 2002. Pesticide illness, farm practices, and neurological symptoms among farm residents in Colorado. Environ Res 90:89–97
- ↑ Strong, LL, Thompson B, Coronado GD, Griffith WC, Vigoren EM, Islas I. 2004. Health symptoms and exposure to organophosphate pesticides in farmworkers. Am J Ind Med 46:599–606
- ↑ Van Maele-Fabry G, Willems JL. 2003. Occupation related pesticide exposure and cancer of the prostate: a meta-analysis. Occupational and Environmental Medicine 60(9): 634–642
- ↑ Alavanja MC, Hoppin JA, Kamel F. 2004. Health effects of chronic pesticide exposure: cancer and neurotoxicity. Annu Rev Public Health 25:155–197.
- ↑ Kamel F, Hoppin JA. 2004. Association of pesticide exposure with neurologic dysfunction and disease. Environ Health Perspect 112:950–958.
- ↑ National Research Council. Pesticides in the Diets of Infants and Children. National Academies Press; 1993. ISBN 0-309-04875-3. Retrieved 10-Apr-2006.
- ↑ Lu, Chensheng, et al. (2006). "Organic Diets Significantly Lower Children’s Dietary Exposure to Organophosphorus Pesticides". Environmental Health Perspectives 114: 260-263.
- ↑ Pesticides: Health and Safety
- ↑ Rabideau, Christine L. [http://e s.epa.gov/ncer/fellow/progress/99/rabideauch00.html Multiple Pesticide Exposure: Immunotoxicty And Oxidative Stress] 2001
- ↑ Spray Drift of PesticidesDec 1999
- ↑ Noyes, Katherine BANISH PESTICIDES FROM YOUR GARDEN
- ↑ HEALTH HAZARDS OF PESTICIDES Natural Resources Defense Council Oct 1998
- ↑ Melissa Lee Phillips Registering Skepticism: Does the EPA's Pesticide Review Protect Children? Environmental Health Perspectives 2006 October; 114(10): A592–A595.
- ↑ DDT Ban Takes Effect EPA press release - December 31, 1972
- ↑ Muckenfuss, A. E.; Shepard, B. M.; Ferrer, E. R. Natural Mortality of Diamondback Moth in Coastal South Carolina Clemson University, Coastal Research and Education Center
- ↑ Pesticides In the Environment
- ↑ Marten, Gerry [http://www.ecotippingpoints.org/pesticidetrapindia.asp ESCAPING THE PESTICIDE TRAP IN INDIA
- ↑ 
- ↑ Sources of Common Contaminants and Their Health Effects USEPA
- ↑ Pesticide exposure raises risk of Parkinson’s
Alberto Ascherio, Honglei Chen, Marc G. Weisskopf, Eilis O'Reilly, Marjorie L. McCullough, Eugenia E. Calle, Michael A. Schwarzschild, Michael J. Thun (2006). "Pesticide exposure and risk for Parkinson's disease". Annals of Neurology.
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-  article on pesticides from the UK
- National Pesticide Information Center (NPIC) - Objective, science-based information about pesticide-related topics.
- Center for Disease Control - Pesticides
- NIH encyclopedia pages with general recommendations regarding risks due to Pesticides and emergency treatment of Insecticide exposure
- Coalition for a Healthy Ottawa - Has municipal pesticide bylaw statistics for Canada and Fact Sheets
- Northwest Coalition for Alternatives to Pesticides - Resource on pesticide hazards and alternatives
- 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.
- National Pesticide Forum- Annual grassroots conference on pesticide policy, science, regulation and activism.
- a list of EPA pesticide labels for pesticides by trade name
- Common bactericides
- Common virucides
- Congressional Research Service (CRS) Reports regarding pesticides
- Compendium of Pesticide Common Names - Maintained by Alan Wood
- UK Pesticide Safety Directorate
- Durango Software - Provides risk assessment tools for pesticide use
- The Pollution in Newborns - From the Environmental Working Group
- The Pesticide Education Network, Ottawa Canada
- Pesticide Action Network UK Aims to minimize pesticide use.
- Banish Pesticides from Your Garden Article on pesticide dangers and alternatives.
- Compilation of multiple regulatory databases into a web-accessible form
- US trade association representing the crop protection and pest control industry
- A dossier on dangers of pesticides by the French NGO MDRGF. MDRGF is a partner NGO of PAN Europe
- Pesticides and Food - Pesticide Residue Limits in Food
- Pesticide Residues in Food - Data and Summary reports from the USDA on pesticide residues in food sold in the United States.
- Pesticides: Use, Effects, and Alternatives to Pesticides in Schools (pdf) from the United States General Accounting Office
- Letter to EPA Administrator Stephen Johnson (pdf) - From Unions representing 9,000 scientists (May 24, 2006)
- Streaming online video about efforts to reduce pesticide use in rice in Bangladesh. Wind