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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".What is a Pesticide? (US EPA definitions) retrieved June 24, 2006

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.

Types of Pesticides

Pesticides can also be classed as synthetic pesticides or biological pesticides, although the distinction can sometimes blur.

A systemic pesticide is a pesticide applied to a plant which is absorbed into its sap and so distributed throughout the plant to make all parts of it poisonous to pests, without harming the plant, although systemic insecticides which poison pollen and nectar in the flowers may kill needed pollinators.

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.

Regulation

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 countries.

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.

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.

On farmers

There have been many studies of farmers with the goal of determining the health effects of pesticide exposure. Organophosphate pesticides have increased in use, and in addition to being more damaging to the environment they are more persistent than organochlorine pesticides.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. These are associated with acute health problems such as abdominal pain, dizziness, headaches, nausea, vomiting, as well as skin and eye problems.Ecobichon DJ. 1996. Toxic effects of pesticides. In: Casarett and Doull's Toxicology: The Basic Science of Poisons (Klaassen CD, Doull J, eds). 5th ed. New York:MacMillan, 643–689. Additionally, many studies have indicated that pesticide exposure is associated with long-term health problems such as respiratory problems, memory disorders, dermatologic conditions,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. cancer,Daniels JL, Olshan AF, Savitz DA. 1997. Pesticides and childhood cancers. Environmental Health Perspectives 105: 1068–1077. depression, neurologic deficits,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. miscarriages, and birth defects. 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.
 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.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.

On consumers

A study published by the National Research Council in 1993 determined that for infants and children, the major source of exposure to pesticides is through diet.National Research Council. Pesticides in the Diets of Infants and Children. National Academies Press; 1993. ISBN 0309048753. Retrieved 10-Apr-2006. 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 was found that levels of organophosphorus pesticide exposure dropped dramatically and immediately when the children switched to an organic diet.

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, cauliflower, 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 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 National Resources Defense Council.

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. 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.

Misuse of pesticides can 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.Pesticide exposure raises risk of Parkinson’s

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.

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.

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.

See also

References

Further reading

Books

  • Miller, G. Tyler Jr. (2002). Living in the Environment (12th Ed.). Belmont: Wadsworth/Thomson Learning. ISBN 0-534-37697-5

Journal Articles

News

External links

Pesticide regulatory authorities

Pesticides | soil contamination

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This article is licensed under the GNU Free Documentation License. It uses material from the "Pesticide".

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