A natural or synthetic agrochemical used to kill insects, rodents, weeds, fungi, or other living things which are harmful to plants, animals, or foodstuffs. Pesticides are designed to target a specific pest in a specific environment, without harming other organisms. However, exposure to long-term or large doses of some pesticides may be toxic to humans and animals, and biological controls are increasingly used to reduce or replace pesticides.
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. Many pesticides, mainly chemical pesticides, are poisonous to humans.
Types of Pesticides
Bactericides for the control of bacteria Herbicides for the control of weeds Fungicides for the control of fungi Insecticides for the control of insects - these can be Ovicides, Larvicides or Adulticides Miticides for the control of mites Nematicides for the control of worms Rodenticides for the control of rodents Virucides for the control of virusesPesticides 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.
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.
Some pesticides are considered too hazardous for sale to the general public and are designated restricted use pesticides.
"Read and follow label directions" is a phrase often quoted by extension agents, garden columnists and others teaching about pesticides. 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.
The use of pesticides also decreases biodiversity in the soil.
On farmers
There have been many studies of farmers with the goal of determining the health effects of pesticide exposure. Research in Bangldesh 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 they are less persistent than organochlorine pesticides.
On consumers
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 was 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.
For example, on page 30 is comprehensive data on pesticides on fruits. Some example data:
|
Fresh Fruit and Vegetables |
Number of Samples Analyzed |
Samples with Residues Detected |
Percent of Samples with Detections |
Different Pesticides Detected |
Different Residues Detected |
Total Residue Detections |
|---|---|---|---|---|---|---|
| Apples | 774 | 727 | 98 | 33 | 41 | 2,619 |
| Lettuce | 743 | 657 | 88 | 47 | 57 | 1,985 |
| Pears | 741 | 643 | 87 | 31 | 35 | 1,309 |
| Orange Juice | 186 | 93 | 50 | 3 | 3 | 94 |
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 &
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. Many food crops, including fruits and vegetables, contain pesticide residues after being washed or peeled (see Pesticide residues in food, above).
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.
Besides human health risks, pesticides also pose dangers to the environment.
Pesticides inflict extremely widespread damage to biota, and many countries have acted to discourage pesticide usage through their Biodiversity Action Plans.
An early discovery relating to pesticide use, is that pests may eventually evolve to become resistant to chemicals.
‘'Persistent Organic Pollutants’' (POPs) are one of the lesser-known environmental issues raised as result of using pesticides.
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
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. 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.
Tankmixing pesticides is the combination of two or more pesticides with different modes of action.
Continuing development of pesticides
Pesticides are often highly efficient for producers who are in the business of large scale agriculture. 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. 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. As a result, older, more hazardous, pesticides are being phased out and replaced with pest controls that reduce these health and environmental risks.
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.
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