Pesticides (Science Experiments)
The good, the bad, and the pesty
Experiment 1 Natural versus Synthetic: How do different types of pesticides compare against a pest?
Design Your Own Experiment
A is any substance that prevents, repels, or kills pests. The definition of a pest is a relative one. A pestAny living thing that is unwanted by humans or causes injury and disease to crops and other growth. is an organism that is unwanted by humans at a specific time or in a specific place. Pests can range from cockroaches and mice, to fungi and plants. In modern day, pesticides are an integral part of food production and household use.
The use of pesticides has a long history. There is evidence that ancient Romans and Chinese, for example, used various minerals and plant extracts as pesticides. Manufactured chemical pesticides began in the 1930s and dramatically increased after World War II (19395). The widespread use of chemical pesticides led to an increased concern for how pesticides were affecting the environment, animals, and people. Over the years, pesticides have undergone much advancement, including the development of natural substances and improvements on the traditional....
(The entire section is 4546 words.)
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Pesticides (Encyclopedia of Public Health)
Pesticides are a broad class of chemicals and biological agents that are specifically designed and applied to kill a pest. Specific types of pesticides target specific types of pests: insecticides kill insects, fungicides kill fungi and bacteria, herbicides kill weeds and other unwanted plant vegetation, molluscacides kill mollusks, acaricides kill spiders, and so on. Pesticide use dates back to ancient times.
Pesticides are regulated in the United States at both the federal and state level. The primary legislation, one of the oldest environmental laws, is the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA, 1972), which is administered by the Environmental Protection Agency (EPA). Each state also has an agency responsible for carrying out FIFRA mandates. These agencies may be environmental or agricultural in nature, depending on the state. State laws can be more restrictive than the federal laws.
Pesticides are sometimes called "economic poisons." They are developed to kill something, and they are, therefore, inherently toxic. Pesticides that are less toxic are classified as "general use pesticides." These can be purchased by the average homeowner and applied without any special license or permits. More toxic compounds are called "restricted use pesticides" and their use requires a license. In some cases the restricted use materials have the same active ingredients as the general use materials, but at a higher concentration.
Anything that claims that it has pesticidal activity is, by law, a pesticide, and is subject to registration by the EPA and local state agencies. Household cleaners and bleach are legally pesticideshe pesticide registration number can be found on the product container.
Within the broad classes of products that have similar types of action (e.g., weed killers, insect killers) there are further distinctions regarding the type of chemistry. For example, among insect killers, there are synthetic pyrethroids, organophosphates, and organochlorines. The most well known are the organochlorines, such as chlordane and DDT, which became popular after World War II, and were used in agriculture, and for home and commercial use, for decades. These compounds have low acute toxicity, but are persistent in the environment and have caused a series of long-term environmental health problems. They remain in soil and tissue for a very long time, and they have been shown to have a harmful impact on animal endocrine systems. Most organochlorines were phased out of use in the 1980s. They were replaced by organophosphate materials that are less persistent, but more acutely toxic. In the beginning of the 1990s these compounds, too, were beginning to be phased out through government actions, and voluntarily by the manufacturers.
Pesticides have entered the food system in many parts of the world. Though credited with an enormous increase in food and fiber production, indiscriminate use of these products has led to acute and long-term health problems for humans and animals. There are risks associated with the application of a pesticide into a system, while at the same time there are benefits for using these materials to reduce disease, increased food production, and lessen the risk of starvation.
Pesticides have been applied in many part of the world to control vector-borne diseases such as malaria, yellow fever, dengue, and others. The most prudent way to balance the benefits with the risks is an integrated approach to pesticide use, combining all control methodshysical, biological, cultural, and chemical.
MARK G. ROBSON
(SEE ALSO: Environmental Movement; Environmental Protection Agency; Fungicides; Toxicology)
Hayes, W., and Laws, E. (1991). Handbook of Pesticide Toxicology, Vol. 1. San Diego, CA: Academic Press.
Wallace, R., ed. (1998). Maxcy-Rosenau-Last Public Health and Preventive Medicine. Stamford, CT: Appleton and Lange.
Pesticides (Encyclopedia of Food & Culture)
PESTICIDES. A pesticide is any agent used to kill or control a pest. Pests include insects, weeds, and diseases, such as fungi. In addition, mice, rats, birds, and algae may become pests at some time. When pests damage plants or property, people often use pesticides to control them. The term "pesticide" can apply to insecticides, herbicides, fungicides, antimicrobials, growth regulators, defoliants, and desiccants, most of which are applied to food or food plants before or after harvest. Common pesticides are encountered every dayn pet flea collars, kitchen disinfectants, cockroach baits, swimming pool chemicals, and mosquito repellents. Pesticide products contain both active and inert ingredients, and both must be specified on the label.
Modern farmers use pesticides to help them to grow almost all of the world's food. In general, pesticides have been a quick, effective, and inexpensive method of control for pests that attack most of the world's food crops. Pesticides are credited with helping to save millions of lives by controlling diseases, such as malaria and yellow fever, which are spread by insects. However, most pesticides present some risk of harm to humans, animals, or the environment because they are designed to kill living organisms.
Sulfur, herbal extracts, tobacco, soaps, oil, arsenic, pyrethrum, and lime have been used as pesticides for many centuries, but the widespread use of synthetic pesticides is a relatively recent phenomenon. Dichlorodiphenyltrichloroethane, or DDT, is probably the best known early pesticide. DDT was created in 1873, but it was not until the late 1930s that Swiss researcher Paul Müller discovered that the compound was effective in killing insects. Müller won the Nobel Prize in Physiology and Medicine in 1948 for his work. DDT was an inexpensive and effective solution to many insect problems, and it virtually eliminated malaria from parts of the world. After World War II, DDT became a common agricultural pesticide. In the 1950s, the United States was producing 220 million pounds of DDT per year.
Insect resistance to the substance developed quickly. DDT residues were found in human milk and fatty tissues, and in wildlife food chains. In 1962 writer and ecologist Rachel Carson wrote Silent Spring to warn the public about the long-term effects of misusing pesticides. Carson challenged the practices of agricultural scientists and the government, and called for a change in the way humankind viewed the natural world. Carson testified before Congress in 1963, calling for new policies to protect human health and the environment. While no longer used in the United States, DDT use continues in other parts of the world. Many tropical countries still use DDT to control malaria.
All pesticides (natural and synthetic) have the potential to cause harm during their manufacture or refinement, at the time of application to crops, as residues that persist on food, and in the disruption of the natural balance that exists between pests and their natural enemies. For example, traces of the natural insecticide "rotenone" may be found on vegetables after cooking. Atrazine, a weed-killer commonly used on corn and soybeans, suburban lawns, and utility rights-of-way, has contaminated groundwater where those crops are grown. Insecticides like DDE and dieldrin, which are related to DDT, were banned in the United States in the 1970s, but still show up in the U.S. food supply. Persistent residues of these chemicals travel long distances in global air and water currents. These insecticides are still produced and used in many countries. Recent studies have linked pesticides with acute poisonings, cancer, brain damage, reproductive harm, and many childhood illnesses and learning problems, leading concerned citizens to feel that pesticides should be banned.
Some agricultural experts predict that the quality and quantity of our food supply would be lessened if pesticides were eliminated. However, practitioners of organic agriculture (organic farmers use no synthetic agricultural chemicals and instead rely on management practices such as crop rotation, disease-resistant varieties, and natural enemies to control crop pests) claim that food quality and yield are equally productive under organic management. Fortunately for conventional and organic farmers, the number of safer, reduced-risk options for pest control is increasing. For example, there were approximately seven hundred new, biological pesticide products registered by 1999. Biological pesticides are certain types of pesticides derived from such natural materials as animals, plants, bacteria, and minerals.
Garlic, mint, and baking soda all have pesticide-like properties and are considered biological pesticides. Biological pesticides include the common cabbage worm killer Bacillus thuringiensis, which produces a protein that helps to kill specific worm pests. Some of the new reduced-risk pesticides, while synthesized in a laboratory, are considered safer because they do not kill beneficial insects (such as lady beetles and lacewings), or they break down quickly to inactive products. In 1977 U.S. president Jimmy Carter issued a Presidential Decree that mandated the use of integrated pest management (IPM) comprehensive approach to pest control that uses a combination of less toxic means to reduce the status of pests to tolerant levels, while maintaining a quality environment. Together, the new reduced-risk pesticides and IPM practices have helped to lessen the amount of pesticides that are used on food and other crops. Levels of pesticide residues on IPM produce have been reported as higher than those of organically grown food, but lower than those in conventionally grown produce.
Pesticides and Their Regulation
In the United States, pesticides are regulated by the Environmental Protection Agency (EPA). EPA regulates the sale, distribution, and use of pesticides and has the authority to suspend or cancel the registration of a pesticide if information shows that continued use would pose unreasonable risks. In 1996 the Food Quality Protection Act (FQPA) was signed into law, giving EPA more effective power. Among its many benefits, the FQPA established a new health-based safety standard for pesticide residues in food; included special provisions for infants and children; required periodic tolerance reevaluations; incorporated provisions for endocrine testing; and allowed for enhanced enforcement of pesticide residue standards.
Scientists predict that, in the future, pesticides will continue to play a role in pest management of food crops, partly because reduced-risk pesticides have become less harmful to the environment, and less toxic to people and wildlife. Societal concerns, scientific advances, and regulatory pressures continue to drive some of the more hazardous pesticides from the marketplace. In addition, consumer interest in safe and healthy food will create more demand for organically grown products.
See also Herbicides; Organic Agriculture; Organic Farming and Gardening; Food Safety; Toxins, Unnatural, and Food Safety.
Cruising chemistry. An introduction to the chemistry of the world around you. "DDT: An Introduction." University of California, San Diego. Available at .
Entomology at Rutgers. Agricultural Entomology and Pest Management course. Entomology 37050pring 2001, Dr. George Hamilton. Available at http://aesop.rutgers.edu/hamilton/agent.htm.
"The Future Role of Pesticides in U.S. Agriculture." 2000. Committee on the Future Role of Pesticides in U.S. Agriculture, Board on Agriculture and Natural Resources and Board on Environmental Studies and Toxicology, Commission on Life. Available at http://books.nap.edu/books/0309065267/html/17.html.
Lear, Linda. The Rachel Carson Website. Available at http://www.rachelcarson.org/.
Natural Resources Defense Council. Available at http://www.nrdc.org/health/pesticides/default.asp.
Paul Hermann Mülleriography. Nobel e-Museum. The Nobel Foundation. The Official Web Site of The Nobel Foundation. Available at http://www.nobel.se/medicine/laureates/1948/muller-bio.html.
Pesticide Action Network Pesticide Database. Available at .
Pesticide Action Network Toxicity Ratings. Available at .
Pesticide Data Program. USDA Agricultural Marketing Service Science and Technology Programs. Progress Report 2001. Available at http://www.ams.usda.gov/science/pdp/progress.htm#skipusers).
U.S. EPA Office of Pesticide Programs. Biopesticides. Available at .
U.S. EPA Office of Pesticide Programs. Highlights of the Food Quality Protection Act of 1996. Available at .
U.S. EPA Office of Pesticide Programs. What the Pesticide Residue Limits Are on Food. Available at http://www.epa.gov/pesticides/food/viewtols.htm.
Patricia S. Michalak
Pesticide (How Products are Made)
The word "pesticide" is a broad term that refers to any device, method, or chemical that kills plants or animals that compete for humanity's food supply or are otherwise undesirable. Pesticides include insecticides, fungicides, herbicides, nematocides (used to kill nematodes, elongated cylindrical worms), and rodenticides. Of these various pesticides, insecticides have a longer and more noteworthy history, perhaps because the number of insects labeled "pests" greatly exceeds the number of all other plant and animal "pests" combined. Hence, this article focuses on the use of agricultural insecticides.
Since they first began cultivating crops (around 7000 B.C.) if not before, humans have devised methods to prevent insects from eating or otherwise destroying precious crops. Some cultures relied on the practice of planting during certain phases of the moon. Other early agricultural practices that indirectly kept insect populations low were rotating crops; planting small, varied crops; and selecting naturally resistant plants. People picked bugs off plants by hand and made noise to ward off grasshoppers. Chemicals were also used early on. The crushed petals of the pyrethrum (a type of chrysanthemum), sulfur, and arsenic were used in the Middle East, Rome, and China, respectively. The Chinese also used natural predators such as ants to eat undesirable insects.
All attempts at pest control were pretty much individual affairs until the 1840s, when a North American fungus called powdery mildew invaded Britain, and the epidemic was controlled with large-scale applications of sulfur. The Colorado beetle in the western United States was the next target: by 1877 western settlers had learned to protect their potato crop by using water-insoluble chemicals such as paris green. Other pesticides such as derria, quassia, and tar oil followed, but nineteenth-century pesticides were weak. They had to be supplemented by introducing natural predators, or, in some cases, by grafting threatened plants onto more resistant rootstock.
By World War II, only about 30 pesticides existed. Research during the war yielded DDT (dichloro-diphenyl-trichloro-ethane), which had been synthesized in 1874 but wasn't recognized as an insecticide until 1942. Other strong pesticides soon followed, such as chlordane in 1945 and endrin in 1951. Poison gas research in Germany yielded the organophosphorus compounds, the best known of which is parathion. These new pesticides were very strong. Further research yielded hundreds of organophosphorus compounds, the most noteworthy being malathion, which was recently used in California against the medfly.
Until the 1800s, when people began to spray personal gardens using fairly large machines, pesticides were generally applied by hand. Airplanes were not used until the 1920s, and slow, well-controlled, low-level flights were not implemented until the 1950s. The first aerial spraying of synthetic pesticides used large amounts of inert materials, 4000 liters per hectare (a hectare equals 2.47 acres). This quantity was rapidly reduced to 100 to 200 liters/hectare, and by the 1970s the amount had been reduced (in some cases) to .3 liters per hectare of the ingredient itself (for example, malathion) applied directly to the fields.
Image Pop-UpIn pesticide manufacturing, an active ingredient is first synthesized in a chemical factory. Next, a formulator mixes the active ingredient with a carrier (for liquid pesticidel or with inert powders or dry fertilizers (for dust pesticidel, then bottles or packages it. Liquid pesticides are packaged in 200-liter drums for large-scale operations or 20-liter jugs for small-scale operations, while dry formulations can be packaged in 5 to 10 kilogram plastic or plastic-lined bags.
Today, some 900 active chemical pesticides are used to manufacture 40,000 commercial preparations. The Environmental Protection Agency (EPA) estimates that the use of pesticides doubled between 1960 and 1980. Currently, over 372 million kilograms a year are used in the United States, with over 1.8 billion kilograms a year used worldwide.
A pesticide consists of an active ingredient coupled with inert ingredients. The active ingredient kills the pests, while the inert ingredients facilitate spraying and coating the target plant; they can also contribute other advantages that are not conferred by the active ingredient alone.
Active ingredients were once distilled from natural substances; now they are largely synthesized in a laboratory. Almost all are hydrocarbons derived from petroleum. Most pesticides contain other elements, the type and number of which depend on the pesticide desired. Chlorine, oxygen, sulfur, phosphorus, nitrogen, and bromine are most common. Inert ingredients can be many substances, dependent on the type of pesticide. Liquid pesticides have traditionally used kerosene or some other petroleum distillate as a carrier, though water has recently begun to replace kerosene. Emulsifiers (such as soap) are also added to distribute the active ingredient evenly throughout the solvent. A powder or dust pesticide will typically contain vegetable matter such as ground up nut shells or corn cobs, clays such as diatomite or attapulgite, or powdered minerals such as talc or calcium carbonate as a base. To cause the pesticide to adhere better
The Manufacturing Process
Manufacturing a pesticide involves at least three separate activities. The active ingredient is first synthesized in a chemical factory, then formulated in the same place or sent to a formulator, who prepares the liquid or powder form. The pesticide is then sent to the farmer or other certified applicator, who dilutes it before applying it to the fields.
Synthesizing the pesticide
- 1 When a new pesticide is first developed, it is manufactured on a small scale in a laboratory. If the substance proves viable, production begins in the factory. Batch or continuous manufacturing insures a high volume, perhaps as much as 500 kilograms per cycle. Synthesizing a pesticide is a complex chemical procedure that requires trained chemists and a large, sophisticated laboratory. The basic procedure entails altering an organic molecule to form a pesticide. This may involve any of a number of specific reagents and catalysts and often must take place in a controlled climate (within a certain temperature range, for example). Once synthesized, the active ingredient is packaged and sent to a formulator. Liquid insecticides can be shipped in tank trucks or 200-liter drums. Transport of the active ingredient follows all regulations for hazardous materials transportation.
Formulating the pesticide
- 2 A formulator accepts the active ingredient, measures out the proper amount, mixes it with carrier if it is to be a liquid pesticide or with inert powders or dry fertilizers if it is to be a dust pesticide, then bottles or packages it. Liquid pesticides are packaged in 200-liter drums if a large-scale farmer is the anticipated customer or 20-liter jugs for small-scale operations. Dry formulations can be packaged in 5 to 10 kilogram plastic or plastic-lined bags. An emulsified formulation is usually concentrated to render transport easier (the active ingredient typically makes up 50 percent of the emulsified concentrate), but granulated and dry pesticides are ready to use.
Diluting the pesticide
- 3 The pesticide might be stored a short time before it is requested. When it is ready for transport, the estimated necessary amount is sent to the farmer, who dilutes the emulsified concentrate to create the amount of pesticide desired. In most instances, the final product consists of only .5 to 1 percent of the original active ingredient. The pesticide is now ready to be applied.
Applying the pesticide
- 4 There are several ways to apply a pesticide. The method with which Americans are most familiar is crop dusting, though its use is generally limited to large, flat areas. A plane loaded with 2000-liter (or larger) tanks flies over a field and sprays out the pesticide from booms. Booms are long, horizontal rods from which several sprinklers spray down. Another method is to attach the tanks and booms to a tractor and spray closer to the ground. For small farmers, the most economical method of spraying is to use one or more workers with hand-held sprayers attached to small tanks. A hand pump can be carried on the shoulder; its tank capacity is only about 3 to 12 liters. Small tanks with a capacity of around 200 liters are also used. The pesticides are applied with a hand gun. A rough estimate of the amount applied is 150 to 300 liters per hectare.
Pesticides are by their very nature toxic substances; hence, a great deal of concern has centered on safety. The laws dealing with pesticide safety are very strict and will become even stricter in the future. Besides legal restrictions, pesticides are also subject to stringent quality control standards like any other manufactured product.
Most large pesticide manufacturers have highly developed quality control laboratories that test each pesticide for potency, emulsification, density, color, pH, particle size (if a dust), and suspension (if a liquid). If the company makes more than one pesticide, the product's identity must also be verified. A pesticide must be stable, easy to apply, and easy to store. Shelf-life must extend past one year. In accelerated tests, the pesticide is subjected to high temperatures for a short period, then checked for effectiveness. A typical pesticide is 95 percent pure. Labels must be easy to read and meet all regulations. The manufacturer keeps files for each raw material, active ingredient, formulation, and packaged item, and samples are stored for three years.
Today's pesticides, when used properly, are very safe. Farmers who apply their own pesticides must be trained by the U.S. Agricultural Extension Service and certified by the state department of agriculture before they can purchase pesticides. Commercial applicators must also undergo training and pass a written test.
When preparing a formulation for application, which in most cases means diluting it, the applicator should wear protective clothing as directed by the label. Often, this protective garb includes an apron or coveralls, a broad-brimmed hat, long-sleeved shirt, long socks, unlined neoprene or rubber gloves, long pants, and unlined neoprene or rubber boots worn over shoes. For some pesticides, applicators must also wear goggles and/or a respirator.
As an additional precaution, application equipment is calibrated before each use. To calibrate a sprayer, the applicator measures off a distance in the field, then sprays it with a neutral substance such as water. The amount of water used is then checked to see if it is appropriate. All equipment is also checked to see if spraying is even, and worn equipment is replaced promptly.
When they were introduced, pesticides were seen as a wonderful technology that would increase crop yields and reduce insect-borne diseases. The first sign that this was a hopeful myth was the discovery in the 1950s that pesticide volume must be increased to have the same effect it once had. With the publication of Silent Spring by Rachel Carson in 1962, an awareness of the danger of unrestricted pesticide use grew.
Pesticides kill the pests they are aiming for most of the time, yet often they also kill the pests' natural predators, thereby exacerbating the problem. In some cases, exterminating a pest merely allows another pest to take its place. After a period of pesticide use, the insects become resistant to the pesticide, and stronger or more pesticides must be used to control the population. There is evidence that pesticides are misused, that their effect in some cases is negligible, and that applicators are not aware of the proper use of pesticides. Coupled with these concerns is the worry over blanket spraying of residential areas and contaminated food.
DDT is the most widely noted case of a pesticide that caused damage far from the farm. High levels of DDT have been found in birds of prey, causing them to become endangered because of the effect it has on their eggs. DDT becomes more concentrated the higher it climbs in the food chain, and many people have voiced their concern about its possible presence in humans. In 1972, the Environmental Protection Agency (EPA) announced a ban on almost all uses of DDT.
Several dozen other pesticides have also been banned, or their use restricted by the EPA. Ironically, these pesticides are still being exported to assist developing countries, where it is estimated that three million acute cases of pesticide poisoning occur per year, along with 20,000 deaths directly related to the misuse of pesticides. Because many of these countries export produce to the United States, the possibility of American contamination is high.
Integrated pest management (IPM) was begun in the 1960s in response to the pesticides dilemma. The idea behind IPM was to use a variety of insect controls instead of relying solely on chemical insecticides. The methods include introducing natural predators, parasites, and bacterial, viral, and fungal insecticides to the fields. Workers may simply vacuum up the insects, or introduce certain plants to ward off pests that attack a particular crop. Farmers may plow at the most effective time, plow their crop residue under, or strip harvest. They may plant pest-resistant plants. Sexual attractant traps may pull pests away from crops. Sterilized males can be released into the field. Insects can be engineered to remain juvenile and never reproduce, molt too rapidly and therefore die rapidly, or become too confused to locate crop foods. Other possibilities are being tested at present. It is possible that in the future pesticide use will diminish as research leads to ways to combat pests with more knowledge and planning and less reliance on chemical intervention.
Where To Learn More
Carson, Rachel. Silent Spring. Houghton Mifflin Company, 1962.
Lee, Sally. Pesticides. Franklin Watts, 1991.
Ware, George W. Pesticides: Theory and Application. W.H. Freeman, 1983.
Gibbons, Ann. "Overkilling the Insect Enemy." Science. August 10, 1990, p. 621.
Holmes, Bob. "The Joy Ride Is Over." U.S. News and World Report. September 14,1992, pp. 73-74.
Reganold, John P., Robert I. Papendick, and James F. Parr. "Sustainable Agriculture." Scientific American. June, 1990, pp. 112-120.
Richmond, Suzan. "Making Sure It's Organic." Changing Times. October, 1990, p. 102.
Satchell, Michael. "A Vicious 'Circle of Poison."' U.S. News and World Report. June 10, 1991, pp. 31-32.