"Chemicals have replaced bacteria and viruses as the main threat to health. The diseases we're beginning to see as the major causes of death in the latter part of this century and into the 21st century are diseases of chemical origin."
-- Dick Irwin, toxicologist at Texas


What are pesticides?
The U.S Environmental Protection Agency (EPA) defines a pesticide as "any substance or mixture of substances intended for preventing, destroying, repelling, or lessening the damage of any pest".

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.
The benefit of pesticides lies in their ability to manage a pest (weed, insect or disease) problem that potentially could become out of control and could threaten your health or the health of your family, pets and plants, or threaten the quality of your home, lawn, school or business. Pesticides also protect roadsides, utilities, rights-of-way, forests and lakes from pest damage.
Pesticides help to limit the damage that can be caused by insects, weeds and plant diseases. Whether it is an insecticide for controlling termites or fleas in your home, a herbicide for ridding your lawn of dandelions or a fungicide that keeps plants alive during a disease outbreak, pesticides are analogous to the medicines we use to preserve our own health.
History
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.
DDT or Dichloro-Diphenyl-Trichloroethane is the first modern pesticide and is arguably the best known organic pesticide. It was developed early in World War II, and initially used with great effect to combat mosquitoes spreading malaria, typhus, and other insect-borne human diseases among both military and civilian populations, and as an agricultural insecticide. The Swiss chemist Paul Hermann Müller of Geigy Pharmaceutical in Switzerland was awarded the Nobel Prize in Physiology or Medicine in 1948 "for his discovery of the high efficiency of DDT as a contact poison against several arthropods."

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.

Pesticide use has diereahh increased 50-fold since 1950, and 2.5 million tons of industrial pesticides are now used each year.

Types of Pesticides
1 Bactericides for the control of bacteria
2 Fungicides for the control of fungi and oomycetes
3 Herbicides for the control of weeds
4 Insecticides for the control of insects - these can be Ovicides, Larvicides or Adulticides
5 Miticides for the control of mites
6 Molluscicides for the control of slugs and snails
7 Nematicides for the control of nematodes
8 Rodenticides for the control of rodents
9 Virucides for the control of viruses
10 Pesticides can also be classed as synthetic pesticides or biological pesticides, although the distinction can sometimes blur.

Pesticide-Organism Interactions
Both the beneficial and harmful effects of pesticides are determined by pesticide-organism interactions or how pesticides and organisms react to each other. To do its job, a pesticide must: 1) penetrate the organism, 2) move or be transported to the site of action, and 3) there disrupt or alter the vital function. The manner in which the pesticide affects the vital function is called its mode of action. Penetration, transport, and mode of action involve pesticide-organism interactions. Pesticide-organism interactions also are involved in the metabolism, accumulation, and elimination of pesticides by the organism as well as in biodegradation and biological magnification.
Selectivity and Resistance
Selectivity (the ability of a pesticide to kill or otherwise alter one organism and not another) and the development of pesticide resistance are often caused by differences in pesticide-organism interactions. Resistance is the inherent ability of a pest to sustain less damage from pesticide application than other individuals of that species under comparable environmental conditions. An example of resistance to pesticides worldwide is in insects and mites. In the early 1990s, more than 500 species of arthropods were known to be resistant to insecticides. Pesticide resistance is not limited to arthropods; there are at least 200 species of fungi, over 200 species of weeds, and several species of nematodes and rodents also resistant to one or more pesticides. Resistance often develops in pest populations that have been repeatedly treated with a single pesticide. Development of resistance in pest populations may sometimes be averted or delayed by avoiding the use of persistent pesticides, reducing the number of treatments and alternating pesticide modes of action.
Penetration
The speed and extent of penetration depends on the permeability of the organism to the specific pesticide. This permeability differs significantly among plants and insects and even among different tissues of the same organism. Among animals, tissues of the respiratory and digestive system are usually much more permeable than the skin. With plants, hardened growth and bark generally provide a more effective barrier than new and succulent growth. The ability of a pesticide to penetrate an organism depends on its chemical nature and the formulation. Penetration may be increased under certain conditions, such as high temperature and application of emulsifiable concentrates, which often contain petroleum solvents as inert ingredients.
Transport
The movement of a pesticide from the place where it entered an organism to its site of action involves the mobility of the pesticide molecule and the efficiency of the transporting mechanism of the plant or animal, i.e., how quickly the pesticide moves through the plant or animals system. Systemic herbicides must move through the plant to areas of interaction. Other herbicides are non-mobile in the plant and only affect the tissue with which they come in direct contact.
Mode of action
A pesticide performs its main function only after it reaches its site of action within an organism. These sites are usually the protoplasm of living cells and often particular kinds of cells. For example, the cells affected by organophosphate insecticides are the nerve cells. The herbicide atrazine affects photosynthesis in the chloroplasts of susceptible plant cells.
Pesticides kill or otherwise alter an organism by disrupting or interfering with some vital physiological function. This is known as the pesticides mode of action. The mode of action of orgranophosphate insecticides (e.g., methyl parathion and malathion) is the inhibition of the breakdown of acetylcholine by cholinesterase, an enzyme that is essential in regulating the proper functioning of the nervous system. When acetylcholine accumulates, muscles and glands become overactive because of excessive stimulation of the nerve cells. Some herbicides, such as 2,4-D, act as plant growth regulators, speeding up or slowing down cell growth and reproduction; other herbicides may target vital plant functions or specific enzymes. For example, one major class of herbicides, the acetolactate synthase inhibitors, blocks the synthesis of an enzyme which is critical for the production of several amino acids within the plant. Fungicides may act as inhibitors of spore germination and fungal growth.
Metabolism
Metabolism is the process by which a pesticide, or other chemical, is changed into one or more different chemicals within a living organism. The metabolic product, or metabolite, may be either more toxic or less toxic than the original pesticide ingredient. Aldicarb, the active ingredient in Temik®, has the metabolites sulfone and sulfoxide, which are much more toxic than the parent molecule. Some pesticides are effective only after they have been metabolized to a lethal compound by an organism. For example, 2,4-DB is changed rapidly to 2,4-D by broadleaf plants other than legumes. Actually, 2,4-DB is relatively harmless to the plant in itself. Enzymes of susceptible broadleaf plants alter the compound, forming the toxic 2,4-D. Given enough time, an organism may be able to metabolize certain pesticides to their nontoxic metabolites. Survival may depend on whether or not the organism can metabolize the pesticide into nontoxic metabolites before the toxic activity is complete or irreversible.
Accumulation, elimination, and detoxification
Pesticide chemicals and their metabolites may be stored or accumulated within an organism or be eliminated as waste. Metabolism can be induced based on exposure.
Because pesticide residues may accumulate within organisms, special precautions in harvest or slaughter must be observed with the treated commodities. Grazing, harvest, and slaughter restrictions provide the necessary time for metabolites to be detoxified or eliminated before safe consumption of the treated product is allowed.
Biological magnification
Biological magnification is the tendency for certain pesticides to progressively become more concentrated in each type of organism when moving from the bottom to the top organism within a food chain. Perhaps the most familiar example of reproductive effects of pesticides on nontarget organisms is the eggshell thinning in birds that was caused by certain organochlorine insecticides such as DDT. This eggshell thinning may have been initiated by a chain of events beginning when invertebrates that consumed plants with DDT residues were, in turn, eaten by rodents, reptiles, amphibians, fish, and insectivores, further concentrating the residues in their fat tissues. These predators were eaten by top predators in the food chain that then received yet higher insecticide concentrations. The majority of organochlorine uses have had their registrations banned in the United States for a number of years, and such biological magnification problems have reversed themselves. Top predators are again increasing in number. During the 1990s, the bald eagle was removed from the endangered species list because the reproductive capacity of the population has been increasing. Thus, awareness of such pesticide-organism interactions is important when working with certain pesticides.

ARE REGISTERED PESTICIDES SAFE?
NO. Many of the "safety tests" used to test these products are fundamentally inadequate: they test for the acute (not chronic) effects of single (not multiple) chemicals on healthy (not sick, chemically sensitive or immuno-suppressed etc.) adult (not feta l or young) animal (not human) subjects exposed over short (not long) periods of time Some of the companies testing pesticides have been charged and convicted of falsifying residue and environmental studies that were used to support pesticide registration in the US and Canada .Some pesticides become even more toxic as they break down. (In the US it is a violation of federal law to state that the use of pesticides is safe.)

__________________
I believe in God even though He is silent.

Effect of pesticides on human health
The nature of a pesticide is to kill or otherwise adversely affect the target pest, be it fungus, insect, weed or rodent. Although efforts are made to design the pesticide in such a way that it affects only the target organism, pesticides do cause harm to non-target organisms. Toxic effects range from acute (poisoning occurring through single or a few exposures) to chronic (occurring through long-term exposure). In humans, pesticides can affect the nervous, reproductive and endocrine systems, and may cause cancer. Laboratory studies conducted on animals also have linked chronic exposure of pesticides to birth defects, tumor development and cancers. The EPA's has classified approximately 165 chemical pesticides as known, probable or possible human carcinogens.
New research suggests that some pesticides may disrupt the body's endocrine system-the set of glands, hormones and target cells that help control growth, development, reproduction and behavior. Endocrine disruptors interfere with this system, causing biological dysfunction. Some endocrine disruptors mimic hormones that occur naturally in the body, fooling the body into a response. Other endocrine-disrupting chemicals can inhibit or stimulate the body's production of hormones. Such disruption is known to cause birth defects in wildlife and laboratory test animals, and is suspected of causing cancer and birth defects in humans. Much is yet to be learned about the effects of pesticides on the human endocrine system, and research in this area is ongoing.
Children, in particular, are susceptible to pesticides for various reasons-they are still developing, have faster metabolisms and are involved in play activities that increase their exposure. A child's small size and quick metabolism means that he or she consumes more fresh produce, breathes more air, and drinks more water than adults relative to his or her body weight. They also play on the ground, swim in lakes and rivers and mouth toys and other objects, all of which lead to increased pesticide exposure. Additionally, a child's growing body is more sensitive to chemical exposures because development is taking place in the brain, nervous system and many other areas. Some studies have shown that children of parents who use pesticides occupationally or in the household are three to nine times more likely develop leukemia.
Determining the levels at which a pesticide causes harm is a complex, scientifically demanding task. Pioneering biomonitoring efforts by the Centers for Disease Control and Prevention have helped reduce the uncertainty involved in estimating human risk involved in pesticide and other chemical exposures. Biomonitoring involves the direct measurement of a toxic substance in blood or urine to assess exposure, and will help to determine which of the thousands of known chemical compounds cause birth defects, cancer and other diseases.

__________________
I believe in God even though He is silent.

Effect of pesticides on Environment
The widespread use and disposal of pesticides by farmers, institutions and the general public provide many possible sources of pesticides in the environment. Following release into the environment, pesticides may have many different fates. Pesticides which are sprayed can move through the air and may eventually end up in other parts of the environment, such as in soil or water.

Pesticides in the Atmosphere
The atmosphere is an important component of the hydrologic cycle to consider when assessing the impact of pesticides on the environment. As part of the hydrologic cycle , precipitation (rain and snow) replenishes both surface and ground waters. Precipitation cleans the atmosphere of airborne pesticide vapors and particles and deposits them to the earth's surface, including lakes, rivers, and streams. In addition, dry deposition in the form of gaseous vapor and particulate matter also deposits airborne pesticides to the earth's surface. Pesticides in both precipitation and dry deposition can reach surface waters by direct deposition or surface runoff and can reach ground water by infiltration through the soil.

In many respects, the greatest potential for adverse effects of pesticides is through contamination of the hydrologic system, which supports not only human life, but aquatic life and related food chains as well. Water is one of the primary means by which pesticides are transported from their application areas to other parts of the environment. Thus, there is potential for movement of pesticides into and through all components of the hydrologic cycle

Until the 1960's, atmospheric pollution from pesticide spray drift was generally thought of as a local problem. Long-range movement of long-lived pesticides through the atmosphere was believed to be minimal. The detection of DDT and other organochlorine compounds in Arctic and Antarctic fish and mammals have changed this notion. The atmosphere is now recognized as a major pathway by which pesticides can be transported and deposited in areas sometimes far removed from their sources. Long-range transport of pesticides can occur over hundreds to thousands of kilometers. Toxaphene, for example, which was used on cotton in the Southern United States and banned in 1982, is still being transported into the Great Lakes region by southerly winds from the Gulf of Mexico. Once deposited on the earth's surface, the pesticide can revolatilize, re-enter the atmosphere, and be transported and deposited downwind repeatedly until it is finally degraded, sometimes over decades. This same process can also occur for the degradation products resulting from chemical or biochemical transformations of pesticides. Some pesticide degradation products are more toxic than the original compound.

Ways to Contaminate Water

Pesticides enter water resources in a variety of ways, including:
• Runoff from field application;
• Direct entry from spray operations;
• Sewage dumping;
• Settling from the atmosphere;
• Leaching from waste dumps;
• Leaching from field application through soils into groundwater
Overapplication or misuse of pesticides can allow them to enter the surface and/or ground water. For some newer pesticides, drift from soil/media particles treated with the pesticide is a potential source of water contamination. These pesticides are often active at low concentrations. When bound to soil/media particles, the pesticide may be picked up by wind and moved over surface water. When deposited in water or a waterway, these particles can then move into the surface water. This is generally not a major problem unless large amounts of contaminated particles are moved and deposited in the same area or the pesticide is active on other target species.
Improperly cleaning pesticide containers and sprayers often leads to pesticide runoff or contamination of the soil/media at the mixing/loading site. Pesticide sprayers should be loaded and cleaned on an impervious pad. This eliminates concern about spills causing runoff or leaching problems, avoiding potential contamination of wells from constant small spillages at the same site.

Effect of pesticides on Food
Many modern pesticides are designed to break down into non-toxic substances with the passage of time. Pesticides are most potent just after application, but should break down to relatively safe levels by the time treated food reaches the table. If the pesticide has not had the required amount of time to break down, is applied too liberally, or a more persistent pesticide is used, some pesticide residue may still be in food at the time of consumption.
The U.S. Food and Drug Administration's Pesticide Program found that 60 percent of the fruits and 37 percent of the vegetables that were sampled in 1995 contained detectable pesticide residues. Approximately 2 percent of these fruit and vegetable samples contained residue amounts that exceeded maximum residue limits set by the EPA. The EPA sets the maximum residue limit (MRL) to be the maximum level of residue legally permitted in or on a crop in commerce. This level is set to insure that there are no adverse effects to the consumer over a lifetime of dietary exposure.
Under the 1996 the Food Quality Protection Act, many of the current MRLs are likely to change, largely since the new act requires that levels be reduced by 90 percent if uncertainty about effects on children exists. The EPA must review all pesticides and their health effects using current methodology, taking into account exposure to pregnant women and developing children, while also including exposures from other sources. Using this new data, EPA must set residue limits accordingly by the year 2000

Effects on aquatic life
Pesticide exposure of fish and other aquatic life may be a more widespread problem than most people realize. Most pesticide-related fish kills go unreported and, in documented cases, the number of fish killed is often underestimated. The underwater conditions, including water clarity and depth, and the small size and camouflage coloring of many fish, particularly young fish, make accurate counts difficult. Scavengers quickly remove carcasses from a kill site. Dying and stressed fish may hide in dense cover or leave the area completely.
The remoteness of many streams and wetlands often diminishes chances of detection of fish kills. When dead fish are found after a pesticide application, the incident may go unreported because it is not considered important, or because of fear of liability. Sometimes no association is made between a kill and a past pesticide application because of the amount of time that has elapsed. These factors and others tend to obscure the full impact that some pesticides are having on fish and aquatic systems.

__________________
I believe in God even though He is silent.

Effect of pesticides on Environment
The widespread use and disposal of pesticides by farmers, institutions and the general public provide many possible sources of pesticides in the environment. Following release into the environment, pesticides may have many different fates. Pesticides which are sprayed can move through the air and may eventually end up in other parts of the environment, such as in soil or water.

Pesticides in the Atmosphere
The atmosphere is an important component of the hydrologic cycle to consider when assessing the impact of pesticides on the environment. As part of the hydrologic cycle , precipitation (rain and snow) replenishes both surface and ground waters. Precipitation cleans the atmosphere of airborne pesticide vapors and particles and deposits them to the earth's surface, including lakes, rivers, and streams. In addition, dry deposition in the form of gaseous vapor and particulate matter also deposits airborne pesticides to the earth's surface. Pesticides in both precipitation and dry deposition can reach surface waters by direct deposition or surface runoff and can reach ground water by infiltration through the soil.

In many respects, the greatest potential for adverse effects of pesticides is through contamination of the hydrologic system, which supports not only human life, but aquatic life and related food chains as well. Water is one of the primary means by which pesticides are transported from their application areas to other parts of the environment. Thus, there is potential for movement of pesticides into and through all components of the hydrologic cycle

Until the 1960's, atmospheric pollution from pesticide spray drift was generally thought of as a local problem. Long-range movement of long-lived pesticides through the atmosphere was believed to be minimal. The detection of DDT and other organochlorine compounds in Arctic and Antarctic fish and mammals have changed this notion. The atmosphere is now recognized as a major pathway by which pesticides can be transported and deposited in areas sometimes far removed from their sources. Long-range transport of pesticides can occur over hundreds to thousands of kilometers. Toxaphene, for example, which was used on cotton in the Southern United States and banned in 1982, is still being transported into the Great Lakes region by southerly winds from the Gulf of Mexico. Once deposited on the earth's surface, the pesticide can revolatilize, re-enter the atmosphere, and be transported and deposited downwind repeatedly until it is finally degraded, sometimes over decades. This same process can also occur for the degradation products resulting from chemical or biochemical transformations of pesticides. Some pesticide degradation products are more toxic than the original compound.

Ways to Contaminate Water

Pesticides enter water resources in a variety of ways, including:
• Runoff from field application;
• Direct entry from spray operations;
• Sewage dumping;
• Settling from the atmosphere;
• Leaching from waste dumps;
• Leaching from field application through soils into groundwater
Overapplication or misuse of pesticides can allow them to enter the surface and/or ground water. For some newer pesticides, drift from soil/media particles treated with the pesticide is a potential source of water contamination. These pesticides are often active at low concentrations. When bound to soil/media particles, the pesticide may be picked up by wind and moved over surface water. When deposited in water or a waterway, these particles can then move into the surface water. This is generally not a major problem unless large amounts of contaminated particles are moved and deposited in the same area or the pesticide is active on other target species.
Improperly cleaning pesticide containers and sprayers often leads to pesticide runoff or contamination of the soil/media at the mixing/loading site. Pesticide sprayers should be loaded and cleaned on an impervious pad. This eliminates concern about spills causing runoff or leaching problems, avoiding potential contamination of wells from constant small spillages at the same site.

Effect of pesticides on Food
Many modern pesticides are designed to break down into non-toxic substances with the passage of time. Pesticides are most potent just after application, but should break down to relatively safe levels by the time treated food reaches the table. If the pesticide has not had the required amount of time to break down, is applied too liberally, or a more persistent pesticide is used, some pesticide residue may still be in food at the time of consumption.
The U.S. Food and Drug Administration's Pesticide Program found that 60 percent of the fruits and 37 percent of the vegetables that were sampled in 1995 contained detectable pesticide residues. Approximately 2 percent of these fruit and vegetable samples contained residue amounts that exceeded maximum residue limits set by the EPA. The EPA sets the maximum residue limit (MRL) to be the maximum level of residue legally permitted in or on a crop in commerce. This level is set to insure that there are no adverse effects to the consumer over a lifetime of dietary exposure.
Under the 1996 the Food Quality Protection Act, many of the current MRLs are likely to change, largely since the new act requires that levels be reduced by 90 percent if uncertainty about effects on children exists. The EPA must review all pesticides and their health effects using current methodology, taking into account exposure to pregnant women and developing children, while also including exposures from other sources. Using this new data, EPA must set residue limits accordingly by the year 2000

Effects on aquatic life
Pesticide exposure of fish and other aquatic life may be a more widespread problem than most people realize. Most pesticide-related fish kills go unreported and, in documented cases, the number of fish killed is often underestimated. The underwater conditions, including water clarity and depth, and the small size and camouflage coloring of many fish, particularly young fish, make accurate counts difficult. Scavengers quickly remove carcasses from a kill site. Dying and stressed fish may hide in dense cover or leave the area completely.
The remoteness of many streams and wetlands often diminishes chances of detection of fish kills. When dead fish are found after a pesticide application, the incident may go unreported because it is not considered important, or because of fear of liability. Sometimes no association is made between a kill and a past pesticide application because of the amount of time that has elapsed. These factors and others tend to obscure the full impact that some pesticides are having on fish and aquatic systems.

__________________
I believe in God even though He is silent.

Approaches for Managing Pesticide Use
Reducing the human health threat of pesticides is possible through combined efforts in different areas, such as improved risk assessment and toxicity testing, better education and training for users of pesticides, and integration of farming practices that require fewer pesticides. Ways to reduce the potential hazards of pesticide use could involve the following.
• Crop rotation helps mitigate weed, disease and pest problems, increases soil nitrogen, and reduces the need for fertilizers. Monoculture-the practice of repeatedly growing one type of crop, such as corn, in the same field year after year-is a common practice throughout the United States. This practice promotes pest problems and depletion of soil nutrients.
• Natural predators and parasites can be used to control pests. Pesticides often destroy predators while the pest gradually grows more tolerant to the pesticide, requiring that increasing amounts of the pesticide be applied.
• Soil and water conserving tillage reduces runoff and helps maintain soil quality.
• Integrated pest management is encouraged by the EPA and U.S. Department of Agriculture. This approach to pest control uses the tactics mentioned above-such as crop rotation, biological controls, resistant varieties of plants, pheromones to attract beneficial insects, efficiently timed spraying-and other methods. Integrated pest management can be more economical because it minimizes the use of costly chemicals.
• The majority of children's pesticide exposure comes from home, lawn, and garden application-reducing this exposure requires a more prudent and controlled use of pesticides in private and public areas

__________________
I believe in God even though He is silent.

Good sharing.......smthing related to GM-crops mst also b added.

Thanks, dear genetically modified crops r different topic than pesticides, they r not coorelated. when i,ll get time i,ll post there soon.Insha Allah.
Regards.

__________________
I believe in God even though He is silent.