26 August 2011


The general term "pesticide" includes herbicides, fungicides, rodenticides, insecticides, and other categories of substances designed to stop unwanted growth. Pesticides and herbicides are designed to kill pests (and plants that are considered pests), but their toxic effects may have unplanned impacts on harmless and even useful organisms, and may be harmful to human health.



The general term "pesticide" includes herbicides, fungicides, rodenticides, insecticides, and other categories of substances designed to stop unwanted growth. Pesticides and herbicides are designed to kill pests (and plants that are considered pests), but their toxic effects may have unplanned impacts on harmless and even useful organisms, and may be harmful to human health.

To produce the various pesticides in use, thousands of active ingredients are used in tens of thousands of combinations for many purposes. The most common use of pesticides is in agriculture.

Because of widespread use, traces of pesticides may be found in water, land, and air, as well as in the bodies of animals and humans.

Sales of pesticides have decreased in industrialized nations but are growing rapidly in developing countries. The worldwide market increased from $41 billion in 2007 to $52 billion in 2008, a record increase.

Even when used correctly, pesticide residue may be found in soil, water, plants, food supplies, and animals. In India, for example, half of the food supply has been found to contain pesticide residues, and out of this amount, 20% had residues above the global average. Even years after they were legally restricted, residues of banned pesticides can still be measured in the environment.

Pesticides may be applied in a variety of ways and locations, including agriculture, water processing (irrigation water, paper mills, swimming pools, etc.), and household uses. In the United States and other developed nations, pesticides are not only used on food crops, but are also applied within and around forests, lakes, parks, lawns, and in hospitals, schools, offices, and residences. In developing nations, pesticide use is less common in cities and more concentrated on farmland.

According to the United States Environmental Protection Agency (EPA), biopesticides are naturally occurring substances that control pests (biochemical pesticides), microorganisms that control pests (microbial pesticides), and pesticidal substances produced by plants containing added genetic material (plant-incorporated protectants or PIPs).The EPA regulates biopesticide use. Chitin and chitosan are examples of biopesticides regulated by the EPA for agricultural and horticultural use.

Integrated Pest Management (IPM) techniques offer preventive pest control without the use of chemical pesticides, except as a last resort. IPM includes prioritizing pests to be controlled, measuring actual pest levels, interrupting pest breeding processes, rotating crops and using pre-resistant species of crops. IPM has not been adopted widely in agriculture or by governments.

While pesticides are designed to kill pest animals and plants, they may also unintentionally kill and harm fish, birds, and mammals, as well as bees and other plant pollinators, consequently disrupting agricultural ecosystems and making it harder for farmers to manage their crops. While science has demonstrated long-term problems with pesticide use, farmers are encouraged to continue by tradition, by pesticide manufacturers, by lack of ecological knowledge, and by short-term competition with other farmers.

Persistent organic pollutants (POPs) are compounds capable of resisting environmental degradation. Because of this capability, they persist in the environment, build up in human and animal tissue, and may have significant side effects on human, animal, and environmental health. Examples include aldrin, chlordane, dichloro-diphenyl-trichloroethane (DDT), dieldrin, endrin, heptachlor, hexachlorobenzene, mirex, polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and toxaphene.

Pesticides may be implicated in declining amphibian populations. Atrazine is widely-used as an active ingredient in herbicides to control broadleaf and grassy weeds in corn, sorghum, and turf grass sod. It can be found at several parts per million in agricultural runoff. In frogs, atrazine produces a decrease in testosterone levels, resulting in demasculinization and production of hermaphrodites. It may also be a factor in global decline in amphibian populations.

Pesticide poisoning is under-diagnosed around the world. Despite recommendations by the EPA, healthcare providers receive limited training in occupational and environmental health, and in pesticide-related illnesses.

The EPA estimates that 10.4% of community water system wells and 4.2% of rural wells are contaminated by one or more pesticides. Pesticides have been documented to have contaminated over 15,000 public and private wells in Florida.

More insect species are becoming resistant to insecticides. Resistant species of fungi, weeds, and rodents are also on the rise.

In 2001, the U.S. Centers for Disease Control and Prevention (CDC) released data collected in 1999 on human exposure levels to 24 chemicals, including phthalates and organophosphate pesticides. The report tested blood and urine of 3,800 children and adults to examine possible links between chemical exposure and disease and reproductive health problems. While some of these toxins had previously been tested for presence in soil, air, and water samples, levels in humans had not been directly measured before. These studies have been repeated in subsequent years.


General: Categories of pesticides include organochlorines (OCs), organophosphates (OPs), and pyrethrins and pyrethroids.

The active chemicals in pesticides affect living systems. At a certain level of exposure, a chemical may cause poisoning. That is the level of acute toxicity.

Acute toxicity is measured as the amount required to kill 50% of the animals in a test population. This measure is usually expressed as the LD50 or simply the LD (lethal dose). In the United States, all pesticide toxicity values, including the LD50, can be found on the product's Material Safety Data Sheet (MSDS). Every chemical used in the United States is required by law to have an MSDS.

Organochlorines: The class of organochlorines includes the well-known pesticide DDT (dichloro-diphenyl-trichloroethane), which is no longer available in the United States. Organochlorines are persistent in the environment and also build up in human fat. They were widely used in insect control efforts from the 1940s to the 1970s. DDT was also used to control typhus and malaria. However, most organochlorines are now banned in the United States because they were connected with the development of cancer in humans and threatening species of animals and birds (particularly the bald eagle).

Organophosphates: Organophosphates are a series of organic compounds containing phosphorus. Organophosphate insecticides (including carbamates) inhibit cholinesterase, which results in a buildup of acetylcholine in the body. With too much acetylcholine, nerve cells fire randomly, and the nervous systems cannot function.

Pyrethrins and pyrethroids: Pyrethrins are naturally occurring compounds with insecticidal properties that are found in pyrethrum extract from certain chrysanthemum flowers. The pyrethrins are often used in household insecticides and products to control insects on pets or livestock.

Pyrethroids are manufactured chemicals that are very similar in structure to the pyrethrins, but are often more toxic to insects and mammals, and last longer in the environment than pyrethrins.

Phthalates: Phthalates are a class of chemicals involved in the manufacture and use of pesticides. They interact with pesticides to produce negative health effects on reproductive systems. Reproductive biologist Earl Gray at the U.S. Environmental Protection Agency (EPA) has led research on low-dose toxicity of phthalates during critical periods of fetal development and has found they interfere with the hormone system. Phthalates have been found in rat studies to cause additive side effects when combined with other phthalates and when combined with pesticides, even when not acting independently.


Organophosphates (OPs) poison insects, birds, amphibians, and mammals by causing the loss of the acetylcholinesterase enzyme (AChE) at nerve endings (by the action of phosphorus and halide ions). The result is an excess of acetylcholine (Ach), which is the impulse-transmitting substance in the nerve ending. Normal transmission of nerve impulses gets out of control, disrupting communication with muscle cells, glandular cells, autonomic ganglia, and within the central nervous system. Death follows the loss of a functioning nervous system.

Since the banning of organochlorine insecticides in the United States and Europe, organophosphate insecticides have become the most widely used insecticides available today. OPs are used in agriculture, in the home, in gardens, and in veterinary practice. They share the mechanism of cholinesterase inhibition; they kill pests in the same way, and can cause similar symptoms in humans. Exposure to multiple OPs by multiple entry points may lead to increased toxicity. These OPs were once considered to be biodegradable and safer than organochlorines (OCs), but have now been found to be toxic and persistent in the environment. When they break down, toxic metabolites may be formed.

Pesticides spread by various means through the environment. For example, runoff in agricultural fields may contain pesticides and may enter water supplies. They can also evaporate and drift in the atmosphere. They may then be consumed by animals, including fish, and then spread in various food chains.

Pesticide spills during transport can be disastrous, as shown in the recent case where a ferry carrying large amounts of five different pesticides capsized in the Philippines, killing hundreds of people and requiring a massive cleanup.

In California, courts have addressed the problem of evaporated and wind-blown pesticides. A jury found that the unintended contamination of organic crops caused by pesticides (chlorpyrifos, diazinon and dimethoate) from nearby fields violated the rights of the organic crop grower. Neither the state Department of Pesticide Regulation (DPR) nor the U.S. Environmental Protection Agency (EPA) has regulated this pesticide drift.


Demonstrating the health effects of pesticides can be difficult and subject to debate. Some argue that no chemical can be said to be completely safe and that the potential benefits outweigh negative impacts, while other disagree. Research and government policies have focused on short-term and heavy exposure, but long-term exposure in smaller doses have not been well studied. Some opponents of pesticides have argued that small-dose exposures may be accumulative, that pesticides interact with other chemicals, and that pesticides act to disrupt complex processes in the body.

There are established guidelines for most chemicals, including pesticides, for how much exposure should be considered dangerous. Even within agreed upon limits, the chemicals in pesticides have been found to be toxic, suggesting that the standards may need re-examination.

Each region of the gastrointestinal tract has its own character that may affect the absorption of a pesticide. If a pesticide enters the bloodstream, its absorption will differ, depending on how it is processed by various tissues and organs.

Pesticides may build up in body tissues, proteins, fat, and bone, making it difficult to determine the amount of exposure. The amount of pesticide absorbed is a critical factor in making treatment decisions. In most cases treated by physicians, the information that the patient provides about exposure can be incomplete and vague.


General: Pesticides can kill pests in various ways. Most pesticides that act on non-plant pests work by interrupting the communication between nerve endings, which confuses the nervous system and stops normal functioning of the muscles and organs.

If pesticides could be used to poison the pests only, they may not be problematic. The problems arise when pesticides poison other living things besides the pests. Because they stay in the environment for a long time and are spread around in air and water, pesticides typically end up as a threat to many species of plants and animals for many years.

Health effects: In general, herbicides and fungicides are less poisonous to humans than other types of pesticides because the physiology of plants differs from that of animals.

Pesticides usually cause skin irritation or rashes soon after people are exposed to them. However, a wide array of health effects from pesticides have been noted in both humans and animals, including nausea, a general feeling of sickness, loss of appetite, weakness, weight loss, irritation to the skin and eyes, numbness, tingling, itching, burning sensations, loss of bladder control, loss of muscle coordination, seizures, irritation to lung, stomach and intestinal linings, gastrointestinal pain, vomiting, breathing problems, problems with heart rate, cancer, central nervous system deficits, liver and kidney problems, reproductive difficulties, spontaneous abortions, birth defects, smaller litters and early death in litters, and demasculinization or hermaphroditism (in frogs).

Exposure to pesticides causes an annual 20,000 deaths worldwide, and at least three million cases of acute poisoning, according to the World Health Organization (WHO). Pesticide ingestion is a common form of suicide. Many cases of poisoning and death are caused when people come into contact with poorly disposed pesticide waste and containers. A common problem is the reuse of pesticide containers to store food and water.

Lists of pesticides and their observed health impacts can be found in a number of government and university databases.

Measuring and regulating pesticide use: While the levels of exposure that cause severe toxicity have been measured and are shown on labels of pesticide products, researchers and industry have been slow to study other important aspects of pesticide exposure. The effects of long-term exposure, the impacts of chemical interactions, and their role in disrupting the hormone system have not been well studied.

Different contexts of use should be considered in determining health effects. Researchers have proposed the idea of "life cycle" to encourage consideration of many different contexts. Pesticides may affect workers involved during manufacturing, or workers in agricultural settings. Pesticides may affect consumers of food, or the mammals, amphibians, birds, and fish that eat the food. If the consumers of pesticide-treated food have babies, the health of the young may be affected, whether human or animal. The impact of pesticides continues during runoff, evaporating and drifting in the air, and during transport over roads and waterways. Proper disposal of pesticides helps minimize potential health concerns.

Exposure to pesticides by humans has been difficult to measure, and the task of analyzing their biophysical impact is complex. Associating pesticides with side effects requires a correlation between exposure and a specific disease, and then ruling out other known causes. Those exposed to pesticides (primarily agricultural workers) have typically been exposed to fertilizers, nitrates, fuels and engine exhausts, solvents, organic and inorganic dusts, electromagnetic radiation, ultraviolet radiation, and animal pathogens, as well. Genetic, behavioral, dietary, and other environmental factors may also impact the risk of disease.

Acute toxicity is measured as the amount required to kill 50% of the animals in a test population. This measure is usually expressed as the LD50 or simply the LD (lethal dose). In the United States, all pesticide toxicity values, including the LD50, can be found on the product's Material Safety Data Sheet (MSDS). Every chemical used in the United States is required by law to have an MSDS.


For toxicity in general, the main idea about the relationship between dose (the amount of the chemical) and response (symptoms) is that higher doses cause greater harm. This idea is built into tests, standards, measurements, warnings, treatments, and documentation. This idea may be true for many chemicals and for many classic health effects, but many researchers are calling for its reexamination in the case of pesticides. Pesticides build up in the body, they interact with other chemicals, and they may disrupt the hormonal and immune systems. For these reasons, the way healthcare workers evaluate pesticide poisoning is different from the way it may usually be done.

Many researchers argue that pesticides should be studied within a new framework. In contrast to the dominant view, which estimates that very few cancers are triggered by the chemicals, a new view is that environmental factors (air and water pollution, chemicals, diet) account for most cancers.

Modern epidemiological studies can use tests and data from tools that were not available in past decades, and which are more capable of recognizing effects of low-dosage toxicity and chemical interactions.

Some are proposing the idea that pesticides function to disrupt the endocrine system and that disturbances and disease reactions can appear without the high levels of exposure that cause acute toxicity.


This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (

  • Agency for Toxic Substances and Disease Registry (ATSDR), US Dept of Health and Human Services (HHS). Accessed December 20, 2008.
  • Al-Badry MS, Knowles CO. Phthalate-organophosphate interactions: Toxicity, penetration, and metabolism studies with house flies. Arch Environ Contam Toxicol 9:147-161. View abstract
  • Carson (1962). Rachel Carson, Silent Spring, Houghton-Mifflin.
  • Centers for Disease Control and Prevention (CDC). National Reports on Human Exposure to Environmental Chemicals. Accessed December 20, 2008.
  • Dietert RR. Developmental immunotoxicity testing and protection of children's health. PLfoS Med. 2006 Aug;3(8):e296 View abstract
  • Environmental Protection Agency (EPA). Accessed December 20, 2008.
  • Cooper GS, Germolec D, Heindel J, et al. Linking environmental agents and autoimmune diseases.. Environ Health Perspect. 1999 Oct;107 Suppl 5:659-60. View abstract
  • Hotchkiss AK, Rider CV, Blystone CR, et al. Fifteen years after "Wingspread"—environmental endocrine disrupters and human and wildlife health: where we are today and where we need to go. Toxicol Sci. 2008 Oct;105(2):235-59. View abstract
  • Jeyaratnam. Acute pesticide poisoning: a major global health problem. World Health Stat Q. 1990;43(3):139-44. View abstract
  • Natural Standard: The Authority on Integrative Medicine. Copyright © 2009. Accessed December 20, 2008.
  • Peto J. Cancer epidemiology in the last century and the next decade. Nature. 2001 May 17;411(6835):390-5. View abstract
  • Repetto R, Baliga SS. Pesticides and the Immune System: The Public Health Risks. Cent Eur J Public Health. 1996 Dec;4(4):263-5. View abstract
  • Roberts EM, English PB, Grether JK, et al. Maternal residence near agricultural pesticide applications and autism spectrum disorders among children in the California Central Valley. Environ Health Perspect. 2007 Oct;115(10):1482-9. View abstract
  • WHO Policy Brief - agrochemicals: linking health and environmental management, Accessed December 20, 2008.

Copyright © 2011 Natural Standard (

Read Health24’s Comments Policy

Comment on this story
Comments have been closed for this article.

Live healthier

Exercise benefits for seniors »

Working out in the concrete jungle Even a little exercise may help prevent dementia Here’s an unexpected way to boost your memory: running

Seniors who exercise recover more quickly from injury or illness

When sedentary older adults got into an exercise routine, it curbed their risk of suffering a disabling injury or illness and helped them recover if anything did happen to them.