Persistent organic pollutants (POPs)


Persistent organic pollutants (POPs) are toxic chemicals that have a worldwide impact on human health and the environment. Since POPs may spread by wind and water, it is possible for them to affect humans and wildlife that are located far from the original source.

The 12 key POPs are collectively known as the "Dirty Dozen." Aldrin, chlordane, dichlorodiphenyl trichloroethane (DDT), dieldrin, endrin, heptachlor, hexachlorobenzene, mirex, and toxaphene were first widely used as insecticides. Polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins, and polychlorinated dibenzofurans were commonly-released industrial byproducts.

Many POPs are currently banned in the United States and other countries due to their harmful side effects in humans. Some of these side effects may include reproductive problems, kidney and liver damage, increased blood pressure, convulsions, and cancer. In some cases, the absorption or ingestion of some POPs may result in death.

The Stockholm Convention on Persistent Organic Pollutants, first held by the United Nations Environment Programme (UNEP) in 2001, developed guidelines for the use of key POPs in order to protect human health around the world. This international agreement took effect in May 2004; it provided the groundwork for enhanced monitoring, POPs evaluation, research, and worldwide collaboration for the 163 member parties (countries).


General: Persistent organic pollutants (POPs) are toxic chemicals that have a worldwide negative impact on human health and the environment.

Long-range transport: An important characteristic of POPs is their ability to travel long distances from where they were originally released, via wind, water, or animal carriers. POPs have been found in clean Arctic regions thousands of miles away from any original chemical sources. It is very difficult to trace the movement of most POPs in the environment since they exist in different phases: They may travel as a result of precipitation, wind, natural water sources (such as lakes and rivers), and through plants and animals that have been exposed.

For example, some POPs may travel for many miles before evaporating into the air from water or land surfaces. Eventually, these POPs return to Earth attached to particles in snow, rain, or mist.

Bioaccumulation: POPs are easily absorbed in fatty tissue, and they may build up in the body fat of living organisms. As POPs move up the food chain, they become more concentrated. As a result of this process (known as biomagnification), POPs found in small amounts at the bottom of the food chain may become dangerous to larger organisms at the top. For example, fish and plants from contaminated environments may be ingested by animals that are then used as fodder higher up the food chain. It is also possible for contaminated fish and plants to be sold directly as food; these products must be carefully inspected before they are distributed for sale.

Reservoirs: Reservoirs are man-made bodies of water that protect the environment by collecting excess water in periods of heavy rainfall or floods. POPs that are released into marine and freshwater environments (such as reservoirs) bond strongly to water particles; as a result, they may remain in the water for long periods of time. Once the area is disturbed by human contact or evaporation, however, these POPs may be reintroduced into the environment; at that point, they have the potential of causing harmful effects to surrounding areas.


General: Persistent organic pollutants (POPs) were widely used after World War II. POPs had a variety of uses in the fields of pest and disease control, as well as in crop production.

Controlling POPs: The United States and other countries have taken the initiative to reduce (and hopefully eliminate) POPs and their effects worldwide. The eight countries of the Arctic Council, including Canada, Denmark, Greenland, Iceland, Norway, Russia, Sweden, and the United States, established the Arctic Monitoring and Assessment Programme (AMAP) in 1991.

The Rio Earth Summit held a meeting of 172 international government representatives in 1992 and created Agenda 21, which established the Intergovernmental Forum on Chemical Safety (IFCS) in 1994. The purpose of the IFCS is to enhance the global management of toxic chemicals, including POPs.

Stockholm Convention: On May 23, 2001 in Stockholm, Sweden, the United States and European Union, along with 90 other countries, signed the Stockholm Convention on the ratification and limitations on the uses of POPs. This agreement is designed to protect human health by preventing environmental exposure and contamination from the 12 key POPs; these POPs include aldrin, chlordane, dichlorodiphenyl trichloroethane (DDT), dieldrin, endrin, heptachlor, hexachlorobenzene, mirex, , polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and toxaphene.

Dichlorodiphenyl trichloroethane (DDT): DDT was used as an agricultural insecticide from 1945 to 1972. During World War II, DDT was sprayed from the air over large areas of land, in order to protect soldiers from insect vectors (carriers) of malaria and typhus. Sweden eventually banned the use of DDT in 1970. The United States followed suit in 1972, when the U.S. Environmental Protection Agency (EPA) canceled the registration of DDT products. Currently, DDT cannot be sold or distributed in the United States, but it has limited uses for the control of malaria in developing countries.

The World Health Organization (WHO) and Stockholm Convention have issued guidelines providing an exception for the indoor application of DDT in order to combat diseases that are spread from insects; these diseases include malaria and typhoid. Evidence suggests that DDT has the longest insecticidal effect of the 12 POPs, ranging from six to 12 months.


Exposure risk: Certain individuals and groups have a higher risk of developing toxicity from exposure to persistent organic pollutants (POPs). These populations include people who eat large amounts of fish, shellfish, or other foods (such as nuts and berries) that are collected and gathered from the wild. High-fat foods that must be monitored carefully for POPs exposure and contamination include fish, meat, eggs, and milk.

Indigenous populations may be at risk of higher exposure to POPs, since they participate in cultural and spiritual customs associated with their diets. Tribal communities with diets that consist of locally-grown plants, nuts, and animals may be unaware of their exposure to POPs: Additionally, POPs may be transferred to fetuses through the placenta and to infants through breast milk. Other populations at risk of POPs exposure include children; the elderly; and people with deficient immune systems due to malnutrition, or due to diseases such as AIDS or cancer.

Aldrin: Aldrin was used worldwide as an agricultural insecticide in the 1970s and was applied to seeds, soil, and plant surfaces. In plants and animals, aldrin quickly breaks down into the toxic chemical known as dieldrin. Aldrin has not been used in the United States since 1987 and it is now banned in many other countries. Short-term side effects may include nausea and vomiting. Long-term side effects may include increased blood pressure, headache, dizziness, and muscle twitching.

Chlordane: Chlordane is used as an insecticide. It may be absorbed through the skin in humans, resulting in severe toxic effects that include hyperexcitability of the central nervous system, tremors, lack of muscular coordination, and convulsions. Additionally, chlordane causes damage to the liver, kidneys, and spleen. Absorption of chlordane may also lead to death. Other potential health concerns include cancer-causing effects or problems with the immune system; however, these effects have not been extensively documented. Chlordane is only mildly toxic to animals.

Dieldrin: Dieldrin is used as an insecticide; it may cause toxic effects in humans and animals that are exposed to its action through skin contact, inhalation, or food contamination. Short-term side effects may include nausea and vomiting. Long-term side effects may include increased blood pressure, headache, dizziness, and muscle twitching.

Dichlorodiphenyl trichloroethane (DDT): DDT has been found in food samples worldwide, even in areas where the chemical has been banned for over a decade. Human side effects may include seizures, memory impairment, and damage to the reproductive, immune, and nervous systems. Also, DDT crosses the placenta; it may lead to fetal exposure with potentially-fatal toxicities. Infants are also at risk of exposure to DDT through breastfeeding.

The greatest source of DDT exposure in humans is through food. The Stockholm Convention and the World Health Organization (WHO) have allowed an exception to DDT regulations so that the chemical may be applied indoors to combat vector-borne diseases such as malaria. Vector-borne diseases are transmitted to humans or other animals by insects. Additionally, the Stockholm Convention and WHO have established strict guidelines for the use of DDT.

The use of DDT must be closely monitored and reported to WHO and the Stockholm Convention. When handling pesticides, including DDT, the Stockholm convention encourages people to use the most effective and advanced techniques available to ensure safety and minimize environmental damage.

When using diluted DDT formulations that are available under restriction, protective clothing and facemasks should be worn to avoid exposure. The WHO also recommends strategies to avoid the leaching of DDT into agricultural lands and the enforcing of strict financial penalties in the event that the guidelines are not followed.

Endrin: Endrin is an insecticide that has been used on field crops (such as cotton, maize, sugar cane, rice, and cereal grains) and to control mice in orchards. Short-term side effects for humans may include tremors, difficulty breathing, mental confusion, and convulsions. Long-term side effects may include convulsions and liver damage.

Heptachlor: Heptachlor was once used as a non-agricultural insecticide. However, most applications of heptachlor were phased out starting in 1978. This chemical is a poison that may enter the body via skin contamination, inhalation, or ingestion. Because of human toxicity concerns, heptachlor has a restricted use for controlling fire ants in power transformers, and in underground cable television and telephone cable boxes.

Hexachlorobenzene (HCB): HCB is not currently manufactured in the United States or in other countries. However, it is formed as a waste product from other chemicals, including tetrachloroethylene, trichloroethylene, and carbon tetrachloride. One of the most common side effects seen in humans is a disease called porphyria cutanea tarda. Most symptoms of this disease occur on the skin, including blisters and increased hair growth. Additionally, the liver and thyroid may become enlarged. Other related health issues include the possibility of calcium depletion and decreased bone density (resulting in osteoporosis) and the possibility of cancer-causing effects. Further studies are necessary to evaluate the chemical's effect on breast milk.

Mirex: Mirex was used as an insecticide against fire ants and as a fire retardant for plastics, rubber, paint, paper, and electrical goods in the Southeastern United States for 16 years. However, the U.S. Environmental Protection Agency (EPA) banned the use of mirex in 1978. Human exposure may occur through the ingestion of contaminated shellfish and through inhalation of the chemical. Additionally, mirex may be found in breast milk. This chemical may negatively affect the stomach, intestines, liver, thyroid, kidneys, and eyes. Also, mirex may have dangerous effects on the human reproductive system, resulting in an increased risk of miscarriages.

Polychlorinated biphenyls (PCBs): PCBs have been banned in most countries. However, evaluation of food and breast milk samples demonstrates that PCBs are still present in the environment. Women with diets consisting mainly of fish from highly-contaminated rivers and lakes, such as the Great Lakes and Baltic Sea, are at the greatest risk of exposure. Serious health issues of PCB ingestion may include cancer in both animals and humans. PCBs pass from the placenta to the fetus, and they may be transferred to infants through breast milk.

Dioxins: Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans are collectively known as "dioxins." These chemicals are produced from high-temperature processes, such as those used in waste incineration; the metal industry; recycling plants; and home energy, such as gas heating systems. Dioxins are still detectable in air, soil, and sediment samples today. These chemicals may cause cancer in humans; they also pass from the placenta to the fetus and may be transferred to infants through breastfeeding.

Polybrominated dibenzo-p-dioxins: The chemical toxaphene falls under this classification. Toxaphene was used as an insecticide in the cultivation of cotton plants, vegetables, livestock, and poultry. Currently, toxaphene use is banned in the United States. Short-term side effects of human exposure to this chemical include restlessness, hyperexcitability, tremors, spasms, and convulsions. Long-term health effects include liver and kidney damage and cancer.

Monitoring: The United Nations Environment Programme (UNEP) established a POPs Global Monitoring Programme in 2004. The purpose of this program is to focus on evaluating the use and safety of the 12 key POPs


Great Lakes research: Much of what is known about persistent organic pollutants (POPs) stems from research performed in the Great Lakes region of the United States, beginning in the 1970s. Some of these studies have shown that a major route of human exposure to POPs is through contaminated food, especially fish.

This research has led to the creation of fish-contaminant monitoring programs and advisories, informing individuals which fish are safe to eat. Additionally, research has found that some POPs enter the Great Lakes region through the air, establishing nearby urban areas as a major source of these pollutants.

Laboratory study: The United Nations Environment Programme (UNEP) began a study (known as the First Worldwide UNEP Intercalibration Study on Persistent Organic Pollutants) in January 2009; it should be completed in June 2010. This study is a Stockholm Convention requirement, in order to show that the data on POPs are comparable among laboratories.

South American workshop: A workshop was held in Peru in March 2009 to discuss strategies to manage and destroy POPs in South American countries: For example, polychlorinated biphenyls (PCBs) are still used to absorb the heat in electrical transformers in South America. Regulations for the proper management and control of POPs waste are also under development.

2009 Stockholm Convention: At the 2009 Stockholm Convention in Geneva, Switzerland, nine new chemicals (octabromodiphenyl ether [octaBDE], pentabromodiphenyl ether [pentaBDE], perfluorooctanesulfonic acid [PFOS], alpha-hexachlorocylohexane [alpha-HCH], beta-hexachlorocyclohexane [beta-HCH], chlordecone, hexabromobiphenyl [HBB], lindane, and pentachlorobenzene [PeCB]) were added to the list of POPs whose uses will be limited and closely monitored; these chemicals have similar environmental safety risks as the twelve POPs discussed at the Stockholm Convention in 2001.


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

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