What Are POPs?

A growing body of scientific evidence indicates that exposure to very low doses of certain POPs – which are among the most toxic substances ever created – can lead to cancer, damage to the central and peripheral nervous systems, diseases of the immune system, reproductive disorders, and interference with normal infant and child development.
Another concern is the growing accumulation of unwanted and obsolete stockpiles of pesticides and toxic chemicals, particularly in developing countries. Dump sites and toxic drums from the 1950s, ‘60s, and ‘70s are now decaying and leaching chemicals into the soil and poisoning water resources, wildlife, and people. A great deal of infrastructure and equipment such as electrical transformers and capacitors are also at or near the end of their useful lives and may leak dangerous chemicals such as PCBs.
General characteristics:

• Man-made -POPs are either used as pesticides, consumed by industry, or generated unintentionally as by-products of various industrial processes.
• Toxic - Of all the pollutants released into the environment every year by human activity, persistent organic pollutants, or POPs, are among the most dangerous. They are highly toxic, causing an array of adverse effects, notably death, disease, and birth defects among humans and animals.
• Persistent - These highly stable compounds can last for years or decades before breaking down.
• Mobile - They circulate globally through a process known as the "grasshopper effect". POPs released in one part of the world can, through a repeated (and often seasonal) process of evaporation, deposit, evaporation, deposit, be transported through the atmosphere to regions far away from the original source.
• Bioaccumulative - In addition, POPs concentrate in living organisms through another process called bioaccumulation. Though not soluble in water, POPs are readily absorbed in fatty tissue, where concentrations can become magnified by up to 70,000 times the background levels.
  The 12 POPs recognized as requiring the most urgent action are: aldrin, chlordane, DDT, dieldrin , endrin, heptachlor, hexachlorobenzene, mirex, toxaphene , PCBs and dioxins and furans.

Aldrin - Aldrin and dieldrin are man-made insecticides that are similar in structure. Aldrin breaks down into dieldrin in the body and in the environment. These chemicals are used to control soil insects, such as termites, corn rootworm, wireworms, rice water weevil and grasshoppers. From 1950 to 1970, aldrin and dieldrin were used on crops such as corn, cotton and potatoes. Aldrin and dieldrin are defined as hazardous solid waste. Aldrin and dieldrin bind tightly to soil and slowly evaporate into the air. Plants take in these chemicals from the soil and store them. Dieldrin is also stored in animal fat and leaves the body slowly. Dieldrin now exists everywhere in the environment, but at very low levels. Aldrin and dieldrin are both known endocrine disruptors. Human studies predict that levels above 0.20 milligrams of dieldrin in a liter of blood may result in harmful effects, such as convulsions or uncontrollable muscle movements. Aldrin treated rice is thought to have been the cause of deaths of waterfowl, shorebirds and passerines along the Texas Gulf Coast, both by direct poisoning by ingestion of aldrin treated rice and indirectly by consuming organisms contaminated with aldrin. Residues of aldrin were detected in all samples of bird casualties, eggs, scavengers, predators, fish, frogs, invertebrates and soil.Ingesting high levels of these chemicals results in convulsions and death. Ingesting moderate levels over a longer period of time may also cause convulsions, because these chemicals build up in our bodies over time Other effects from long-term exposure include headaches, dizziness, vomiting, irritability and uncontrolled muscle movements.

Chlordane - Chlordane is a broad spectrum contact insecticide that has been used on agricultural crops including vegetables, small grains, maize, other oilseeds, potatoes, sugarcane, sugar beets, fruits, nuts, cotton and jute. It has also been used extensively in the control of termites. Adheres strongly to soil particles and is not likely to enter groundwater, but can stay in soil for more than 20 years because it is slow to break down. It does not dissolve easily in water but does evaporate into the air. Builds up in the tissues of fish, birds and mammals. Chlordane is a known endocrine disruptor. Exposure by: Eating crops grown in contaminated soil, such as corn, root crops, citrus; eating fish or shellfish caught in water contaminated by chlordane; breathing air or touching soil near homes treated for termites with chlordane; breathing air or touching soil near waste sites or landfills that contain chlordane.. The U.S. Environmental Protection Agency ranks chlordane in the top 10 percent of the most toxic chemicals for human health. High levels of chlordane can cause damage to the nervous system or liver. People who breathed air containing high concentrations of chlordane or who accidentally swallowed small amounts of it have experienced headaches, irritability, confusion, weakness, vision problems, vomiting, stomach cramps, diarrhea and jaundice People and animals who ingested large amounts of chlordane have suffered convulsions and died. Japanese workers who used chlordane over a long period of time suffered minor liver damage. The International Agency for Research on Cancer has classified chlordane as a possible human carcinogen. Action to ban the use of chlordane has been taken in many countries

DDT - DDT was widely used during the Second World War to protect the troops and civilians from the spread of malaria, typhus and other vector borne diseases. After the war, DDT was widely used on a variety of agricultural crops and for the control of disease vectors as well. It is still being produced and used for vector control. Growing concern about adverse environmental effects, especially on wild birds, led to severe restrictions and bans in many developed countries in the early 1970s. The largest agricultural use of DDT has been on cotton, which accounted for more than 80% of the US use before its ban there in 1972. DDT is still used to control mosquito vectors of malaria in numerous countries. DDT is highly insoluble in water and is soluble in most organic solvents. It is semi-volatile and can be expected to partition into the atmosphere as a result. Its presence is ubiquitous in the environment and residues have even been detected in the arctic. It is lipophilic and partitions readily into the fat of all living organisms and has been demonstrated to bioconcentrate and biomagnify. The breakdown products of DDT, 1,1-dichloro-2,2-bis(4-chlorophenyl)ethane (DDD or TDE) and 1,1-dichloro-2,2bis(4-chlorophenyl)ethylene) (DDE), are also present virtually everywhere in the environment and are more persistent than the parent compound. DDT enters the body through food such as fruits, vegetables, meat, fish, and poultry, especially imported foods. DDT is found in soil, and can be transferred to crops grown on this soil. Root and leafy vegetables contain the highest amounts. DDT primarily affects the nervous system. People more susceptible to the toxic effects of DDT are individuals with diseases of the nervous system, liver or blood. Ingestion or exposure may cause excitability, tremors, seizures, rashes, confusion, convulsions and parethesia (paralysis) of the tongue and lips. Long-term, low doses have caused changes in levels of liver enzymes, harmful effects on reproduction, and an increased occurrence of liver tumors. Its continuing presence raises serious concerns regarding potential effects on developing infants.

Dieldrin- Dieldrin has been used in agriculture for the control of soil insects and several insect vectors of disease but this latter use has been banned in a number of countries due to environmental and human health concerns. Principle contemporary uses are restricted to control termites and wood borers and against textile pests. As aldrin is readily and rapidly converted to dieldrin in the environment and in organisms, the levels of dieldrin detected likely reflect the total concentrations of both compounds Dieldrin binds strongly to soil particles and hence is very resistant to leaching into groundwater. Volatilization is an important mechanism of loss from the soil and, because of its persistent nature and hydrophobicity, dieldrin is known to bioconcentrate. The half life of dieldrin in temperate soils is approximately 5 years. This persistence, combined with high lipid solubility, provides the necessary conditions for dieldrin to bioconcentrate and biomagnify in organisms. It is likely that dieldrin is bioconcentrated by aquatic organisms rather than bioaccumulated. Dairy products, such as milk and butter, and animal meats were the primary sources of exposure.

Endrin - Can contaminate surface water from soil runoff. Doesn't dissolve well in water. Clings to the bottom sediments of rivers, lakes and other bodies of water. Generally not found in the air except when applied to fields during agricultural applications. May stay in the soil for more than 10 years. Endrin is a foliar insecticide used mainly on field crops such as cotton and grains. It has also been used as a rodenticide to control mice and voles. It is rapidly metabolised by animals and does not accumulate in fat to the same extent as other compounds with similar structures. Endrin is highly toxic to fish. The chemical properties of endrin (low water solubility, high stability in the environment, and semi-volatility) favour its long range transport, and it has been detected in arctic freshwater. The main source of endrin exposure to the general population is residues in food however, contemporary intake is generally below the acceptable daily intake.

Heptachlor - Insoluble in water, Heptachlor binds to aquatic sediments and bioconcentrates in the fat of living organisms. It evaporates slowly in air. The half life of Heptachlor in temperate soil is up to two years. An insecticide used primarily to kill soil insects and termite, it has also been used to control cotton insects, grasshoppers, and some crop pests, especially for corn. In addition, it has been used to combat malaria. Heptachlor is metabolised in animals to heptachlor epoxide, whose toxicity is similar to that of heptachlor, and which may also be stored in animal fat. WHO suggests that food is the major source of exposure of heptachlor to the general population, as well as: ingestion of residues in food, i.e., eating crops grown in soil that contains Heptachlor or eating fish, dairy products, and fatty meats from animals exposed to Heptachlor in their food, inhalation in homes treated for termite control, drinking contaminated water, or skin contact with soil near waste sites or landfills, breast milk from mothers who had high exposures. IARC has classified heptachlor as a possible human carcinogen. It has been banned in more than 50 countries and severely restricted in seven.

Hexachlorobenzene (HCB) - Hexachlorobenzene is a fungicide that was first introduced in 1945 for seed treatment, especially for control of bunt of wheat. HCB is also a byproduct of the manufacture of industrial chemicals including carbon tetrachloride, perchlorethylene, trichloroethylene and pentachlorbenzene. Also a by-product of manufacturing industrial chemicals. Used to make fireworks, ammunition, wood preservatives, dyes and synthetic rubber. Processes that form HCB as byproducts are: manufacture of other chemicals, chemical interactions in waste streams of chloralkali and wood-preserving plants and burning of municipal waste. HCB is toxic to humans and animals when long-term exposure occurs (consuming dairy products or meat from cattle grazing on contaminated pastures, eating low levels in contaminated food, eating or touching contaminated soil, or drinking small amounts in contaminated water, breathing low levels in contaminated air, For babies, drinking contaminated breast milk from exposed mothers, working in a factory that uses or produces HCB unintentionally. Unintentional production is possible since HCB is formed as a byproduct of chemical manufacture and waste incineration). Its main health effect is liver disease. HCB was determined to be a probable human carcinogen.

Mirex - Considered one of the most stable and persistent pesticides, with a half life of up to 10 years. Does not dissolve easily in water, but it easily sticks to soil and sediment particles. It is not likely to travel far through the soil and into underground water but can build up in fish or other organisms that live in contaminated water or that eat other contaminated animals. It has been used to combat termites and ants. It is also used as a flame retardant in plastics, rubber, paint, paper and electrical goods. Exposure: touching or ingesting contaminated soil near hazardous waste sites or ingesting contaminated fish or other animals living near hazardous waste sites. IARC has concluded that while there is inadequate evidence for the carcinogenicity of Mirex in humans, there is sufficient evidence in experimental animals. IARC has classified Mirex as a possible human carcinogen. Crustaceans are the most sensitive aquatic organisms, with larval and juvenile stages being the most sensitive. Delayed mortality is typical of Mirex poisoning in crustaceans.

Toxaphene - Used primarily to control insect pests on cotton, cereal grains, fruits, nuts and vegetables. It has also been used to control ticks and mites in livestock. A solid or gas. In its original form it is a yellow to amber waxy solid that smells like turpentine. It may enter the air by evaporation. It does not dissolve well in water, so it is more likely to be found in air, soil, or sediment at the bottom of lakes or streams. Has a half life in soil of up to 12 years, has been shown to bioconcentrate in aquatic organisms and undergoes long-range transport. Exposure of the general population is most likely through food, however levels detected are generally below maximum residue limits. while there is inadequate evidence for the carcinogenicity of Toxaphene in humans, there is sufficient evidence in animals. Brook trout exposed to Toxaphene for 90 days experienced a 46% reduction in weight at 0.039 µg/L, the lowest concentration tested. Egg viability in female trout was significantly reduced upon exposure to a concentration of 0.075 µg/L or more. Long term exposure to 0.5 µg/L reduced egg viability to zero. IARC has classified Toxaphene as a possible human carcinogen. It is banned in 37 countries and severely restricted in 11 others.

Polychlorinated biphenyls (PCBs) - PCBs are used in a variety of industrial uses, including as dielectrics in transformers and large capacitors, as heat exchange fluids, as paint additives, in carbonless copy paper and in plastics. The degradation of PCBs in the environment depends largely on the degree of chlorination of the biphenyl, with persistence increasing as the degree of chlorination increases. Half-lives for PCBs undergoing photodegradation range from approximately 10 days to 1.5 years. There is growing evidence linking persistent halogenated aromatic hydrocarbons such as PCBs to reproductive and immunotoxic effects in wildlife. The main source of PCB exposure to the general population is through food, especially fish. Children born seven to twelve years after maternal exposure experienced mildly delayed development, but no differences in behaviour. Effects observed in these children is likely a result of the persistence of PCBs in the human body, resulting in prenatal exposure long after the exposure took place. there is limited evidence for the carcinogenicity of PCBs in humans, and there is sufficient evidence in experimental animals. PCBs are therefore classified as probable humans carcinogens.

Polychlorinated dibenzo-para-dioxins (dioxins) and polychlorinated dibenzofurans (furans) - are two groups of planar tricyclic compounds that have very similar chemical structures and properties. Neither dioxins nor furans are produced commercially, and they have no known use. They are by-products resulting from the production of other chemicals. Dioxins may be released into the environment through the production of pesticides and other chlorinated substances. Furans are a major contaminant of PCBs. Both dioxins and furans are related to a variety of incineration reactions, and the synthesis and use of a variety of chemical products. Dioxins and furans have been detected in emissions from the incineration of hospital waste, municipal waste, hazardous waste, car emissions, and the incineration of coal, peat and wood. Dioxins and furans are considered to be very stable and persistent, as illustrated by the half life of TCDD in soil of 10-12 years. As with most other organochlorines, food is a major source of dioxins and furans in the general population, with food of animal origin contributing the most to human body burdens. IARC has concluded that while there is inadequate evidence for the carcinogenicity of 2,3,7,8-TCDD in humans, there is sufficient evidence in experimental animals. IARC has classified 2,3,7,8-TCDD as a possible human carcinogen.