A Persistent Organic Pollutant (or ‘POP’) is a carbon-based chemical substance which deteriorates slowly and therefore remains in the environment for a long time. Furthermore, as the name suggests, they bio-accumulate in fatty bodily tissues and bio-magnify throughout the food web - i.e. higher-order predators ingest larger doses as they feed upon lower-order organisms. As they work their way through ecosystems so thoroughly (with trace elements of some having been found in Arctic and Antarctic ice) and as many were employed to remedy problems in food production (generally pest control), they threaten human health, as well as indiscriminately poisoning wildlife which comes into contact with them. The international community, recognising the threat, has now acted to ban or restrict many of these toxins.

UNEP Governing Council Decision 19/13C (February 7, 1997) suggested that an international body be formed in order to create legally binding measures to achieve consensus and determine a course of action in regard to POPs (to the limited extent that international law can be legally binding, anyway). The Stockholm Convention (2000 onwards), the manifestation of these concerns and the organ of their resolution, is a global treaty which aims to protect both human health and the broader environment. The Convention determined that twelve particularly dangerous chemicals (unflatteringly described as ‘The Dirty Dozen’) were of special concern and that it was necessary to take immediate steps taken to rectify the damage done by their use. These chemicals and their effects (known and speculated) are described below, along with the names of substances which contain them1.


The Dirty Dozen

Aldrin
Intended to cure problems with soil and crop pests (including corn rootworm, wireworm, rice water weevil and grasshoppers) the crops most frequently exposed to it were corn, potatoes and cotton, although it was also used as a means of protecting timber from termites. Aldrin is not highly toxic to plants, but it is lethal even in minute doses to most aquatic invertebrates, especially insects. Larger doses can even prove fatal to birds, fish and human beings (approximately 5 grams in the latter case). Usually, the only reason for people to be exposed to this chemical is via ingesting contaminated food. Most countries (particularly industrialised countries) have banned this chemical. It decays quickly, but converts to dieldrin inside plants and animals.
Synonyms and trade names: Aldrec, Aldrex, Aldrex 30, Aldrite, Aldrosol, Altox, Compound 118, Drinox, Octalene, Seedrin.

Chlordane
Used as a general insecticide (running the gamut of protecting vegetables, grains, maize, potatoes, sugarcane, fruits, nuts, cotton and jute), chlordane has been observed to kill aquatic invertebrates, fish and birds. In humans, it has been linked to neural damage and may be a carcinogen - contact with the chemical most commonly occurs during respiration. It has been banned or severely restricted in dozens of countries, but some parties to the Stockholm Convention insist on seeing more evidence to validate banning its use entirely. It has a half-life of 1 year.
Synonyms and trade names: Aspon, Belt, Chloriandin, Chlorkil, Corodan, Cortilan-neu, Dowchlor, HCS 3260, Kypchlor, M140, Niran, Octachlor, Octaterr, Ortho-klor, Synklor, Tat-chlor 4, Topichlor, Toxichlor, Veliscol-1068.

DDT
Due to its prolific use, this may be the most dangerous chemical. It was primarily employed to kill mosquitoes during World War II (to combat the spread of Malaria, Typhus and Dengue Fever) and it was realised after the war that it could also be used to protect cotton crops. The detrimental effects of DDT are myriad, with demonstrable links between DDT use and behavioural changes in many animals, the thinning of birds’ eggshells (particularly birds of prey, who suffer higher concentrations) and lowered birth rates (each of which is attributed to the effects of DDT’s breakdown products, DDD/TDE and DDE, affecting hormone levels). For the same reasons, human beings so afflicted see increased cancer rates and oestrogen-like alterations during developmental phases. DDT accumulates with particular tenacity and can even be found in breast milk. 34 countries have banned the chemical and a further 34 placed severe restrictions on its use, although the Convention recognises the fact that other means of treating infectious diseases are often not available in developing countries. It has a half-life of 10-15 years.
Synonyms and trade names: Agritan, Anofex, Arkotine, Azotox, Bosan Supra, Bovidermol, Chlorophenothan, Chlorophenothane, Chlorophenotoxum, Citox, Clofenotane, Dedelo, Deoval, Detox, Detoxan, Dibovan, Dicophane, Didigam, Didmac, Dodat, Dykol, Estonate, Genitox, Gesafid, Gesapon, Gesarex, Gesarol, Guesapon, Gyron, Havero-extra, Ivotan, Ixodex, Kopsol, Mutoxin, Neocid, Parachlorocidum, Pentachlorin, Pentech, Ppzeidan, Rudseam, Santobane, Zeidane, Zerdane.

Dieldrin
Another insecticide, dieldrin is applied to termites, crops and insects which bear highly infectious diseases. Like aldrin (which readily converts into dieldrin in plants and animals), it is applied to corn, potatoes and cotton. Also like aldrin, it does little harm to plants but enormous amounts to aquatic invertebrates, fish and birds (with evidence of dieldrin-affected frog embryos bearing spinal defects). Finally, it also finds its way into human beings via food contamination (especially meat and dairy products). As aldrin converts to dieldrin in plants and animals, the quantity of Dieldrin measured in any given organism reflects the total quantity of both aldrin and Dieldrin. It has a half-life of 5 years.
Synonyms and trade names: Alvit, Dieldrite, Dieldrix, Illoxol, Panoram D-31, Quintox.

Endrin
Another insecticide, this one is applied to pests which thrive on cotton, rice and corn and has been used as a rodenticide. It is not quite as broad-reaching as the others as many (particularly larger) animals are able to metabolise it, although fish cannot and there is speculation that it suppresses the human immune system. Like most others, it is consumed in contaminated food products. It has a half-life of up to 12 years.
Synonyms and trade names: Compound 269, Endrex, Hexadrin, Isodrin Epoxide, Mendrin, Quintox.

Heptachlor
Used to combat termites, fire ants, mosquitoes and grasshoppers, heptachlor is metabolised to form heptachlor epoxide, which is similarly toxic - worse yet, the quantity of heptachlor which has proved fatal to small animals is very low. Other adverse effects include hormonal changes (leading to lowered birth rates). It is listed as a human carcinogen and is consumed via contaminated food. It has a half-life of up to 2 years.
Synonyms and trade names: Aahepta, Agroceres, Baskalor, Drinox H-34, Heptachlorane, Heptagran, Heptagranox, Heptamak, Heptamul, Heptasol, Heptox, Soleptacx, Rodiachlor, Veliscol 104, Veliscol heptachlor.

Mirex
This insecticide has been used to combat a variety of pests in a variety of situations and countries, most prominently ants and wasps in North and South America America, harvester termites in South Africa and mealy bugs in Hawaii. It is also fire retardant and so can be found in plastic, rubber, paper, paint and electrical goods. This chemical stunts the growth of plants and crustaceans (especially crabs), causes behavioural changes in fish, reproductive disorders in birds and carcinogenic effects in humans. Although mirex is absorbed via ingestion of food, the quantity present is usually significantly below tolerance levels. It has a half-life of up to 10 years.
Synonyms and trade names: Dechlorance, Ferriamicide, GC 1283.

Toxaphene
Used to protect the same diversity of crops as chlordane, toxaphene also kills the ticks and mites which feed on livestock. (This diversity of functions is due to the fact that toxaphene is composed of 670 separate chemicals.) It does no harm to plants, enormous damage to fish and causes reproductive disorders in birds as well as being a possible human carcinogen. The levels detected in human diets are very low. Its half-life is between 100 days and 12 years.
Synonyms and trade names: Alltex, Alltox, Attac 4-2, Attac 4-4, Attac 6, Attac 6-3, Attac 8, Camphechlor, Camphochlor, Chemphene M5055, chlorinated camphene, Chloro-camphene, Clor chem. T-590, Compound 3596, Huilex, Kamfochlor, Melipax, Motox, Octachlorocamphene, Penphene, Phenacide, Phenatox, Phenphane, Polychlorocamphene, Strobane-T, Strobane T-90, Texadust, Toxakil, Toxon 63, Toxyphen, Vertac 90%.

Polychlorinated biphenyls or PCB
This is a family of substances, rather than a single one - all 209 compounds, composed of benzene rings and distinguished by the quantity and location of attached chlorine atoms, are heat resistant, have a low vapour pressure and a high dielectric constant. They were initially (in 1929) employed in industry as heat exchange fluids and insulating mediums, although they have subsequently been used to produce weatherproof sealants, carbonless copy paper, paint, adhesives and plastics. They are also produced by incomplete combustion and some of these substances resemble dioxins. They cause immune system suppression and reproductive failures in numerous animals, as well as being highly toxic to smaller wildlife. In humans, PCBs can cause eyelid swelling, nail and mucous membrane pigmentation, fatigue and nausea. In extreme cases, they can cause severe rashes, damage to internal organs (including cancer) and developmental problems. They are very tenacious and can even affect developing babies via placental transfer or via breast milk after birth. Vegetable oils and dairy products are potent contaminants for human beings (already prone to contamination, as are many mammals due to their high fat levels). These chemicals have a half-life of between 10 days and 1.5 years.
Synonyms and trade names: Aroclor, Pyranol, Pyroclor, Phenochlor, Pyralene, Clophen, Elaol, Kanechlor, Santotherm, Fenchlor, Apirolio, Sovol.

Hexachlorobenzene
This chemical was originally manufactured in 1945 for use as a seed treatment, although it can also be produced as an unintentional by-product of pesticide or industrial chemical manufacture, as well as via incomplete combustion. HCB appears as a contaminant in chlorinated pesticides and in instances where it was used in the manufacture of synthetic rubber, PVC, dyes and in wood preservation. Its detrimental effects include photosensitive skin lesions, colic, unusual hair growth, severe weakness, kidney and liver damage, circulatory system collapse and central nervous system, arthritic, urinary tract, neurological and respiratory system disorders. Speculation also indicates that it could also induce spontaneous abortions and could function as a carcinogen. All types of foods, but particularly dairy and meat products, have been found to contain HCB and all of the above symptoms have been observed in animals subject to the toxin, even at low levels - it does not bio-accumulate, but it is invariably released back into the environment when materials containing it are burned; virtually 100% of HCB used in pesticides is released. By 1980 most nations had ceased its manufacture in light of these effects. Its half-life fluctuates wildly from 2.7-22.9 years.
Synonyms and trade names (see above for products which, pre-1970s, may contain HCB): Atrazine, Chlorothaloril, Dacthal, Pentachlorophenol, Pentachloronitrobenzene dicloram, Picloram, Simozine.

Dioxins or PCDF
These substances have no discernible use - they are produced exclusively as a by-product of industrial processes, including the combustion of chlorine-based compounds with hydrocarbons. It is worth noting that certain natural processes (forest fires, for instances) can produce these chemicals and not only human activities (such as chlorine-based paper bleaching, pesticide manufacture and waste burning). There are 75 of these, 7 of which are extremely toxic (and classified as human carcinogens). In wildlife, they cause behavioural changes or death (depending upon dosage). Humans may experience altered cellular and hormone levels (a result of immune, enzyme reproductive and developmental disorders). It is also thought that exposure to dioxins accelerates endometriosis in women and diabetes in both genders - animal fats are the source of these contaminants in human beings. Half-life of 10-12 years.
Synonyms and trade names: The US EPA lists over 160 substances which are contaminated by dioxins. 2

Furans
Finally, these (along with dioxins) are products of PCB manufacture, motor vehicle emissions and waste incinerators. Although they have no discernible effect upon human beings, they cause the same detrimental effects to wildlife as dioxins. Also similar to dioxins is their half-life of 10-12 years.
Synonyms and trade names: N/A



1 All information provided is derived from Persistent Organic Pollutants and the Stockholm Convention: a Resource Guide, prepared by Resource Futures International (2001). Synonym and trade name lists are not exhaustive.
2 http://www.proxyinformation.com/dow/links.htm

Sources:
http://www.chem.unep.ch/pops/
http://www.pops.int/
http://www.proxyinformation.com/dow/links.htm
Persistent Organic Pollutants and the Stockholm Convention: a Resource Guide, Resource Futures International.

Corrections? Suggestions? /msg me

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