The GEF Small Grant Programme

POPs Awareness Training Module

Read, learn and test your POPs knowledge

Chapter II: Sources and Uses of POPs

A. POPs Pesticides

Figure 1. Integrated pesticide management to avoid POPs pesticide, Trinidad & Tobago
Figure 1. Integrated pesticide management to avoid POPs pesticide, Trinidad & Tobago
POPs pesticides are chemical compounds that contain carbon, hydrogen, and chlorine. They break down slowly, and they remain in the environment and in living organisms long after use and exposure. The nine POPs pesticides listed in the Stockholm Convention were developed and brought into use during and after the Second World War, mainly to control agricultural pests.1 DDT was also widely used to control household insects, including the mosquitoes that spread malaria.2 Chlordane, Heptachlor and Mirex have been widely used to control termites and ants, especially to protect structures and building materials.  The listed POPs pesticides are no longer widely used in agriculture and POPs pesticides make up only a small part of all pesticides, but they are still used in some countries to control disease vectors such as mosquitoes, and to control termites.  Historically, POPs pesticides have been used in the following manner:

Aldrin: Aldrin was used to kill soil insects such as termites and grasshoppers to protect crops such as corn and potatoes.3

Chlordane: Chlordane has been used since the 1950s as a broad-spectrum contact insecticide, mainly for nonagricultural purposes and to a lesser extent on crops and on livestock. Since the mid-1970s, its use has generally been restricted to control of termites.4

DDT:  DDT has been extensively used as an insecticide. Its legal use is currently restricted to disease vector control in some countries, but it may also be illegally diverted for agricultural use.

Dieldrin: Dieldrin has been used in fruit orchards, for soil pest in corn, cotton and potato fields; and for ecto-parasite control in livestock.
Endrin – Endrin has been used as a rodenticide and as an insecticide used on cotton, rice and corn crops, and for ectoparasite control in livestock.

Heptachlor – Heptachlor was widely used to kill termites, ants, and soil insects in seed grains and on crops.5

Mirex - Mirex has been used as insecticide on various agricultural crops, and in ant and termite control; also as a flame retardant.

Toxaphene– Toxaphene was used as an insecticide for cotton and vegetables, and on livestock and poultry.6 It was manufactured by chlorinating an extract from pine trees called camphenes, and is a complex mixture of 670 chemical substances.7

Hexachlorobenzene (HCBs)Hexachlorobenzene is a fungicide formerly used as a seed treatment, especially on wheat.8

B. Industrial Chemicals and Compounds (PCBs and HCB)

Chemical structure of PCBs

Chemical structure of PCBs
PCBs contain 12 carbon atoms, in two connect rings.
They contain at least 2 and as many as 10
chlorine atoms at the numbered positions.9

Polychlorinated biphenyls (PCBs) are oils and solids that are tasteless, odorless and colorless to light yellow. PCBs are a class of chemicals with similar structure that come in a possible 209 different configurations.10 The only known sources of PCB substances are anthropogenic.

The production and industrial use of PCBs began in 1929, when they were used as coolants, insulation oils and lubricants in electrical transformers, capacitors, electrical and hydraulic equipment and as plasticizers in paints, plastics, and rubber products.  

There have been hundreds of other commercial and industrial applications of PCBs including in motors and electromagnets; as heat transfer fluids; and in switches, liquid filled cables and circuit breakers. They have been used in insulating materials and lubricants; surface coatings such as paints; textile treatment, carbon-less copy paper; flame retardants; plasticizers, filling material in joints of concrete, PVC, rubber seals, adhesives and printing inks.11 PCBs are widely present in old fluorescent light fixtures.12

PCBs can also be produced unintentionally during the incineration of hazardous, hospital and municipal waste; burning contaminated oils and other chlorinated wastes in cement ovens, burning tires, and in the manufacture of PVC and magnesium. 13 An estimated 70% of the PCBs that have been produced still persist in the environment worldwide.14

Hexachlorobenzene (HCB) was formerly used as a pesticide and is also produced as an unintentionally produced by-product. HCB has also been used as an industrial chemical in the manufacture of fireworks, ammunition, and synthetic rubber. There exist, in some countries, very large stocks of HCB wastes that were produced during munitions manufacture. In some countries where it has been studied, including Spain, Slovakia, and the Czech Republic, significant human body burdens of HCB has been found in the general population.15 Health and environmental effects of HCB are similar to those of PCBs and dioxins.

C. Combustion and Unintentional By-products (Dioxins, Furans, PCBs and HCB))

Figure 2.  Unintentional creation of POPs, Ixopo Incinerator, South Africa
Figure 2. Unintentional creation of POPs, Ixopo Incinerator, South Africa
Dioxins, furans and other unintentionally-produced POPs are produced as by-products in combustion processes and chemical reactions when organic matter and chlorine are present.  Dioxins and furans are never intentionally produced.16 The Stockholm Convention lists four categories of POPs that are unintentionally formed and released to the environment as by-products of these processes: polychlorinated dibenzo-p-dioxins (dioxins); polychlorinated dibenzofurans (furans); polychlorinated biphenyls (PCBs); and hexachlorobenzene (HCB).17

PCBs have been intentionally produced in large quantities, but they too also arise as unintended by-products under similar conditions. Dioxins, furans and PCBs are related groups with similar chemical structures. Each is a family of chemicals whose individual members are called congeners. 18 The Congeners of dioxins, furans and PCBs have varying degrees of toxicity.  There are 75 possible dioxin congeners (types); 135 possible furan congeners; and 209 possible PCB congeners. HCB comes in only one form.

The Stockholm Convention lists sources that have the potential for comparatively high formation and  release of unintentional POPs into the environment: waste incinerators (primarily municipal, hazardous or medical waste or sewage sludge); cement kilns that fire hazardous waste; pulp production (for paper making) that uses chlorine for bleaching; thermal processes in the metallurgical industry including secondary copper production; sinter plants in the iron and steel industry; secondary aluminum production and secondary zinc production.19

The Stockholm Convention also lists other source categories that may form and release unintended POPs into the environment: open burning of waste (including burning of landfills); thermal processes in the metallurgical industry not mentioned above; residential combustion; fossil fuel fired utility and industrial boilers; firing installations for wood or other biomass; some specific chemical production processes; crematoria; motor vehicles (especially  those that burn leaded gasoline); destruction of animal carcasses; textile and leather dyeing (using chloranil) and finishing (using alkaline extraction); shredder plants for end of life vehicles; smoldering of copper cables, waste oil refining20 and burning of tires and plastics.21

Dioxins can also be generated as a byproduct during pesticide manufacture. The general public first became broadly aware of dioxins during and following the Vietnam War when it was learned that the herbicide “Agent Orange,” which was widely used during the war as a defoliant, was heavily contaminated with the most toxic of the dioxins, 2,3,7,8-tetrachlorodibenzo-p-dioxin or TCDD.   US soldiers involved in the spraying suffered serious health impairments affecting them and their children. Vietnamese civilians and soldiers were also heavily exposed and continue to be so in areas where the spraying took place, causing serious and ongoing health problems. 22
Structure of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

Structure of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

1, pg. 21
2Id at pg. 20
3Definition of Aldrin, available at:
4International Agency for Research on Cancer (IARC) - Summaries & Evaluations, CHLORDANE AND HEPTACHLOR, available at:
5Department of Health and Human Services; Agency for Toxic Substances and Disease Registry; available at:
6U.S. Environmental Protection Agency, Ground Water and Drinking Water, Consumer Fact sheet on Toxaphene, available at:
7, pg. 21
8Definition of Hexachlorobenzene, available at:
9Definition of PCBs, available at:
10, pg. 73
11Id, Table 10, pg. 74
12Id, Table 10 at pg. 74
13Id at pg. 75. This information is also confirmed by the: Department of Health and Human Services; Agency for Toxic Substances and Disease Registry; available at:
14Id at pg. 75
15Van Birgelen, Angélique P.J.M; Hexachlorobenzene as a Possible Major Contributor to the Dioxin Activity of Human Milk, Environmental Health Perspectives Vol 106, Number 11, November 1998, available at:
16Note: small amounts of dioxins of furans may be produced at laboratory scale as reference standards or for experiments
17Stockholm Convention, Annex C, available at:
18U.S. Environmental Protection Agency; Polychlorinated Biphenyls (PCBs), PCB ID Definitions, available at:
19Stockholm Convention, Annex C, Part II Source Categories,
20Stockholm Convention, Annex C, Part III Source Categories:
21Global Alliance for Incinerator Alternatives (GAIA), available at:
22, pg. 28

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II Review Quiz:

  1. PCBs have been used in the following:
    1.   In electrical transformers and capacitors
    2.   as pesticides
    3.   in cooking oils
    4.   in ceramics
    5.   all of the above
    6.   none of the above
  2. The herbicide, "Agent Orange" was known to be contaminated with which type of persistent organic pollutants?
    1.   POPs pesticides
    2.   POPs industrial checmicals
    3.   Unintentionally-produced POPs
    4.   None of the above
  3. Aldrin was traditionally used as a:
    1.   Plasticizer
    2.   Insecticide
    3.   Substance for malaria control
    4.   None of the above
  4. "Congener" is the name used for a type of POP that is more toxic than other POPs.
    1.   True
    2.   False
 Chapter 1: ‘The Dirty Dozen’ and their Characteristics
 Chapter 2: Sources and Uses of POPs
 Chapter 3: Impacts of POPs on Health and Environment
 Chapter 4: Global Institutions and Policies to Reduce and Eliminate POPs
 Chapter 5: Harnessing the Power of NGOs and Communities
 Chapter 6: Case Studies: Local Actions; Global Results
 Chapter 7: Opportunity for National Coordinators and National Steering Committees to Facilitate Results in POPs Focal Area
 Final Quiz: POPs Awareness Self-Test
Quick Reference and Additional Information