About Persistent Organic Pollutants

Persistent Organic Pollutants (POPs), in the narrow sense, refers to the first 12 chemicals listed under the Stockholm Convention. In the generic sense it refers to a wide variety of toxic substances that potentially could be included in the Stockholm Convention.

Strategies to address the first 12 POPs are relevant to a broad range of chemicals and will create the foundation for a chemical management framework.

POPs are highly stable organic compounds produced by man or generated as by-products of human activity though there are a few natural sources of POPs. Intentionally produced POPs are used in a number of applications while others, referred to as unintentionally produced POPs, are generated and emitted as by-products of a number of manufacturing and production processes.

Once released in the environment, POPs exhibit the following behaviour:

  • Become distributed in different media and biological systems (air, water, sediment, soil, plants, animals and humans);
  • Undergo transport over short and long distances as a result of natural environmental processes, usually involving air and/or water; and
  • Undergo transformation and degradation into other chemicals that will, in turn, be distributed in the environment and living organisms.

The most common characteristics of POPs are summarized as follows:

  • POPs are Environmentally Persistent: They resist breakdown by natural processes and remain in the environment for years, even decades.
  • POPs are Semi-Volatile: They are capable of traveling thousands of miles through cycles of evaporation and atmospheric cycling and deposition.
  • POPs are Lipophilic: They are soluble in fatty tissues and bioaccumulate up the food chain, reaching the greatest concentrations in predatory birds and mammals that have consumed contaminated animals lower in the food chain.
  • POPs are Toxic: They are linked to a range of health effects, including acute poisoning, chronic long-term effects on the nervous or immune systems and cancer in humans and wildilfe. Foetuses and infants exposed to POPs via the placenta and breast-feeding are especially vulnerable.

These properties make POPs amongst the most dangerous pollutants released into the environment. Biological exposures to them have likely contributed to disturbing public health trends and they have become an issue of significant local, regional and global concern for all the countries of the world.

The international community has entered into a legally binding global treaty, the Stockholm Convention on POPs. It establishes an evaluation process that assesses potentially hazardous chemicals for their persistence, bioaccumulation potential and toxicity and determines whether they should be controlled as POPs under the convention. It has singled out twelve POPs, often referred to as the "dirty dozen", for urgent action. The POPs specifically named in the convention are a subset of toxic chemicals known as Persistent Bioaccumulative Toxics (PBTs). POPs can be grouped into three categories based on their usage or emissions characteristics:

  • Pesticides: aldrin, chlordane, dieldrin, DDT, endrin, heptachlor, hexachlorobenzene (HCB), mirex and toxaphene;
  • Industrial Chemicals: HCB and polychlorinated biphenyls (PCBs); and
  • Unintended by-products of Combustion and Industrial Processes: dioxins and furans, HCB and PCBs.

In India in recent years post ratification of the Stockholm Convention, more attention has been paid to addressing the risks posed by POPs specially on human health and the environment because of their special physical and chemical properties and their behaviour in the environment. Even when released in relatively small quantities, POPs can lead to regional and global contamination and adversely impact global commons. They are resistant to degradation and can remain in environmental media and organisms for years or even decades. Due to their volatile nature, natural environmental processes can distribute them over long distances. POPs are said to be bioaccumulative because wildlife retain them in their bodies at concentrations higher than in food and water that originally contain them. When predators higher in the food chain consume wildlife contaminated with POPs this results in very high concentrations of contaminants in their bodies. This effect is referred to as biomagnification. Subsequrntly, POP exposure can cause death and illnesses including disruption of the endocrine, reproductive, and immune systems; neurobehavioral disorders; and cancers possibly including breast cancer. Exposure to POPs can take place through diet, environmental exposure, or accidents.