POPs - Polychlorinated biphenyl (PCBs)

Polychlorinated biphenyls (PCBs) are a class of chlorinated hydrocarbons that have been widely used as industrial chemicals since 1930. There are 209 varieties PCBs and most commercial PCB applications are in the form of mixtures of varieties. Large quantities of PCBs were produced for use as a cooling and dielectric fluid in electric transformers and in large capacitors. These have also been widely used as hydroulic fluids and as a heat exchange fluids. PCBs applications have included use as a sealant, as paint additive, additive in some plastics, as a component of carbonless copy papers etc. These can also be formed and released as unwanted byproducts in some chemical and combustion processes.

PCBs are linked to reproductive failure and suppression of the immune system in various wild animals, severe human intoxication occurred due to accidental consumption of PCB-containing oils. IARC classified PCB into Group 2B (possibly carcinogenic to human)
International production of PCBs were ended in most countries by 1980. The major exception to this was in the former soviet Union and some Central European countries. No country presently reports intentional PCB production.

Dioxin and Furans are class of chlorinated hydrocarbons. They have never been produced commercially or intentionally except in small qualities for laboratory purposes and or as reference standards. There are 75 different dioxin congeners and 135 different furan congeners. IARC classified one congner of dioxin as group 1 carcinogen (human carcinogen); all others are carcinogenic in animals. Non carcinogenic effects on the immune, the reproductive, the developmental and the nervous systems are considered to be of great concern.

Dioxins and furans are generated as unwanted by-products in a variety of combustion and chemical process. The major sources include waste incinerators combusting municipal waste, hazardous waste, medical waste, sewage sludge etc. Incineration of medical wastes in small and poorly controlled incinerators was found to be a major source of dioxin and furans. Kilns firing of cement/tiles industries, open burning of wastes etc. may also generate dioxins and furans. Other dioxin and furan sources are: pulp and paper mills using chlorine bleach processes, certain thermal processes in metallurgic industry and chemical production process.

Though dioxins and furans are formed as byproducts in a wide range of processes, they are directly dispersed to the environment may also be present in manufacturing processes as raw materials or products.

Dioxins and furans are persistent in the environment and transfers can occur between media, e.g. from air to water through rain water and by run off from soil to water reservoir. This type of transfer may also make an important contribution to human exposure to these organic compounds.

Direct release or transfer of dioxins and furans follow in to the following five components mainly:
4 Air
4 Water (fresh, marine, estuarine; then subsequently into sediments)
4 Land (soil)
4 Waste (including liquid, sludge, and solid residues which are handled and disposed of as waste or recycled)
4 Products (such as chemical formulations ar consumer goods such as paper, textiles, ceramics etc.).

It is said that dioxins are “more toxic than cyanide and the most toxic of the manmade chemicals” . Toxicity of dioxin overall is expressed as Toxic Equivalents (TEQs). Internationally, FAO and WHO Expert Committee on Food Additives decided to express the tolerable intake of dioxins as a monthly value, the Provisional Tolerable Monthly Intake (PTMI). Recommended PTMI is 70 pg dioxin toxic equivalent (TEQ)/kg body weight. The Tolerable Daily Intake of dioxins in Japan was set at 4 pg in 1999.

4 Reproduction failure and population declines;
4 Abnormal functioning of thyroids and other hormone system;
4 Feminization of males and masculization of females;
4 Immune system becomes weaker;
4 Abnormalities in behavior;
4 Tumors and cancer;
4 Birth defects;

Human exposure to POPs are either directly from the environment a occupational and through food chain. Some groups of people like farmers and workers are exposed to POPs in their occupations. POPs can be found in the blood, muscles and other tissues particularly in fatty tissues of the general human population in all over the world. Research on the ways POPs impact on human health is continuing.

Good evidences are there that human exposure to specific POPs or classes of POPs may cause following injuries:

4 Cancers and tumors at multiple sites;
4 Neurobehavioral impairment including learning disorders, reduced performance on standard tests and changes in temperament;
4 Immune system weaker;
4 Reproductive deficits and sex-linked disorders;
4 Shortened period of location in nursing mothers;
4 Diseases such as endometriosis (a painful, chronic gynecological disorder in which uterine tissues are affected), increased incidence of diabetes and others.

The evidence suggests that women, infants, and children are especially vulnerable to certain effects of POPs. POPs are transferred from mother to the child both prenatal and postnatal, ultimately causing harm to the developing infant.
For more than 2 decades awareness has grown about the toxic effects to human health and the environment caused by certain chemicals that persist for decades in the environment, travel great distances through various media from their point of origin, bio-accumulate in humans and other organisms, and are bio-concentrated through food chains. The evidence of detrimental effects on living organisms at the population level demonstrates that POPs are a thread to biodiversity and even have potential for disruption at the ecosystem level.