Non Com POPs Project

POLYCHLORINATED BIPHENYLS (PCBs)

              Structural formula of PCB

Polychlorinated biphenyls are oily liquids which contain chemically two aromatic cores with 209 different compound combinations (so-called congeners), which differ in toxicity potential and physico-chemical properties.

PCBs started to be produced in the thirties of the last century and used largely on industrial purposes (transformers' charge, condensers, hydraulic liquids, heating mediums, plasticisers, lubricants, impregnation material, dyes, glues, waxes, additions to building materials, adhesives, combustion inhibitors, pesticides and so on).

In water, PCBs are generally contained in sediments and have high adsorption affinity. Thanks to adsorption and low solubility, they do not tend to spread massively in soils.

PCBs decomposition is very slow - the more chlorinated the substance is, the slower is the process. According to studies from 1998, the half-time decomposition in atmosphere is estimated to 3-21 days, in water to more than 5 days and in soil to more than 40 days (which means that the absolute substance's decomposition can take until 2 years). The biodegradation via micro-organisms is also slow. However, PCB get to the plants, some of which can accumulate them. These substances can accumulate in animals from vegetable nutrition, but also directly from sea or fresh water. The highest PCB concentrations were found in tissues of sea fish, prawns and oysters.  In human body, they accumulate especially in adipose fibres, from which they can be gradually given off to the blood circuit for a long time. An important fact is that they are contained in adipose cells of mothers' milk, so already new-borns can often receive this toxic substance.

Health effects are derived usually from experiments on animals, workplace high dose exposure, environmental catastrophes (like in Japan and Taiwan) and only recently also from epidemiological studies on different populations. Toxic effects on respiratory and digestive system, liver malfunction, neurological and developmental changes (child growth's deceleration, low birth weight, breaking in psychomotor development, eventually decrease in intelligence quotient), skin pigmentation to rashes like acne is being supposed. Human carcinogenity was not proven, but PCBs are considered as a suspicious carcinogens. PCBs fall newly in substances that damage human immune system, the so-called endocrine disruptors.

Among the world populations with highest environmental exposure to POPs, in particular PCBs, are fishing community in Faroe Islands, Inuit population in Canada, inhabitants living near Anniston, Alabama, USA, and people living in Eastern Slovakia. These populations are exposed either as a result of their dietary habits (diet involving eating of whale blubber, seal fat, other marine products), misuse of pesticides or environmental pollution resulting from former production of POPs in the region.

The World Health Organisation (WHO) considered in 1989 that 10 pg/kg of body weight is an acceptable daily intake (ADI) of PCB, but nowadays in some countries like Germany and the USA, ADI are determined in considerably sharper way. For example 1 pg/kg of weight is considered as admissible daily intake of PCBs and dioxins altogether.

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