What are PCBs?
Polychlorinated biphenyls belong to the class of persistent organic pollutants (POPs), have toxic properties, resist degradation and bioaccumulate, are transported across large distances through various environments.
Industrial polychlorinated biphenyls are transparent viscous liquids, colourless or pale-yellow in colour. Physical and chemical properties of the commercial PCBs are determined by the composition of their constituents, as well as by the total amount of chlorine. The following properties of PCBs have contributed to their wide use in industry:
- Resistant to acids and bases
- Resistant to oxidation and hydrolysis
- Not easily soluble in water
- Resistant to high temperatures
In industry PCBs are used as heat transfer substances, in paint and ink, duplicating paper and plastics, as well as in transformers and capacitors. 13 out of 209 types of PCBs are as toxic as dioxins. The resistance of PCBs depends on the degree of chlorination; for example, the half-life in soil of certain PCBs may be as long as 45 years.
PCBs are toxic for fish: big doses are lethal, smaller ones may disrupt the spawning. A number of studies have identified the damaging effect of PCBs on the reproductive and immune systems of certain animal species, for example, of seals and minks.
PCBs may affect humans through contaminated food supplies. In 1968 in Japan and in 1979 in Taiwan the consumption of the contaminated rice oil caused pigmentation of nails and mucous membranes, thickening of eyelids, fatigue, nausea, and vomiting among the population. In Taiwan women, who got pregnant within seven years after being affected by PCBs, gave birth to children with developmental and behavioural disorders. There were also identified disorders in short-term memory among children, born to mothers which consumed a lot of contaminated fish from the Lake Michigan. PCBs disturb the normal functioning of the immune system and belong to the class of potential human carcinogens.