4. What happens to PCBs when they enter the body?
PCBs can enter human cells and tissues when contaminated air is breathed in, when contaminated food enters the digestive system, or through contact with the skin. Tests on laboratory animals show that PCBs are readily absorbed
through the digestive tract when swallowed, and to a lesser extent through the skin. The main PCB elimination routes are through the faeces, urine, and breast milk.
Once in the gastrointestinal tract, ingested PCBs diffuse across cell membranes and enter blood vessels and the lymphatic system. PCBs, especially those that contain a greater number of chlorine atoms, are readily soluble in fats and thus tend to accumulate in fat-rich tissues such as the liver, brain and skin.
In mothers, PCBs have also been found to pass into the placenta, umbilical cord blood, and breast milk.
PCBs can undergo different transformations in the body and then either be stored in certain tissues or excreted.
Transformations that lead to accumulation: PCBs can easily be transformed into persistent metabolites that are not readily excreted and that can accumulate in specific tissues and body fluids. The biological half-life of these persistent metabolites depends on the structure of the original PCB.
Transformations that lead to excretion: PCBs can leave the blood and enter tissues very rapidly and be transformed into water-soluble substances. These can combine with glutathione and glucuronic acid, that are naturally present in the body, forming a substance that is then excreted in urine and feces. The speed of this process depends on the number and position of chlorine atoms of the original PCB. It is, for instance, slower when there are more chlorine atoms on both phenyl rings and faster if there are two carbon atoms without any attached chlorine atoms next to each other.
In a case where both children and their mothers were exposed to PCBs through their diet, levels of PCBs in blood dropped more rapidly in the children. This may be partly explained by the children’s growth, as their increasing tissue mass may lower the PCB concentration in blood due to dilution, rather than elimination.
This text is a summary of: IPCS - WHO
Polychlorinated biphenyls : Human health aspects. Concise international chemical assessment document 55
Section 7, Comparative kinetics and metabolism in laboratory animals and humans