Many studies have been performed in order to know the effects of PCBs on human health. Some of these studies suggest that PCBs are a possible factor in the appearance of cancer in humans who have been in contact with the substance, while they have already been demonstrated to cause a variety of adverse health effects and have been shown to cause cancer in animals.
Other demonstrated effects of PCBs in animals are effects on the immune system, reproductive system, nervous system, and endocrine system. Studies in humans provide supportive evidence for potential carcinogenic and non-carcinogenic effects of PCBs. The different health effects of PCBs may be interrelated, as alterations in one system may have significant implications for the other systems of the body.
It has been demonstrated many times that PCBs cause cancer in animals, and although there is no evidence of the same effect in humans, there exist a lot of clues to it. Scientists from the whole world and organizations as the EPA, the National Toxicology Program, the Institute for Occupational Safety and Health or the International Agency for Research on Cancer, describe every commercial PCB as 'probable human carcinogens'. These conclusions are reinforced after observing workers exposed to PCBs, who are more likely to develop a malignant melanoma than persons who were not in contact with the substance. EPA's cancer reassessment was peer reviewed by 15 experts on PCBs, including scientists from government, academia and industry. The reassessment concluded also that the types of PCBs likely to be bioaccumulated in fish and bound to sediments are the most carcinogenic PCB mixtures. A very important aspect of PCBs is that its composition changes following their release into the environment, and people who ingest PCB-contaminated fish or other animal products have many risks of developing some of the illness related to PCBs.
Extensive studies have been realized including primates and other animals, using environmentally relevant doses. EPA has found clear evidence that PCBs have significant toxic effects in animals, including effects on the immune system, the reproductive system, the nervous system and the endocrine system. Following is a little description of all the most important non-carcinogenic effects caused by PCBs.
They have been studied in Rhesus monkeys (these monkeys are generally regarded as the best laboratory species for predicting adverse reproductive effects in humans) and other animals. These studies have revealed a number of serious effects on the immune system following exposures to PCBs, as for example:
- a significant decrease in size of the thymus gland (which is critical to the immune system) in infant monkeys,
- reductions in the response of the immune system following a challenge with sheep red blood cells (a standard laboratory test),
- decreased resistance to Epstein-Barr virus and other infections. It was not possible to identify a level of PCB exposure that did not cause effects on the immune system.
Granted that PCBs suppress the immune system, which has been demonstrated as a risk factor for non-Hodgkin's lymphoma, PCBs are a more than possible carcinogenic factor.
Many different species have been used to study the effects in the reproductive system, for example the already mentioned Rhesus monkeys, rats, mice and mink. Most significantly, PCB exposures are in relation with the reduction of the birth weight, conception rates and live birth rates of monkeys and other species. It has also been observed that PCB exposure reduced sperm counts in rats. Concerning humans, children born from women who worked with PCBs in factories showed decreased birth weight and a significant decrease in gestational age. Results are approximately the same in fish populations and in other species of animals, and these results suggest that reproductive effects may be important in humans following exposure to PCBs.
Proper development of the nervous system is critical for early learning and can provoke significant consequences for the health of individuals. Effects of PCBs on the nervous system have been studied in monkeys and other animal species. Newborn monkeys exposed to PCBs showed persistent and important deficits in neurological development, resulting in visual recognition, short-term memory and learning. Some of these studies were conducted using the types of PCBs most commonly found in human breast milk. Results obtained after observing humans exposed to PCBs are very similar, including learning deficits and changes in activity.
PCBs have been demonstrated to exert effects on thyroid hormone levels in animals and humans. Thyroid hormone levels are critical for normal growth and development, and alterations in these levels could provoke very weighty effects, as for example deficits in hearing (which has been demonstrated in rodents). Additional research will be required to determine the significance of these effects in the human population.
Other Non-Carcinogenic Effects
Many other non-carcinogenic effects of PCBs have been observed in humans, as dermal and ocular effects and elevations in blood pressure, serum triglyceride, and serum cholesterol. In animals, dermal and ocular effects (monkeys) and liver toxicity (rodents) habe also been observed.