However, there are many difficulties doing these studies: small numbers of people known to be exposed to a chemical; the fact that people suffer from many cancers without any chemical exposure; the fact that in some cases these people were exposed to a number of other chemicals; and the need to demonstrate high cancer rates that cannot be random in order to draw conclusions.
Acute toxic effects. People exposed directly to high levels of PCBs, either via the skin, by consumption, or in the air, have experienced irritation of the nose and lungs, skin irritations such as severe acne chloracne and rashes, and eye problems. Women exposed to PCBs before or during pregnancy can give birth to children with significant neurological and motor control problems, including lowered IQ and poor short-term memory.
A group of children in Michigan whose mothers had been exposed to PCBs were found to have decreased birth weight and head size, lowered performance on standardized memory, psychomotor and behavioral tests, and lowered IQ. These effects lasted through at least 7 years. Women who consumed PCB-contaminated fish from Lake Ontario were found to have shortened menstrual cycles. More highly-chlorinated PCBs with more chlorine atoms act like dioxins in altering the metabolism of sex steroids in the body, changing the normal levels of estrogens and testosterone.
Immune system and thyroid effects. In a study of adolescents Mohawk males in New York State, PCBs were shown to upset the balance of thyroid hormones, which may affect growth as well as intellectual and behavioral development.
The most common route of exposure to PCBs is from eating contaminated fish. By one estimate, residents of the Hudson Valley may inhale as many PCBs as they would get by eating one contaminated fish per year. Municipalities that use the Hudson River as a drinking water source carefully monitor the water for PCBs, and there are no detectable levels in the water supplies.
Unlike water-soluble chemicals, they are not excreted, so the body accumulates PCBs over years. When a larger fish eats the small fish, it also eats and absorbs all the PCBs that have built up in the small fish. In this way, larger fish and animals can build up a highly concentrated store of PCBs. Some types of PCBs may degrade into nontoxic form while they are stored in the body, but this process can take many years. In the same way, PCBs accumulate in women and pass on to their infants through breast milk.
This accumulation means that nursing infants may ingest PCB levels much higher than the levels in fish and other foods consumed by their mothers. In fact, several studies have found very high levels of PCBs in the blood and breast milk of Inuit women. Polychlorinated Biphenyls and Human Health. Johnson, B. Agency for Toxic Substances and Disease Registry. Environmental Protection Agency, and U.
Army Corps of Engineers. Antiestrogenicity of environmental polycyclic aromatic hydrocarbons in human breast cancer cells.
Toxicology , PCB exposure is also associated with reproductive deficiencies, such as reduced growth rates, retarded development, and certain neurological effects which may or may not persist beyond infancy. The immune system can also be affected, leading to increased infection rates, and changes in the skin such as chloracne and pigmentation disturbances.
Concise international chemical assessment document 55 Section 9. Fifty studies conducted since , mainly on people exposed to PCBs at work, indicated increases in mortality from cancers of the gastrointestinal tract , the liver, the organs and tissues involved in the production of blood, including bone marrow, the spleen , tonsils, and lymph nodes , and from malignant melanoma.
Exposure at workplaces was studied at several plants manufacturing PCB -impregnated capacitors , where exposure occurred through the air. Other studies involved exposure through foods, such as fish and rice oil or rice bran-oil, which had been contaminated with PCBs , but also with other toxic chemicals.
However, one study found a strong dose-response relationship between serum PCB levels and non-Hodgkin lymphoma , a cancer of the lymphatic system. Various studies examined effects on fertility due to PCB exposure through fish consumption and at the work place. In a study of New York women , a decrease in the ability to conceive was observed amongst those who regularly ate locally-caught fish that were contaminated with PCBs.
In men , a study of 55 transformer repair workers found no association between exposure to PCBs and sperm counts. However, in another study, for men with a low sperm count the ability of sperm to move decreased as the concentration of three coplanar PCBs in their blood serum increased.
Another study reported higher levels of certain PCBs in infertile men compared with the control population. Since the s numerous studies have investigated the effects of PCB exposure both during and after pregnancy on child growth and development. Researchers can estimate the degree of PCB exposure in the womb by measuring the level of PCBs in the umbilical cord blood serum. By analyzing breast milk samples, the extent of PCB transmission from mother to child can be deduced.
Effects of exposure to PCBs on the developing fetus have been investigated in women who consumed PCB-contaminated fish from Lake Michigan over a 6-year period. Overall fish consumption and levels of PCBs in cord blood serum were associated with lower birth weight, smaller head circumference, and shorter pregnancies. Fish consumption during pregnancy was related to lesser neuromuscular maturity of the newborn.
PCB -contaminated fish consumption has also been linked to impaired involuntary muscle actions and abnormally weak reflexes. High levels of PCBs in umbilical cord blood serum have repeatedly been linked with poor performance in standard tests carried out to assess the mental and motor abilities of the newborn.
Follow-up studies on children aged 4 and 11 indicated that PCB exposure in the womb was linked to impaired memory and attention, specifically short term memory and performance in IQ tests. Contrastingly, other follow up studies have shown that psychomotor deficits do not persist beyond childhood. Although one study indicated exposure to PCBs through breast-milk did not affect memory performance, another study showed lower mental development in 7-month old infants fed with breast milk containing high levels of three common non-planar PCBs.
The effects of PCBs exposure on the immune system of adults and children have been examined in two different studies.
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