What makes pcbs dangerous

On the other hand, specific PCBs to which humans are exposed may be more or less toxic than the PCB mixtures used for the studies on monkeys.

PCBs are a group of man-made chemicals that have been used in a variety of manufactured goods since PCBs can tend to persist in the environment and accumulate in the food chain.

Many countries have banned or severely restricted the production of PCBs. Humans may be exposed to PCBs by consuming contaminated food, and also by drinking contaminated water and breathing contaminated air.

Mothers exposed to PCBs may transmit them to their child. The speed at which PCBs are transformed in the body and the extent to which they are either stored or excreted vary according to the type of PCB. Depending on the dose, the type of PCBs , and other factors, exposure to PCBs can affect fertility , child development, the immune system , and possibly increase the risk of certain cancers. This summary is free and ad-free, as is all of our content.

You can help us remain free and independant as well as to develop new ways to communicate science by becoming a Patron! Home » PCBs » Level 1. Because these compounds are generally very stable, they remain present in the environment today. What are the health risks associated with PCBs?

Level 1: Summary Level 2: Details. What are PCBs? What happens to PCBs in the environment? PCBs can build up along the food chain. Source: Wisconsin Dept. To what extent are humans exposed to PCBs? The PCBs alter thyroid and reproductive function in both males and females and increase the risk of developing cardiovascular and liver disease and diabetes. Women are at high risk of giving birth to infants of low birth weight, who are at high lifetime risk for several diseases.

As knowledge of their toxic effects has grown faster than environmental levels have declined, PCBs remain dangerous contaminants. Developmental delays were seen at all ages and were greater in children who were smaller and had neonatal signs of intoxication or nail deformities, or both. Follow-up testing indicated that effects on cognitive development persisted for several years after exposure [Guo et al.

In rhesus monkeys, exposure to PCBs is associated with alterations in the menstrual cycle, decreases in fertility, increases in spontaneous abortion, and a reduced number of conceptions [Arnold et al. Limited but corroborative occupational data indicate a potential for toxic effects in the thyroid system in humans. Studies that have examined relationships between exposure to PCBs and thyroid hormone status have reported a variety of results.

Findings include both negative and positive significant correlations between exposure to PCBs and circulating levels of thyroid-stimulating hormone TSH , T4, or T3. These findings are dependent on the:. In a Dutch population, elevated levels of PCBs correlated with lower maternal levels of circulating triiodothyronine and total thyroxine and with higher plasma levels of TSH in infants during the second week and third month after birth.

Infants exposed to higher levels of PCBs also had lower plasma levels of free thyroxine and total thyroxine in the second week after birth [Koopman-Esseboom et al. In addition, a significantly elevated odds ratio for goiter was found among the Yu-Cheng cohort [Guo et al. Thyroid hormones are essential for normal behavioral, intellectual, and neurologic development. Thus, the deficits in learning, memory, and attention processes among the offspring of women exposed to PCBs are partially or predominantly mediated by alterations in hormonal binding to the thyroid hormone receptor [ATSDR and EPA ].

Some PCB congeners are capable of competing with endogenous hormone for binding to this receptor, suggesting a possible mechanism of thyroid toxicity. Studies in animals, including rodents and primates, provide evidence of thyroid hormone involvement in PCB toxicity.

The most convincing evidence that PCBs can exert toxicity by disrupting thyroid hormone system derives from two studies in rats [Cooke et al. The contribution of persistent organic pollutants POPs exposure to the incidence of diabetes has received little attention until recently.

Recent studies in populations exposed to PCBs and chlorinated pesticides found a dose-dependent elevated risk of diabetes [Carpenter ]. Evidence for liver effects of occupational exposure to PCBs is essentially limited to elevation of serum liver enzymes that are routinely examined in clinical assays.

A cross-sectional survey found no significant differences in liver function test results between workers who manufacture capacitors with low-level chronic exposure and non-exposed controls [Fischbein et al. However, in another cross-sectional study, liver function tests showed abnormalities that seemed to correlate with serum PCB levels [Maroni et al. Increases in urinary excretion of porphyrins appear to be associated with occupational exposure to PCBs, an effect that is believed to be secondary to the induction of hepatic microsomal enzymes.

Total bilirubin levels exhibit a positive correlation with serum PCB levels [Colombi et al. PCBs are more potent enzyme inducers than phenobarbital, a drug that occasionally causes clinical problems due to its microsomal enzyme-inducing effects. The health implications of enzyme induction include the occurrence of disease secondary to increased metabolism of endogenous or exogenous substances and interference in medical therapy due to increased metabolism of administered drugs.

The enzyme-inducing effects of PCBs can persist long after cessation of exposure [Letz ]. In the Yu-Cheng population, the incidence of chronic liver disease and cirrhosis was significantly higher than the incidence of these conditions in the general population of Taiwan.

Asymptomatic hepatomegaly has been reported in exposed workers, many of whom had concomitant elevated serum PCB levels.

Liver damage is a consistent and prominent finding among animals exposed to PCBs, particularly rats and monkeys, which are the species tested most extensively. Liver effects are similar in nature among species and appear to be reversible when mild. Liver effects characteristically include. A retrospective analysis of a study of two plants that manufactured electrical capacitors in the United States found a significant increase in the incidence of cancer.

The primary target tissues for the cancers were the liver, gallbladder, and biliary tract [Brown ]. Likewise, an increased incidence of melanomas associated with exposure to PCBs has also been observed for workers who manufactured capacitors [Bahn et al.

Sinks et al. One study suggests that exposure to electrical insulating fluids, for which the main constituent is PCBs, may cause malignant melanoma of the skin [Loomis et al. The results of a mortality study of workers employed between and at an electrical capacitor manufacturing plant were recently reported.

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 ,