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PCBs and Dioxins


PCBs or polychlorinated biphenyls, are biphenyls which are chlorinated to varying degrees and are generally mixtures of polychlorinated compounds. They are persistent in the environment and are absorbed in humans via ingestion, inhalation, and dermal exposure after which, they are circulated systemically throughout the body. They tend to deposit in fatty tissue since they are lipophilic and they can pass to offspring via the placenta and through mothers milk.


PCBs range in their properties according to the extent of chlorination. They can be colorless mobile oils in the lower chlorinated compounds(Aroclors 1221, 1232, 1016, 1242, 1248) and white powders when more heavily chlorinated (Aroclor 1268, 1270). They are practically odorless and have extremely limited solubility in water.

Non-Cancer Effects in Man
  • The following toxicological effects have been noted in man in response to exposure to PCBs: hyperpigmentation of skin, hyperactive meibomian glands, conjunctivitis, edema of eyelids, subcutaneous edema, keratin cysts in hair follicles, hyperplasia of hair follicle epithelium, hepatic hypertrophy, decreased numbers of red blood cells, decreased hemoglobin, serum hyperlipidemia, leucocytosis, chloracne, weakness and numbness in extremities. Symptoms of significant acute exposures to PCBs include abdominal pain, anorexia, nausea, vomiting, jaundice, headache, dizziness, depression, nervousness, fatigue, weight loss, loss of libido, muscle pains and joint pains.
  • PCBs are known inducers of liver enzyme activity and liver cirrhosis.
  • PCB-exposed patients exhibited immunosuppression, in particular, suppression of cellular immunity.
Reproductive Effects in Man
  • Causes irregular menstrual cycles, early abortions and birth of small, hyperpigmented and hyperkeratotic infants.
  • PCBs can cross the placental barrier and are excreted in mother’s milk.
  • Four babies born to mothers who had ingested rice oil contaminated with PCBs showed the following problems: 1) intrauterine retardation of growth in three cases. 2)dark brown pigmentation of the skin and mucous membranes similar to that in Addison’s disease especially on the genitalia, axilla, and on the mucous membranes of the mouth, palpebra and limbic conjunctiva. 3) gingival hyperplasia in three cases and eruption of teeth at birth in two cases. 4) spotted calcification on the parieto-occipital-skull and large or wide frontal and occipital fontanellis and sagittal suture in three cases. 5) edematous face and exophthalmic eyes in three babies.
  • Pre-natal exposure to PCBs has been associated with reduced birth weight, neonatal behavioral abnormalities, and poorer recognition memory as a result of pregnant women consuming PCB contaminated fish from lake Michigan.
  • Pre-natal exposure to PCBs has been associated with deficits in birth size, gestational age, postnatal growth, motor development, and short term memory function in both infancy and childhood.
  • PCB exposure is thought to induce a developmental hypothyroidism causing growth deficits, motor dysfunction and hearing disorders in humans.


In animals
  • PCBs have been reported to significantly increase the incidence of liver tumors in rats.
  • PCBs are suspected of promoting tumors by different modes of action.
  • Animal studies have shown that PCBs can produce benign and malignant liver cell tumors, lymphomas and leukemias, and carcinomas of the gastrointestinal tract.
  • PCBs have been shown to cause hepatocellular carcinomas in rats and mice.
In man
  • A retrospective cohort mortality study of workers exposed to PCBs showed excess deaths in women caused by liver cancer, cancer of the gall bladder or biliary cancer.
  • Increased mortality from pancreatic cancer has been reported in several studies of those exposed to PCBs.
  • A study of capacitor workers exposed to PCBs reported elevated mortality from cancers of the GI tract, lung and blood in males and blood only in females.
  • Workers exposed to PCBs have been reported to show excess mortality from liver cancer.
  • Contaminated rice oil is reported to have caused increased mortality from malignant neoplasms, liver neoplasms, lung, trachea and bronchial neoplasms and leukemia.
  • A retrospective cohort mortality study of 2567 workers involved with PCBs discloses and excess mortality from both rectal and liver cancer.
  • One study of electrical workers claims excess mortality from both malignant melanoma and brain cancer.
  • PCBs are classified by the US EPA as probable human carcinogens based on animal studies showing.
  • Environmental cycling occurs and involves volatilization from ground surfaces (soil, water) into the atmosphere with subsequent removal via wet/dry deposition and then revolatilization.
  • Persistent in the environment is dependent on the degree of chlorination of the specific PCB. Less chlorinated biphenyls (mono-, di- and tri-substituted; Aroclor 1221, 1232) biodegrade rather rapidly, tetra chlorinated biphenyls (Aroclor 1016, 1242) biodegrade slowly and highly chlorinated biphenyls (Aroclor 1248, 1254, 1260) are resistant to biodegradation.
  • Absorption on soil increases and volatilization decreases with increasing chlorine substitution.


Because PCBs are persistent in the environment and are easily absorbed into systemic human circulation by ingestion, dermal contact or by inhalation, they represent a significant threat to human health. Although PCBs are not thought to be acutely toxic, continuing exposure to low levels of this toxin produces well document effects as described above. Cancer is one of the endpoints relating to PCB exposure. PCBs are thought to be initiators of the carcinogenic process, are thought to be promoters of the carcinogenic process and are thought to produce immunosuppression in exposed individuals allowing for the expression of incipient cancers. Because of its ability to pass the placental barrier and be excreted in mother’s milk, fetuses and children are at high risk relative to developmental effects of PCB exposure. PCBs are persistent and toxic and represent a significant health threat to those living in a contaminated environment.

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