There are numerous reports of large population exposures to PCBs. A serious exposure to PCBs—lasting several months— occurred in Japan in 1968 as a result of cooking oil contamination with PCB-containing transfer medium (Yusho disease). A similar outbreak called Yucheng disease occurred at about the same time in Taiwan. Effects on the fetus and on the development of the offspring of poisoned women were reported. It is now known that the contaminated cooking oil contained not only PCBs but also polychlorinated dibenzofurans (PCDFs) and polychlorinated quaterphenyls (PCQs). It is likely that the effects initially attributed to the PCBs were actually caused by a mixture of contaminants. Workers occupationally exposed to PCBs develop dermatologic problems that include chloracne, folliculitis, erythema, dryness, rash, hyperkeratosis, and hyperpigmentation. Some hepatic abnormalities have been found in PCB poisoning, and plasma triglycerides are elevated.
Information about the effects of PCBs on reproduction and development is accumulating. The halogenated pesticides are potent endocrine disrupters and there is widespread concern about the persistent estrogenic effect of these chemicals. Adverse reproductive impacts of PCBs have been found in many animal studies. Direct teratogenic effects in humans have yet to be established: studies in workers and in the general population exposed to moderate or to very high levels of PCBs have not been conclusive. Some adverse behavioral effects in infants have been reported. An association between prenatal exposure to PCBs and deficits in childhood intellectual function was described for children born to mothers who had eaten large quantities of contaminated fish. Epidemiologic studies have established increases in various cancers including melanoma, breast, pancreatic, and thyroid cancers. These findings and animal studies provided a sufficient basis for the IARC to classify some co-planar PCBs as class 1, carcinogenic to humans, in volume 100 of the IARC monographs.
Introduction to Toxicology: Occupational & Environmental 1015
A comprehensive EPA fact sheet on PCBs may be found at https:// www.epa.gov/pcbs.
The polybrominated biphenyls (PBBs) and their ethers (PBDEs) share many of the toxic and environmentally damag ing persistent qualities of PCBs. They were introduced as fire retardants in the 1950s and have been used in massive quantities since that time. The biphenyls are no longer produced and may no longer be used, but the biphenyl ethers remain in use as fire retardants in plastics for bedding and in automobile upholstery.
PBB fire retardant contamination has been extensive in the
Great Lakes region, resulting in large exposure to the population.
PBBs are considered IARC class 2a: probable human carcino gens. PBDEs are not classified. An EPA technical fact sheet on
PBB and PBDEs may be found at http://www2.epa.gov/fedfac/ polybrominated-biphenyls-pbbs.
The polychlorinated dibenzo-p-dioxins (PCDDs), or dioxins, are a group of halogenated congeners of which tetra chlorodibenzodioxin (TCDD) has been the most carefully stud ied. There is a large group of dioxin-like compounds, including biphenyls. While PCBs were used commercially, PCDDs and