Centers for Disease Control and Prevention (CDC) National Report of Human Exposure to Environmental Chemicals, the 95th percentile of the distribution of PCB 153 levels in the US population was 126 ng/g serum lipid (CDC, 2005d).

Animal studies carried out by CDC suggest that it is likely cancer risks were overstated and animal-specific. PCBs have been associated with health effects in laboratory animals, but typically at very high doses, possibly not relevant to noncatastrophic exposure for humans. Similar conclusions have been derived from looking at animal studies of exposure to high levels of PCBs resulting in tumor formation. Although there is evidence to substantiate PCB-associated health problems, several epidemiological studies of occupational workers exposed to PCBs found no evidence of ill health associated with their exposure. Even the PCB-chloracne association may be due to co-exposure to DLCs, and there is concern that multiple confounding factors make it difficult to interpret epidemiological studies in the workplace. Some studies of PCB workers found increases in rare liver cancers and malignant melanoma (US EPA, 2006). Thus, the US EPA found that the epidemiological studies are inconclusive; based on animal and recent human studies, PCBs are probable human carcinogens.

The earliest reported incidents of adverse effects from PCB poisoning occurred in Japan and Taiwan following widespread consumption of contaminated rice oil. The high-level exposure to PCBs resulted in skin lesions (acneform dermatitis) and peripheral nerve damage among adults, and similar effects among their offspring. Children born to exposed mothers also showed inhibition of growth and tissue maintenance (Kimbrough, 1987; Erickson, 1997). NRC (1999) also identified low birth weight and shorter gestation, and both neurological and neuromuscular deficits as adverse outcomes associated with prenatal PCB exposure.

Reports from occupational exposure to PCBs have identified several subclinical adverse health effects. The US EPA reviewed and identified many potentially serious noncancer adverse health effects associated with PCB exposure. These adverse effects included impairment of immune, reproductive, and neurological systems. The long-term impact of low-level exposure to PCBs is unclear, particularly on the endocrine system (US EPA, 2006) and will require further research to understand.

As PCB exposure levels continue to decline subsequent to federal laws banning PCB production, it may be difficult to characterize adverse health effects from low-level exposure (WHO Consultation on Risk Assessment of Non-Dioxin-Like PCBs, 2001; Ross, 2004) and to determine the significance of these exposure levels to health outcomes among the general population. Advances in analytic techniques may enhance data gathering and analysis efforts and improve our understanding of risks associated with low-level

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