Public Health Assessment Public Comment Release
Ward Transformer NPL Site
positions 4 and 4' are called para positions. The benzene rings can rotate around the bond
connecting them; when the rings are in the same plane, they are referred to as planar or coplanar
PCBs. Planar PCBs have a structure similar to the chlorinated dioxins and furans and generally
are more toxic than nonplanar PCBs. When the relatively large chlorine atoms are attached in
opposing ortho positions, the molecule cannot lie flat; therefore, only non-ortho or mono-ortho
PCBs can assume the planar configuration.
Union of Pure and Applied Chemistry (IUPAC) rules for substituent characterization in
biphenyls [5]. Using this system, congeners PCB-1 through PCB-209 are ordered, with
increasing numbers increasing in degree and complexity of substitution, according to standard
IUPAC rules.
The major U.S. producer of PCBs until 1977 marketed mixtures of PCBs under the trade name
indicate the approximate weight percentage of chlorine in the mixture (e.g., Aroclor 1260
contains about 60% chlorine). Each Aroclor is a mixture of various PCB congeners.
Health Effects Caused by PCB Exposure
Exposures of workers to high levels of airborne PCBs--many times higher than are likely to be
changes in blood and urine that might indicate liver damage. In animal studies, long-term oral
exposure to PCBs caused various health effects, including liver damage, skin conditions,
impaired reproduction, and immunologic and behavioral changes. PCBs are not known to cause
serious birth defects. However, evidence exists that children exposed to PCBs in the womb
(through their mother's consumption of contaminated fish) had neurobehavioral and
developmental deficits [5,7]. In human and animal studies, PCBs are associated with certain
kinds of cancer, such as cancer of the liver and biliary tract [5]. EPA considers PCBs probable
human carcinogens. The evidence of PCBs' carcinogenicity in animal studies is sufficient and
current evidence in humans is inadequate but suggestive [8].
Certain PCB congeners may exhibit toxicity similar to the chlorinated dibenzodioxins and
dibenzofurans, structurally similar molecules. One of the most toxic and most studied of these
molecules, 2,3,7,8-tetrachlorodibenzodioxin (2,3,7,8-TCDD), can cause acne-like skin lesions,
rashes, liver damage, hormonal changes, and increase the theoretical risk of cancer [9]. Toxicity
of dioxin-like PCB congeners can be expressed as a fraction of the toxicity attributed to 2,3,7,8-
TCDD, or a toxicity equivalency factor (TEF) [9,10,11]. Table 1 shows the TEF weighting
congeners are multiplied by their respective TEF and summed, along with comparably weighted
dioxins and furans, to obtain the toxicity equivalency quotient (TEQ). The TEQ can be compared
directly with 2,3,7,8-TCDD toxicity information. This public health assessment evaluated PCBs
individually and (when congener data were available) using TEQs to determine the specific
dioxin-like toxicity.
Table 1. TEF Weighting Factors for PCB Congeners at the Ward Transformer Site
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