Polychlorinated Biphenyls

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Public Health Assessment Public Comment Release

Ward Transformer NPL Site

chemical is greater than the health guideline, then the exposure dose is compared with known

health effect levels identified in ATSDR=s toxicological profiles and other current reference

sources. If the COC is a carcinogen, the theoretical cancer risk is also estimated. These

comparisons provide the basis for determining whether the exposure is a health hazard.

Because the Ward Transformer business involved recycling used transformers since the 1960s,

the main contaminants of concern at the site are PCBs, which were used in transformers before

1977. Data were screened for all contaminants of concern, but an overview of PCBs is given

here because they are likely to be the most important contaminants of concern at this site and

because completed pathways for exposure were identified.

Polychlorinated Biphenyls

Overview

PCBs are a group of synthetic organic chemicals that exhibit insulating and flame retardant

properties. They were first manufactured and used in the late 1920s. PCBs were used widely as

coolants and lubricants in transformers and other electrical equipment and as process chemicals

in the manufacture of common products including plastics, fluorescent lighting fixtures, and

pesticides. PCBs are also relatively inert and take a long time to break down. In 1977, evidence

that PCBs build up in the environment and may cause harmful effects led to a halt in the

manufacture of PCBs in the United States. However, PCBs are still found throughout the world

because they break down so slowly and may be transported long distances in the environment.

People can be exposed to PCBs in air, water, soil, or sediments. Most exposure to PCBs,

however, probably results from eating contaminated fish or meat. Because PCBs break down so

slowly, tissue levels of PCBs tend to increase up the food chain as predators eat smaller species.

In this way, the fish and meat people eat can be contaminated with higher levels of PCBs than

those existing in the air, water, soil, or sediments.

Chemical Structure

The chemical structure of PCBs determines their toxicity. The base of every PCB is the biphenyl

molecule, which consists of two benzene rings joined together (Figure 2). Hydrogen atoms are

attached to each of the numbered corners representing carbon atoms in the diagram. To form a

PCB, 210 chlorine atoms substitute for these hydrogen molecules [5].

Figure 2. Biphenyl Chemical Structure (from [6])

Chlorine atoms can substitute for hydrogen at any of the 10 numbered carbon atoms shown. The

209 possible combinations that can be formed are known as PCB congeners. One numbering

system for naming PCBs is derived from the carbon atom numbers shown in Figure 2. Positions

2, 2', 6, and 6' are called ortho positions, positions 3, 3', 5, and 5' are called meta positions, and