7 - A history of PCB biodegradation

Summary

Introduction

Polychlorinated biphenyls (PCBs) are a group of related chemicals (congeners) which were produced during the middle of this century as chlorinated derivatives of biphenyl. There are 209 congeners distinguished by the number and position of chlorine atoms on a biphenyl backbone, although many of these congeners are not found in the commercial PCB mixtures (marketed under the tradename ‘Aroclor’ in the U.S., ‘Clophen’ in Europe, and ‘Kaneclor’ in Japan) (Ballschmiter & Zell, 1980; Hutzinger et al., 1983; Erickson, 1992). The chemical and thermal stability of these compounds formed the basis for the widespread use of PCBs as the fire-retardant fluid in electrical equipment, heat exchangers, hydraulic fluids, and compressor fluids. However, this chemical stability also carried with it a degree of biological stability that has resulted in the accumulation of PCBs at sites of its manufacture, use, storage, and disposal.

Although the term PCBs has evoked the specter of the grim reaper, at the outset of this review it should be stated that this visceral response to PCBs has at times bordered on the irrational. As our society moves into the next century and we increasingly address our environmental problems, we must take a realistic view of the true risks posed by each of the chemical targets that we address. It should also be remembered that in their time PCBs were an important life-saving invention. Prior to 1929 electrical equipment contained flammable fluids which often ignited, creating conflagrations that truly posed serious risks to human health. The use of chlorinated organics, including PCBs, as fire-retardant liquids helped create a safer environment for our growing industrial society.