Polychlorinated biphenyls (PCBs) are a family of commercially produced compounds that have been used extensively since 1930 in a variety of industrial applications, including as dieletrics in transformers and large capacitors, as heat exchange fluids, as paint additives, in carbonless copy paper and in plastics. These persistent organic chemicals accumulate in the environment and humans and are associated with a broad spectrum of health effects. Due to their toxicity and classification as persistent organic pollutants, processing and distribution of PCBs has been prohibited in almost all industrial countries since the late 1980s. However, they can still be released into the environment from building paint and sealants and poorly maintained hazardous waste sites that contain PCBs.
The basic structure of PCBs is shown in Figure 1. In this structure, 1 to 10 hydrogen atoms can be replaced by chlorine atoms, ranging from three monochlorinated isomers to the fully chlorinated decachlorobiphenyl isomer. In total, there are 209 different PCBs (congeners). Ballschmiter and Zell have proposed a numbering of the PCB congeners in 1980, which has been adopted by the International Union of Pure and Applied Chemistry (IUPAC).
Figure 1. Basic structure of PCBs.
Based on structural characteristics and toxicological effects, PCBs are divided into dioxin-like PCBs (dl-PCBs), showing toxicological properties similar to dioxins and non-dioxin like PCBs (non-dl PCBs), which do not share the dioxin’s toxic mechanism. Some non-dioxin like PCBs have been shown to elicit neurological, endocrine, immunological and carcinogenic effects.
In evaluating the contamination situation, six congeners, i.e. PCB 28, 52, 101, 138, 153 and 180, were chosen as indicators for the occurrence of non-dioxin like PCBs. The Scientific Panel on Contaminants in the Food Chain of EFSA (CONTAM panel) noted in its Scientific Opinion related to the presence of non-dioxin like PCBs in feed and food that the sum of the six indicator PCBs represented about 50 % of the total non-dioxin like PCB concentration in food.