PCB 47
22'44'-Tetrachlorbiphenyl

In the context of using Bis(2,4-dichlorobenzoyl) peroxide (DCBP) as a radical chain initiator for polymerization and as a cross-linking or vulcanizing agent, the formation of 2,4-dichlorobenzoic acid (see BfR Recommendation XV, Silicones dated 1st September 2017) is discussed alongside the formation of 1,3-dichlorobenzene and especially PCB 47 as undesirable decomposition products.

An American study detected the congeners PCB 51, PCB 47 and PCB 68 in the indoor air of residences, classifying them primarily as PCB congeners not originating from technical PCB mixtures. The authors hypothesize that these PCBs are produced from the decomposition of DCBP during the manufacture of polymeric sealants used in, among other things, the production of kitchen furniture, and are ultimately released from these sources (Herkert et. al, Environ Sci Technol. 2018, 52, 9, 5154-5160).

In Germany and Europe, PCB contamination is usually monitored using 6 indicator PCBs (Ballschmitter PCB 28, PCB 52, PCB 101, PCB 153, PCB 138, and PCB 180), identified as the main components of technical PCB mixtures such as those of the Clophen or Aroclor types.

However, if a source other than technical PCB mixtures is responsible for PCB contamination—as in the case of PCB 51, PCB 47, and PCB 68—the contamination may not be adequately detected by analysing only the 6 indicator PCBs. As an alternative or supplement to the 6 indicator PCBs, determining the sums of PCB homologues is recommended. By measuring from Mono- to NonaCB, together with DecaCB, all 209 possible PCB congeners can be summed up in the analysis.