By-Product PCB

By-product PCBs are polychlorinated biphenyls formed unintentionally as contaminants during industrial processes rather than manufactured deliberately. They arise in pigment and dye production, chlorinated solvent manufacture, and combustion, with congeners such as PCB-11 marking these non-Aroclor sources. The Stockholm Convention captures them under Annex C, the unintentional-production annex, separate from the Annex A ban on intentional PCB production and use. By-product PCBs reach the sea through wastewater effluent and atmospheric deposition, and their share of marine sediment loads has grown as legacy Aroclor and Kanechlor inputs decline.