A polychlorinated biphenyl – PCB is an organic chlorine compound. Monsanto took over commercial production of PCBs in its original mixtures in 1935. PCB’s utility was based largely on their chemical stability, including low flammability and high dielectric constant. PCBs do not easily break down or degrade, which made them attractive to industry.

Because of PCBs’ environmental toxicity it was classified as a persistent organic pollutant, and its production was banned by the United States Congress in 1979 and by the Stockholm Convention on Persistent Organic Pollutants in 2001. The Italian company Caffaro, located in Brescia specialized in producing PCBs from 1938 to 1984, following the acquisition of the exclusive rights to use the patent in Italy from Monsanto.
The pollution resulting from this factory and the case of Anniston, in the USA, are the largest known cases in the world of PCB contamination in water and soil, in terms of the amount of toxic substance dispersed, size of the area contaminated, number of people involved and duration of production.