Polychlorinated biphenyls in pigments: Inadvertent production and environmental significance

Polychlorobiphenyls are toxic, bioaccumulative, and persistent chemicals whose intentional manufacture has been banned throughout the developed world. Polychlorobiphenyls may be generated inadvertently during the production of certain pigments, including diarylides. This inadvertent production is allowed under various regulatory schemes, such as the Toxic Substances Control Act in the United States and the Stockholm Convention on Persistent Organic Pollutants. Generally, these regulations require polychlorobiphenyl levels in batches of pigment to be less than certain regulatory limits, usually 50 ppm. A growing body of evidence suggests that the use of pigments is dispersing polychlorobiphenyls throughout the environment. Polychlorobiphenyl congeners associated with pigments have been found throughout the United States in sediments and in surface waters at levels exceeding the prevailing water quality standards. A recent Japanese government study reported measured polychlorobiphenyl concentrations well above 50 ppm in several commercial batches of azo pigments. A strong case may thus be argued that pigment manufacturers should modify existing production processes to reduce, ideally prevent, the formation of polychlorobiphenyls, or develop new pigments that do not have the potential to form polychlorobiphenyls. This paper, the result of a collaboration involving environmental scientists (LR and JG) and a pigment chemist (RC), reviews the evidence for environmental contamination from inadvertent polychlorobiphenyl production in specific pigments, together with a rationalisation of the conclusions based on the reaction mechanisms involved in their manufacture. Broad measures are proposed that might address these issues, both from environmental and from chemical perspectives.