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Benzidine, (4,4′-diaminobiphenyl), is the solid organic compound with the formula (C6H4NH2)2.  It is a manufactured chemical that does not occur naturally. Benzidine is a crystalline (sandy or sugar-like) solid that may be greyish-yellow, white, or reddish-grey. It will evaporate slowly from water and soil. Its flammability, smell, and taste have not been described. In the environment, benzidine is found in either its “free” state (as an organic base), or as a salt (for example, benzidine dihydrochloride or benzidine sulphate). In air, benzidine is found attached to suspended particles or as a vapour.  Benzidine has been linked to bladder and pancreatic cancer. Since August 2010 benzidine dyes are included in the EPA’s List of Chemicals of Concern.