The U.S. Environmental Protection Agency's (EPA) Office of Toxic Substances (OTS) evaluates submissions to the Premanufacture Notification process under section 5 of the Toxic Substances Control Act. Azo dyes constitute a significant portion of these submissions. OTS is concerned because some of the dyes, dye precursors or their degradation products such as aromatic amines, which are also dye precursors, have been shown to be, or are suspected to be, carcinogenic. Therefore, EPA's Water Engineering Research Laboratory, Office of Research and Development has an ongoing study to determine the fate of specific water soluble azo dye compounds in the activated sludge process.