BACKGROUND: Endocrine disrupting chemicals are widely distributed in environment. o-Phenylenediamine (OPD), anendocrine disruptor, is widely used in the leather, dyeing and polymer industries. There have been studies on the photocatalytic and biological degradation of OPD but there is no single report on the enzymatic degradation of OPD. RESULTS: In the present investigation, purified mixed intracellular enzymes (MIE) were used for the degradation of aqueous OPD from Citrobacter freundii, a marine bacterium. The degradation rate of OPD (concentration, 333 ppm) by MIE was achieved with maximum removal of 93%. The degrading efficiency using MIE was enhanced by Zn2+ to about 95.87%. The degradation of OPD using MIE of C. freundii followed pseudo-second-order rate kinetics. Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, fluorescence spectroscopy, high-performance liquid chromatography and cyclic voltammetry were used to characterise the degradation of OPD by enzymatic treatment. Nuclear magnetic resonance spectroscopy and gas chromatography-mass spectrometry were used for confirmation of the end product of OPD in enzymatic treatment. CONCLUSION: The endocrine disruptor OPD was degraded into pyruvic acid, a non-toxic end product, using MIE. (C) 2014 Society of Chemical Industry