In this paper we describe the electrochemical properties of vitamin K-3 (denoted VK3) in aerated solutions, and the application potential of VK3 in the degradation of 4-chlorophenol, 3-chloropropanl and sodium 2,3-dichloropropionate. Cyclic voltammetry revealed that the cathodic current of VK3 decreased systematically with the addition of 3-chloropropanol and sodium 2,3-dichloropropionate. Concomitantly, a pair of new waves grew at less negative potentials. This electrode behavior suggested that VK3 might form 1:1 complexes with 3-chloropropanol and sodium 2,3-dichloropropionate. The equilibrium constants were estimated to be about 1000 and 100 M-1, respectively, for the reactions of VK3 with 3-chloropropanol and sodium 2,3-dichloropropionate. Emission spectroscopy supported our postulate, although the determined equilibrium constants (10(4) M-1) had deviations from those obtained based on the electrochemical method. Apart from these discrepancies, VK3 was found to be an effective catalyst for the reduction of oxygen as it was reduced. By using superoxide dismutase (SOD) and amplex red as probes, we confirmed that superoxide anion radical could be produced in aerated VK3 solutions. In the light of these properties, attempts were made using the reduced VK3 to degrade 4-chlorophenol, 3-chloropropanol and sodium 2,3-dichloropropionate in aerated solutions. According to the in-situ monitoring of proton levels in aerated solutions biased at -0.80 V versus SCE, 4-chlorophenol, 3-chloropropanol and sodium 2,3-dichloropropionate could be oxygenated under the catalysis of VK3, Fe2+ and SOD. (C) 2003 Elsevier Science B.V. All rights reserved.