Horseradish peroxidase-catalysed oxidation of aqueous natural and synthetic oestrogens

The horseradish peroxidase (HRP)-catalysed oxidation of selected potent oestrogens, including the natural oestrogens 17 beta-oestradiol and oestriol and the synthetic oestrogen ethinyloestradiol, was studied and compared with that of phenol. HRP catalysed the oxidation of these oestrogens and phenol over a wide range of pH values, with optimal performance around neutral pH, which is in the range of typical urban wastewaters. In comparison with that of phenol, the oxidation of oestrogens consistently required less hydrogen peroxide. In addition, the rate of oxidation of oestradiol was equivalent, twofold faster and fivefold faster compared with that of ethinyloestradiol, oestriol and phenol respectively. For all substrates studied, similar kinetics of removal were observed provided that sufficient enzyme was added to reactions to compensate for differences in substrate affinity. In contrast with earlier studies with phenols in which HRP was observed to be susceptible to significant inactivation due to interactions with hydrogen peroxide and reaction products, minimal inactivation of HRP was observed during the present study, probably owing to the very low concentration of target substrates used here (i.e. 10 mu mol dm(-3)) relative to earlier studies with other phenolic substrates. These observations suggest that this enzymatic approach has strong potential to be used to target the treatment of oestrogenic compounds. (C) 2007 Society of Chemical Industry.