Elimination of selected heterocyclic aromatic emerging contaminants from water using soybean peroxidase

Widespread occurrence of various heterocyclic aromatic compounds is reported in concentrations from 1 to 20 μg/L in surface and groundwater as well as influents and effluents of wastewater treatment plants around the world. These so-called emerging contaminants and their metabolites can cause adverse effects on the environment and humans, even at very low concentration, hence raised environmental concerns. In this study, feasibility of soybean peroxidase-catalyzed removal of three selected heterocyclic aromatics from water was investigated, including sensitivity to the most important operational conditions, pH (range 3.6-9.0), H₂O₂ concentration (range 0.10-1.50 mM), and enzyme activity (range 0.001-5.0 U/mL). 3-Hydroxycoumarin and 2-aminobenzoxaozle were found to be substrates for the enzyme, having ≥95% and 45% removal efficiency with most effective pHs of 7.0 and 6.0, respectively. Time course study was also conducted to determine the initial first-order rate constants and half-lives; half-lives normalized for enzyme activity (0.0257 and 452 min for the respective substrates) are compared with those of 21 other compounds reactive with soybean peroxidase. High-resolution mass spectrometry was employed to characterize the plausible oligomerization products of enzymatic treatment, which revealed formation of dimers and trimers of the two substrates.