Identification and application of Phyto-Fenton reactions

The formation of hydroxyl radicals (•OHs) by aquatic plants was investigated using electron-spin-resonance (ESR) spectroscopy and fluorescence microscopy. ESR observations, using 5- (diethoxyphosphoryl)-5-methyl-pyrroline N-oxide as a trapping agent, indicated that the signals produced by aquatic plants ground with ferrous iron ions are almost identical to those produced by Fenton's reagent. In addition, fluorescence was observed in the oxidized form of aminophenyl fluorescein in the presence of ferrous ions as well as any particles of colloidal ferrihydrite, magnetite, and ferric-ion-exchanged zeolite, while no fluorescence appeared in the absence of these iron compounds. Moreover, fluorescence-microscopy observations demonstrated that fluorescence mainly occurs on the surface of aquatic plants at neutral pH in the presence of the latter three solid iron compounds, implying the occurrence of heterogeneous phyto-Fenton reactions utilizing endogenous hydrogen peroxide (H₂O₂) in the aquatic plants. Furthermore, batch treatments of the pollutant 17α-ethinylestradiol (EE2), using colloidal ferrihydrite iron, indicated the feasible removal of EE2 with enhanced performance, lower-or apparently no-consumption of endogenous H₂O₂, and no significant stress to the aquatic plants. We concluded that the treatment of environmental pollutants through •OH formations via heterogeneous phyto-Fenton reactions should be a feasible alternative to conventional wastewater and water-treatment processes.