Enzymatic degradation of endocrine-disrupting chemicals in aquatic plants and relations to biological Fenton reaction

In order to evaluate the removal performance of trace phenolic endocrine-disrupting chemicals (EDCs) by aquatic plants, batch and continuous experiments were conducted using floating and submerged plants. The EDCs used in this study were bisphenol A, 2,4-dichlorophenol, 4-tert-octylphenol, pentachlorophenol, and nonylphenol. The feed concentration of each EDC was set at 100 mu g/L. Continuous experiments showed that every EDC except pentachlorophenol was efficiently removed by different aquatic plants through the following reaction, catalyzed by peroxidases: EDCs vertical bar H2O2, Products vertical bar H2O2. Peroxidases were able to remove phenolic EDCs in the presence of H2O2 over a wide pH range (from 3 to 9). Histochemical localization of peroxidases showed that they were located in every part of the root cells, while highly concentrated zones were observed in the epidermis and in the vascular tissues. Although pentachlorophenol was not removed in the continuous treatment, it was rapidly removed by different aquatic plants when Fe2+ was added, and this removal occurred simultaneously with the consumption of endogenous H2O2. These results demonstrated the occurrence of a biological Fenton reaction and the importance of H2O2 as a key endogenous substance in the treatment of EDCs and refractory toxic pollutants.